The dynamics of the restoration of mechanical damage to colonies of the scleractinian coral Porites lutea under conditions of competition with algal settlers for substratum

Natural and anthropogenic catastrophes in the last decades of the 20th century and at the beginning of the new century have evoked significant changes in the biological diversity of coral reefs, viz., the mortality of hermatypic scleractinian corals that are replaced by communities of marine algae and seaweeds. In this connection, the study of the dynamics of algal colonization of a newly formed substratum and competition for the substratum between hermatypic corals and algae is of topical interest. This paper describes the results of investigations conducted in 2003 at the Sesoko Marine Biological Station of Ryukyu University (Okinawa, Japan). Colonies of the massive scleractinian coral Porites lutea were sampled from a fringing reef of Sesoko Island. Damages were inflicted on the upper portions of the colonies, the damaged coral fragments were placed in aquaria and maintained for six months under different light intensities in the absence of herbivorous and corallivorous animals. The experiments showed that under bright (70-90% of incident photosynthetically active radiation, PAR(0)) and under moderate light (20-30% of PAR(0)), the damaged parts of colonies of about 25 cm(2) were overgrown by newly formed polyps within six months. Under dim light (2-5% of PAR(0)), this period was not sufficient for recovery from lesions. During the first month, the recovery rate of colonies was the highest and depended on the physiological state of the corals and light intensity: in bright and moderate light it was two times and more higher than under low light. During the subsequent months, the recovery rate was significantly lower and depended mainly on the degree of overgrowth of dead portions with algae and on their species composition. Under bright and moderate light, algal colonization of damaged colonies started with the settling of colonial and filamentous diatoms, cyanobacteria and green algae, followed by the formation of the algal turf community. Communities of red calcareous crusts and fleshy algae were mainly formed on damaged corals under low light. A comparison of experimental results showed that damaged colonies maintained in aquaria in the absence of herbivorous and corallivorous animals recovered 1.5 times faster than in the sea. We hypothesize that herbivorous fish have a negative rather than positive influence on the recovery of damaged colonies.