Editing IPCC:AR6/WGII/Chapter-10 (section)

=== 10.4.3 Ocean and Coastal Ecosystems ===

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Coastal habitats of Asia are diverse, and the impacts of climate change, including rising temperatures, ocean acidification and SLR, are known to affect the services and livelihoods of the people depending on them. The risk of irreversible loss of many marine and coastal ecosystems increases with global warming, especially at 2°C or more ( ''high confidence'' ) ( [[#IPCC--2018b|IPCC, 2018b]] ). In the South China Sea, coral growth and sea surface temperature (SST) have shown regional long-term trends and inter-decadal variations, while coral growth is predicted to decline by the end of this century ( [[#Yan--2019|Yan et al., 2019]] ). Increasing human impacts have also been found to reduce coral growth ( [[#Yan--2019|Yan et al., 2019]] ). In the South China Sea, nearly 571 coral species have been severely impacted by global climate changes and anthropogenic activities ( [[#Huang--2015a|Huang et al., 2015a]] ).

The 2014–2017 global-scale coral bleaching event (GCBE) resulted in very high coral mortality on many reefs, rapid deterioration of reef structures and far-reaching environmental impacts ( [[#Eakin--2019|Eakin et al., 2019]] ). The thermally tolerant Persian Gulf corals ( [[#Coles--2013|Coles and Riegl, 2013]] ) are facing an increasing frequency of mass bleaching ( [[#Riegl--2018|Riegl et al., 2018]] ) and each event leaves a substantial long-term impact on coral communities (Burt, 2014) with low capacity for recovery indicating a bleak future for Persian Gulf reefs ( [[#Burt--2019|Burt et al., 2019]] ).

One of the probable results of global warming is high SLR. Scientists believe that increasing GHGs (the Earth’s temperature controllers) is the cause of this global warming, and by using satellite measurements, these scientists have forecasted on average 1–2 mm for SLR ( [[#Jafari--2016|Jafari et al., 2016]] ). The level of thermal stress (based on a degree heating month index, DHMI) at these locations during the 2015–2016 El Niño was unprecedented and stronger than previous ones ( [[#Lough--2018|Lough et al., 2018]] ). In the Persian Gulf, the reef-bottom temperatures in 2017 were among the hottest on record, with mean daily maxima averaging 35.9 ± 0.10°C across sites, with hourly temperatures reaching as high as 37.7°C ( [[#Riegl--2018|Riegl et al., 2018]] ). About 94.3% of corals were bleached, and about 66% perished, in 2017 ( [[#Burt--2019|Burt et al., 2019]] ). In 2018 coral cover averaged just 7.5% across the southern basin of the Persian Gulf. This mass mortality did not cause dramatic shifts in community composition as earlier bleaching events had removed the most sensitive taxa. An exception was the already rare ''Acropora'' spp. which were locally extirpated in summer 2017 ( [[#Burt--2019|Burt et al., 2019]] ). During 2008–2011 also the coral communities of Musandam and Oman showed changes depending on the stress-tolerance levels of the species and the local environmental disturbance level ( [[#Bento--2016|Bento et al., 2016]] ).

The health and resilience of corals have been found to be associated with beneficial microorganisms of coral (BMC) which alter during environmental stress. Increasing seawater temperatures have been found to affect the functioning of the symbiotic algae of corals ( [[#Lough--2018|Lough et al., 2018]] ; [[#Gong--2019|Gong et al., 2019]] ) and its bacterial consortia leading to coral bleaching and mortality ( [[#Bourne--2016|Bourne et al., 2016]] ; [[#Peixoto--2017|Peixoto et al., 2017]] ; [[#Bernasconi--2019|Bernasconi et al., 2019]] ; ( [[#Motone--2020|Motone et al., 2020]] ).

Coral reefs were found to be affected differentially during bleaching episodes, and those species which survived had more stress-tolerant symbionts and higher tolerance to thermal changes ( [[#Majumdar--2018|Majumdar et al., 2018]] ; [[#Thinesh--2019|Thinesh et al., 2019]] ; [[#van%20der%20Zande--2020|van der Zande et al., 2020]] ). Rare thermally tolerant algae and host species-specific algae may play important roles in coral bleaching ( [[#van%20der%20Zande--2020|van der Zande et al., 2020]] ). Along the Indian coast, in the coral reefs of Palk Bay (Bay of Bengal), varied bleaching and recovery patterns among coral genera was observed during the 2016 bleaching episode ( [[#Thinesh--2019|Thinesh et al., 2019]] ). Bleaching was high in ''Acropora'' spp. (86.36%), followed by ''Porites'' (65.45%), while moderate to no bleaching was observed in ''Favites Symphyllia, Favia, Platygyra'' and ''Goniastrea'' .

