Chemical warfare among scleractinians: bioactive natural products from Tubastraea faulkneri Wells kill larvae of potential competitors

Competition for space among scleractinians by overgrowth, overtopping, extr acoelenteric digestion and the use of sweeper tentacles is well recognized, bat another potential mode of competitive interaction, allelopathy, is lar gely uninvestigated. In this study, chemical extracts from Tubastraea faulk neri Wells were tested for deleterious effects on competent larvae of 11 ot her species of coral belonging to seven genera of four scleractinian famili es. Larvae exposed to extract concentrations from 10 to 500 mu g ml(-1) con sistently suffered higher mortality than larvae in solvent controls. Larvae of Platygyra daedalea (Ellis and Solander) and Oxypora lacera (Verrill) we re the most sensitive, experiencing high mortality even at the lowest extra ct concentration. The toxic compounds from T. faulkneri did not kill any co nspecific larvae. The estimated concentrations of active compounds within T . faulkneri tissues were 100-5000 times higher than the experimental concen trations. Pure compounds isolated from bioactive fractions of the extract w ere indole alkaloids identified as aplysinopsin, 6-bromoaplysinopsin, 6-bro mo-2'-de-N-methylaplysinopsin and its dimer. The first three occur in other non-zooxanthellate corals in the same family as T.faulkneri, whereas the d imer is novel. These compounds could act as allelochemicals that prevent po tential competitors from recruiting in the vicinity of T. faulkneri colonie s and help to pre-empt interactions with competitively dominant species. (C ) 2000 Elsevier Science B.V. All rights reserved.