Editing IPCC:AR6/SROCC/Chapter-5 (section)

=== 5.4.1 Changes in Key Ecosystem Services ===

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AR5 WGII concluded that climate change increases the risk of impacts on the goods and services derived from marine biodiversity and ecosystems (Pörtner et al., 2014). SR15 concluded that current ecosystem services from the ocean are expected to be reduced at 1.5°C of global warming, with losses being even greater at 2°C of global warming. These reductions in services are driven by decreasing ocean productivity, biogeographic shifts, damage to ecosystems, loss of fisheries productivity and changes to ocean chemistry ( ''high confidence'' ) (Hoegh-Guldberg et al., 2018). Building on these previous assessments, this section assesses new evidence on observed impacts and future risk of climate change on ecosystem goods and services from the open ocean (Section 5.2) and coastal ecosystems (Section 5.3). Chapter 3 assesses ecosystem services in polar oceans.

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==== 5.4.1.1 Provisioning Services ====

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Fisheries are an important provisioning service from marine ecosystems, providing food, nutrition, income and livelihoods for many millions of people around the world (FAO, 2018). Globally, total fish catches amount to 80‒105 Mt annually in the 2000s (FAO, 2016; FAO 2018; Pauly and Zeller, 2016), directly generating over 80 billion USD of revenue (Sumaila et al., 2015). Most global fisheries are considered to be fully- to over-exploited (FAO, 2018). Over 80% of the global fish catch is estimated to be from coastal and shelf seas with less than 20% from the high seas (Sumaila et al., 2015) (Figure 5.17).

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'''Figure 5.17'''

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'''Figure 5.17 | Global distribution of fish catches (average 2010–2014, based on (Pauly and Zeller, 2016)), coastal habitats including seagrasses (UNEP-WCMC and FT, 2017) salt marshes (Mcowen et al. 2017), mangrove forests (Spalding, 2010), coral reefs (UNEP-WCMC and WRI, 2010) and an index (called Marine Focus Factor) for the inclusion of the ocean in the […]'''
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Figure 5.17 | Global distribution of fish catches (average 2010–2014, based on (Pauly and Zeller, 2016)), coastal habitats including seagrasses (UNEP-WCMC and FT, 2017) salt marshes (Mcowen et al. 2017), mangrove forests (Spalding, 2010), coral reefs (UNEP-WCMC and WRI, 2010) and an index (called Marine Focus Factor) for the inclusion of the ocean in the Nationally Determined Contributions (NDCs) published by each country (Gallo et al. 2017). The higher the Marine Focus Factor, the more frequent use of ocean in the country’s NDCs.

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'''Figure 5.18'''

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'''Figure 5.18 | Historical and projected maximum sustainable yield (MSY) and maximum fish catch potential by region. Historical trends in MSY is based on time series of fish stock assessment data (Free et al. 2019) represented as circles in panels (a) and (b). The size of the circle represents the number of assessed fish stocks […]'''
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Figure 5.18 | Historical and projected maximum sustainable yield (MSY) and maximum fish catch potential by region. Historical trends in MSY is based on time series of fish stock assessment data (Free et al. 2019) represented as circles in panels (a) and (b). The size of the circle represents the number of assessed fish stocks while the number in the circle represents the estimated percent change in MSY since the 1930s. Projected changes in maximum catch potential by 2050 (average between 2041–2060) relative to 2000 (1991–2010) under (a) RCP2.6 and (b) RCP8.5 scenarios from two models: Dynamic Bioclimate Envelope Model and dynamic size-spectrum foodweb model with the colour in each ocean region representing the projected level of change and the shading representing where both models agree in the direction of change (Cheung et al. 2018a). Also presented is the scaling between projected global atmospheric warming (relative to 1950–1961) and (c) changes in maximum fish catch potential and (d) species turnover using the Dynamic Bioclimate Envelope Model and outputs from three Coupled Model Intercomparison Project Phase 5 (CMIP5) Earth System Models (ESMs) (Cheung and Pauly, 2016). Model projections (a,b) are provided by Plymouth Marine Laboratory, Euro-Meditteranean Centre for Climate Change and Fisheries and Marine Ecosystem Impact Model Intercomparison Project (FISHMIP) of coastal ecosystems.

