Integrated watershed management and river-coastal engineering in Eastern philosophy

Photosynthesis in marine environment: An important role in controlling sea surface temperatures

                                                                                           Haruka Yoshimura, Ph.D.

Fig. 1 Conceptual diagrams: (a) temperate coastal vegetation and phytoplankton; (b) hard engineering coastal protection. (a) Photosynthetic ecosystems in marine environment heavily distribute in coastal zone: the continental shelves (0–200 meters) and the adjacent slopes. Coastal vegetation (salt marshes, mangrove forests, seagrasses, and kelp forests) provides important nurseries for marine fisheries. Marine phytoplankton, known as invisible forests (Falkowski 2002), produce approximately half of global net primary production. Supply of nutrients and organic material such as organic silicon ‘Si’ and iron ‘Fe’ compounds from terrestrial vegetation plays an essential role in the high primary productivity of coastal vegetation and active phytoplankton growth. Via CO₂ sequestration, phytoplankton (e.g., Field et al. 1998; Falkowski et al. 1998) and coastal vegetation (e.g., Duarte 2017) have an important influence on global climate. When they complete their life cycle, the organic matter sinks into the deep ocean, sequentially fixed CO₂ is locked over millennia. (b) Hard engineering structures such as seawalls and bulkheads destroy the most important part of marine photosynthesis. The loss of contiguous habitats between land and sea leads to deficiency of essential elements such as organic ‘Si’ and ‘Fe’ compounds for photosynthesis in marine environment. Declines marine photosynthetic production alter solar radiation balance: Increased evaporation and increased fraction of heat (sensible heat and longwave radiation). The alteration of surface energy balance accelerates negative impacts of climate change. 

1.     Introduction

 

Landscape architecture and management for coastal ecosystem functions. Photosynthesis in marine environment is a biological process of global importance, having an influence on climate and providing a basis for resilience of fisheries.

In historical Eastern philosophy, management of marine resources was considered as a core issue of governance for food security to supply affordable and high-quality animal protein for people. Japanese land governance in coastal zones was unique in translating learning-based knowledge into effective policy and management strategies.    

At the beginning of the 21st century, photosynthesis in marine environment has degraded, causing adverse effects in climate change and losing resilient fisheries. Edo, estimated population of over 1,000,000 as early as the middle of the eighteenth century (Sansom 1963; Uspensky 2003), is a success case in land governance and coherent national coastal strategy.

Ancient Japanese architects and decision-makers were aware that cool, clean and clear seawaters are essential for abundant fisheries resources, through the learning-based approach over millenniums via dialogue with dynamic earth-surface system. For marine ecosystems restoration, the unique learning-based approach in Eastern philosophy is applicable for planning/management of coastal zones around the world. Scientific translation of the historical Eastern philosophy facilitates the application in land-use planning/management.

Photosynthesis in marine environment. All life in earth, including human beings, stems primarily from the conversion of solar radiation energy by photosynthesis into biochemical energy. Photosynthesis plays a major role in conversion of the inorganic carbon in atmosphere (carbon dioxide, CO₂) into organic matter—the sugars, amino acids and other biological molecules.  In marine environment, photosynthetically active solar radiation (400 to 700nm) or sunlight penetrates with a maximum depth of 200 meters based on the light absorption properties of salt water. Therefore, marine ecosystems that contribute the conversion of CO₂ into organic matter, also known as primary production, heavily distribute the zones from the coastlines to a depth of 200m of continental shelves (Fig. 1). Marine photosynthetic organisms use the dissolved CO₂ in the ocean to produce organic matter.   

Most of earth—70.8%, or 362 million square kilometers—is covered by oceans and major seas. The continental shelves (0–200 meters) and adjacent slopes, that covers less than 10% of the world ocean (32 million km²), yield 90% of marine fisheries annually (Garibaldi and Limongelli 2002; Pauly et al. 2002). In contrast, the open ocean is often referred as ‘the blue desert’ owing to low primary production. Large pelagic fishes such as tunas migrate over the long distances that separate isolated food patches.

2.     Declining marine photosynthetic production (conversion of CO₂ into organic matter)

 

Vegetation in sea-land interface

Salt marshes. Salt marshes and their associated networks of drainage channels and embankments are major coastal habitats in temperate zones. Salt marshes occur the transition zones between land and sea where are subject to extreme daily and seasonal changes of water levels and salinity, while they are one of the most productive ecosystems (Odum 1971; Whittaker and Likens 1973).

Human society has frequently classified coastal wetlands as ‘worthless’ areas. Over time, coastal wetlands have been drained and filled to provide space for agriculture, and building/industrial sites. Approximately, 50% of the original salt marshes have been degraded or lost globally (Barbier et al. 2011). In some areas in US, Canada, Europe and Australia, 67% of the original wetland vegetation of estuarine and coastal seas was lost (Lotze et al. 2006). 

Mangrove forests. On tropical and sub-tropical coastlines, the sea-land interface is covered mangrove forests. The dense thickets of mangroves create shallow water swamps that extend along estuaries and/or along coastlines. The tree foliage of thick leaves shields intense solar radiation and limits temperature extremes, and interconnecting aerial roots (roots above ground) systems attenuate wave energy. Accordingly, the mangrove swamps provide important nurseries for marine fisheries (Moyle and Cech 2004).

Mangroves are highly productive ecosystems with net primary production (difference between autotrophic photosynthesis and respiration) equivalent to that of tropical humid evergreen forests. Mangroves that thrive in soft sediments have been evolved unique forms in CO₂ sequestration; Mangroves allocate much more fixed carbon into soil than tropical humid evergreen forests (Alongi 2014).

Total area of mangrove habitats along the shorelines of the world is estimated roughly 1.7 × 10 km² (Valiela et al. 2001). Mangroves occupy 0.5% of total global coastal area but account for approximately 10–15% of total CO₂ sequestration in the coastal ocean (Alongi 2014). At least 35% of the original mangrove forests has been lost since the early 1980s, due to human activities such as aquaculture mainly shrimp farming, wood exploitation for industrial-level lumber and wood-chip production, and industrial/urban development (Valiela et al. 2001).

Although rates of mangrove deforestation have decreased (Friess et al. 2019), mangrove habitats are regressing and fragmenting globally (Carugati et al. 2018; Bryan-Brown et al. 2020).  

Seagrasses. Seagrasses are flowering plants (angiosperms), which form seagrass meadows in shallow seas on all continents except Antarctica. In temperate zones, seagrass meadows distribute from the intertidal to about 60m (200ft) depth in clear waters. The dominant species in temperate regions is eelgrass (Zostera marina) that adapts to thrive better in cooler waters (Unsworth et al. 2015). Seagrass meadows are among the most productive plant communities, comparable to intensively cultivated crops (Duarte and Chiscano 1999). Owing to the provision of nursery and foraging grounds for invertebrates and fish, seagrass meadows support major fishery productivity such as Alaska (Walleye) Pollock (介宗鱈, Theragra chalcogramma), Atlantic Cod (Gadus morhua), Pacific Cod (真鱈, Gadus macrocephalus), Atlantic Herring (Clupea harengus), and Pacific Herring (鰊, Clupea pallasii) (Unsworth et al. 2018).

In tropical regions the dominant species is turtle grass (Thalassia testudinum), which distributes often associated with coral reefs and mangroves. Historically, seagrass meadows provided forage and habitat for enormous numbers of sirenians (dugong and manatee) and sea turtles, as well as commercially important fish species (Jackson et al. 2001).      

Seagrass meadows are lost globally at fast rates. At least one third of the area has been lost since World War Ⅱ (Orth et al. 2006; Waycottet al. 2009). In some temperate sites in US, Canada, Europe, and Australia, 65% of the original seagrasses was lost (Lotze et al. 2006).

 

Kelp forests. Kelp forests—undersea forests of brown alae (order Laminariales)—form unique habitats in coastal regions of temperate and Arctic areas worldwide. In temperate waters, they are typically found 6m (20ft) and 30m (98ft). The kelps are anchored to rocky or sandy bottoms with holdfasts (not roots), and have long fronds (resembling to true leaves) extending to the surface. The fronds of a species of kelps (Saccharina angustata, an edible kelp highly flavorsome for Japanese cuisine, occurs in northern Japan) grow up to 20m (66ft). The complicated canopy structure of the kelp forests provides a variety of habitats for invertebrates and fishes (Moyle and Cech 2004). Kelp forests have high rates of primary production. The net primary production (the difference between the amount of photosynthetically produced organic matter and respiration) is comparable to a tropical rain forest (Mann 1973).

In some temperate sites in US, Canada, Europe, and Australia, 48% of the original kelp forests was lost (Lotze et al. 2006). The kelps grow best cold waters. Therefore, increased ocean temperatures, together with cumulative effects of other stressors, reduce their growth, consequently have resulted in collapse of kelp forests along many temperate coasts globally (Filbee-Dexter and Wernberg 2018).

 

Ocean’s invisible forests: marine phytoplankton. Phytoplankton constitute the basis of marine food webs. Each year, marine phytoplankton generate approximately half of global net primary production (the net mount of photosynthetically fixed carbon minus the organic matter used up in respiration) (Field et al. 1998; Falkowski 2002). They proliferate quickly, increasing in number by many orders of magnitude in just a few days. Despite accounting for only 0.2% of global producer biomass, marine phytoplankton attain such high net primary production by its rapid life cycle (Field et al. 1998; Falkowski 2002).

Tiny single-celled algae, “diatoms, dinoflagellates, and haptophytes,” are dominants of photosynthetic producers in continental shelves and seasonal blooms in temperate waters (Simon et al. 2009). The diatoms, with an estimated 200,000 different species ranging in size from a few micrometers to a few millimeters, are the most essential group of eukaryotic phytoplankton. They have been estimated to contribute about 40% of marine primary productivity (Tréguer et al. 2018). Diatoms generate most of the organic matter that serve as food for life in the sea: diatoms are consumed by zooplankton (small crustaceans such as copepods and krill; larva of fish, squid, lobsters and crabs). Sequentially, these smaller herbivorous zooplankton provide food for larger zooplankters and for forage fish: small, schooling, filter-feeding fish such as herring, sardines, and anchovies. The forage fish are then consumed by larger predators including diverse fish species of commercial importance (Fig. 2). In coastal waters, diatoms support the productive fisheries. They produce most of the organic matter consumed rapidly by zooplankton and serve as a base for marine food webs (Armbrust 2009).

