Multiple functions for secondary metabolites in encrusting marine invertebrates

We used three chemical fractions (spanning a wide range of polarities) from the extracts of four marine invertebrates, the sponges Crambe crambe and Hemimycale columella and the ascidians Cystodytes dellechiajei and Polysyncraton lacazei, to test inhibition of cell division, photosynthesis, and settlement. We used assay organisms from the same habitat, seeking to determine whether a species may display diverse, ecologically relevant bioactivities and, if so, whether the same types of compound may be responsible for such activities. Cell division was strongly inhibited by the sponge C. crambe. A dichloromethane fraction from C. crambe prevented development of sea urchin Paracentrotus lividus eggs at a concentration of 10 mu g/ml, as did the butanolic fraction, but at higher concentrations (50 and 100 mu g/ml). At 50 mu g/ml, the aqueous fraction of C. crambe allowed cell division but prevented eggs from developing beyond the gastrula stage. Similar results were recorded with the dichloromethane fraction of P. lacazei and from the aqueous fraction of H. columella. Photosynthesis was unaffected by any of the species at 50 mu g/ml. Larval settlement was inhibited by one or another fraction from the four species surveyed at a concentration of 50 mu g/ml, although C. crambe exhibited the greatest amount of activity. We therefore found that various fractions displayed the same type of bioactivity, while compounds from the same fraction were responsible for multiple activities, suggesting that secondary metabolites are multiple-purpose tools in nature, which is relevant to our understanding of species ecology and evolution. Moreover, results showed that the assessment of the role of chemical compounds is significantly influenced by the assay organism, fractionation procedure, concentration, and duration of experiments. All these factors should he carefully considered when testing ecological hypotheses of the roles of chemically-mediated bioactivities.