The Response Of Reef-Building Corals To Environmental Changes In Wuzhizhou Island,Sanya

The health of coral reef has declined significantly around the world due to the impact of human activities and natural environment changes,and corals have to develop effective resistance mechanisms to survive.The spatial and temporal variation of benthic communities and ecological adaptability of corals in Wuzhizhou island?WZZ?of Sanya are studied by combining the field monitoring data with laboratory test experiments,including environment parameters,benthic substrata,coral community composition,dominant population,physiological ecology and so on.This study is to assess the status of coral reefs,elucidate the effects of water environmental changes on the physiological characteristics of corals,and discuss the intrinsic metabolic strategies of coral under environment stress.This study provides a theoretical basis for further understanding the impact of environmental changes on coral reef communities and the adaptive mechanism of corals under environmental stress.And it provides theoretical guidance for the protection and scientific development of coral reef ecosystems.The main research results are as follows:1.A total of 90 species of hermatypic coral corals belonging to 40 genera and 12families,and 2 species of millepora were recorded in the 2018 annual survey of WZZ.And Porites was the first dominant genus,accounting for 31.87%of reef-building corals.Comparison of previous years,the overall coral coverage rate of WZZ increased in 2018.In particular,reef-building corals in the reef area of WZZ are recovering after“Paka”typhoon hit the reef in 2017.2.In the investigation of the water environment in the coral reef area of WZZ,we found that the dissolved inorganic nitrogen and phosphate levels were higher than that in the healthy coral reef,and were significantly higher than that in the standards of type?seawater.This may be linked to the fact that the 9,11 and 13 stations selected in this survey?5 stations?are all open-diving areas.In addition,we observed that temperature,salinity,nitrate,ammonium,phosphate and other environmental factors had obvious seasonal changes.For example,with the coupling effect of typhoon,rainstorm,Qiongdong upwelling,and human activities in the summer,the environmental characteristics were the most complex and changeable,which showed low temperature,low ammonium,high nitrate,and high turbidity.3.From spring to winter in 2018,the coverage of live coral increased steadily and slowly from 25.92 to 33.64%.In addition to the increase of typhoons,rainstorms and the coverage of rubble increased in the summer,the coverage of living coral and reef-building coral decreased.A similar,trend in the coverage of soft coral,reef-building coral,Porites spp.and sea anemone.4.There was the different spatial gradient of turbid-nutrient between the south and north of WZZ.The temperature,turbidity and DIN in the north were significantly higher than in the south,which was related to the increasing number of tourists and the great intensity of human activities?such as regional flood discharge?in the north of WZZ.Compared with the north,the south of WZZ had the healthier water quality and coral reef communities.It has been suggested that the coverage of soft coral and reef-building coral,and coral species diversity were significantly higher in the south than in the north,whereas,the coverage of sand and rubble were significantly lower the south than in the north.The greater intensity of human activities and the weaker of water quality environment in the north of WZZ may be the main reasons for the difference in the spatial distribution of biological communities in the coral reef areas between the south and north.5.The four dominant coral species were selected from the coral reef of WZZ,including Galaxea fascicularis,Pocillopora verrucosa,Montipora truncata and Porites lutea.As a result,significant spatial distribution differences were found for the four dominant coral species in their physiological characteristics,including r ETR_max,SOD,and protein content,between the north and the south.Compared with the south,the r ETR_maxand protein content of the four corals significantly decreased in the north,while the SOD enzyme activity significantly increased.These data indicated that the photosynthetic and antioxidant system of the corals were subjected from pressure disturbance in the north.Corals at the waters about the WZZ suffer from greater environmental stress in the north than in the south,including higher turbidity,and nutrients and more suspended particles.Overall,the physiological states were healthier in the south than in the north,matched the spatial variation of coral communities.6.The four dominant reef-building corals had their unique physiological conditions and Symbiodiniaceae types,and they had different responses to complex environmental stress in the north.M.truncata and P.verrucosa were mainly associated with the zooxanthellae type C1.M.truncata and P.verrucosa increased their density of the main symbiotic zooxanthellae C1 in the north to offset the decline of photosynthetic efficiency and thus supply energy.Besides,P.lutea was mainly associated with the zooxanthellae type C15,had lower Chl a content of single zooxanthellae cell than the other three coral species,and had higher energy reserve.Interestingly,ITS2 genotyping showed that G.fascicularis contained Symbiodiniaceae either genotype C21 or D1a depending on the regional environmental stress,and had stronger heterotrophy than the other three coral species.For P.lutea and G.fascicularis,their half saturating irradiance declined sharply in the north,which affected the autotrophic input.where P.lutea largely released the weak C15 zooxanthellae to reduce load consumption,and resorted to improve heterotrophic feeding,and/or change the energy budget mode to maintain energy balance.While G.fascicularis alters its primary symbiotic zooxanthellae type and reduced its energy reserve significantly.These corals maintain their presence by adopting their own successful resistance mechanisms at symbiotic relationship and energy metabolism level over time against long-term disturbances such as elevated turbidity or temperature.7.Although the impact of marine tourism on the ecological environment is inevitable,its impact degree is controllable.It is suggested to improve the sewage treatment capacity of WZZ and reduce the impact on environment under the premise of overall control of tourist capacity.At the same time,it's necessary to strengthen the environmental protection publicity to tourists and staff,such as the training of tourists in diving area,fishing area,nearshore swimming area,the enhancement of their awareness that protect the environment and marine animals.