Marine phytoplankton have declined in the world’s oceans by about 40% since 1950, possibly in response to increasing sea surface temperatures (Boyce et al. 2010, 2014). Higher ocean temperatures inhibit normal metabolism and lower productivity of marine phytoplankton (Toseland et al. 2013). 

Fig. 2 Schematic representation: (a) example food web sustaining resilient fisheries; (b) example of collapse of trophic transfer in marine food web. (a)　Phytoplankton constitute the basis of marine food webs, providing resilience for fisheries (e.g., Pauly and Christensen 1995). (b) Rising water temperatures along with nutrient pollution fundamentally alter structure of primary production, known as ‘harmful algae blooms.’ Changes in the species composition of primary production, in turn, degrade the food webs. For instance, bloom of dinoflagellate green Noctiluca in tropical waters causes modification of trophic transfer in food webs and leads to collapse of fisheries (do Rosário Gomes et al. 2014; Goes et al. 2020). The most important zooplankton such as copepods and krill do not feed on green Noctiluca, while salpas and jellyfish proliferate consuming it.

3.   

3.     Marine photosynthesis: influence on climate 

3.1  Structure and function of marine photosynthesis in solar radiation balance

In terrestrial biosphere, leaf canopy structure, photosynthesis and transpiration dissipate solar radiation energy and control temperature (http://harukanoor4.blogspot.com/2019/). Plant pigments absorb the visible range of solar radiation. Subsequently, most of the absorbed energy is used in biochemical pathways of photosynthesis (Blackburn 2007). On land, stratified canopy foliage of vegetation shields solar radiation, keeping soil and soil moisture cool. Deep and extensive root systems uptake cool moisture from the soil and extract cold groundwater, and accordingly cool moisture is releasing via transpiration.

In marine environment, vegetation structure and photosynthesis dissipate solar radiation energy without a large increase in temperature. The vegetated coastal habitats and phytoplankton absorb solar radiation energy and control temperature. As mechanisms of photosynthesis on land and in the oceans are essentially similar, absorbed solar radiation energy by the photosynthetic pigments of coastal vegetation and phytoplankton is used in biochemical pathways of photosynthesis.

By the floating canopies of seagrass meadows consist of long green leaves over 1.0m (39.4in) and of kelp forests consist of long ribbon-like fronds, submerged coastal vegetation shields solar radiation and controls temperatures suitable for their growth. Free-floating phytoplankton, distribute three quarters of the earth’s surface, shield solar radiation (like a cloud in the sky) and moderate temperatures over vast extent of oceans.

 

3.2 Photosynthesis in marine environment: A role of global CO₂ sequestration

Marine phytoplankton’s primary production (conversion of CO₂ into organic matter) has an influence on global climate via CO₂ sequestration (Field et al. 1998; Falkowski et al. 1998; Falkowski 2002). When marine phytoplankton complete their life cycle, the organic matter sinks from the surface layer into the deep ocean before it decays. The organic matter released below about 200m is locked over millennia, because the colder temperature—and higher density—of this water prevents it from mixing with the warmer waters above (Falkowski 2002). In this process, known as the biological pump, diatoms play a key role, because diatoms’ silica shells provide ballast in transporting carbon to the deep ocean (Tréguer et al. 2017).

Similarly, primary production of vegetated coastal habitats (salt marshes, mangrove forests, seagrasses, macroalgal beds) has an influence on global climate via CO₂ sequestration. The vegetated coastal habitats produce organic carbon far in excess of local requirements, subsequently a large surplus of organic carbon (about 40% of their net primary production) sink as sediments in the continental shelf or the deep ocean, providing a function of CO₂ sequestration. Despite occupying only 0.2% of the ocean area, coastal angiosperms (flowering plants) dominated ecosystems contribute approximately half of the total CO₂ sequestration in the ocean (Duarte et al. 2005; Duarte 2017).

Through the biological pump, phytoplankton and coastal vegetation remove CO₂ from the surface waters and atmosphere and store it in the deep ocean. However, the capacity of CO₂ sequestration in the deep sea is rapidly weakening by the declining phytoplankton and vegetated coastal habitats.

 

3.3 Declines of marine photosynthesis cause increase in sea surface temperatures

Decline of marine photosynthesis (coastal vegetation and phytoplankton) alters solar radiation balance (Fig. 1). The decline of marine photosynthesis leads to decrease of absorbed solar radiation energy by photosynthetic pigments. The fraction of solar radiation energy previously absorbed by photosynthetic pigments is absorbed sea water. Loss of shield-effect of biological structure in marine environment increases absorbed solar radiation energy by sea water. These factors possibly result in increase in sea surface temperatures.

Marine heatwaves—ocean areas of extreme high sea surface temperatures that persist for days to months—have increased sharply in all major ocean basins over the recent decade (Frölicher and Laufkötter 2018; Oliver et al. 2018; Smale et al. 2019). The longer and more frequent marine heatwaves (Oliver et al. 2018) are already impacting marine ecosystems: the submerged aquatic vegetation, seagrass meadows and kelp forests, has been lost (Smale et al. 2019).

Marine phytoplankton (mostly diatoms), that sustain the marine food webs, thrive better in cooler waters. As higher ocean temperatures significantly affect metabolism and lower productivity of phytoplankton (Toseland et al. 2013), the extreme high sea surface temperatures negatively affect phytoplankton productivity. If phytoplankton are lost by these extreme temperatures, the marine food webs could collapse.

 

3.4 Rising sea surface temperature: influence in weather and climate

The marine heatwaves induce photosynthesis decline. Which in turn causes additional increase in sea surface temperatures, as the fraction of solar radiation energy that was once absorbed by photosynthetic pigments is absorbed by sea water.

Warmer sea surface temperatures could increase the frequency and severity of tropical cyclones (Trenberth 2005; Hoyos et al. 2006; Kerr 2006).

Evaporation from the oceans can increase, as the fraction of solar radiation energy that was previously absorbed by photosynthetic pigments and used photosynthesis processes is allocated to latent heat flux (solar radiation energy used to evaporate water from the ocean surface). Due to moisture source of precipitation supplied by the warmer wetter marine air, increased evaporation from the oceans may cause changes in precipitation pattern: torrential rainfalls by frontal systems and/or tropical cyclones, and heavy snows by squall lines along cold fronts, which occur occasionally and irregularly.

 

4.     Rising sea surface temperatures degrade resilience of marine ecosystems: Harmful algal blooms

 

Rising water temperatures along with nutrient pollution (e.g., Anderson et al. 2008; Heisler et al. 2008) fundamentally alter the phytoplankton community structure in various ways. Harmful algal blooms have a negative impact on marine ecosystems and coastal fisheries worldwide. Among the 5,000 species of marine phytoplankton, some 300 species produce blooms with water discoloration (known as ‘red tides’), while 80 or so species have the capacity to produce potent toxins (Hallegraeff 2003).

 

Dinoflagellate genus Alexandrium. The dinoflagellate genus Alexandrium is a globally distributed harmful algal genus with many species and strains that are known to produce paralytic shellfish toxins, known as saxitoxins. The impacts of paralytic shellfish toxins include human intoxications and death through the marine food webs: filter-feeding bivalves, such as mussels, cockles, oysters and scallops consume the dinoflagellates, transferring them from the gills to digestive organs where the toxins concentrated. The concentrated toxins are passed to higher trophic levels of the food webs. The incidence of human paralytic shellfish toxins poisoning could occur by the consumption of the contaminated shellfish or fish (Anderson et al. 2008, 2012). Saxitoxins are also produced by dinoflagellate genus Gymnodinium and Pyrodinium, as well as several genera of predominantly freshwater cyanobacteria (e.g., Anderson et al. 2012).　

                                                                

Dinoflagellate genus Karenia. Florida red tides are predominantly associated with the blooms of the toxic dinoflagellates Karenia brevis (Fleming et al. 2011). This dinoflagellate produces a suite of potent natural neurotoxins, called brevetoxins. Brevetoxins are neurotoxins that interfere with proper nerve transmission, which in turn affects the central nervous system and induces immune depression. Human intoxication from neurotoxic shellfish poisoning is caused by consuming contaminated shellfish, because filter-feeding shellfish accumulate the neurotoxins. The brevetoxins are tasteless, odorless, and heat and acid stable, and cannot be removed by food preparation (e.g., cooking contaminated seafood).        

Due to relatively fragile unarmed cell structure, the Karenia brevis organism is easily broken open by in wave action along beaches, releasing the toxins. Inhalation of the aerosol of contaminated salt spray containing the toxins and organism fragments is causing respiratory irritation to humans and mammals. Symptoms in humans of exposure include stinging eyes and nose, dry choking cough and onset of asthmatic attack (Pierce and Henry 2008; Fleming et al. 2011).    

The toxins cause severe impacts on natural resources: mass mortalities of fish, marine mammals, sea turtles and sea birds (e.g., NOAA 2021). Although Florida red tide blooms have been documented since the 1840s, these and other red tides appear to be increasing in incidence, duration and geographic spread. The brevetoxin-producing Karenia brevis is found throughout the world’s ocean, including New Zealand (Nozawa et al. 2003) and Mediterranean Sea (Tsikoti and Genitsaris 2021).

The other toxin-producing blooms in the genus, Karenia, have been identified in diverse geographic locations worldwide. Karenia selliformis is responsible for the production of the toxins gymnodimines that block nicotine acetylcholine receptor in our human nerve system. The toxins gymnodimines along with the hemolytic capability, the blooms of K. selliformis are causing mass mortalities of a variety of coastal wildlife (Tatters et al. 2010). The blooms of K. selliformis have been reported from coastal waters of New Zealand, Mexico, Tunisia, Kuwait, Iran, China and Chile (Mardones et al. 2020).