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Observed fish catches have been related to NPP and water temperature, with the direction and magnitude of the relationship varying between regions and fish stocks (Cheung et al., 2008 <sup>[[#fn:r1212|1212]]</sup> ; McOwen et al., 2015; Britten et al., 2016 <sup>[[#fn:r1214|1214]]</sup> ; Stock et al., 2017 <sup>[[#fn:r1215|1215]]</sup> ). The maximum catch potential of large marine ecosystems generally increases with their NPP and energy transfer efficiency, but the relative importance of total NPP to fisheries production is lower in nutrient-poor systems with microbially-dominated foodwebs (Section 5.2) and empirical relationships between NPP and fisheries production over-estimate potential catches in polar regions (Stock et al., 2017 <sup>[[#fn:r1216|1216]]</sup> ) (Chapter 3). Here, potential fish catch or maximum catch potential refers to the potential of the fish stocks to provide long-term fish catches; it is considered a proxy of maximum sustainable yield (MSY). However, the actual catches realised by fisheries will depend strongly on past and present fishing effort and the exploitation status of the resources (Cheung et al., 2018a <sup>[[#fn:r1217|1217]]</sup> ; Barange, 2019 <sup>[[#fn:r1218|1218]]</sup> ). Observed variations between regions suggest that changes in temperature and NPP in the past (Section 5.2.2, 5.2.3) may have also affected maximum catch potential ( ''medium evidence, high agreement, medium confidence'' ).

Changes in fish catches from 1998 to 2006 in 47 large marine ecosystems around the world were found to be significantly related to: changes in estimated cholorophyll ''a'' (a proxy for phytoplankton biomass) in 18 of these ecosystems (mostly tropical and eastern boundary upwelling systems); changes in SST in 12 of these ecosystems (mostly mid-latitude); and changes in fishing intensity in 16 of these ecosystems (widely spread) (McOwen et al., 2015). Analysis of population data since the 1950s for 262 fish stocks across 39 large marine ecosystems and the high seas suggest that average recruitment to the stocks has declined by around 3% of the historical maximum per decade with variations between regions and stocks (Britten et al., 2016 <sup>[[#fn:r1219|1219]]</sup> ). The declines (69% of the studied stocks, 31 of the 39 assessed large marine ecosystems) are significantly related to estimated chlorophyll ''a'' concentration and the intensity of fishing, with the North Atlantic showing the steepest declines (Britten et al., 2016 <sup>[[#fn:r1220|1220]]</sup> ). In addition, recent meta-analysis of population data from 235 fish stocks worldwide from 1930 to 2010 suggest that the maximum catch potential from these populations decreased by 4.1% (95% confidence span 9.0% decline to 0.3% increase) during this period with variations between fish stocks and regions (Free et al., 2019 <sup>[[#fn:r1221|1221]]</sup> ). Specifically, temperature is a significant factor explaining changes in catch potential of 12% of the fish stocks, with East Asian regions having the largest stock declines related to warming. In intermediate latitudes across the Atlantic, Indian and Pacific Oceans, catches of tropical tunas, including skipjack and yellowfin tuna, are significantly and positively related to increases in SST, although the overall catches across latitudinal zones do not show significant change (Monllor-Hurtado et al., 2017 <sup>[[#fn:r1222|1222]]</sup> ). Observational evidence from spatial and temporal linkages between catches and oceanographic variables therefore supports the conclusions from AR5 WGII and SR15 that potential fisheries catches have already been impacted by the effects of warming and changing primary production on growth, reproduction and survival of fish stocks ( ''robust evidence'' , ''high agreement'' , ''high confidence'' ).

There are substantial variations in the direction of changes and the attribution of climatic drivers between regions and fish stocks, and the availability of datasets is biased towards mid-latitude areas and epipelagic and coastal ecosystems. As a result, quantitative attribution of climate impacts on the productivity of specific fish stocks has ''low confidence'' . Changes in catch potential for fish stocks and regions worldwide that were considered overfished were most sensitive to warming (Essington et al., 2015 <sup>[[#fn:r1226|1226]]</sup> ; Britten et al., 2016 <sup>[[#fn:r1227|1227]]</sup> ; Free et al., 2019 <sup>[[#fn:r1228|1228]]</sup> ). This suggest that climatic drivers and overfishing have interacted synergistically in impacting some fish stocks and their catches ( ''high confidence'' ). In addition, analysis of historical catch records since AR5 show further warming related changes in species composition, with an increased dominance of warm water species in coastal and shelf seas since the 1970s (Cheung et al., 2013 <sup>[[#fn:r1229|1229]]</sup> ; Keskin and Pauly, 2014 <sup>[[#fn:r1230|1230]]</sup> ; Tsikliras et al., 2014 <sup>[[#fn:r1231|1231]]</sup> ; Maharaj et al., 2018 <sup>[[#fn:r1232|1232]]</sup> ). Many marine ecosystems worldwide have shown an increased dominance of warm water species following increases in sea water temperature (Section 5.2.3, 5.3), with parallel changes in the species composition of fish catches since the 1970s in many of the studied shelf seas ( ''high confidence'' ).

