Evolvement And Influential Factors Of Coral Community Over Past Three Decases In Weizhou Island Reef,Beibu Gulf

Weizhou Island Reef is located in the northern distribution of coral reefs,relatively high latitude area in the South China Sea,the environmental conditions of Weizhou Island are suitable for the growth of corals.Since 1980s,Weizhou Island Reef has been suffering heavy anthropogenic pressures observably and some degradation evidences occur.Currently,it lacks systematic researches of long-term monitoring and systematic research on the coral community evolvement,the status of coral community of Weizhou Island reef are studied based on the ecological materials from diving observation,transects videos,quadrats photos and Porites lutea colonies measurements in 2015,comparing with previous documents,we analyzed the evolvement of coral community over past 30 years in changes of coral cover,species diversity and community structure,to estimate the variation tendency of coral community,we also explored the effect from enviromental changes and human activities,the results were shown as follows:(1)Weizhou Island reef consists of 41 species of hermatypic corals belonging to 11 genera and 41 families,the most dominant species are Porites lutea and Favites halicora,with importance value percentages as 29.45%and 12.06%,respectively.The mean live coral cover is 6.02%,with 1.67%at shallow sites(1m?depth?3m)and 10.37%at deep sites(3m<depth<10m).The avarage age of Porites lutea is 21.44a,and about 84.34%of P.lutea are less than 30 years old.The supplement of abundent young colones indicates that corals in relatively high-latitude area benefit from global warming.(2)Weizhou Island reef has an obvious declining trend over past three decases.Mean live coral cover decreased from 50%in 1984 to only 6%in 2015.There were 8 species(-29%of total coral species)from the investigation in 1960s were absent in 2000-2015,and 4 species(?13%of total coral species)from the investigation in 1980s were also lost in 2000-2015.The dominant coral species has shifted from group with high complexity and high growth rate,which consist of branching(Acropora,Montipora),foliaceous(Pavona)and massive(Favia,Goniastrea,Platygyra)colonies to simplex group of massive(Porites,Favites)morphologies.Althrough Acropora corals was reported growing profusely with coral cover up to 90%on the individual region of Weizhou Island in 1984,they have almost disappeared from the same area in 2015.It implied the detrimental habit made sensitive species(e.g.Acropora)drop out of dominant groups,as well as massive corals occupy a great advantage throughout,because of holding wide ecological niche.(3)As the development of economic construction and tourism,high-intensity and unreasonable anthropogenic activities disturb growing environment of corals at Weizhou Island reef,these are the main factor contributing to persistent decline of the coral community in Weizhou Island reef over past three decases.