Karenia mikimotoi is a bloom-forming toxic dinoflagellate. In Japan, blooms of K. mikimotoi caused mass mortality of pearl oyster (Pinctada fucata) have been documented since the 1930s, and these blooms appear to be increasing in incidence, duration and geographic spread (Go et al. 2016). Blooms of K. mikimotoi have been reported widely in subarctic (Scottish waters around 60°N, Davidson et al. 2009), temperate (e.g., Qinhuangdao in China around 40°N, Chen et al. 2021; the Aegean Sea around 40°N, Tsikoti and Genitsaris 2021) to sub-tropical (Zhanjiang in China around 21°N, Chen et al. 2021) coastal waters. The production of reactive oxygen species by the dinoflagellate (Li et al. 2019) leads to mass mortalities: Most of marine faunas use gills as respiratory organ to extract dissolved oxygen from water and to excrete carbon dioxide. The gills are oxidative damaged by the reactive oxygen species (e. g., Kim et al. 1999, López-Cortés et al. 2019 in dinoflagellate Margalefidinium polykrikoides). Due to the toxic effect of reactive oxygen species along with the hemolytic and cytotoxic capability of K. mikimotoi (Li et al. 2019), blooms of K. mikimotoi resulted in extensive mortalities of marine organisms: benthic organisms including annelids and molluscs and some species of fish (Davidson et al. 2009); filter-feeding bivalves such as clam (Ruditapes philippinarum), oyster (Crassostrea gigas) and scallop (Mimachlamys nobilis) (Go et al. 2016).

In autumn 2021, blooms of K. selliformis in association with K. mikimotoi in Hokkaido Island in northern Japan (around 43°N) killed nearly 30,000 salmons (Oncorhynchus keta and O. masou) and resulted in extensive mortalities of benthic organisms including commercially important sea urchin (Strongylocentrotus intermedius) and sea cucumber, caused a catastrophic damage to the local fisheries (Hokkaido government Japan, 2021).           

 

Dinoflagellate Noctiluca scintillans. The globally distributed dinoflagellate Noctiluca scintillans (quite large, 0.2–2mm, typically around 0.5mm) is one of most important and abundant red tide organisms. It is known that bioluminescent Noctiluca scintillans occurs in two forms. Red Noctiluca acts as a microzooplankton grazer in the marine food webs, which occurs widely in temperate to sub-tropical coastal waters. The other form of green Noctiluca can survive without an external food supply owing to source of photosynthetic products from symbiont Pedinomonas noctilucae inside the cell. Though it also feeds on other plankton, protozoans, detritus, and fish eggs, when the food supply is abundant. Green Noctiluca occurs mainly in tropical waters (Turkoglu 2013). The photosynthetic symbionts in the cells of green Noctiluca have higher carbon fixation capability than trophically important diatoms at lower oxygen concentrations (do Rosário Gomes et al. 2014). In the tropical oceans, zones of low oxygen concentrations have expanded since the 1960s (Stramma et al. 2008) due to nutrient loading from synthetic fertilizers in agriculture and from treated/untreated sewage effluent. As the dinoflagellate green Noctiluca can thrive under hypoxic conditions (do Rosário Gomes et al. 2014), low oxygen concentrations of seawaters give green Noctiluca a competitive advantage, suppressing diatoms.    

Green Noctiluca. Blooms of green Noctiluca were first observed in the open ocean waters of the Arabian Sea in the early 2000s, have occurred every year during the winter monsoon, from January to March (do Rosário Gomes et al. 2014; Goes et al. 2020). Although Noctiluca blooms are non-toxic, they can cause massive fish and marine invertebrates kills. The cells of Noctiluca accumulate toxic levels of ammonia, which is excreted into surrounding waters. The ammonification of seawater and excavating oxygen deficiency have caused the severe mortality of fish and marine invertebrates.

Winter phytoplankton blooms that previously comprised mainly diatoms have been replaced by widespread blooms of green Noctiluca. Diatoms dominant blooms provide basis for marine biodiversity, sustaining resilience of fisheries: diatoms feed a wide range of primary consumers (copepods, krill, shrimp, forage fish), which in turn are consumed by higher trophic levels of predators including diverse fish species of commercial importance (Fig. 2, a).

Green Noctiluca are largely unpalatable and they are not consumed by most of zooplankton (small crustaceans such as copepods and krill; larva of fish, squid, lobsters and crabs), except salps (small, gelatinous, filter-feeding tunicate) and jellyfish (Goes et al. 2020). The abundance of green Noctiluca causes low abundance of other zooplankton, which in turn has led to reduction of food availability to higher trophic levels of predators including diverse fish species of commercial importance. Thus, collapse of the traditional diatom-sustained food webs causes decline of fisheries (Fig. 2, b).  

Fisheries plays an important role as the primary source of protein and income for a coastal population of nearly 120 million people in the countries of the coast of the Arabian Sea, India, Pakistan, Somalia, Yemen, and Oman. The collapse of marine food web and resulting loss of fishery resources has the potential to exacerbate socio-economic turmoil in countries like Somalia and Yemen where are currently being challenged by unrest, poverty, and deprivation (do Rosário Gomes et al. 2014; Goes et al. 2020).

Red Noctiluca. Red Noctiluca is one of the most common red tide forming organisms. Blooms of red Noctiluca, occur frequently in temperate to subtropical coastal waters, are considered benign. However, red Noctiluca blooms may lead to collapse of marine food webs and consequent loss of fishery resources. Red Noctiluca does not support food webs, because they are not consumed by most of zooplankton except salps and jellyfish. Batistić et al. (2019) suggest that blooms of Noctiluca and resulting salp blooms alter marine food webs by the reduction of food availability to primary consumers and consequential decrease of higher trophic levels of predators, in a case of the temperate sea of the southern Adriatic. Thus, common red tides of Noctiluca may have caused decline of fisheries in temperate to subtropical regions in the world.

  

Pennate diatom genus Pseudo-nitzschia. Diatoms represent one of the most important groups within marine phytoplankton, forming the base of the food web in many marine ecosystems. Most diatoms are considered benign, but some are known to cause harm by the production of a phycotoxin. Several species of the pennate diatom belong to the genus Pseudo-nitzschia are known to produce the neurotoxin domoic acid. A toxic bloom of Pseudo-nitzschia occurred in 1987 in the estuaries of Cardigan Bay, eastern Prince Edward Island, Canada, and led to an outbreak of human poisoning due to consumption of contaminated mussels: at least 107 illness and killed at least 3 elderly people. Symptoms included abdominal cramps, vomiting, and neurologic responses involving disorientation and memory loss. Due to the neurological disorder, this human poisoning is known as amnesic shellfish poisoning (Bates et al. 1998).

Domoic acid interferes neurotransmission in glutamate receptors, subsequently causes damage and death of nerve cells of glutamate receptors. These receptors are widely distributed in the hippocampus (associated with memory retention) in human brain, hence domoic acid poisoning induces the memory loss (Bates et al. 1998). 

 Blooms dominated by toxic Pseudo-nitzschia are increasing in frequency and duration along most of the world’s coasts: United States, Canada, Mexico, South America (Chile, Argentina, Uruguay, and Brazil), Australia, New Zealand, Africa (South Africa, Namibia, Tunisia, and Morocco), Europe (UK, Ireland, France, Denmark, Portugal, and Spain), also in upwelling regions of open oceans (where deep, cold, nutrient-rich water rises toward the surface) (Trainer et al. 2012).

The trophic transfer of domoic acid has led to dramatic mortality events of marine mammals and birds. For instance, over 400 sea lions died and many others displayed signs of neurological dysfunctions along the central California coasts linked to a toxic Pseudo-nitzschia bloom in 1998 (Scholin et al. 2000).     

Toxic Pseudo-nitzschia cells are consumed by sardines and anchovies, subsequently the neurotoxin domoic acid transfers higher levels of the marine food webs. Meanwhile, the toxin-containing diatom cells during senescence transport downward rapidly and reach the benthos, as the siliceous cell walls of diatoms act as ballasting material. The toxin in bottom sediments persists long in colder deeper waters in dark conditions and be readily available for bioaccumulation. Resulted high level of domoic acid in benthic organisms (e.g., crabs; spiny oyster; flatfish; cephalopods; filter-feeding bivalves such as mussels, scallops, calms) adversely affects marine ecosystems (Sekula-Wood et al. 2009). Which, in turn lead to economically disruptive fishery closure required to protect human health (Trainer et al. 2012; Ryan et al. 2017).

 

‘Brown tides’ picoplankton Aureococcus anophagefferens. ‘Brown tides’ caused by the harmful picoplankton (0.2–2 µm) Aureococcus anophagefferens had never been documented before 1985 but have recurred in shallow bays/estuaries in the United States and South Africa since that time (Bricelj and Lonsdale 1997; Gobler et al. 2011). Brown tides of Aureococcus anophagefferens occurred in 2009 in the north-western Bohai Sea, China, and have recurred since then (Zhang et al. 2012; Huang et al. 2020).

 Brown tides have caused inhibitory effects on growth in suspension-feeding bivalves such as hard clams, mussels and bay scallops throughout their larval development (Bricelj and MacQuarrie 2007). Recent research shows that the brown tide alga Aureococcus anophagefferens produces a potent toxin of hemolytic and cytotoxic effects (Huang et al. 2020). Due to severe mortalities in wild and cultured bivalves, brown tides have caused collapses of the shellfish industry.

The brown tides result in marine food web collapses. Under the progressive changes by urban runoff in coastal seawaters: increasing water turbidity and organic matter, the brown tide alga Aureococcus anophagefferens outcompetes other useful phytoplankton as primary producer such as diatoms. By the loss of the base for marine food webs, energy flow from the first trophic level (diatoms) to higher trophic levels does not occur.

In addition, severe light attenuation due to brown tides led to massive loss of eelgrass meadows (Bricelj and Lonsdale 1997). These loss of eelgrass meadows serving as important spawning and nursery grounds for shellfish and fishes has had indirect impact on fisheries. Brown tides alter the once productive shallow bays/estuaries to the seas of ecological degradation.

