Editing IPCC:AR6/WGII/Chapter-9 (section)

==== 9.6.1.4 Marine Ecosystems ====

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Anthropogenic climate change is already negatively impacting Africa’s marine biodiversity, ecosystem functioning and services by changing physical and chemical properties of seawater (increased temperature, salinity and acidification, and changes in oxygen concentration, ocean currents and vertical stratification) ( ''high confidence'' ) ( [[#Hoegh-Guldberg--2014|Hoegh-Guldberg et al., 2014]] ; 2018). Coastal ecosystems in west Africa are among the most vulnerable because of extensive low-lying deltas exposed to sea level rise, erosion, saltwater intrusion and flooding ( [[#Belhabib--2016|Belhabib et al., 2016]] ; [[#UNEP--2016b|UNEP, 2016b]] ; [[#Kifani--2018|Kifani et al., 2018]] ). In southern Africa, shifting distributions of anchovy, sardine, hake, rock lobster and seabirds have been partly attributed to climate change ( [[#Crawford--2015|Crawford et al., 2015]] ; [[#van%20der%20Lingen--2018|van der Lingen and Hampton, 2018]] ; [[#Vizy--2018|Vizy et al., 2018]] ), including southern shifts of 30 estuarine and marine fish species attributed to increased temperature and changes in water circulation from decreased river inflow ( [[#Augustyn--2018|Augustyn et al., 2018]] ). Warming sea surface temperatures inhibiting nutrient mixing have reduced phytoplankton biomass in the western Indian Ocean by 20% since the 1960s, potentially reducing tuna catches ( [[#Roxy--2016|Roxy et al., 2016]] ).

Mangroves, seagrasses and coral reefs support nursery habitats for fish, sequester carbon, trap sediment and provide shoreline protection ( [[#Ghermandi--2019|Ghermandi et al., 2019]] ). Climate change is compromising these ecosystem services ( ''medium confidence'' ). Marine heatwaves associated with ENSO events have triggered mass coral bleaching and mortality over the past 20 years ( [[#Oliver--2018|Oliver et al., 2018]] ). Mass coral bleaching in the western Indian Ocean occurred in 1998, 2005, 2010 and 2015/2016 with coral cover just 30–40% of 1998 levels by 2016 ( [[#Obura--2017|Obura et al., 2017]] ; [[#Moustahfid--2018|Moustahfid et al., 2018]] ). The northern Mozambique Channel has served as a refuge from climate change and biological reservoir for the entire coastal east African region ( [[#McClanahan--2014|McClanahan et al., 2014]] ; [[#Hoegh-Guldberg--2018|Hoegh-Guldberg et al., 2018]] ). A southern shift of mangrove species has been observed in south Africa ( [[#Peer--2018|Peer et al., 2018]] ) with loss in total suitable coastal habitats for mangroves and shifts in the distribution of some species of mangroves and a gain for others ( [[#Record--2013|Record et al., 2013]] ). Mangrove cover was reduced 48% in Mozambique in 2000 from Tropical Cyclone Eline, with 100% mortality of seaward mangroves dominated by ''Rhizophora mucronata'' ( [[#Macamo--2016|Macamo et al., 2016]] ). Recovery of mangrove species was observed 14 years later in sheltered sites. There is ''low confidence'' these cyclone-induced impacts are attributable to climate change owing, in part, to a lack of reliable long-term data sets ( [[#Macamo--2016|Macamo et al., 2016]] ). In west Africa, oil and gas extraction, deforestation, canalisation and de-silting of waterways have been the largest factors in mangrove destruction ( [[#Numbere--2019|Numbere, 2019]] ).

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