Based on CMIP5 ESM projections of changes in temperature, net primary production, oxygen, salinity and sea ice extent, two marine ecosystem and fisheries models project a decrease in maximum catch potential under RCP 2.6 of 3.9–8.5% by 2041-2060 and 3.4–6.4% by 2081-2100 relative to 1986-2005 (based on model projections described in Barange et al. 2018). Under RCP 8.5, the projected decrease was larger: 8.6–14.2% and 20.5–24.1% by the mid- and end- of the 21st century (Figure 5.18). The trends agree with the projected changes in total marine animal biomass for the 21st century (Blanchard et al., 2017 <sup>[[#fn:r1233|1233]]</sup> ; Lotze et al., 2018 <sup>[[#fn:r1234|1234]]</sup> ) (Section 5.2.3). A single fisheries model with atmospheric warming projected a potential catch loss of 3.4 million tonnes and decreases of 6.4% of catch potential of the exploited species per degree Celsius atmospheric warming relative to 1951–1960 level (Cheung et al., 2016b <sup>[[#fn:r1235|1235]]</sup> ) (Figure 5.18). Interactions between temperature, net primary production and transfer efficiency of energy across the foodweb are projected to amplify these trends, with projected decreases greater than 50% in some regions by 2100 under high emissions scenarios (Stock et al., 2017 <sup>[[#fn:r1236|1236]]</sup> ). Thus, there is high model agreement that ocean warming and changes in NPP in the 21st century will reduce the global maximum catch potential, particularly in tropical oceans ( ''high confidence'' ) and alter the distribution and composition of exploited species ( ''high confidence'' ). The projected risk of these fisheries impacts increases with increasing greenhouse gas emissions ( ''high confidence'' ). However, given the uncertainties of projected changes in ocean conditions from ESMs (Section 5.2.2), and that most global scale fisheries models are largely driven by changes in temperature and primary production while other changes in ocean biogeochemical changes are not explicitly considered (Tittensor et al., 2018 <sup>[[#fn:r1237|1237]]</sup> ), the quantitative magnitude of the projected changes in maximum catch potential is considered to have ''medium'' and ''low'' confidence at global and regional scales, respectively. Given the significant interactions between catch potential and level of fisheries exploitation, the realised catches in the 21st century would depend on future scenarios of fishing and fisheries governance (Section 5.4.2, 5.5). As a result, projections of realised catches have ''low confidence'' .

Tropical oceans are projected to experience much larger impacts (three times or more decrease in catch potential) than the global average, particularly the western central Pacific Ocean, eastern central Atlantic Ocean and the western Indian Ocean, by the end of the 21st century under RCP8.5 (Blanchard et al., 2017 <sup>[[#fn:r1238|1238]]</sup> ). For example, around the exclusive economic zones of the Pacific Islands states, more than 50% of exploited fishes and invertebrates are projected to become locally extinct in many regions by 2100 relative to the recent past under RCP8.5 (Asch et al., 2018 <sup>[[#fn:r1239|1239]]</sup> ). These factors cause 74% of the area to experience a projected loss in catch potential of more than 50%. Under RCP2.6, the area of large projected catch loss is projected to be halved (Asch et al., 2018 <sup>[[#fn:r1240|1240]]</sup> ). However, while temperate commercially-important tunas species such as albacore, Atlantic and southern bluefin) are projected to shift poleward and decrease in abundance in the tropics, some tropical species such as skipjack tuna are projected to remain abundant, but with changes in distribution patterns in low-latitude regions by the mid-21st century, with some models projecting subsequent decrease under RCP8.5 (Lehodey et al., 2013 <sup>[[#fn:r1241|1241]]</sup> ; Dueri et al., 2014 <sup>[[#fn:r1242|1242]]</sup> ; Erauskin-Extramiana et al., 2019 <sup>[[#fn:r1243|1243]]</sup> ). Recent evidence therefore supports the conclusion from previous assessments (Pörtner et al., 2014 <sup>[[#fn:r1244|1244]]</sup> ; Hoegh-Guldberg et al., 2018 <sup>[[#fn:r1245|1245]]</sup> ) that low-latitude fish catch potential are projected to have a high risk of climate impacts, which will be exacerbated by higher greenhouse gas emissions ( ''medium evidence, high agreement, high confidence'' ). Tropical fish catch potential of some species resilient to the changing environment may have lower climate risk in the near-term although their risk increases substantially further into the 21st century under RCP8.5 ( ''medium confidence'' ). In contrast, the catch potential in the Arctic is projected to increase, although with high inter-model variability ( ''medium evidence, low agreement, low confidence'' ) (Cheung and Pauly, 2016 <sup>[[#fn:r1246|1246]]</sup> ; Blanchard et al., 2017 <sup>[[#fn:r1247|1247]]</sup> ) (Chapter 3).