Broad geographic distribution of brown tide alga Aureococcus anophagefferens has been identified in USA, from Maine to Florida (Bricelj and MacQuarrie 2007). In anthropogenically modified bays/estuaries, conditions of increasing water turbidity and organic matter that promote the harmful agal proliferation have become prevalent, suggesting a potential risk of further expansion of brown tides (Gobler et al. 2011).

 

Cyanobacteria. Cyanobacteria (in the size 0.2–2 µm) are oxygen-producing bacteria (not algae) that use sunlight to convert CO₂ into biomass. Cyanobacteria generally grow better higher temperatures (often above 25℃) than do other phytoplankton such as diatoms (Paerl and Huisman 2008). Consequently, cyanobacterial blooms in freshwater and marine environments are currently increasing globally owing to rising temperatures coupled with nutrient loading from urban, industrial and agricultural sources (Huisman et al. 2018).

Bloom-forming cyanobacteria produce a variety of cyanotoxins damaging liver, digestive and neurological systems of birds, mammals and humans (Carmichael and Boyer 2016; Huisman et al. 2018). In terms of global hydrological cycle, fresh water contributes only 2.5% of the total volume of water in Earth. Only a tiny proportion (0.296%) of the world’s fresh water is present as surface water (water reserves in lakes: 0.26%; swamp water: 0.03%; river flows: 0.006%) (Shiklomanov 1993). Cyanobacterial blooms in freshwater, including Lake Victoria in Africa, Lake Erie in North America, Lake Taihu (太湖) in China, and Lake Biwa (琵琶湖) in Japan (Ishikawa et al. 2002), are a growing concern for our drinking water that rely on surface water.        

The North American Great Lakes are a vital freshwater resource, containing roughly 20% of the Earth’s available surface freshwater. Cyanobacterial blooms have recurred annually since the late 1990s’ in some of the most populated areas of the Lakes (Steffen et al. 2014). In early August 2014, a ‘do not drink’ advisory was issued for Toledo, Ohio, USA, due to high concentrations of microcystins (potent liver toxins produced by a variety of cyanobacteria), which resulted in over 400,000 residential customers and hundreds of businesses being without tap water for nearly 48 hours (Huisman et al. 2018). Microcystins, potential carcinogen, are stable in water, and boiling does not remove or destroy these toxins (Falconer and Humpage 2005).  

Cyanobacterial blooms are also expanding in estuarine and marine ecosystems throughout the world, including the Baltic Sea in Europe (Stal et al. 2003; Kahru et al. 2020), the Mediterranean Sea (Spatharis et al. 2012), and Florida bay in USA (Butler et al. 1995; Glibert et al. 2009). The microcystins are produced by cyanobacterial blooms in the enclosed Isahaya Bay in southern Japan by dyke defense structure against coastal floods (7km or 4.4mi long, constructed in 1997) (Takahashi et al. 2014). Owing to cyanobacteria’s intracellular gas vesicles acting as flotation devices, cyanobacteria float upward and accumulate in dense surface blooms with a wide array of colors, various shades of green, red, brown, yellow and pink. These surface blooms increase light attenuation, and have been implicated in the massive loss of seagrass meadows (Butler et al. 1995; Glibert et al. 2009). Decreased light penetration suppresses the essential phytoplankton that serve as a base for marine food webs through competition for light (Paerl and Huisman 2008).          

Die-off of blooms may deplete oxygen. Consequent hypoxia (having too little oxygen) causes the death of fish and benthic invertebrates (Diaz and Rosenberg 2008; Huisman et al. 2018). Cyanobacteria thrive well under hypoxic conditions, as they originated around 3 billion years ago in the absence of oxygen in the ocean-atmosphere system of the early Earth (Schirrmeister et al. 2015).                                        

5.     Photosynthesis in marine environment supported by land-sea interactions

 

Marine productivity needs essential elements supply from land. Organic matter dynamics by land-sea interactions play an essential role in nutrient supply to marine primary productivity to support bodily structure (such as organic silicon ‘Si’ compounds) and metabolism (such as organic iron ‘Fe’ compounds).

Terrigenous input of nutrients and organic material makes an important contribution in estuarine and coastal productivity. For instance, the highly productive coastal Mediterranean fishery off the Nile River delta collapsed after the construction of the Aswan Dam, due to decreased nutrients in the floodwater that supported large diatom blooms and a productive fishery, particularly for sardines (Milliman 1997).

 Diatoms, the most essential group of marine phytoplankton, are unique because of their cell walls made of silica, and the growth rates are limited by the supply of silicate (Smetacek 1998). Dam construction in the Danube River is a notable case. Decreased dissolved silica discharge to the Black Sea due to the dam crosses the Danube River has led to a shift in the composition of phytoplankton species form diatoms (siliceous) to non-siliceous such as dinoflagellates. The observed changes in Black Sea surface waters strongly suggest that materials form the terrestrial environment such as silica support the food web structure in coastal seas (Humborg et al. 1997; Milliman 1997).  

Many plants, particularly grasses (Poaceae) including common reed (Phragmites australis, found riparian zones and wetlands throughout temperate and tropical regions of the world), Equisetaceae (horsetail family) and Cyperaceae (family of graminoid) are rich in silica as structural materials (Currie and Perry 2007). Rivers are the main transporters of silica from the terrestrial environment to the oceans (Smetacek 1998). Supply of silica derived from terrestrial vegetation may play an essential role in primary productivity in the coastal and marine environments (Conley 2002).

In many ocean realms, iron (Fe) deficiency is limiting phytoplankton production (Martin and Fitzwater 1988). The growth rates of marine phytoplankton are restricted by the availability of soluble Fe (e.g., Kuma and Matsunaga 1995).

Matsunaga et al. (1999) indicate that the macroalgae growth is also restricted by the availability of soluble Fe, which derives from humic substances of forests via the decomposition of leaf litter.

All living things are made of one or more cells, and all the cells are mostly composed the same substances that carry out similar life functions. Cytochromes, a group of hemoprotein cell protein with a central Fe atom at its core, serve a vital function in both photosynthesis and cellular respiration. As cytochromes are found all animals and plants, and many microorganisms, humus and organic matter from terrestrial vegetation (e.g., leaf litter, wood, and other plant parts) that falls into rivers and coastal seas contains cytochromes. Hence, soluble Fe and/or cytochromes derived from an enormous amount of organic matter from terrestrial primary productivity may contribute marine primary production such as phytoplankton and macroalgae.

Coastal forests as critical juncture. Coastal zone plays a significant role in Fe supply pathway of land-sea connectivity. In the second half of the twentieth century, Hokkaido Island in northern Japan has experienced a collapse of fisheries coincide with decline of kelp forests, which occurred concurrent with massive deforestation of old-growth boreal forests. Until 1960s, Hokkaido Island was covered with old-growth boreal forests, dominated by conifers (e.g., spruce, Picea jezoensis, up to 40m; fir, Abies sachalinensis, up to 35m), mixed with deciduous trees such as birch (e.g., Betula ermanii, up to 30m). Massive deforestation particularly in coastal zones has led to lack of supply source of soluble Fe. Urban land expansion in coastal zones and hardening of coastal areas by hard defense structures (e.g., breakwaters, seawalls, dykes or other armoured structures) have caused the interruption of Fe supply pathway from terrestrial primary productivity to the oceans.  

Organic matter required to support marine primary production are supplied within the euphotic (sunlit) zone by a ‘recycling’ of nutrients (Field et al. 1998; Raven and Falkowski 1999), and are provided from organic matter sinks in the deep ocean by the transient physical processes, such eddies, coastal upwelling, and wind or convective mixing (Field et al. 1998; Falkowski et al. 1998; Falkowski 2002). However, a significant fraction of organic matter from terrestrial primary productivity is exported and sinks in oceans, sequentially the nutrients are used by primary production in the ocean euphotic zone (Raven and Falkowski 1999).

Coastal forests play a crucial role in biogeochemical connectivity between land and sea, by the supply of essential elements such as organic silicon ‘Si’ and iron ‘Fe’ compounds. Humus and organic matter such as leaf litter that falls into coastal seas from coastal forests facilitates the resilience of seagrass meadows, kelp forests, and diatoms-dominated phytoplankton.

 

Solutions for eutrophication: closing biogeochemical cycles between land and ocean. There is mounting evidence that excessive nutrient inputs (fertilizer runoff from agriculture, treated sewage discharge and combined sewer outfall, and urban stormwater) lead to harmful algal blooms (e.g., Anderson et al. 2008; Heisler et al. 2008). Furthermore, nutrient pollution is causing the widespread degradation of nearshore ecosystems, including salt marshes (Deegan et al. 2012), mangroves (Lovelock et al. 2009), seagrasses (Orth et al. 2006; Waycott et al. 2009; Jones and Unsworth 2016), and kelp forests (Filbee-Dexter and Wernberg 2018; Feehan et al. 2019).

Seagrass meadows are considered as biological sentinels, or “coastal canaries” (Orth et al. 2006), owing to the importance of these ecosystems that support fisheries production. Nutrient pollution from sewage and livestock waste enhances excessive growth of epiphytes (microscopic algae) on seagrass leaves, smothering and decreasing seagrass’s ability to capture light (Jones and Unsworth 2016).

Globally, canopy-forming kelp forests have been replaced by mats of turf-forming algae or turfs (a diverse group of macroalgae). Eutrophication, including sewage and urban pollution, reduces light penetration in coastal waters and turfs outcompete canopy-forming kelps by the turfs’ high growth rates and rapid nutrient-uptake rates (Filbee-Dexter and Wernberg 2018; Feehan et al. 2019).

Wastewater treatment plants are common worldwide and a required process to improve the quality of wastewater before it is discharged to water bodies. However wastewater treatment plants discharge significant quantities of nutrients (Howarth et al. 2002; Carey and Migliaccio 2009). A crucial challenge in nutrient loading is increasing recycling and safe reuse of human excreta (e.g., van Puijenbroek et al. 2019), as eutrophication is amplifying the risks of climate change via rising sea surface temperatures, increased evaporation from the oceans, and decreased CO₂ sequestration.       

