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

===== 3.2.3.2.5 Pelagic foodwebs and ecosystem structure =====

This section assesses the impacts of ocean and sea ice changes on pelagic foodwebs and ecosystem structure. The ecological impacts of loss of ice shelves and retreat of coastal glaciers around Antarctica are assessed in Section 3.3.3.4. Recent syntheses of Southern Ocean ecosystem structure and function recognise the importance of at least two dominant energy pathways in pelagic foodwebs—a short trophic pathway transferring primary production to top predators via krill, and at least one other pathway that moves energy from smaller phytoplankton to top predators via copepods and small mesopelagic fishes—and indicate that the relative importance of these pathways will change under climate change (Murphy et al., 2013 <sup>[[#fn:r823|823]]</sup> ; Constable et al., 2016 <sup>[[#fn:r824|824]]</sup> ; Constable et al., 2017 <sup>[[#fn:r825|825]]</sup> ; McCormack et al., 2017 <sup>[[#fn:r826|826]]</sup> ) ( ''medium confidence'' ). Using an ecosystem model, Klein et al. (2018) <sup>[[#fn:r827|827]]</sup> found that the effects of warming on krill growth off the AP and in the Scotia Sea translated to increased risks of declines in krill predator populations, particularly penguins, under both RCP2.6 and RCP8.5. The relative importance of different energy pathways in Southern Ocean foodwebs has important implications for resource management, in particular the management of krill and toothfish fisheries by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) (Constable et al., 2016 <sup>[[#fn:r828|828]]</sup> ; Constable et al., 2017 <sup>[[#fn:r829|829]]</sup> ) (Sections 3.2.4.1.2, 3.5.3.2.2).

In summary, advances in knowledge regarding the impacts of climate change on Antarctic marine ecosystems since AR5 are consistent with the impacts described in Larsen et al. (2014) <sup>[[#fn:r830|830]]</sup> (also summarised in Figure 3.6). These advances include further descriptions of local-scale, climate-related influences (sea ice and stratification) on primary productivity, particularly in the West Antarctic Peninsula region (Section 3.2.3.2.1) ( ''medium confidence'' ). At the circumpolar scale, primary production is projected to increase in regions south of 65°S over the period from now to 2100 under RCP8.5 (Leung et al., 2015 <sup>[[#fn:r831|831]]</sup> ) ( ''low confidence'' ). However, ocean acidification may have a detrimental effect on coastal phytoplankton communities around the Antarctic continent (Section 3.2.3.2.1) ( ''medium confidence'' ). Increased information is also available regarding climate-driven changes in Antarctic krill populations in the south Atlantic, including the observed southward shift in the spatial distribution of krill in this region (Atkinson et al., 2019 <sup>[[#fn:r832|832]]</sup> ) ( ''medium confidence'' ) but evidence of a long-term trend in overall abundance in the region is equivocal (Section 3.2.3.2.1). Further habitat contraction for Antarctic krill is predicted in the future ( ''medium confidence'' ) (references detailed in Section 3.2.3.2.1). Under high emissions scenarios the majority of Antarctic seafloor species are projected to be negatively impacted by the end of the century (Griffiths et al., 2017a <sup>[[#fn:r833|833]]</sup> ) ( ''low confidence'' ). Observed changes in the geography of ice-associated habitats (sea ice, ice shelves and polynyas) have both positive and negative effects on seabirds and marine mammals, and will interact with ice dependent changes in Antarctic krill populations to compound the impacts on krill dependent predators (Klein et al., 2018 <sup>[[#fn:r834|834]]</sup> ) (Sections 3.2.3.2.1, 3.2.3.2.4) ( ''medium confidence'' ).

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'''Figure 3.6'''

<span id="schematic-summary-of-key-drivers-that-are-causing-or-are-projected-to-cause-direct-effects-on-southern-ocean-marine-ecosystems.-effects-presented-here-are-described-in-the-main-text-sections-3.2.3.2-3.3.3.4-with-associated-confidence-levels-and-citations.-projected-changes-indicated-by-an-asterisk-are-for-high-emissions-scenarios.-the-cross-sectional-view-of-the-southern"></span>
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'''Schematic summary of key drivers that are causing or are projected to cause direct effects on Southern Ocean marine ecosystems. Effects presented here are described in the main text (Sections 3.2.3.2, 3.3.3.4), with associated confidence levels and citations. Projected changes (indicated by an asterisk) are for high emissions scenarios. The cross-sectional view of the Southern […]'''
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[[File:49e88a41905cd8a2599ddce0e9957444 IPCC-SROCC-CH_3_6.jpg]]

Schematic summary of key drivers that are causing or are projected to cause direct effects on Southern Ocean marine ecosystems. Effects presented here are described in the main text (Sections 3.2.3.2, 3.3.3.4), with associated confidence levels and citations. Projected changes (indicated by an asterisk) are for high emissions scenarios. The cross-sectional view of the Southern Ocean ecosystem shows the association of key functional groups (marine mammals, birds, fish, zooplankton, phytoplankton and benthic assemblages) with Southern Ocean habitats. The configuration of the Southern Ocean foodweb is described in SM3.2.6.

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