The presence of stress-tolerant symbiont Durusdinium (Clade D) during the post-bleach period indicated the high adaptive capacity of ''Acropora'' spp. in tropical waters ( [[#Thinesh--2019|Thinesh et al., 2019]] ). Also ''Porites'' spp. were found to have higher thermal thresholds and showed better resilience to bleaching than species like ''Fungiid'' spp. ( [[#Majumdar--2018|Majumdar et al., 2018]] ). In the Philippines, during the 2010 bleaching event, the size structure of the mushroom coral was found to be affected ( [[#Feliciano--2018|Feliciano et al., 2018]] ). In Indonesia, it was found that branching coral diversity may decrease relative to massive, more resilient corals ( [[#Hennige--2010|Hennige et al., 2010]] ). This would have large-scale impacts upon reef biodiversity and ecosystem services, and reef metabolism and net reef accretion rates, since massive species are typically slow growers ( [[#Hennige--2010|Hennige et al., 2010]] ).

Macro-tidal coral reefs are particularly sensitive to medium- to long-term changes in sea-level Andaman trenches ( [[#Simons--2019|Simons et al., 2019]] ). Data compiled from 11 cities throughout East and Southeast Asia, with particular focus on Singapore, Jakarta, Hong Kong and Naha (Okinawa), highlights several key characteristics of urban coral reefs, including ‘reef compression’ (a decline in bathymetric range with increasing turbidity and decreasing water clarity over time and relative to shore), dominance by domed coral growth forms and low reef complexity, variable city-specific inshore–offshore gradients, early declines in coral cover with recent fluctuating periods of acute impacts and rapid recovery, and colonisation of urban infrastructure by hard corals ( [[#Heery--2018|Heery et al., 2018]] ).

In Taiwan, Province of China, the calcification rate of the model reef coral ''Pocillopora damicornis'' was higher in coral reef mesocosms featuring seagrasses under ocean acidification conditions at 25°C and 28°C. The presence of seagrass in the mesocosms helped to stabilise the metabolism of the system in response to simulated climate change ( [[#Liu--2020a|Liu et al., 2020a]] ).

An increase in host susceptibility, pathogen abundance or virulence has led to higher prevalence and severity of coral diseases and to decline and changes in coral reef community composition ( [[#Maynard--2015|Maynard et al., 2015]] ). Relative risk has been found to be high in the province of Papua in Indonesia, the Philippines, Japan, India, northern Maldives, the Persian Gulf and the Red Sea. For the combined disease-risk metric, relative risk was considered lower for locations where anthropogenic stress was low or medium, a condition found for some locations in Thailand ( [[#Maynard--2015|Maynard et al., 2015]] ).

Degradation and loss of coral reefs can affect about 4.5 million people in Southeast Asia and the Indian Ocean ( [[#Lam--2019|Lam et al., 2019]] ). In the coral reef fisheries sector, there are about 3.35 million fishers in Southeast Asia and 1.5 million fishers in the Indian Ocean ( [[#Teh--2013|Teh et al., 2013]] ). The economic loss under different climate-change scenarios and fishing efforts were estimated to range from 27.78 to 31.72 million USD annually in Nha rang Bay, Vietnam. A survey conducted in Taiwan, Province of China, showed that the average annual amount that people were personally willing to pay was 35.75 USD and the total amount was 0.43 billion USD. These high values indicate the need to preserve these coral reef ecosystems ( [[#Tseng--2015|Tseng et al., 2015]] ). In Bangladesh, the coral reef of St. Martin’s Island contributes 33.6 million USD yr –1 to the local economy, but climate change, along with other anthropogenic activities, has been identified as a threat these habitats ( [[#Rani--2020a|]] [[#Rani--2020|Rani et al., 2020]] a ).

Mitigation of global warming has been identified to be essential to maintain healthy coral reef ecosystems in Asia ( [[#Comte--2018|Comte and Pendleton, 2018]] ; [[#Heery--2018|Heery et al., 2018]] ; [[#Lam--2019|Lam et al., 2019]] ; [[#Yan--2019|Yan et al., 2019]] ). Restoration of reefs ( [[#Nanajkar--2019|Nanajkar et al., 2019]] ) and building resilience through multiple mechanisms, such as innovative policy combinations, complemented by environmental technology innovations and sustained investment ( [[#Hilmi--2019|Hilmi et al., 2019]] ; [[#McLeod--2019|McLeod et al., 2019]] ), are suggested.

An ecosystem-based approach to managing coral reefs in the Gulf of Thailand is needed to identify appropriate marine protected area (MPA) networks and to strengthen marine and coastal resource policies in order to build coral reef resilience ( [[#Sutthacheep--2013|Sutthacheep et al., 2013]] ). Broadening the scope to develop novel mitigation approaches towards coral protection through the use of symbiotic bacteria and their metabolites ( [[#Motone--2018|Motone et al., 2018]] ; [[#Motone--2020|Motone et al., 2020]] ) has been suggested. Coral culture and transplantation within the Gulf are feasible for helping maintain coral species populations and preserving genomes and adaptive capacities of Gulf corals that are endangered by future thermal-stress events ( [[#Coles--2013|Coles and Riegl, 2013]] ). Greater focus on understanding the flexibility and adaptability of people associated with coral reefs, especially in a time of rapid global change ( [[#Hoegh-Guldberg--2019|Hoegh-Guldberg et al., 2019]] ), and a well-designed research programme for developing a more targeted policy agenda ( [[#Lam--2019|Lam et al., 2019]] ), is also recommended. Cutting carbon emissions ( [[#Bruno--2016|Bruno and Valdivia, 2016]] ) and limiting warming to below 1.5°C is essential to preserving coral reefs worldwide and protecting millions of people ( [[#Frieler--2013|Frieler et al., 2013]] ; [[#Hoegh-Guldberg--2017|Hoegh-Guldberg et al., 2017]] ). Many visitors to coral reefs have high environmental awareness, and reef visitation can both help to fund and encourage coral reef conservation ( [[#Spalding--2017|Spalding et al., 2017]] ).

