Editing IPCC:AR6/WGII/Chapter-11 (section)

==== 11.3.2.2 Projected Impacts ====

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Future ocean warming, coupled with periodic extreme heat events, is projected to lead to the continued loss of ecosystem services and ecological functions ( ''high confidence'' ) ( [[#Smale--2019|Smale et al., 2019]] ) as species further shift their distributions and/or decline in abundance ( [[#Day--2018|Day et al., 2018]] ). Compounding climate-driven changes in the distribution of habitat-forming species, invasive macroalgae are predicted to exhibit higher growth under all higher pCO 2 and lower pH conditions ( [[#Roth-Schulze--2018|Roth-Schulze et al., 2018]] ). Corals and mangroves around northern Australia and kelp and seagrass around southern Australia are of critical importance for ecosystem structure and function, fishery productivity, coastal protection and carbon sequestration; these ecosystem services are therefore ''extremely likely'' [[#footnote-000|2]] to decline with continued warming. Equally, many species provide important ecosystem structure and function in New Zealand’s seas including in the deep sea ( [[#Tracey--2019|Tracey and Hjorvarsdottir, 2019]] ). The future level of sustainable exploitation of fisheries is dependent on how climate change impacts these ecosystems. Native kelp is projected to further decline in southeastern New Zealand with warming seas (Table 11.6). Climate change could affect New Zealand fisheries’ productivity ( [[#Cummings--2021|Cummings et al., 2021]] ), and both ocean warming and acidification may directly affect shellfish culture ( [[#Cunningham--2016|Cunningham et al., 2016]] ; [[#Cummings--2019|Cummings et al., 2019]] ) and indirectly through changes in phytoplankton production ( [[#Pinkerton--2017|Pinkerton, 2017]] ).

Climate-change-related temperature and acidification may affect species sex ratios and, thus, population viability ( ''medium confidence'' ) (Table 11.3) ( [[#Law--2016|Law et al., 2016]] ; [[#Tait--2016|Tait et al., 2016]] ; [[#Mikaloff-Fletcher--2017|Mikaloff-Fletcher et al., 2017]] ). Acidification may alter sex determination (e.g., in the oyster ''Saccostrea glomerate'' ), resulting in changes in sex ratios ( [[#Parker--2018|Parker et al., 2018]] ), and may thus affect reproductive success ( ''low confidence'' ). Decreasing river flows ( [[#Chiew--2017|Chiew et al., 2017]] ) are projected to cause periodically open estuaries across southwest Australia to remain closed for longer periods, inhibiting the extent to which marine taxa can access these systems ( [[#Hallett--2017|Hallett et al., 2017]] ) and with warming predicted to constrain activity in some large fish ( [[#Scott--2019b|Scott et al., 2019b]] ). Major knowledge gaps include environmental tolerances of key life stages, sources of recruitment, population linkages, critical ecological (e.g., predator–prey interactions) or phenological relationships and projected responses to lowered pH ( [[#Fleming--2014|Fleming et al., 2014]] ; [[#Fogarty--2019|Fogarty et al., 2019]] ).

Black-browed albatrosses breeding on Macquarie Island may be more vulnerable to future climate-driven changes to weather patterns in the Southern Ocean and potential latitudinal shifts in the sub-Antarctic Front ( [[#Cleeland--2019|Cleeland et al., 2019]] ). New Zealand coastal ecosystems face risks from sea level rise (SLR) and extreme weather events ( [[#MfE--2020a|MfE, 2020a]] ).

Nutrient availability and productivity in the sub-tropical waters of New Zealand are projected to decline due to increased SST and strengthening of the thermocline, but they may increase in sub-Antarctic waters, potentially bringing some benefit to fish and other species ( ''low confidence'' ) ( [[#Law--2018b|Law et al., 2018b]] ). For New Zealand waters as a whole, declines in net primary productivity of 1.2% and 4.5% are projected under RCP4.5 and RCP8.5 respectively by 2100, and declines in the primary production of surface waters by an average 6% from the present day under RCP8.5, with sub-tropical waters experiencing the largest decline ( [[#Tait--2016|Tait et al., 2016]] ).

The pH of surface waters around New Zealand is projected to decline by 0.33 under RCP 8.5 by 2090 ( [[#Tait--2016|Tait et al., 2016]] ), and the depth at which carbonate dissolves is projected to be significantly shallower ( [[#Mikaloff-Fletcher--2017|Mikaloff-Fletcher et al., 2017]] ), affecting the distribution of some species of calcifying cold water corals ( ''medium confidence'' ) ( [[#Law--2016|Law et al., 2016]] ). However, model projections suggest that the top of the Chatham Rise may provide temporary refugia for scleractinian stony corals from ocean acidification because the Chatham Rise sits above the aragonite saturation horizon ( [[#Anderson--2015|Anderson et al., 2015]] ; [[#Bostock--2015|Bostock et al., 2015]] ). For sub-tropical corals, skeletal formation will be vulnerable to the changes in ocean pH, with implications for their longer-term growth and resilience ( [[#Foster--2015|Foster et al., 2015]] ).

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