Editing IPCC:AR6/WGII/Cross-Chapter-Paper-4 (section)

=== CCP4.3.1 Ocean Systems ===

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With warming, marine primary production is projected to decrease in the western and increase in the eastern Mediterranean Sea ( [[#Macias--2015|Macias et al., 2015]] ). The diversity of copepods (species which dominate the meso-zooplankton communities feeding Mediterranean fishes) is projected to decline over most of the Mediterranean, albeit with regional variation ( [[#Benedetti--2018|Benedetti et al., 2018]] ). Total marine biomass (and fishery potential) is projected to increase in the southeastern Mediterranean, whereas significant decreases are most likely in the west ( [[#Moullec--2019|Moullec et al., 2019]] ). The projected increase of marine heat waves in the Mediterranean Sea will add additional pressures to coastal and marine ecosystems. Warm-water fish species are expected to move northwards, while cold-water species will decline, and invasions of thermal-tolerant tropical species will increase ( ''high confidence'' ) ( [[#Lloret--2015|Lloret et al., 2015]] ; [[#Corrales--2018|Corrales et al., 2018]] ). Fish species richness is predicted to increase in the eastern and decrease in the western Mediterranean by 2050 but, by 2100, the cooler areas in the north will become a ‘cul-de-sac’ for many species ( [[#Albouy--2013|Albouy et al., 2013]] ; [[#Burrows--2014|Burrows et al., 2014]] ). Out of 75 endemic fish species, 14 are projected to go extinct, almost all of them benthic and demersal species ( [[#Ben%20Rais%20Lasram--2010|Ben Rais Lasram et al., 2010]] ). The abundance of small and medium-sized pelagic fish (e.g., European anchovy) is projected to decline by 15–33% by 2100 ( [[#Stergiou--2016|Stergiou et al., 2016]] ; [[#Raybaud--2017|Raybaud et al., 2017]] ).

Heat waves will ''likely'' cause increasing mass mortality events of benthic species, mostly invertebrate organisms, such as corals, sponges, bivalves, ascidians and bryozoans, increasing the risks of abrupt collapse of endemic species ( [[#Kersting--2013|Kersting et al., 2013]] ; [[#Rivetti--2014|Rivetti et al., 2014]] ; [[#Rivetti--2017|Rivetti et al., 2017]] ; [[#Garrabou--2019|Garrabou et al., 2019]] ; [[#Garrabou--2021|Garrabou et al., 2021]] ). Deep-water corals live near their upper thermal tolerance and further warming could thus reduce their biotic potential and long-term survival ( [[#Nannini--2015|Nannini et al., 2015]] ; [[#Yasuhara--2016|Yasuhara and Danovaro, 2016]] ; [[#Marchini--2019|Marchini et al., 2019]] ), although there are some exceptions ( [[#Naumann--2013|Naumann et al., 2013]] ) and also knowledge gaps ( [[#Maier--2019|Maier et al., 2019]] ). Warming has been shown to severely reduce the metabolism of some Mediterranean coral species ( [[#Gori--2016|Gori et al., 2016]] ). In summary, the observed shift in marine ecosystems since 1980 is projected to continue and intensify, resulting in very high risks for marine ecosystems between 1.5°C–2°C global warming levels (GWL) (Figure CCP4.8; Chapters 3; 13; CCP1; [[#Manes--2021|Manes et al., 2021]] ).

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