Natural chemical control of marine associated microbial communities by sessile Antarctic invertebrates

Organisms living in the sea are exposed to fouling by other organisms. Many benthic marine invertebrates, including sponges and bryozoans, contain natural products with antimicrobial properties, since microbes usually constitute the first stages of fouling. Extracts from 4 Antarctic sponges (Myxilla (Myxilla) mollis, Mycale tylotornota, Rossella nuda, and Anoxycalyx (Scolymastra) joubini) and 2 bryozoan species (Cornucopina pectogemma and Nematoflustra flagellata) were tested separately for antifouling properties in field experiments. The different crude extracts from these invertebrates were incorporated into a substratum gel at natural concentrations for an ecological approach. Treatments were tested by submerging plates covered by these substratum gels under water in situ during 1 lunar cycle (28 d) at Deception Island (South Shetland Islands, Antarctica). Remarkably, the butanolic extracts of M. tylotornota and C. pectogemma showed complete growth inhibition of microscopic eukaryotic organisms, one of the succession stages involved in biofouling. Our results suggest that different chemical strategies may exist to avoid fouling, although the role of chemical defenses is often species-specific. Thus, the high specificity of the microbial community attached to the coated plates seems to be modulated by the chemical cues of the crude extracts of the invertebrates tested.