The largest mangrove forests are in Asia contributing to about 42% of the world’s mangroves. This includes Sundarbans, the world’s largest remaining contiguous mangrove forest ( [[#Dasgupta--2020|Dasgupta et al., 2020]] ). Mangrove ecosystems are rich in biodiversity. The ecosystems are supported and maintained by both flora and a large array of living things, which include mammals, birds, fish, crustaceans, shrimps, insects and microbes [[#footnote-010|3]] . Contemporary rates of mangrove deforestation are lower than in the late 20th century ( [[#Gandhi--2019|Gandhi and Jones, 2019]] ; [[#Friess--2019|Friess et al., 2019]] ); however, some areas in Asia continue the trend. Myanmar is the primary mangrove-loss hotspot in Asia, exhibiting 35% loss from 1975 to 2005 and 28% from 2000 to 2014. Rates of loss in Myanmar were four times the global average from 2000 to 2012. The Philippines is additionally identified as a loss hotspot, with secondary hotspots including Malaysia, Cambodia and Indonesia ( [[#Gandhi--2019|Gandhi and Jones, 2019]] ).

Mangrove deforestation is expected to increase as many tropical nations utilise mangrove areas for economic security. Increased river damming would reduce fluvial sediment sources to the coast making mangroves more vulnerable to SLR, and uncertain climate with extreme oscillations can create unstable conditions for survival and propagation of mangrove ( [[#Friess--2019|Friess et al., 2019]] ).

Valuation of ecosystem services of mangroves have indicated that they prevent more than 1.7 billion USD in damages for extreme events (i.e., one event in 50 years) in the Philippines ( [[#Menéndez--2018|Menéndez et al., 2018]] ). They reduce flooding to 613,500 people yr –1 , 23% of whom live below the poverty line and avert damages up to 1 billion USD yr –1 in residential and industrial property. Mangroves have also become a very popular source of livelihood in Asia through tourism ( [[#Dehghani--2010|Dehghani et al., 2010]] ; [[#Kuenzer--2013|Kuenzer and Tuan, 2013]] ; [[#Spalding--2019|Spalding and Parret, 2019]] ; [[#Dasgupta--2020|Dasgupta et al., 2020]] ) and they also support fisheries ( [[#Hutchison--2014|Hutchison et al., 2014]] ).

Mangroves, tidal marshes and seagrass meadows (collectively called coastal blue carbon ecosystems) have sequestered carbon dioxide from the atmosphere continuously over thousands of years, building stocks of carbon in biomass and organic rich soils. Carbon dynamics in mangrove-converted aquaculture in Indonesia indicate that the mean ecosystem carbon stocks in shrimp ponds are less than half of the relatively intact mangroves ( [[#Arifanti--2019|Arifanti et al., 2019]] ). Conversion of mangroves into shrimp ponds in the Mahakam Delta have resulted in a carbon loss equivalent to 226 years of soil carbon accumulation in natural mangroves. In the Philippines, abandoned fishpond reversion to former mangrove has been found to be favourable for enhancing climate change mitigation and adaptation ( [[#Duncan--2016|Duncan et al., 2016]] ). Integrated mangrove-shrimp farming, with deforested areas not exceeding 50% of the total farm area, has been suggested to support both carbon sequestration as well as livelihood ( [[#Ahmed--2018|Ahmed et al., 2018]] ).

Globally, the extent of the blue carbon ecosystem has been estimated at 120,380 km 2 , with the highest spread by mangroves at 114,669 km 2 (95.3%), followed by seagrass meadows at 2,201 km 2 (1.8%) and salt marshes at 3510 km 2 (2.9%) ( [[#Himes-Cornell--2018|Himes-Cornell et al., 2018]] ). In Asia, the total extent of these three ecosystems is 33,224 km 2 , forming 27.6% of the global total with the highest spread of mangrove at 32,767 km 2 , which forms 28.6% of the global mangrove coverage. The area of seagrass meadows spread in Asia has been estimated as 236 km 2 and salt marsh 220 km 2 ,which forms 10.8 and 6.03% of the respective ecosystems globally ( [[#Himes-Cornell--2018|Himes-Cornell et al., 2018]] ). Found at the land–sea interface, seagrasses provide varied services apart from acting as ecosystem engineers providing shelter and habitat for several marine fauna which are fished in several Asian countries ( [[#Jeyabaskaran--2018|Jeyabaskaran et al., 2018]] ; [[#Nordlund--2018|Nordlund et al., 2018]] ; [[#Unsworth--2019b|Unsworth et al., 2019b]] ) thereby providing livelihood to millions across the continent ( [[#UNEP--2020|UNEP, 2020]] ).