The key to solving eutrophication is to keep large quantities of undesirable nutrients on the land out of the sea. Comprehensive land-use planning and management that close the land and ocean biogeochemical cycles need to be developed (Tilman et al. 2001; Diaz and Rosenberg 2008). 

Fig. 3 Nihon-bashi (Tokyo: 35°41′N, 139°46′E) from the series Famous Places in the Bay Capital, Hiroshige, originally published mid-1830’s to early 1840’s (Image courtesy of the British Museum: https://www.hiroshige.org.uk by Chiappa JN). A perspective view from the Nihon-bashi Bridge (the important commercial center in Edo) with a distant Mount Fuji, farsighted the Edo Castle (now the Imperial Palace). On the north bank of the bridge, there lay the largest fish-market in the Edo period, known as Uogashi (魚河岸). Hiroshige depicts natural abundance of marine fishery resources: Retailers with baskets full of fresh fish and all manner of seafood slung over their shoulders head for all parts of the city after making their purchases. Notably, two of Pacific bluefin tuna (Thunnus orientalis, up to 3m or 9.8ft) are carrying with a wooden pole. In Edo, Tuna was common and highly prized for Japanese cuisine sashimi and/or Edo-style sushi. The coherent coastal national strategy leaded to abundant and diverse fish resources, which in turn attracted large pelagic predators such as Tuna.

6.     Comprehensive land-use planning/management in Eastern philosophy: For keeping cool, clear and clean waters

 

High primary productivity of vegetation over large geographic areas. Japan had an abundance of diverse fisheries resources (Fig. 3). Acknowledged that abundance of fisheries resources is supported by self-organizing ability of ecosystems, the approaches that had been adopted for fisheries resources management was unique: comprehensive land-use planning/management. In Eastern philosophy, land-use planning/management of high primary productivity of vegetation over large geographic areas was considered the first principle, part of the critical infrastructure for socio-economic sustainability via food security. The philosophy was documented in the early Edo period, by Banzan Kumazawa (熊沢蕃山, 1619–1691). His theory emphasizes importance of forestry development and riparian forest restoration over the whole country (e.g., Sansom 1963) owing to their synergistic functions: Forests play a key role in moderating temperatures, keeping soil, groundwater, and running water in rivers/streams cool; forests stabilize the soil, preventing erosion, in turn contribute to reduction of sedimentation type pollution keeping clear waters. Notably, mixed broad-leaved early successional secondary forests dominated by deciduous oaks (e.g., Quercus serrata, up to 25m or 82 ft; Quercus crispula, up to 35m or 115 ft) are effective in these functions.

Fig. 4 Bowl of Sushi, Hiroshige, 1830s. To avoid eutrophication, disposal of any kind of waste to rivers/streams and seas was strictly prohibited in 1655 (Endoh 2004). Human excreta had been used for fertilization and soil improvement to close biogeochemical cycle as a useful resource. The clean seawater policy contributed to high standards of hygiene of sea foods, and underpinned the Japanese cuisine culture serving raw fish/shellfish such as sashimi and/or Edo-style sushi. 

Clean seawaters: governance approaches in closing biogeochemical cycles.  All living things are made of one or more cells, and all the cells are mostly composed the same substances that carry out similar life functions. When the living cells complete their life cycle, all the essential elements of cells tend to circulate in the biosphere, known as biogeochemical cycle. In Eastern philosophy, one of the important concepts of land-use planning/management was to close biogeochemical cycle, calling rinne輪廻: ‘cycle of life.’

Edo’s management of human excreta/sewage and waste. The underlying challenges of oceans—eutrophication, rising sea surface temperatures, harmful algae blooms—require solutions of ‘large quantities of nutrients on the land out of the sea’ via comprehensive land-use planning and management (Tilman et al. 2001; Diaz and Rosenberg 2008).

Management of human excreta/sewage and waste in Edo is one of encouraging examples of success. In Edo, political decisions were made to keep clean seawaters, maintaining high standards of hygiene of sea foods. A traditional form of Japanese cuisine such as sashimi (sliced fresh fish served raw with garnished herbs) and/or Edo-style sushi (sliced raw/cooked fish/shellfish on an oval-shaped ball of vinegared rice) was supported by the clean seawater policy (Fig. 4).

As improper waste management caused hygiene problems and had negative effects in fisheries in the early Edo period, disposal of any kind of waste to urban areas and water bodies (rivers/streams and seas) was severely prohibited in 1655 (Endoh 2004). Due to urban expansion of Edo, the salt marshes of the eastern parts of the Sumida-gawa River had been reclaimed from around 1596 to meet rapidly increased needs for residential areas. Household waste (mostly food scraps, paper, wood) from urban area was collected and used to fill up the salt marshes with a unique way that closed the biogeochemical cycles.    

In Edo, human excreta from urban areas had been collected and used in agriculture (Tajima 2007). In Edo, clean sea waters were maintained by the management of waste and human excreta/sewage.

River engineering and coastal architecture for land-sea interaction dynamics. Photosynthesis in marine environment requires the essential elements including silicon ‘Si’ compounds and iron ‘Fe’ compounds from land-sea connectivity. Primary production in marine environment is enormous: Marine phytoplankton produce nearly half of global net primary production each year (Field et al. 1998). While angiosperm-dominated coastal ecosystems (salt marshes, mangroves and seagrass meadows) are occupied only 0.2 % of the ocean area, the vegetated coastal habitats have been estimated to be responsible for 50 % of global CO₂ sequestration in marine sediments (Duarte et al. 2005; Duarte 2017). To sustain these huge primary productions, an enormous amount of essential nutrients must be supplied from terrestrial vegetation.

Rivers/streams are the main transporters of the organic matter from the terrestrial environment to the oceans. Large quantities of organic matter enter rivers/streams, subsequently slow decomposition of leaf litter, wood, and other plant parts constantly supplies as essential nutrients to productivity of estuaries and coastal zones, without nutrient pollution. Vast areas of coastal forests play a vital role as nutrient source for the coastal ecosystems of critical importance. To close biogeochemical cycles between land and ocean, architecture of connectivity between terrestrial and marine primary productivity is essential.

In terms of organic matter supply, the large amounts of essential nutrients equivalent to approximately half of global net primary production are required. Therefore, strategies of high primary productivity of vegetation over the whole country and/or over entire continents are vital for organic matter dynamics by land-sea interaction.

Noncontiguous dyke system to support productive terrestrial ecosystems and to preserve natural corridors of land-sea linkage. From a viewpoint of the global hydrological cycle, the overall quantity of freshwater is only about 2.5% and two-thirds of this fresh water is locked in glaciers and ice caps. Approximately 0.3% of the Earth’s freshwater is held in rivers, lakes and reservoirs (Shiklomanov and Rodda 2003). This small fraction of freshwater plays a vital role to support the terrestrial primary productivity.

Water management is essential for maintaining high primary productivity of vegetation over large geographic areas. Japan had unique flood-water management to retain water for longer residence time in land over large geographic areas (e.g., Okuma 1981). Unique noncontiguous dyke system was developed by Japanese architects to sustain productive terrestrial ecosystems and to preserve natural corridors of land-sea linkage (Fig. 6, 7, 8).

Strategical allocation of vast areas of riparian zones. Stratified foliage of riparian forests shields solar radiation, which in turn keeps river water cool. The large quantity of leaves, twigs, and other types of organic matter from riparian forests provides favorable form of nutrient for freshwater phytoplankton, the basis of stream food webs. Slow decomposition of leaf-litter constantly supplies essential nutrients without “nutrient pollution.”   

Many fish species of commercially importance require habitats of linkage between river and sea: anadromous fish migrate from the sea up into fresh water to spawn, such as salmon, Shishamo (柳葉魚, Spirinchus lanceolatus), striped bass (Morone saxatilis), and alewife (Alosa pseudoharengus); catadromous fish migrate from fresh water down into sea to spawn, such as eels, flathead grey mullet (Bora, 鰡, Mugil cephalus), and the Japanese sea bass (Suzuki, 鱸, Lateolabrax japonicus). Rivers are migration corridors for both anadromous and catadromous fishes. The elaborately shaped landscapes of riparian zones created favorable conditions for freshwater phytoplankton proliferation, and served as nursery and foraging grounds for these migratory fishes.

In terms of organic matter supply, high Si accumulation plants of the families of Poaceae (grass family), Equisetaceae (horsetail family) and Cyperaceae (family of graminoid) flourish in riparian zones may play a vital role in silica supply for diatoms (important in marine wood-webs). High primary productivity of forests over large geographic areas yields enormous amount of ‘cytochromes,’ which in turn may contribute to availability of Fe for photosynthesis in marine environment.

Fig. 5 River divert project in Edo started from around 1594 (a) Location of project sites. (b) Coastal area of Tokyo in 1959 (the Geographical Survey Institute, Japan). A: Imperial Palace (Edo Castle); B: Sumida-gawa River 隅田川; C: Nihon-bashi (important commercial center in Edo); D: Akabori-gawa River, 赤堀川, man-made channel about 8.6km or 5.3mi long to flow out Tone-gawa River to the Pacific Ocean, started from around 1594 completed in 1654; E: levee to check flow for separation of Tone-gawa River and Ara-kawa River in 1629; F: Edo-gawa River, 江戸川, man-made channel to control flood-flow started from 1635 completed in 1654; G: ancient estuary of Sumida-gawa River; H: man-made channel of Ara-kawa River, 荒川放水路, excavated in 1911–1930 from the site I; I: Senjyu Great Bridge, near the branching off point of the man-made channel of Ara-kawa River completed in 1930 from Sumida-gawa River; J: reclaimed marsh land from around 1596; K: hard ground of the Kono-dai plateau; L: Horie and Nekozane, landscaping levee to protect hinterland below sea level; M: hunting reserve for shogun family (currently belonging to the Imperial Household Ministry)

7.     A case of successful land-use planning/management: Edo

 

7.1 The largest metropolis in the 18th century: Edo

Hiroshige Utagawa (歌川広重, 1797–1858) illustrated many landscape prints depicting land-use planning/management of Eastern philosophy, owing to his background of samurai: ruling class obliged their duties and moral.     

