Interaction of chemical and structural components providing defences to sea pansies Renilla reniformis and Renilla muelleri

摘要

Chemical and structural defence mechanisms are reported to co-occur in both terrestrial and marine systems. Among benthic marine organisms, the common co-occurrence of secondary metabolites and calcium carbonate (CaCO_3) in soft corals provides an opportunity for testing synergistic interactions between these traits. Defensive properties of crude extracts, chemical fractions and CaCO_3 sclerites from two sympatric species of soft corals, Renilla reniformis and R. muelleri, from Guanabara Bay, southeastern Brazil, were examined against fishes. To evaluate a potential interaction (secondary metabolites versus sclerites), both crude extracts and sclerites were evaluated as isolated defences and in combination in field assays against generalist fishes during the austral summer of 2007. While neither sclerites nor crude extracts from R. reniformis deterred feeding when offered individually in artificial food, both traits from R. muelleri offered individually provided effective defence. For both species, however, the combination of secondary metabolites and sclerites significantly deterred feeding, indicating that these traits are more effective in combination than in isolation.