The seagrass meadows are also good sinks of carbon ( [[#Fourqurean--2012|Fourqurean et al., 2012]] ) capable of storing 19.9 petagrams (pg) of organic carbon, but with very high regional and site- and species variability ( [[#Ganguly--2017|Ganguly et al., 2017]] ; [[#Stankovic--2018|Stankovic et al., 2018]] ; [[#Gallagher--2019|Gallagher et al., 2019]] ; [[#Ricart--2020|Ricart et al., 2020]] ). As highly efficient carbon sinks, they store up to 18% of the world’s oceanic carbon, and they also reduce the impacts of ocean acidification ( [[#UNEP--2020|UNEP, 2020]] ).

The deterioration of this ecosystem is fast, 7% yr –1 since 1990 ( [[#Waycott--2009|Waycott et al., 2009]] ), which has led to development of restoration protocols across Asia ( [[#Paling--2009|Paling, 2009]] ; [[#van%20Katwijk--2016|van Katwijk et al., 2016]] ). In Vietnam, the loss of seagrass has been estimated as above 50% and in some regions complete loss has been observed ( [[#Van%20Luong--2012|Van Luong et al., 2012]] ). The seagrass meadows of Indonesia are fast deteriorating, and the need for increased local autonomy for the management of marine resources and restoration has been highlighted ( [[#Unsworth--2018|Unsworth et al., 2018]] ). Development of science-based policies for conservation, including participatory methods ( [[#Fortes--2018|Fortes, 2018]] ; [[#Ramesh--2019|Ramesh et al., 2019]] ; [[#Unsworth--2019a|Unsworth et al., 2019a]] ) and large-scale planting ( [[#van%20Katwijk--2016|van Katwijk et al., 2016]] ), has been recommended to preserve the ecosystem services of these habitats.

Globally, the diversity of the plankton community has been predicted to be affected by warming and related changes ( [[#Ibarbalz--2019|Ibarbalz et al., 2019]] ), and these changes are expected in Asia also. Combined effects of high temperature, ocean acidification and high light exposure would affect important phytoplankton species in the SCS, ''Thalassiosira pseudonana'' ( [[#Yuan--2018|Yuan et al., 2018]] ) and ''Thalassiosira weissflogii'' ( [[#Gao--2018b|Gao et al., 2018b]] ). Also in the SCS the phytoplankton-assemblage responses to rising temperatures and CO 2 levels were found to differ between coastal and offshore waters and the predicted increases in temperature and ''p'' CO 2 may not boost surface-phytoplankton primary productivity ( [[#Zhang--2018|Zhang et al., 2018]] ).

Ocean warming and acidification can affect the functioning and ecological services of sedentary molluscs like the bivalves ( [[#Guo--2016|Guo et al., 2016]] ; [[#Zhao--2017b|Zhao et al., 2017b]] ; [[#Cao--2018|Cao et al., 2018]] ; [[#Zhang--2019c|Zhang et al., 2019c]] ; [[#Liu--2020b|Liu et al., 2020b]] ) and gastropods ( [[#Leung--2020|Leung et al., 2020]] ), and also sea urchins ( [[#Zhan--2020|Zhan et al., 2020]] ). The oyster ''Crassostrea gigas'' becomes more vulnerable to disease when exposed to acidification conditions and pathogen challenge indicating incapability for supporting long-term viability of the population ( [[#Cao--2018|Cao et al., 2018]] ). More tolerance and benefits to rising ''p'' CO 2 was observed in clam species like ''Paphia undulate'' which has been attributed to adaptation to its acidified sediment habitat ( [[#Guo--2016|Guo et al., 2016]] ). Warming boosted the energy budget of marine calcifiers like the gastropod ''Austrocochlea concamerata'' , by faster shell growth and greater shell strength, making them more mechanically resilient while acidification negatively affected shell building thereby impacting the physiological adaptability ( [[#Leung--2020|Leung et al., 2020]] ). It is expected that there will be transgenerational acclimation to changes in ocean acidification in marine invertebrates ( [[#Lee--2020b|Lee et al., 2020b]] ).

Assessment of the potential impacts and the vulnerability in marine biodiversity in the Persian Gulf under climate change has suggested a reduction of up to 35% of initial species richness and habitat loss for hawksbill turtles in the southern and southwest parts of the Persian Gulf ( [[#Wabnitz--2018|Wabnitz et al., 2018]] ).

