Allelopathic activities of sponge extracts

Although there is anecdotal evidence for allelopathic interactions between benthic invertebrates engaged in spatial competition, only a few studies have established the involvement of chemical agents in field experiments. We have developed a technique in which crude organic extracts of marine sponges were incorporated into hard, stable gels that serve as a substratum for overgrowth by invertebrates in the field. Overgrowth organisms were secured to the center of assay plates and allowed to grow laterally over control gels and gels containing a crude organic sponge extract that was volumetrically equivalent to the concentration found in sponge tissues. Extracts of 20 species of Caribbean sponges were assayed in Florida using 3 overgrowth sponges: Tedania ignis, Lissodensoryx isodictialis, and Haliclona hogarthi. In addition, extracts of the sponge Aplysilla longispina were assayed in North Carolina using the tunicate Diplosoma listerianum as the overgrowth organism. The allelopathic effects varied between extracts of different sponge species, but were consistent across overgrowth organisms. Of the sponge extracts tested, 30% inhibited sponge growth (Amphimedon compressa, Aplysilla longispina, Aplysina cauliformis, Dysidea etheria, Ectyoplasia ferox, and Phorbas amaranthus), while 15% promoted overgrowth (Agelas wiedenmeyeri, Geodia gibberosa, and Halichondria sp.). The remaining 55% of sponge extracts had no effect on sponge growth. The technique described herein represents a more ecologically relevant method than past techniques for assaying the allelopathic properties of extracts of marine organisms. Moreover, this study provides evidence that sponge metabolites may act as allomones by preventing overgrowth of some sponge species, and as both allomones and kairomones by enhancing overgrowth of others.