Temporal and spatial variation in defensive metabolites of the tropical Pacific soft corals Sinularia maxima and S-polydactyla

The soft corals Sinularia maxima and S. polydactyla contain identical bioac tive metabolites which, at natural concentrations, deter feeding by many ge neralist predatory reef fishes. The range of these metabolite concentration s in the soft corals can vary over time and between sites. During a 2 year period between October 1994 and September 1996 on Guam there were significa nt temporal differences in concentrations of the two major defensive metabo lites, pukalide and 11 beta -acetoxypukalide, of these soft corals. However , no seasonal patterns emerged from the temporal analyses. There were also site-specific differences in these chemical constituents despite habitat si milarities; two sites on Guam separated by approximately 30 km exhibited a twofold difference in levels of the defensive metabolite pukalide, and site s throughout the tropical Northwest Pacific showed as much as a fivefold di fference. Transplantation of the soft corals between the two sites on Guam for an 8 month period resulted in as much as a 27% change in pukalide conce ntrations, while back-transplanted handling controls exhibited no change. T here were also significant differences in the number of bite scars (i.e. fi sh predation events) on the soft corals at the two sites following transpla ntation, suggesting the intensity of predation might be responsible for sit e-specific changes in defensive metabolite levels, although it is impossibl e to rule out other interactive effects at this time. Video transects indic ated a six- to sevenfold greater number of butterflyfish at one of these si tes, which resulted in a higher predation rate (as bites m(-2) h(-1)); the populations of soft corals at this site exhibited higher levels of pukalide than populations at the low-predation site. This study provides preliminar y evidence that the spatial variability in the chemical constituents of the soft corals S. maxima and S. polydactyla is a plastic phenotypic response that might be due to localized predation pressures.