Seaweeds are an important biotic resource capable of capturing carbon and used widely as food, medicine and as raw material for industrial purposes. Warming and altered pH can affect seaweeds in different ways ( [[#Gao--2016|Gao et al., 2016]] ; [[#Gao--2017|Gao et al., 2017]] ; [[#Gao--2018a|Gao et al., 2018a]] ; [[#Wu--2019b|Wu et al., 2019b]] ). Outbreak of intense blooms of species like ''Ulva rigida'' ( [[#Gao--2017|Gao et al., 2017]] ) and ''Ulva prolifera'' (Zhang et al., 2019 f) have increased due to varied factors including climate change. These blooms have created huge economic losses in the Yellow Sea affecting local mariculture, tourism and the functioning of the coastal and marine ecosystems (Zhang et al., 2019 f). Increased temperature was found to enhance the dark respiration and light compensation point of ''Ulva conglobate'' , which thrives in the mid-intertidal to upper subtidal zones, while the altered pH showed a limited effect ( [[#Li--2020|Li et al., 2020]] ). Elevated temperature significantly enhanced growth, photosynthetic performances and carbon-use efficiency of ''Sargassum horneri'' in both elevated and ambient CO 2 levels suggesting that the present greenhouse effect would benefit the golden tide blooming macroalgae ''Sargassum horneri'' , which might enhance both the frequency and scale of golden tide ( [[#Wu--2019b|Wu et al., 2019b]] ).

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==== 10.4.3.1 Key Drivers to Vulnerability ====

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The vulnerabilities to disaster in coastal regions with high population densities are reported in several studies ( [[#Sajjad--2018|Sajjad et al., 2018]] ) that have assessed the vulnerabilities of coastal communities along the Chinese coast and shown that roughly 25% of the coastline, and more than 5 million residents, are in highly vulnerable coastal areas of mainland China, and these numbers are expected to double by 2100. [[#Husnayaen--2018|Husnayaen et al. (2018)]] assessed the Semarang coast in Indonesia and showed that 20% of the total coastline (48.7 km) is very highly vulnerable. Mangroves continue to face threats due to pollution, conversion for aquaculture, agriculture, apart from climate-based threats like SLR and sea erosion ( [[#Richards--2016|Richards and Friess, 2016]] ; [[#Romañach--2018|Romañach et al., 2018]] ; [[#Wang--2018b|Wang et al., 2018b]] ; [[#Friess--2019|Friess et al., 2019]] ). Hypersalinity, storm effects on sediment deposition, fishery development and land erosion are responsible for most of the Sunderban mangrove degradations leading to loss of livelihood (Uddin, 2014; Paul, 2017). In the Sunderbans of Asia, climate change is expected to increase river salinisation, which in turn could significantly negatively impact the valued timber species, ''Heritiera fomes'' ( [[#Dasgupta--2017b|Dasgupta et al., 2017b]] ). Augmented potential for honey production is also predicted, which could increase the conflict between humans and wildlife ( [[#Dasgupta--2017b|Dasgupta et al., 2017b]] ).

Destruction by natural hazards was found to remove the above-ground C pool, but the sediment C pool was found to be maintained ( [[#Chen--2018b|Chen et al., 2018b]] ). In the Andaman and Nicobar Islands, the 2004 Indian Ocean tsunami severely impacted mangrove habitats at the Nicobar Islands ( [[#Nehru--2018|Nehru and Balasubramanian, 2018]] ), although new inter-tidal habitats suitable for mangrove colonisation did develop. Mangrove species with a wide distribution and larger propagules showed high colonisation potential in the new habitats compared with other species ( [[#Nehru--2018|Nehru and Balasubramanian, 2018]] ). Mangrove sites in Asia are predominantly minerogenic, so continued sediment supply is essential for the long-term resilience of Asia’s mangroves to SLR ( [[#Lovelock--2015|Lovelock et al., 2015]] ; [[#Balke--2016|Balke and Friess, 2016]] ; [[#Ward--2016a|Ward et al., 2016a]] ; [[#Ward--2016b|Ward et al., 2016b]] ).

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==== 10.4.3.2 Observed Impacts ====

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Primary production in the western Indian Ocean showed a reduction by 20% during the past six decades, attributed to rapid warming and ocean stratification which restricted nutrient mixing ( [[#Roxy--2016|Roxy et al., 2016]] ). Variation in secondary-production zooplankton densities and biomass in the East Asian Marginal Seas affected the recruitment of fishes due to mismatch in spawning period and larval-feed availability during the last three climate regime shifts (CRS) in the mid-1970s, late 1980s and late 1990s, which were characterised by the North Pacific index and the Pacific Decadal Oscillation index (Kun [[#Jung--2017|Jung et al., 2017]] ). In the western North Pacific, climate change has affected recruitment and the population dynamics of pelagic fishes, such as sardine and anchovy ( [[#Nakayama--2018|Nakayama et al., 2018]] ), and also shifts in the spawning ground and extension of the spawning period of the chub mackerel ''Scomber japonicas'' ( [[#Kanamori--2019|Kanamori et al., 2019]] ).

