Comments on coral reef regeneration, bioerosion, biogeography, and chemical ecology: future directions

Abstract

This paper represents a brief review of three processes operating on coral reefs and the results of studies of a fourth process, and how those results may be applied to the benefit of humankind. The areas are reef regeneration processes; bioerosion; dispersal, recruitment and biogeography of corals; and chemical ecology and natural products chemistry of reef organisms. Possible future directions for research will also be considered in each area. Regarding reef regeneration processes, coral reefs are degrading rapidly on a global scale due to over-fishing, fishing techniques causing habitat destruction, deforestation, mass mortalities of key reef species, nutrient enrichment and sedimentation. Seeding of reefs with the larvae of corals and other key reef organisms, such as echinoids, may help to promote and enhance reef regeneration in the future. Such techniques will be made possible by studies of the embryology, larval ecology, dispersal and recruitment processes, and related local physical oceanographic processes. Regarding bioerosion, both internal and external bioerosion are affected by grazers and predators. Bioerosion is also affected by nutrient enrichment, as shown through correlative studies (Great Barrier Reef) and studies of opportunity (Kaneohe Bay). Ongoing experiments such as ENCORE will help to answer questions about the role of dissolved nutrients in enhancing internal bioerosion. Questions still remain, however, regarding the role of particulates in promoting internal bioerosion and the resultant weakening of and negative growth in the reef framework. Regarding dispersal, recruitment and the biogeography of corals, it is now known that most species of coral reproduce via broadcasting, although there appear to be proportionally more brooders in the Caribbean than in the western Pacific. Differential extinctions in the western Pacific vs. the western Atlantic have contributed to the biogeographic distribution of corals we observe today and the concentric isoclines of species diversity in numerous reef organisms in the western Pacific. The role of reproductive mode in contributing to these patterns is, however, still not understood. Investigations into the roles of different larval longevities and reproductive modes may help us answer questions regarding their differential distribution and the potential effects of major perturbations such as global warming on future distributions. With respect to the chemical ecology of alcyonacean octocorals (soft corals), four functions have been determined thus far for secondary metabolites in this group, anti-predation, anti-competition (allelopathy), anti-fouling, and enhancement of reproductive success. Investigations of alcyonacean reproduction has revealed that it may be necessary for several secondary metabolites to be present simultaneously before a function may be realized or fully manifested. This raises questions regarding the manner in which novel compounds are tested by medical laboratories for bioactivity using a single compound. Simultaneously testing of multiple compounds derived from a single organism may be necessary in the future to reveal potential valuable synergistic bioactivity. Also, some novel secondary metabolites may have other valuable commercial applications, as is the case with the UV-absorbing compounds of corals and other reef organisms found on the Great Barrier Reef. In order to avoid overlooking medically or commercially valuable functions of these compounds, broader testing may be necessary.