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

=== 3.4.1 Introduction ===

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Ocean and coastal ecosystems and their resident species are under increasing pressure from a multitude of climate-induced drivers and non-climate drivers ( [[#3.1|Section 3.1]] ; Figure 3.12; [[#Bindoff--2019a|Bindoff et al., 2019a]] ). This section builds from the assessment of biological responses to climate-impact drivers ( [[#3.3|Section 3.3]] ) to examine the new evidence about climate-change impacts at the level of marine ecosystems. It focuses on detection and attribution of observed changes to marine ecosystems and the projected changes under different future climate scenarios. This assessment considers emerging evidence on the effects of multiple non-climate drivers and physiological acclimation and/or evolutionary adaptation on these observations and projections.

The section focuses first on coastal ecosystems and seas ( [[#3.4.2|Section 3.4.2]] ), which have high spatial variability in physical and chemical characteristics, are affected by many non-climate drivers ( [[#3.1|Section 3.1]] ; Figure 3.12) and support rich fisheries, high biodiversity and high levels of species endemism. The assessment begins with warm-water coral reefs ( [[#3.4.2.1|Section 3.4.2.1]] ) because these highly threatened systems are at the vanguard of research on acclimation and evolutionary adaptation among coastal ecosystems. It follows with the other shallow, nearshore ecosystems dominated by habitat-forming species (e.g., rocky shores, kelp systems) and then nearshore sedimentary systems (estuaries, deltas, coastal wetlands and sandy beaches), before moving on to semi-enclosed seas, shelf seas, upwelling zones and polar seas.

The section continues on to oceanic and cross-cutting changes ( [[#3.4.3|Section 3.4.3]] ), which influence large areas of the epipelagic zone (&lt;200 m depth) while also affecting the mesopelagic (200–1000 m), the perpetually dark bathypelagic (depth &gt;1000 m) and the deep seafloor (benthic ecosystems at depths &gt;200 m) zones. Assessed in this section are species range shifts ( [[#3.4.3.1|Section 3.4.3.1]] ), phenological shifts and trophic mismatches ( [[#3.4.3.2|Section 3.4.3.2]] ), changes in communities and biodiversity ( [[#3.4.3.3.2|Section 3.4.3.3.2]] ), time of emergence of climate-impact signals in ecological systems from background natural variability ( [[#3.4.3.3.4|Section 3.4.3.3.4]] ) and changes in biomass, primary productivity and carbon export (Sections 3.4.3.4–3.4.3.6).

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