Varied responses to CRS in the China seas have been observed for small pelagic fishes ( [[#Ma--2019|Ma et al., 2019]] ) and cephalopods ( [[#Ichii--2017|Ichii et al., 2017]] ). The winter and summer SSTs have shown evidence of decadal variability with abrupt changes from cold to warm in substantial association with climate indices to which coastal cephalopods in the China seas respond differentially, with some benefiting from warmer environments while others respond negatively ( [[#Pang--2018|Pang et al., 2018]] ). In the western and eastern North Pacific marine ecosystem, it is indicated that groundfish may suffer more than pelagic fish ( [[#Yati--2020|Yati et al., 2020]] ). Habitat Suitability index models using SST, chlorophyll- ''a'' , sea surface height anomaly (SSHA) and sea surface salinity (SSS), as well as fishing effort, strongly indicate that Neon flying squid is affected by interannual environmental variations and undertakes short-term migrations to suitable habitat, affecting the fisheries ( [[#Yu--2015|Yu et al., 2015]] ). The 2015–2016 El Niño was found to impact coral reefs of shallower regions (depth of 5–15 m) in South Andaman, India, more than those beyond 20 m ( [[#Majumdar--2018|Majumdar et al., 2018]] ). On the southeast coast of India, with bleaching largely mediated by the SST anomaly and during the recovery period, macroalgae outgrowth has been observed (2.75%) indicating impacts on the benthic community ( [[#Ranith--2019|Ranith and Kripa, 2019]] ). In the South China Sea, the increase in SST was found to be higher than predicted in recent decades, while the pH decreased at a rate of 0.012–0.014 yr –1 , more than the predicted level, due to high microbial respiratory processes releasing CO 2 ( [[#Yuan--2019|Yuan et al., 2019]] ). Simulation experiments have shown differential adaptation capacity of common species (Zheng, 2019; [[#Yuan--2019|Yuan et al., 2019]] ).

The UN’s (2019) report on climate action and support trends highlights that the impacts of climate change on coastal ecosystems are mainly increased risks due to flooding, inundation due to extreme events, coastal erosions, ecosystem processes and, in the case of fisheries, variations in population or stock structures due to ocean circulation pattern, habitat loss degradation and ocean acidification. Analysis of data on the occurrence of varied natural hazards from 1900 to 2019 has shown that tropical cyclones, riverine floods and droughts have increased significantly, and the impacts of these events on coastal communities are also severe and destructive. The UN’s average score for SDG Goal 14 (Life Under Water) for Asia was estimated as 46 among the scores of 40 nations, and the Ocean Health Biodiversity index was comparatively high (average 87.9); however, the indices show that more region-specific action plans are required to achieve the UN 2030 goal for Life Under Water.

Apart from the human impacts, the ecology and resource abundance of coastal waters have been found to be impacted by extreme events. During tropical cyclones ecological variations, like lowering of SST, an increase in chlorophyll- ''a'' and a decrease in oxygen ( [[#Chacko--2019|Chacko, 2019]] ; [[#Girishkumar--2019|Girishkumar et al., 2019]] ) have been observed. Global analyses of such events have indicated that they may have an impact on the fishery directly by creating unfavourable ecological conditions and destruction of critical habitats indirectly by affecting the eggs and larvae as well as subsequent fishery recruitment ( [[#McKinnon--2003|McKinnon et al., 2003]] ; [[#Bailey--2016|Bailey and Secor, 2016]] ). In the South China Sea in July 2000, during a 3-day cyclone period, an estimated thirtyfold increase in surface chlorophyll- ''a'' concentration was observed ( [[#Lin--2003|Lin et al., 2003]] ). The estimated carbon fixation resulting from this event alone is 0.8 Mt, or 2–4% of the SCS’s annual new production ( [[#Lin--2003|Lin et al., 2003]] ). Since an average of 14 cyclones pass over this region annually, the contribution of cyclones to the annual new production has been estimated to be as high as 20–30% ( [[#Lin--2003|Lin et al., 2003]] ).

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==== 10.4.3.3 Projected Impacts ====

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Water pollution and climate stressors have been considered major challenges to ecosystem sustainability, and now it has been shown that the combined effect these two stressors would be more damaging ( [[#Buchanan--2019|Buchanan et al., 2019]] ). For seagrass beds the pollution stress was found to increase by 2.6% (from 39.7 to 42.3%) when climate factors were added. Assuming the pollution levels remain at the 2014 levels, different scenarios including RCP2.6 and RCP8.5 were worked out for the Bohai Sea, and the results indicated amplification of the impacts on the ecosystem. Pollutants like petroleum hydrocarbons, dissolved inorganic nitrogen and soluble reactive phosphorus were the major pollution stressors ( [[#Lu--2018|Lu et al., 2018]] ). In the future, policies that focus strictly on pollution control should be changed and take into account the interactive effects of climate change for better forecast and management of potential ecological risks ( [[#Lu--2018|Lu et al., 2018]] ).