Japan had coherent coastal national strategy until the mid-19th century. Although urban development of Edo radically changed natural geographical features (http://harukanoor4.blogspot.com/2019/), decisions were made to enhance ecological resilience for fisheries.

Edo (lit., bay-entrance or estuary) is the former name of the Japanese capital Tokyo (35°41′N, 139°42′E) developed at estuaries of Tone-gawa River system, facing on Edo (Tokyo) Bay. In 1590, Ieyasu Tokugawa (徳川家康1542–1616) settled in Edo, and established his Shogunate (military governing dynasty) in 1603. Edo began to increase in extent and population, and had over one million inhabitants as early as the middle of the eighteenth century, making it the largest metropolis in the worlds (Sansom 1963; Uspensky 2003).

In Fig. 3, Hiroshige depicts a perspective view from the Nihon-bashi Bridge (the important commercial center in Edo) with a distant Mount Fuji, farsighted Edo Castle (the current Imperial Palace). On the north bank of the bridge, there lay the largest fish-market in the Edo period, known as Uogashi (魚河岸).

It must be early in morning: fishmongers with baskets full of fresh-caught fish and other seafood slung over their shoulders head for all parts of the city, after making their purchases. Notably, two of Pacific bluefin tuna (Thunnus orientalis, up to 3m or 9.8ft) are carrying with a wooden pole. In Edo, Tuna was common and highly prized for Japanese cuisine sashimi and/or Edo-style sushi. The coherent coastal national strategy leaded to abundant and diverse fish resources, which in turn attracted large pelagic predators such as Tuna. Accordingly, off-shores of Edo were good fishing spots for Tuna.

 

7.2 Ambitious divert project of Tone-gawa River in Edo

To reduce flood-risks in Edo, an ambitious project to divert the flow of the Tone-gawa River was accomplished (Okuma 1981). In ancient times, several distributaries of Tone-gawa River, forming meandering streams with no firm channels, flowed into Edo Bay. The Sumida-gawa River was one of the distributaries flowed into Edo Bay. As soon as Ieyasu settled in Edo in 1590, he started to the extremely complicate project of river diversion.

In 1594, one of the main flows of the Tone-gawa River was checked by a levee structure at a site of the upper stream (熊谷, Kumagaya, around 70km or 44mi from Edo Bay; 36°11′N, 139°31′E). Thereafter two stream channels were excavated: Shinkawadoori (新川通8km or 5mi long; width: 18m or 59ft in 1621) was followed by Akahori-gawa (赤堀川about 8.6km or 5.3mi long, width: 18m in 1654). (These man-made channels were widened to 72m or 236ft and deepened until 1809.) By the excavation work of the channel Akahori-gawa (Fig. 5, D), the main flow of Tone-gawa River was connected with Hitachi-gawa River that pours into the Pacific Ocean. Accordingly, the flows of the two rivers were merged into one huge flow, which discharges into the Pacific Ocean (Fig. 5).

Simultaneously, a river system of the Sumida-gawa River was separated from the Tone-gawa River system to reduce flood risks in Edo area. In ancient times, the Sumida-gawa River was one of several distributaries of Tone-gawa River flowed into Edo Bay. Flow from the Tone-gawa River system was checked by a levee structure at a point of the upper stream (Kumagaya, 熊谷, about 64km or 40mi from Edo Bay; 36°13′N, 139°40′E; Fig. 5, E) in 1629. Accordingly, a distributary system (Ara-kawa River, 荒川) was separated from Tone-gawa River. Which in turn decreased volume of water flow to Edo area. As so often with Edo’s rivers, it had a local name in Edo—Sumida-gawa River (Fig. 5, B). (To reduce flood risks in Tokyo, man-made channel of Ara-kawa River, 荒川放水路, was excavated in 1911–1930. Hence, the Sumida-gawa River branches off from the Ara-kawa River shown in Fig. 5, I.)

In addition, a man-made channel, from the main stream of the Tone-gawa River to Edo Bay, was excavated to control flood-flow (江戸川, Edo-gawa River about 18km or 11mi long; Fig. 5, F) in 1635. For the excavation work of the channel to flow out flood waters toward the outskirts of Edo, natural courses of a distributary system were partly used, besides sites of hard ground were selected to stabilize the stream flow (Fig. 7-1).

Eventually, a series of the river diversion works and the excavation works of the channels contributed to an element of importance in Edo’s waterborne transport system (Okuma 1981). Owing to its military importance, a hunting preserve for the shogun family was placed at the estuary (Fig.5, M). As forbidden land, coastal forests and wetlands were maintained. Notably, a variety of habitats for fisheries were elaborately shaped in the landscape architecture of the river divert project, as Hiroshige depicts: e.g., Sumida-gawa River (Fig. 6), man-made channel of Edo-gawa River (Fig. 7), and coastal engineering of estuarine of Edo-gawa River (Fig. 8). 

Fig. 6-1 Senju Great Bridge (Tokyo: 35°44′ N, 139°48′ E) from the series One Hundred Views of Edo, Hiroshige, originally published 1856–59. Japanese architects developed unique ‘dam’ system to retain flood-water on the either side of the river in desolate areas. An extensive area of flood-water retarding zone checked by embankment enables allocated vast areas of riparian forests, and preserves natural drainage corridors of land-sea linkage for abundant supply of organic matter. This bridge in the outskirts of Edo over the Sumida-gawa River (Fig. 5, I) was built in 1594 using wood of the evergreen yew plum pine (Podocarpus macrophyllus, up to 20m, endemic to the ancient supercontinent of Gondwana). The wood did not rot over 300 years, owing to resistance to rot and termites. In ancient times, the Sumida-gawa River was one of several distributaries of Tone-gawa River poured into Edo Bay. To reduce flood risks in Edo, the Sumida-gawa River was separated from the Tone-gawa River system in 1629, by construction of a levee to check flow of the Tone-gawa River system at a site (Fig. 5, E, about 64km or 40mi of upper-stream). Eventually, the Ara-kawa River originates from the Chichibu-santi mountain chain ran in Edo. As so often with Edo’s rivers, it had a local name in Edo—Sumida-gawa River. Hiroshige depicts corridor architecture of land-sea linkage. Cool river water originates from deep forests of distant Mount Buko meanders along contiguous deep riparian forests. The cool river water in turn cools coastal seawater together with supply of important terrigenous organic matter, including silica within the plant cell wall and soluble Fe in cell structure, which are required to support marine primary productivity.

7.3 Land governance and unique design of river engineering to maintain cool, clean and clear waters   

 

7.3.1 Total land-use planning/management.

 

In Eastern philosophy, sustaining forests from mountainous areas of river headwaters toward coastal areas and watershed management of running clear waters were regarded as the first principle in the critical infrastructure for sustainability of society. In Fig. 6-1, Hiroshige depicts a perspective view form the Senjyu-Ohashi Bridge built in 1594, the first and largest bridge over the Sumida-gawa River with a distant Mount Buko (elevation: originally 1,336m or 4,383ft, Fig. 5a), one of the peaks of the Chichibu-santi mountain chain. In 1629, in one phase of the series of the large-scale river diversion works (Fig. 5), Ara-kawa River was separated from the Tone-gawa River system by a levee (Fig. 5, E, about 64km or 40mi from Edo Bay). The Ara-kawa River originating from the Chichibu-santi mountain chain ran in Edo (local name of the Ara-kawa River in Edo—Sumida-gawa River). Since ancient times, the Chichibu-santi mountain chain, the headwaters of the Ara-kawa River, had been the subject of sacred mountain religious worship.

Shugendo (修験道, meaning “the path of training and testing”), founded by En no Ozunu (役小角 or En no Gyoja 役行者, 634–701), was later combined with Buddhism mainly the Shingon Sect established by Kūkai (空海, 774–835). The deep old-growth forests were maintained as forbidden land over a millennium, allowing only shugenja (修験者, Shugendo monks) to enter these areas for their religious experience/training (http://harukanoor4.blogspot.com/2016/). As monks of Shugendo devoted to helping people via medication using diverse herbs gathered from the sacred mountains along with performance of Buddhist rituals, people adored them.

The mountains of Chichibu-santi are incorporated in their myths and legends as sacred sites: The name of Mount Buko has a legendary explanation. Fascinated by the imposing mountain, the legendary Prince Yamato-takeru (http://harukanoor4.blogspot.com/2019/) ascended the mountain, and he dedicated his armor helmet (甲) to the spirit of mountains. This was taken up as Buko (武甲, brave armor helmet) and became a name of the mountain. It was noted for the cool artesian springs. In ancient times, En no Ozunu often visited the deep old-growth forests for his religious experience/training.   

On the other hand, the foothills were venues for numerous pleasurable activities for people. Pilgrimage in Japan has its roots in ancient times, by the Edo period pilgrimages had become generally practiced. A route of Chichibu Pilgrimage along the foot of Mount Buko, a multi-site pilgrimage of 34 temples, was noted for the beauty of the surrounding countryside and traditional inns with hot springs and bathing facilities. The pilgrim of roughly 100km (62mi) long way near Edo became exceptionally popular.

In terms of land-sea interactions, deep old-growth forests forming the headwater sources play a profound role. For the abundance and high primary productivity of marine phytoplankton, large quantities of the essential elements such as iron ‘Fe’ compounds are supplied from the high primary productivity of forests to the productive ocean margins. The stratified canopy foliage of deep forests shields solar radiation, which in turn keeps soil moisture and groundwater cool. As a significant amount of the water flowing in rivers comes from groundwater, cool groundwater discharge into river streams keeps stream water cool. The inflow of cool river water makes an important contribution to marine primary productivity, providing favorable temperature conditions for productive diatoms-dominated phytoplankton blooms.

