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

==== 5.2.4.4 Chemosynthetic Ecosystems ====

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Despite having nutrition derived largely from chemosynthetic sources fueled by fluids from the earth’s interior, hydrothermal vent and methane seep ecosystems are linked to surface ocean environments and water-column processes in many ways that can expose them to aspects of climate change ( ''medium confidence'' ). The reliance of vent and seep mussels on surface-derived photosynthetic production to supplement chemosynthetic food sources (Riou et al., 2010 <sup>[[#fn:r778|778]]</sup> ; Riekenberg et al., 2016 <sup>[[#fn:r779|779]]</sup> ; Demopoulos et al., 2019 <sup>[[#fn:r780|780]]</sup> ), and in some cases as a cue for synchronised gametogenesis (sperm and egg production) (Dixon et al., 2006 <sup>[[#fn:r781|781]]</sup> ; Tyler et al., 2007 <sup>[[#fn:r782|782]]</sup> ) can make them vulnerable to changing amounts or timing of POC flux to the deep seabed in most areas except high latitudes, or to changes in timing of surface production (see Section 5.2.2.5) ( ''limited evidence'' ) Most of the large, habitat-forming (foundation) species at vents and seeps such as mussels, tubeworms, and clams require oxygen to serve as electron acceptor for aerobic hydrogen-, sulfide- and methane oxidation (Dubilier et al., 2008 <sup>[[#fn:r783|783]]</sup> ) and appear unable to grow under dysoxic conditions (&lt;5–10 µmol kg –1 O 2 ) (Sweetman et al., 2017 <sup>[[#fn:r784|784]]</sup> ) ( ''medium confidence'' ). The distributions of these taxa at seeps could be constrained by climate-driven expansion of midwater oxygen minima (Stramma et al., 2008 <sup>[[#fn:r785|785]]</sup> ; Schmidtko et al., 2017 <sup>[[#fn:r786|786]]</sup> ), which is occurring at water depths where seep ecosystems typically occur on continental margins (200–1000 m). Rising bottom temperatures or shifting of warm currents on continental margins could increase dissociation of buried gas hydrates on margins (Phrampus and Hornbach, 2012 <sup>[[#fn:r787|787]]</sup> ) ( ''low confidence'' ) potentially intensifying anaerobic methane oxidation (which produces hydrogen sulfide) (Boetius and Wenzhoefer, 2013 <sup>[[#fn:r788|788]]</sup> ) and expanding cover of methane seep communities ( ''limited'' evidence). Larvae of vent species such as bathymodiolin mussels, alvinocarid shrimp, and some limpets that develop in or near surface waters (Herring and Dixon, 1998 <sup>[[#fn:r789|789]]</sup> ; Arellano et al., 2014 <sup>[[#fn:r790|790]]</sup> ), are likely to be exposed to warming waters, decreasing pH and carbonate saturation states, and in some places, reduced phytoplankton availability (Section 5.2.2), causing reduced calcification and growth rates (as in shallow water mussel larvae, Frieder et al. (2014)) ( ''limited evidence, low confidence'' ). Larvae originating at vents or seeps beneath upwelling regions may also be impaired by effects of hypoxia associated with expanding OMZ (Stramma et al., 2008 <sup>[[#fn:r791|791]]</sup> ) during migration to the surface ( ''limited evidence)'' . Warming and its effects on climate cycles have the potential to alter patterns of larval transport and population connectivity through changes in circulation (Fox et al., 2016 <sup>[[#fn:r792|792]]</sup> ) or surface generated mesoscale eddies (Adams et al., 2011 <sup>[[#fn:r793|793]]</sup> ) ( ''limited evidence'' ; ''low confidence'' ). Climate-induced changes in the distribution and cover of vent and seep foundation species may involve alteration of attachment substrate, food and refuge for the many habitat-endemic species that rely on them (Cordes et al., 2010 <sup>[[#fn:r794|794]]</sup> ) and for the surrounding deep sea ecosystems which interact through transport of nutrients and microbes, movement of vagrant predators and scavengers, and plankton interactions (Levin et al., 2016 <sup>[[#fn:r795|795]]</sup> ) ( ''limited evidence'' ; ''low confidence'' ). There is, however, insufficient analysis of faunal symbiont and nutritional requirements, life histories, larval transport and cross-system interaction to quantify the extent of the consequences described above under future climate conditions.

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