No abstract

A mesocosm experiment was conducted to determine the effects of nutrient enrichment on competitive interactions between a hard coral, a green alga, and a sea anemone. In the low-nutrient controls, abundances of the green alga, Codium edule, and a sea anemone, Mesactinia genesis, remained low, and they coexisted with the live or dead scleractinian coral, Acropora muricata. Combined nitrogen and phosphorus additions markedly increased the photosynthetic efficiencies of zooxanthellae in A. muricata, the coverage of C. edule, and the asexual reproduction by M. genesis. After 35 d of nutrient addition, C. edule had begun to overgrow live A. muricata, but not dead coral. A. muricata finally died after 105 d, after being totally overgrown by C. edule. Within a few days of contact with live A. muricata, M. genesis was observed for the first time to have induced inflation of modified marginal aggressive organs known as acrorhagi tentacles, which it uses to attack neighboring coral. Nevertheless, M. genesis was not observed to attack C. edule, but moved away from it in the nutrient-enriched tanks. The hierarchy of competitive superiority under nutrient enrichment was in the order of C. edule > M. genesis > A. muricata. From this experiment, it was evident that nutrient enrichment inhibits corals' ability to compete with sea anemones and algae in Nanwan Bay, southern Taiwan

Recurrent disturbances can have a critical effect on the structure and function of coral reef communities. In this study, long-term changes were examined in the hard coral community at Wanlitung, in southern Taiwan, between 1985 and 2010. In this 26 year interval, the reef has experienced repeated disturbances that include six typhoons and two coral-bleaching events. The frequency of disturbance has meant that species susceptible to disturbance, such as those in the genus Acropora and Montipora have almost disappeared from the reef. Indeed, almost all hard coral species have declined in abundance, with the result that total hard coral cover in 2010 (17.7%) was less than half what it was in 1985 (47.5%). In addition, macro-algal cover has increased from 11.3% in 2003 to 28.5% in 2010. The frequency of disturbance combined with possible chronic influence of a growing human population mean that a diverse reef assemblage is unlikely to persist on this reef into the future.