Fig. 6-2 Sekiya Village from the series Thirty-six Views of Eastern Capital, Hiroshige Ⅱ (1826–1862), originally published 1861–62 (Image courtesy of the National Diet Library, Japan). Salt-marshes along the ancient estuarine of the Sumida-gawa River had been reclaimed from around 1590. To reduce flood hazards in urban area of Edo, an extensive area of flood-water retaining zone was allocated here (Fig. 5, G). Owing to abundant organic matter supply by floods and retaining soil moisture, the man-made flood recurring zone was very fertile. Vegetables of all sorts were grown. Sekiya village was also noted for its abundant fisheries resources, as intricate channels from the Sumida-gawa River to diffuse flood-waters into low-lying plains and numerous man-made sandbanks covered with dense riparian forests to dissipate flood-water wave-energy created diverse habitats for resilient inland fisheries. The benefits of the flood recurring zone, local societies and economics supported by high productivity, balanced with the threats posed by floods.

Fig. 6-3 Sekiya Village on Sumida-gawa River from the series Thirty-six Views of Mount Fuji, Hokusai Katsushika (1760–1849), originally published around 1831 (Image courtesy of the Adachi Institute of Woodcut Prints https://www.adachi-hanga.com/). In outskirts of Edo, an extensive area of flood-water retarding zone was allocated on either side of the Sumida-gawa River. Senju Great Bridge (Fig. 6-1) was positioned in the flood-water retarding zone. Flood-waters were allowed to flow into the low-lying plains of ancient estuarine of the Sumida-gawa River. To check the flood-waters, this meandering embankment (distance from the Senju Great Bridge, around 1,650m or 1mi) was built in 1616. Hokusai depicts the embankment, featuring the unique shape and the vastness of the flood-water retarding zone. 

7.3.2 Unique design of river engineering

 

Noncontiguous dike system in Edo. Noncontiguous dike system to retain flood-waters in desolate areas was ordinarily adopted in river engineering in the Edo era. In this system, an extensive area of flood-water retaining zone was allocated, which in turn enabled placement of vast areas of riparian forests and wetlands.   

Flood-water retaining system served as a sort of ‘dam’ not to block river. To decrease peak discharge, volume, and frequency of floods in urban area of Edo, an extensive area of flood-water retarding zone was strategically allocated on either side of the upper-stream of the Sumida-gawa River. The Senjyu-Ohashi Bridge (Fig. 5, I; Fig. 6-1) was situated in the flood-water retarding zone in the outskirts of Edo. Landscape architecture of the man-made flood recurring zone was depicted by Hiroshige Ⅱ (1826–1862) (Fig. 6-2).  

The large tracts of salt-marshes extended along Edo Bay at the ancient estuarine of the Sumida-gawa River (Fig. 5, G) had been reclaimed from around 1590 (Endoh 2004). To retain flood-water, long embankments in slanted angle to the river flow were raised from a point of the ancient estuarine, and low-lying flood plains were semi-enclosed by the embankment. The V-shaped embankment on the either side of the Sumida-gawa River served as a sort of ‘dam.’

When Ieyasu settled in Edo in 1590, the embankment system in left side of the river from Kumagaya (熊谷, about 60 km or 37 mi upper-stream) to the point (Fig. 5, G) was already partly existed. The meandering embankment (Fig. 6-3, length: 3.8km or 2.4mi, distance from the Senju-Ohashi Bridge: around 1,650m or 1mi) was built in 1616. Hokusai depicts the meandering embankment, featuring the uniqueness of the shape and the vastness of the flood-water retaining zone.       

Some quarters of Asakusa (right side of the river) had been seriously affected by flooding of the Ara-kawa River. In 1620, an embankment (length: 860m or 0.53mi; height: 3m or 9.8ft; width of levee crown: 7.2m or 24ft) along a moat connecting the Musasino Plateau was constructed. Flood-waters overflowed in the outskirts of upper-stream Asakusa, and prevented recurrence of flooding in important areas of Asakusa.

In Fig. 6-1, Hiroshige depicts a view of the Sumida-gawa River in the flood-water retarding zone. A series of man-made sandbanks that directed water-flows into low-lying plains are constructed as parallel each other with a slanted angle.

Architecture of flood-water retarding zone. In Fig. 6-2, Hiroshige Ⅱ depicts the man-made flood recurring zone, just across the Senju-Ohashi Bridge from Edo. The existence of the Sumida-gawa River is indicated by the sail of ships, beyond dense riparian forests and constructed wetlands. To diffuse flood-waters toward into low-lying plains, intricate channels from the Sumida-gawa River are excavated. Numerous Man-made sandbanks are raised to dissipate flood-water wave energy.   

Strategically allocated vast areas of riparian zones are able to perform ecosystem functions of retaining and filtering flood-waters, while keeping organic matter dynamics by land-sea interactions. To construct irregular-shaped wetlands covered with common reed (Phragmites australis), closely spaced wooden piles made from pine wood were driven into the riverbed. Pine wood does not rot in wet and oxygen-poor conditions and become as hard as stone when left in immersed in water. Along the wetlands, numerous ‘loosing spaced wooden piles’ driven into riverbed served as a sort of breakwater, preventing the bank from being washed away by the strong current (http://harukanoor4.blogspot.com/2019/).

The man-made flood recurring zone was very fertile, as flood-waters carried abundant organic matter and distributed it across a wide area. Sekiya village was noted for its production of all sorts of vegetables and abundant inland fisheries resources. Created open space of vast emptiness provided venue for pleasurable activities for people (Fig. 6-2, 6-3).

Flood-water retaining system in man-made channel of the Edo-gawa River.

As part of the ambitious river divert project, Edo-gawa River (Fig. 5, F) was excavated to redirect Tone-gawa River flood waters to the outskirts of the Eastern Capital, in 1635 (Okuma 1981). In the excavation work of flood-flow control, a site of hard ground was selected. Hard ground of Kono-dai Hill in the foreground in Fig. 7-1 served as a sort of ‘rigid structure of dyke.’ On the other side, an extensive area of flood-water retaining zone was allocated in the west-side of the Edo-gawa River. Numerous man-made sandbanks that directed water-flow into low-lying plains are raised together with dense riparian forests and constructed wetlands.

Need for land governance. Land-use planning is connected important policy issues: flood management, aquatic resource management for food security, and CO₂ sequestration in a vast area of ocean. Edo’s flood-water retaining zone projects suggest that a multidimensional approach is required with a wide range of policies.

Fig. 7-1 The Edo-gawa River at Kono-dai Hill (Chiba: 35°45′ N, 139°54′ E) from the series Thirty-Six Views of Mount Fuji, Hiroshige, originally published 1852 (Image courtesy of the British Museum: https://www.hiroshige.org.uk by Chiappa JN). The Edo-gawa River (Fig. 3, F) was excavated to flow out flood-waters of the Tone-gawa River to the peripheries of Edo in 1635. To create a firm channel, hard ground of plateau was selected. Earthen groynes (groins), sandbars that extended into river from river-shore, were constructed in the man-made meandering channel. The landscaping groynes covered with riparian forests were fringed with constructed wetlands created by closely spaced wooden piles driven into riverbed. ‘Loosely spaced wooden piles’ driven into riverbed served as a sort of breakwater, preventing the shorelines being washed away. These river engineering structures create a variety of habitats: riffles, calmer flows, and deep pools. Man-made riffles serve to aerate the running river water by babbling currents, increasing the amount of dissolved oxygen. Diatoms-dominated freshwater phytoplankton, the basis of stream food webs, thrive better in cool, clear, clean, and oxygen-rich waters. In Eastern philosophy, unique design of river engineering had been developed taking into account of aquatic resources management.

7.3.3 Maintaining freshwater quality: The landscaping river groynes serve to aerate the cool river water.

 

Biological processes in the integrity of terrestrial and aquatic ecosystems, constituting a complex and dynamic system, play a pivotal role in qualitative restoration of freshwater. In Eastern philosophy, unique design of river engineering had been developed to maintain freshwater quality.

In recent decades, toxic cyanobacterial blooms represent a serious threat for water quality of surface waters worldwide (e.g, Paerl and Huisman 2008). In stagnant waters like lakes, ponds, or reservoirs, toxic cyanobacteria thrive better under the condition of excessive nutrients (fertilizer runoff from agriculture, sewage and industrial discharges, and urban stormwater) in warmer water temperatures.

In Fig. 6-1, 7-1, 7-2, Hiroshige depicts a unique design of river engineering: irregular-shaped river groynes covered with riparian forests. These sandbars, that extend into river, create a variety of habitats: riffles (瀬), calmer flows, and deep pools (淵). Man-made riffles serve to aerate the cool running river water by babbling currents, increasing the amount of dissolved oxygen. Diatoms-dominated freshwater phytoplankton, the basis of stream food webs, thrive better in cool, clear, clean, and oxygen-rich waters. Even in construction of man-made channel of Edo-gawa River, the landscaping earthen groynes covered with riparian forests fringed with constructed wetlands were created.

In land governance of Eastern philosophy, ‘steady streaming water flows’ and ‘babbling currents’ were highly prized for the function of maintaining freshwater quality. From the Edo period onward, ‘civil engineering’ is referred to doboku土木working with earth and trees/woods. Japanese engineers pursued aesthetic works in river engineering using earth and trees/woods.

Fig. 7-2 Scattered Pines, Edo-gawa River from the series One Hundred Views of Edo, Hiroshige, originally published 1856–59 (Image courtesy of the Adachi Institute of Woodcut Prints https://www.adachi-hanga.com/). Hiroshige depicts a near estuaries landscape of man-made channel of the Edo-gawa River. The net being cast in the foreground and the fishing boat that part of it seen through the net imply abundance of fisheries resources. The fishermen are working along the constructed reedbeds. The river engineering of Eastern philosophy, the deep riparian forests in the backdrop of this print and earthen groynes with pine groves fringed with reedbeds, created a man-made channel of abundant fisheries resources.

7.4 Coastal landscape architecture for keeping cool, clean and clear seawaters

 

7.4.1 Coastal protection integrated with diverse habitats for resilient fisheries.

 

At the river mouth of the Edo-gawa River, excavated in 1635 to discharge flood waters of Tone-gawa River to the remote coast from the heart of the city of Edo (Fig. 5, F), coastal landscapes were shaped by unique design of coastal engineering in Eastern philosophy.    

