Editing IPCC:AR6/SROCC/Chapter-3 (section)

===== 3.2.3.1.2 Benthic communities =====

There is evidence that earlier spring sea ice retreat and later autumn sea ice formation (Section 3.2.1.1) are changing the phenology of primary production with cascading effects on Arctic benthic community biodiversity and production (Link et al., 2013 <sup>[[#fn:r579|579]]</sup> ) ( ''medium confidence'' ). In the Barents Sea, evidence suggests that factors directly related to climate change (sea ice dynamics, ocean mixing, bottom-water temperature change, ocean acidification, river/glacier freshwater discharge; Sections 3.2.1.1, 3.2.1.2) are impacting the benthic species composition (Birchenough et al., 2015 <sup>[[#fn:r580|580]]</sup> ). Other human influenced activities, such as commercial bottom trawling and the introduction of non-native species are also regarded as major drivers of observed and expected changes in benthic community structure (Johannesen et al., 2017 <sup>[[#fn:r581|581]]</sup> ), and may interact with climate impacts.

Rapid and extensive structural changes in the rocky-bottom communities of two Arctic fjords in the Svalbard Archipelago during 1980–2010 have been documented and linked to gradually increasing seawater temperature and decreasing sea ice cover (Kortsch et al., 2012 <sup>[[#fn:r582|582]]</sup> ; Kortsch et al., 2015) <sup>[[#fn:r583|583]]</sup> . Also, there are indications of declining benthic biomass in the northern Bering Sea (Grebmeier and Cooper, 2016 <sup>[[#fn:r584|584]]</sup> ) and southern Chukchi Sea (Grebmeier et al., 2015 <sup>[[#fn:r585|585]]</sup> ). It is unclear whether these rapid ecosystem changes will be tipping points for local ecosystems (Chapter 6, Table 6.1; Wassmann and Lenton, 2012 <sup>[[#fn:r586|586]]</sup> ). However, biomass of kelps have increased considerably in the intertidal to shallow subtidal in Arctic regions over the last two decades, connected to reduced physical impact by ice scouring and increased light availability as a consequence of warming and concomitant fast-ice retreat (Kortsch et al., 2012 <sup>[[#fn:r587|587]]</sup> ; Paar et al., 2016 <sup>[[#fn:r588|588]]</sup> ) ( ''medium confidence'' ) (see Section 5.3.3 and SM3.2.6 for further information on kelp).

The growth, early survival and production of commercially important crab stocks in the Bering Sea are influenced by time-varying exposure to multiple interacting drivers including bottom temperature, larval advection, predation, competition and fishing (Burgos et al., 2013 <sup>[[#fn:r589|589]]</sup> ; Long et al., 2015 <sup>[[#fn:r590|590]]</sup> ; Ryer et al., 2016 <sup>[[#fn:r591|591]]</sup> ). In Newfoundland and Labrador waters and on the western Scotian Shelf, snow crab ( ''Chionoecetes opilio'' ) productivity has declined (Mullowney et al., 2014 <sup>[[#fn:r592|592]]</sup> ; Zisserson and Cook, 2017 <sup>[[#fn:r593|593]]</sup> ). Contrary to this, snow crabs have expanded their distribution in the Barents Sea and commercial harvesting increased (Hansen, 2016 <sup>[[#fn:r594|594]]</sup> ; Lorentzen et al., 2018 <sup>[[#fn:r595|595]]</sup> ) ( ''high confidence'' ).

Bering sea crabs exhibit species-specific sensitivities to reduced pH (Long et al., 2017 <sup>[[#fn:r596|596]]</sup> ; Swiney et al., 2017 <sup>[[#fn:r597|597]]</sup> ; Long et al., 2019 <sup>[[#fn:r598|598]]</sup> ). However, current pH levels do not appear to have negatively impacted crab production in the Bering or Barents Seas (Mathis et al., 2015 <sup>[[#fn:r599|599]]</sup> ; Punt et al., 2016 <sup>[[#fn:r600|600]]</sup> ).

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