Vulnerability Assessment And Conservation Gaps Of Scleractinian Corals In Guangdong-Hong Kong-Macao Greater Bay Area

Scleractinian corals are keystone species for coral reef ecosystems and have important social,economic,and ecological benefits.However,global climate change and increased anthropogenic disturbances directly threaten the survival of scleractinian corals.Given their function important roles and the degradation status of global coral reefs,identifying the main threats to scleractinian corals is one of the most critical issues for coral reef conservation and management.In the present study,we first applied Max Ent models to predict the scleractinian corals distributions in the Guangdong-Hong Kong-Macao Greater Bay Area(GBA).Second,we identified the main environmental limiting factors influencing spatial distributions of scleractinian corals in GBA.Lastly,based on the Exposure-Habitat Suitability-Adaptation model framework,the potential distributions of scleractinian corals in GBA predicted by Max Ent model was then combined with in-situ coral investigation as well as human activities data to establish the assessing index system of ecological vulnerability for scleractinian corals in the help of spatial analysis technology.The results were conducive to improve the coral management in GBA.Max Ent model showed that the key environmental limiting factors influencing potential suitable habitat distribution for scleractinian corals in the GBA was followed by water depth,substrate type,suspended sediment,inorganic nitrogen,dissolved oxygen,and salinity.Moreover,scleractinian corals tend to distribute in those areas with 2-15 m of water depth,rock or reef substrate,less than 10 mg/L of suspended particle matter,<0.25 mg/L of dissolved inorganic nitrogen concentration,as well as dissolved oxygen concentration and salinity ranging from 5 to6.5 mg/L and from 30‰to 34‰,respectively.The high,medium,and low suitable areas for scleractinian corals in the GBA is 116 km~2,1149 km~2 and 1343 km~2,respectively.Additionally,high probability of presence for scleractinian corals was predicted mainly along the southern Hong Kong,in the top of Dapeng Bay and in Sanmen Island in Daya Bay.In Wanshan Islands and Huizhou waters,high suitable habitat is characterized by patchy distribution.The exposure assessment based on ESA models showed that human activities pressure in the study area was generally high with 84%of the area judged to be moderately to highly exposed(0.5-1),and an average exposure index was 0.58.In regional scales,the exposure assessment values were high in the Pearl River Estuary,Hong Kong,Dapeng Bay and eastern Shenzhen waters,while relatively low in Huizhou waters.The population density and tourist functional areas were the main exposure factors,threating the survival and growth for local scleractinian corals.In addition,the suitability assessment showed that only 28%of the most suitable areas,40%of the medium suitable areas and 27%of the low suitable areas were partially protected,only accounting for 41.5%of the potential suitable areas for scleractinian corals,implying that there is still a large conservation gap for scleractinian corals in GBA.Finally,we found that 30%and 36%of suitable habitat for scleractinian corals in the GBA are moderately and highly vulnerable,respectively,while only 34%of suitable habitat is relatively well-protected(mildly vulnerable).The highest average vulnerability assessment for scleractinian corals habitats was in Hong Kong(1.50)and the lowest in Shenzhen(1.32).To sum up,this study suggests that strengthening the control of existing protected areas,implementing zoning management plans,carrying out regional initiatives for marine ecosystem management and establishing specific coral protection zones in areas with concentrated coral distribution can effectively enhance the conservation and management of scleractinian corals in the GBA.