As the Japanese archipelago is prone to tropical cyclone and tsunami, ancient Japanese architects were aware that local geographical features such as island and/or coastal hill/mountain contribute to coastal protection by reducing wave energy. Through the learning-based approach over millenniums via dialogue with dynamic earth-surface system, designs and techniques in shaping landscapes contribute to coastal protection by reducing wave energy were developed. Japan had unique design and techniques in construction of coastal protection integrated with a variety of habitats for resilient fisheries.　　　

Hiroshige depicts landscapes of estuarine zone of the man-made channel of Edo-gawa River that intricately shaped by humans, Gyotoku (行徳, Chiba, 35°41′ N, 139°54′ E), featuring unique design of coastal and estuarine engineering (Fig. 8). 

When Ieyasu settled in Edo in 1590, the mouth of the Sumida-gawa River was situated in north-east site of the Edo Castle (Fig. 3, I). At that time, Gyotoku was an island. The estuarine zone near the mouth of the Edo-gawa River covered by large tracts of salt marshes and mud flats was reclaimed from around 1596 (Fig. 5, J) (Endoh 2004).

In Fig. 8-1, Hiroshige depicts a distant view of the unique feature of irregular-shaped embankment system from the hinter land. Gyotoku was noted for its salt production. Beyond the irregularly bending dyke that local villagers walking along it with their carrying poles, the salt beach is spreading. On the solar evaporation pans the workers occupy with obtaining salt. On the right the embankment projects into the broad forested coastal hills at the river mouth. The unique design of the embankment system in the estuary of the man-made channel of Edo-gawa River: irregularly bending dyke and forested coastal hills that project into sea were effective in dissipating wave energy of tropical cyclone, storm surge and tsunami.

Fig. 8-1 Salt Beach at Gyōtoku (Chiba, 35°41′ N, 139°54′ E) from the series Famous Views in the Vicinity of Edo, Hiroshige, originally published 1839 (Image courtesy of the Museum of Fine Art, Boston). In 1635, the Edo-gawa River (Fig. 5, F) was excavated to flow out flood-waters of the Tone-gawa River to the outskirts of the Eastern Capital. Large tracts of salt marshes in the man-made channel’s estuarine areas were reclaimed from around 1596. Hiroshige depicts a distant view of the unique design of the embankment system in the estuary of the man-made channel: irregularly bending dyke and broad forested coastal hills that project into sea.

In Fig. 8-2, Hiroshige depicts the mouth of the Edo-gawa River from offshore. To reduce wave energy, Japanese engineers often placed man-made islands in entrance of bay and/or river mouth. Behind the passenger boat in the foreground, a man-made island fringed with irregular-shaped man-made sandbanks is placed. The man-made island served as a sort of caisson breakwater, absorbing wave energy and providing safe harborage. To create the island, closely spaced pine piles were driven into sea-floor. Along the man-made sandbanks, numerous ‘loosing spaced wooden piles’ are driven into sea-floor served as a sort of breakwater to reduce the intensity of wave action and thereby reduce erosion.

At the upper right of this print, the town of Gyotoku lay behind large expanses of ‘solar evaporation salt pans’ with pine trees evenly spaced along the bank. The tall and dense coastal forests at the upper left of this print were belonged to villages of Horie and Nekozane (Fig. 3, M), depicted as the broad forested coastal hills. The coastal shoreline was shaped by the techniques of closely spaced pine piles driven into sea-floor and ‘loosing spaced wooden piles’ breakwaters.

Fig. 8-2 Returning Sails at Gyotoku from the series Eight Views of the Environs of Edo, Hiroshige, originally published mid-1830’ (Image courtesy of the National Diet Library, Japan). Hiroshige depicts a view of the irregular-shaped embankment system, broad forested coastal hills that project into sea (Fig. 8-1), from offshore of the mouth of the Edo-gawa River. To dissipate wave energy, Japanese engineers often placed man-made islands at the entrance of bay and/or river mouth, serving as a sort of caisson breakwater. The estuary architecture of coastal protection, the broad forested coastal hills and man-made island surrounded with irregular-shaped sandbanks, performs function of organic matter dynamics by land-sea interactions.

7.4.2 Land-sea connectivity via non-fragmented ecosystems  

 

Construction of a variety of habitats: Intricate estuarine channels, man-made sandbanks, mudflats, man-made islands, and salt marshes. In Fig. 8-3, Hiroshige depicts a closer view of the unique feature of embankment system in Horie and Nekozane. At the river mouth, the man-made channel of Edo-gawa River divides into two branches so as to form two forks. Two villages, Nekozane on right and Horie on the left of the Sakai-gawa canal (a branch of the Edo-gawa River), are depicted from the direction of Edo Bay. The existence of the Edo-gawa River is indicated by the masts of two boats seen in the depths of the print below with dense riparian forests on the other side of the river, to the right of Mount Fuji.

The name Nekozane is derived from a folk-lore: in the era of the Kamakura shogunate (1185–1333), local people, who suffered recurrent coastal floods, raised the ground level and constructed hills. Pine trees (Pinus thunbergii) were planted on the hills. The dike system was very effective to absorb storm energy, hence wave overtopping of tsunami/cyclone did not pass over (kosanu, 越さぬ) the tree bases (ne, 根) of the pine trees: ‘ne kosanu’ changed to ‘Nekozane.’

A prized clam (Mactra chinensis), supplied to city market from these two villages, was popular as topping of Edo-style sushi known as aoyagi, 青柳. The clams were gathered on the many man-made sandbanks. In Fig. 8-3, the presence of local villagers on the levee road indicates height of the hill embankment. A gentle slope run up from the dyke to the precincts of the shrine, shielded with tall and dense sacred groves.

Placement of non-fragmented ecosystems for land-sea connectivity. Estuarine and coastal ecosystems play a significant role in closing biogeochemical cycle of land-sea connectivity. Continuous vegetation: dense estuarine forests (Fig. 8-3), man-made islands/coastal hills covered with thick coastal forests (Fig. 8-2) and lush tidal marshes, facilitates habitat connectivity between land and sea, leading to the resilience of seagrass meadows and kelp-forests. As biochemical materials such as silicon ‘Si’ compounds and iron ‘Fe’ compounds are supplied from estuarine and coastal vegetation, high productivity of marine photosynthesis of seagrass meadows and kelp-forests maintains and recovery from disturbance is easy.   

Japanese engineers constructed extensive salt marshes that fringe man-made island (Fig. 8-2) and coastal hills (Fig. 8-3). Salt marshes act as natural filter that trap sediments and purify seawater (e.g., Barbier et al. 2011), reducing sedimentation type pollution and enhancing clarity of seawaters.     

Estuarine and coastal ecosystems control seawater temperatures via foliage shield effects, solar radiation balance, and cool groundwater discharge to coastal seas (Fig.1).

Countless sandbanks along with numerous ‘loosing spaced wooden piles’ driven into sea-floor served as a sort of breakwater create a variety of habitats: riffles, calmer flows, and deep pools. These man-made structures serve to aerate the cool seawaters by babbling waves, increasing the amount of dissolved oxygen.

Offshore of Gyotoku was noted for its high quality fisheries resources, and was esteemed as one of Osaiura (御菜浦, His Excellency’s fishing zones). This fact suggests that the landscape elaborately shaped by humans created resilient sea: diatoms-dominated phytoplankton, the basis of marine food webs, flourished in cool, clear, clean, and oxygen-rich seawaters, with huge amounts of organic matter (e.g., leaf litter, wood, other plant parts, and humus) supply from coastal vegetation; flourishing seagrass meadows and kelp-forests provided fish and invertebrate nursery ground and foraging. 

Fig. 8-3 Villages of Horie and Nekozane from the series One Hundred Views of Edo, Hiroshige, originally published 1856–59 (Image courtesy of the British Museum: https://www.hiroshige.org.uk by Chiappa JN). In a closer view of the broad forested coastal hills in Horie and Nekozane, Hiroshige depicts the estuary landscape architecture that enables organic matter dynamics by land-sea interactions. Aware that lush landscapes of estuaries and coastal zones play an important role in marine photosynthesis and fisheries, a variety of habitats were elaborately shaped: man-made sandbanks, mudflats, man-made islets, salt marshes, and thick coastal forests. The coastal fishery villages were renowned for its supply of a particular edible clam (Mactra chinensis), popular as topping of Edo-style sushi, gathered on the many man-made sandbanks. Because of the excellent point for gathering shellfish and fishing, the coastal sea of the man-made channel of Edo-gawa River was designated as one of Osaiura, 御菜浦, His Excellency’s fishing zones. The catches were delivered to shogun’s court.

8.     Land governance and climate change

 

Photosynthesis in marine environment heavily distributes in the coastal areas, that covers less than 10% of the world ocean. The dynamic biological process of marine photosynthesis influences climate, via CO₂ sequestration in the deep sea (phytoplankton: Field et al. 1998, Falkowski et al. 1998, Falkowski 2002; coastal vegetation: Duarte et al. 2005, Duarte 2017) and via solar radiation valance (Fig. 1). Decline of photosynthesis in the coastal area allows increase in sea temperatures and causes amplified evaporation from the oceans.

In Edo, the approaches that had been adopted to manage fisheries resources for food security were unique and effective. The diatoms-dominated marine phytoplankton, the basis of abundant fisheries resources, requires supply of essential elements such as iron ‘Fe’ and silica ‘Si’ compounds from terrestrial vegetation, in addition to cool, clear, clean seawaters. To meet the basic requirements, policy of human excreta management and watershed management sustaining forests along with running waters were implemented. The unique design and techniques of river/coastal engineering, closing the biogeochemical cycles and maintaining organic matter dynamics by land-sea interactions had been developed.

The Edo’s estuarine and coastal transformation by humans created diverse and productive habitats. The abundance and high primary productivity of marine environment led by the land governance of Edo, in turn, contributed to reducing negative impacts on climate. The unique learning-based approach in Eastern philosophy provides guidance for productive future, as fisheries resource management integrated with climate change mitigation/adaptation is a major global challenge. 

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