Projected changes in catch potential (in percent) by 2050 and 2100 relative to 2000 under RCP2.6 and RCP8.5, based on outputs from the dynamic bioclimate envelop model and the dynamic size-based food-web models, indicate that the marine and coastal resources of most Asian countries will be impacted with varying intensity ( [[#FAO--2018b|FAO, 2018b]] ).

Better management of resources through projections of resource distribution, abundance and catch is required; however, lack of data (e.g., oceanographic surveys) and scientific knowledge is a constraint to this aim ( [[#Maung%20Saw%20Htoo--2017|Maung Saw Htoo et al., 2017]] ). Effective forecasts of areas of resource abundance based on habitat preference have to be worked out for Asian regions.

Modelling and assessment of the vulnerability and habitat suitability of the Persian Gulf for 55 species to climate change indicated that there is a high rate of risk of local extinction in the southwest part of the Persian Gulf, off the coast of Saudi Arabia, Qatar and the United Arab Emirates (UAE). Likelihood of reduced catch was observed, and Bahrain and Iran were found to be more vulnerable to climate change ( [[#Wabnitz--2018|Wabnitz et al., 2018]] ). Projected changes in fish catches can impact the supply of fish available for local consumption (i.e., food security) and exports (i.e., income generation) ( [[#Wabnitz--2018|Wabnitz et al., 2018]] ). As per ( [[#UNESCAP--2018a|UNESCAP, 2018a]] ), over 40% of coral reefs and 60% of coastal mangroves in the Asia-Pacific region have already been lost, and approximately 80% of the region’s coral reefs are currently at risk.

Regionally, the escalation in thermal stress estimated for the different global warming scenarios is greatest for Southeast Asia and least for the Pacific Ocean ( [[#Lough--2018|Lough et al., 2018]] ). For the 100 reef locations examined here and given current rates of warming, the 1.5°C global warming target represents twice the thermal stress they experienced in 2016 ( [[#Lough--2018|Lough et al., 2018]] ).

In the Southeast Asia region threats from both warming and acidification has indicated that by 2030, 99% of reefs will be affected, and by 2050, 95% are expected to be in the highest levels of the ‘threatened’ category ( [[#Burke--2011|Burke et al., 2011]] ), similar to global corals ( [[#Frieler--2013|Frieler et al., 2013]] ; [[#Bruno--2016|Bruno and Valdivia, 2016]] ). Modelling results indicate that even under RCP scenarios, the functional traits of coral reefs can be affected ( [[#van%20der%20Zande--2020|van der Zande et al., 2020]] ) and coral communities will mainly consist of small numbers of temperature-tolerant and fast-growing species ( [[#Kubicek--2019|Kubicek et al., 2019]] ). Increases in temperature (+3°C) and ''p'' CO2 (+400 matm) projected for this century can reduce the sperm availability for fertilisation, which along with adult population decline either due to climate change or anthropogenic impacts ( [[#Hughes--2017|Hughes et al., 2017]] ) can affect coral reproductive success thereby reducing the recovery of populations and their adaptation potential ( [[#Albright--2013|Albright and Mason, 2013]] ; [[#Hughes--2018|Hughes et al., 2018]] ; [[#Jamodiong--2018|Jamodiong et al., 2018]] ). In the southern Persian Gulf, increased disturbance frequency and severity has caused progressive reduction in coral size, cover and population fecundity ( [[#Riegl--2018|Riegl et al., 2018]] ), and this can lead to functional extinction. Connectivity required to avoid extinctions has increased exponentially with disturbance frequency and correlation of disturbances across the metapopulation. In the Philippines experiments have also proved that scleractinian corals, such as ''A. tenuis, A. millepora'' and ''F. colemani'' , which spawn their gametes directly into the water column, may experience limitations from sperm dilution and delays in initial sperm–egg encounters that can impact successful fertilisation ( [[#de%20la%20Cruz--2020|de la Cruz and Harrison, 2020]] ).

Apart from these threats, natural hazards have also been found to affect coral reefs of Asia. The extensive and diverse coral reefs of Muscat, Oman, in the northeast Arabian Peninsula were found to have long-term effects from Cyclone Gonu, which struck the Oman coast in June 2007, more than coastal development ( [[#Coles--2015|Coles et al., 2015]] ).

Sandy beaches are subject to highly dynamic hydrological and geomorphological processes, giving them more natural adaptive capacity to climate hazards ( [[#Bindoff--2019|Bindoff et al., 2019]] ). Progress is being made towards models that can reliably project beach erosion under future scenarios despite the presence of multiple confounding drivers in the coastal zone (Chapter 3). Assuming minimal human intervention and projected impacts of SLR by 2100 under RCP8.5-like scenarios, 57–72% of Thai beaches (Ritphring, 2018), at least 50% loss of area on around a third of Japanese beaches (Mori, 2018) will disappear.

