Risk Assessment And Management Of Tropical Coral Reef Ecosystems

Located far away from the mainland, the tropical coral reefs with small areas are simplification of ecosystem structure, low-level of biodiversity and fragility of ecosystems, which make tropical coral reefs easily suffered from natural disasters and human disturbances. Recently, with the rise of tourism economy and other needs, the development intensity of some islands were enhanced, resulted in some ecological problems such as the degradations of coral reefs, the losses of biodiversity and the invasions of exotic species. In a word, the ecological security is extremely severe. On the basic of scientific assessment the current state of ecological security by appropriate indicators and methods, the paper suggested the reasonable measures of the safety management. Therefore, ecological security management is an urgent and important project at present.Based on the summary of related researches, the paper proposed the framework and the methodology of the ecological risk assessment of tropical coral reefs. The main conclusions are as follows:(1) The index system of ecological risk assessment includes natural disasters, ecological degradation and environmental pollution that is suitable for tropical coral reefs had been constructed. The selection of indicators based on the analysis of ecosystem characteristic, risk sources and risk receptors.(2) The assessment results of the natural disasters risk showed that:from1949to2011, the number of tropical cyclones which affected the study erea was269,63.94%of which was from the Pacific and the remaining was from the South China Sea. General and severe disasters cause of tropical cyclone disasters respectively accounted for65.06%and34.94%. The interannual variability of typhoons was random. Compared with Taipei and Haikou, the study erea were more frequently and severely suffered from typhoons, which concentrated from early June to early December and even last longer in years. The disaster losses were mainly concentrated in constructions, power supply facilities and landscape plants, etc. In addition to include damages of the ecosystem structure and function that could not be directly measured by economic indicators. What’s more, the losses increased by years. (3) The assessment results of the ecological degradation risk showed that:①In recent7years, the vegetation coverage rate was reduced from73.2%to62.1%on the island, and its natural habitats were reduced by a rate of7.4hm2/a, even the degree of habitat fragmentation went up year by year.14.6%of the shifted habitats types accounted for10.34%of the total area of the island. The degraded areas of habitats were mainly located on the northwest and northeast coasts, or near the internal residence zones and roads. It is that port engineering, land reclamation, refuse landfill, residence, office, transportation, tourism, agriculture, landscaping and other human interferences are the main driving factors.②From1978to2004, the number of reef-building coral species was reduced from42to29, the diversity level was significantly decreased on the island. In2008, the living coral coverage rates in the north, east and west were25.2%,13.0%and1.1%, and the corals in the west and southwest were close to extinction. The damaged reefs, accounting for19.97%of the total area of the reef, mainly distributed in the northwest port, northeast reef beach, airport, and the west in the island. The deaths and damages of corals and reefs that caused by human activities, the overfished coral bleaching and the outbreak of crown-of-thorns starfish, the black death of corals that caused by the growth of black sponges, and El Nino events, all of which were the main factors resulting in degradation of corals and reefs.③The main invasive species included Cocos nucifera, Tridax procumbent, Eupatorium odoratum and Brontispa longissima. The invasion of Cocos nucifera, Tridax procumbent and Brontispa longissima were from the introduction of human conscious. While the invasion of Eupatorium odoratum with a long history, may was from the introduction of human unconscious. Cocos nucifera and Brontispa longissima were mainly distributed in the central and west of the island, on both sides of roads or around buildings. Tridax procumbent was located in the lawn around buildings or under the Cocos nucifera forests in the west of the island. Eupatorium odoratum was mainly found surrounding the south natural forest. These invasive species damaged the balance of coral reef ecosystems severely.(4) The assessment results of the environmental pollution risk showed that:①The pollution of heavy metals in soil was extremely serious on the island. The pollution degree of each element was in turn for:Cd>Hg>Cr>Pb>As>Ni. The spatial distribution of risk was shown as:cultivated land> artificial woodland> natural forest> areas around the power station> areas around the garbage dump.②Recently, trends of eutrophication and mild acidification in seawater occurred around the island. The pollution of heavy metals in seawater was also serious, the risk degree was in turn for:Hg>As>Cu>Cd>Zn>Pb. The spatial distribution of risk was shown as:section B> section C> section A.③The pollution of heavy metals in groundwater was quite severe. The risk degree was in turn for: As>Hg>Ni>Cd>Pb>Cu>Zn>Mn. The spatial distribution of risk was shown as:G1>G3>G4> G2>G5.④Heavy metals may derive from waste emissions caused by living and production process emissions of waste, the bioaccumulation of seabirds and the legacies through bird droppings, or were caused by chemical spills.⑤Owing to complicated processes of leaching, osmosis and migration of heavy metals among soil, seawater and groundwater, the paper built the conceptual model. Based on the hydrodynamic system, substance system and feedback system, the conceptual model described the migration and diffusion of environmental pollutants.(5) The assessment results of the integrated ecological risk show that:The areas of high risk degree were mainly distributed in the northwest port, the reef beach on the northeast coast, the airport, and the residential and office areas in the west. The areas of middle risk degree were mainly concentrated near the docks, pier and residential and office space, the reef flat in the northwest, and the reef flat between the airport and the Shi Island. The risk degree of other regions was low.(6) On the basic of the risk assessment, in the view of different type and size of risk, prevention and early warning, response and the recovery, the paper put forward some management measures to avoid, reduce, restrain and transfer risks, aiming for maintaining the health and safety of coral reef ecosystems.