Although demersal fisheries in the deep ocean represent a small proportion of global fisheries catches, they are economically valuable for some countries, and there is increasing commercial interest in mesopelagic (deep pelagic ocean) fisheries (St. John et al., 2016). Commercially-exploited fish and shellfish from deep sea ecosystems will be exposed to climate risks from physical and chemical changes in ocean conditions including warming, decreased oxygen, reduced aragonite saturation state, and decreased supply of particulate organic matter from the upper ocean (Section 5.2.3, 5.2.4) (FAO, 2019). These biogeochemical changes may reduce the growth, reproduction and survivorship of deep-ocean fish stocks, which will alter their distributions, in similar ways to those in the surface ocean, impacting their fish catch potential (FAO, 2019). For example, in the eastern Pacific near-bottom oxygen concentration is positively correlated with biomass of commercially harvested species (Keller et al., 2010 <sup>[[#fn:r1248|1248]]</sup> ) and catch per unit effort (Banse, 1968 <sup>[[#fn:r1249|1249]]</sup> ; Rosenberg et al., 1983 <sup>[[#fn:r1250|1250]]</sup> ; Keller et al., 2015 <sup>[[#fn:r1251|1251]]</sup> ); some commercially harvested species only appear during oxygenation events associated with El Niño (Arntz et al., 2006 <sup>[[#fn:r1252|1252]]</sup> ). In the mesopelagic zone, expansion of the OMZ results in habitat compression that can increase catchability of fish stocks such as tunas (Prince et al., 2010 <sup>[[#fn:r1253|1253]]</sup> ; Stramma et al., 2011 <sup>[[#fn:r1254|1254]]</sup> ). Also, as OMZ expands, the potential may exist for increased availability and harvest of hypoxia-tolerant species such as Humboldt squid ( ''Dosidicus gigas'' ), thornyheads ( ''Sebastolobus'' spp.) or dover sole ( ''Microstomus pacificus'' ) (Gilly et al., 2013 <sup>[[#fn:r1255|1255]]</sup> ; Gallo and Levin, 2016 <sup>[[#fn:r1256|1256]]</sup> ). However, any expansion of the OMZ will interact with other climatic hazards such as warming, which then adds to the overall risk of impacts on fish stocks and their catches (Breitburg et al., 2018 <sup>[[#fn:r1257|1257]]</sup> ). Overall, the abundance of fisheries resources and potential catches from the deep sea will be at high risk of impacts in the 21st century under RCP8.5 ( ''low confidence'' ), with reduced risk under RCP2.6 ( ''medium confidence'' ).

In addition to capture fisheries, mariculture (marine aquaculture) is also an important marine ecosystem provisioning service, contributing about 27.7 million tonnes of seafood in 2016 (FAO, 2018). Recent projections of climate change impacts on mariculture, based on thermal tolerance and the effects of changing temperature, primary production and ocean acidification, suggest an overall decline in mariculture potential by 2100 under RCP8.5 with large regional variations (Froehlich et al., 2018 <sup>[[#fn:r1258|1258]]</sup> ). Modelling analyses for farmed Atlantic salmon, cobia and seabream also suggest that climate change would reduce their growth potential in ocean areas where temperature is projected to increase to levels outside the thermal tolerance ranges of these species (Klinger et al., 2017 <sup>[[#fn:r1259|1259]]</sup> ). This decrease in growth could therefore translate into a decrease in the general productivity of the sector ( ''limited evidence, low confidence'' ); however, new potential areas and the use of more climate resilient strains or species for mariculture may emerge that could reduce the risk of impacts on potential mariculture production ( ''limited evidence, low confidence'' ).

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