Marine heatwaves (MHWs) in Asia have been making changes to the structure and functioning of coastal and marine ecosystems ( [[#Kim--2017|Kim and Han, 2017]] ; [[#Oliver--2017|Oliver et al., 2017]] ; [[#Frölicher--2018|Frölicher and Laufkötter, 2018]] ; [[#Oliver--2019|Oliver et al., 2019]] ; [[#Smale--2019|Smale et al., 2019]] ), affecting resources like copepods ( [[#Doan--2019|Doan et al., 2019]] ) and coral reefs ( [[#Zhang--2017c|Zhang et al., 2017c]] ). Coral reefs of the southeast Indian Ocean have been affected by MHWs ( [[#Zhang--2017c|Zhang et al., 2017c]] ).

Simulation of RCP scenarios have shown that continued warming can drive a poleward shift in distribution of the seaweed ''Ecklonia cava'' of Japan, and under the lowest-emissions scenario (RCP2.6) most populations may not be impacted, but under the highest-emissions scenario (RCP8.5) the existing habitat may become unsuitable and it can also increase predation by herbivorous fishes ( [[#Takao--2015|Takao et al., 2015]] ).

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<span id="adaptation-options-2"></span>
==== 10.4.3.4 Adaptation Options ====

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The UN (2019) has identified establishment of protected areas, restoring ecosystems like mangroves and coral reefs, integrating coastal-zone management practices, sand banks and structural technologies, and implementing local monitoring networks for increasing adaptive capacity and protecting the biodiversity of the coastal ecosystem. In Asia, management of marine sites by earmarking protected areas (SDG 14) has been found to be low with only 27% of areas being protected. In India, detailed CCA guidelines for coastal protection and management has been prepared considering various environmental and social aspects ( [[#Black--2017|Black et al., 2017]] ). The Ocean Health index for clean waters was also low (54.6), and the threat to the ecosystem due to the combined effects of pollution and climate change was high. Table 10.2 shows the ocean and MPAs.

'''Table 10.2 |''' Status of ocean health and mean of marine protected areas (MPA) a

{| class="wikitable"
|-
!
! Ocean Health index: Clean waters (0–100)

! Fish stocks overexploited or collapsed (%)

! Ocean Health index: Fisheries (0–100)

! Fish caught by trawling (%)

! Ocean Health index: Biodiversity (0–100)

! Mean MPA (%)

|-
| Eastern Asia

| 54.0

| 29.1

| 49.5

| 39.8

| 89.6

| 32.5

|-
| Southeast Asia

| 54.1

| 28.5

| 54.9

| 34.7

| 84.6

| 25.0

|-
| Western Asia

| 54.3

| 28.3

| 46.2

| 20.4

| 89.4

| 18.3

|-
| Southern Asia

| 50.3

| 17.4

| 51.0

| 15.1

| 88.3

| 41.2

|-
| Northern Asia

| 91.6

| 55.4

| 57.6

| 60.0

| 93.4

| 30.0

|-
| Asia (whole)

| 54.6

| 26.9

| 50.3

| 27.3

| 87.9

| 27.0

|}

(a) Data are from [[#Sachs--2018|Sachs et al. (2018)]] .

Conservation and restoration of mangroves were found to be effective tools for enhancing ecosystem carbon storage and an important part of Reducing Emissions from Deforestation and forest Degradation plus (REDD+) schemes and climate-change mitigation ( [[#Ahmed--2016|Ahmed and Glaser, 2016]] ). In East Asia, restoration success has been attributed to choosing the right geomorphological locations ( [[#Van%20Cuong--2015|Van Cuong et al., 2015]] ; [[#Balke--2016|Balke and Friess, 2016]] ) and co-management models ( [[#Johnson--2016|Johnson and Iizuka, 2016]] ; [[#Veettil--2019|Veettil et al., 2019]] ).

In South Asia, restoration programmes have been largely successful ( [[#Jayanthi--2018|Jayanthi et al., 2018]] ) but in some regions partly a failure due to inappropriate site selection, poor post-planting care and other issues ( [[#Kodikara--2017|Kodikara et al., 2017]] ). Using remote sensing it has been observed that there are high recovery rates of mangroves in a relatively short period (1.5 years) after a powerful typhoon, indicating that natural recovery and regeneration would be a more economically and ecologically viable strategy. Better mangrove management through mapping is suggested ( [[#Castillo--2018|Castillo et al., 2018]] ; [[#Gandhi--2019|Gandhi and Jones, 2019]] ). Statistical tools developed for modelling biomass and timber volume ( [[#Phan--2019|Phan et al., 2019]] ), and allometric models to estimate above-ground biomass and carbon stocks ( [[#Vinh--2019|Vinh et al., 2019]] ), will be useful in estimating stocks in mangroves. Future mangrove loss may be offset by increasing national and international conservation initiatives that incorporate mangroves, such as the SDGs, Blue Carbon, and Payments for Ecosystem Services ( [[#Friess--2019|Friess et al., 2019]] ). Since seagrass meadows and marine macroalgae are important habitats capable of combating impacts of climate change, the need for a global networking system with participation of stakeholders has been suggested ( [[#Duffy--2019|Duffy et al., 2019]] ).

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<span id="freshwater-resources"></span>