Ecological roles of renieramycins on the blue sponge Xestospongia sp.

Abstract

The blue sponge, Xestospongia sp., is a coral reef inhabitant occurring in the Gulf of Thailand. The distribution pattern of Xestospongia sp. and its association with other organisms were investigated. The results showed that the most frequently coexisting organisms were the massive coral, Porites lutea, and the colonial zooanthid, Palythoa caesia. However, Xestospongia sp. was also found with algal patches and dead coral rubble. The largest individuals of Xestospongia sp. were found growing on Pa. caesia while the smallest individuals were found on the algal patches. This sponge has been known to produce renieramycins (Frincke and Faulkner 1982). The results also showed that concentrations of renieramycin M, the main alkaloid with highly potent cytotoxicity, extracted from this sponge differed significantly among sites. Carbon-nutrient contents and renieramycin M concentrations were found to be significantly different between the areas of Xestospongia sp. (edge, inner and outer) whereas carbon-nutrient contents and renieramycin M concentration of Xestospongia sp. coexisting with different organisms were not significantly different. In the laboratory renieramycin M did not show any allelopathic effect on its coexisting organisms (Porites lutea). Furthermore, it did not inhibit the growth of aerobic bacteria. However, renieramycin M inhibited settlement of acorn barnacle (Semibalanus balanoides) but did not inhibit the settlement of pelecypods. In the experiments, renieramycin M concentrations increased immediately after Xestospongia sp. was wounded. Renieramycin M was also detected in Jorunna funebris, specifically the predatory nudibranch on Xestospongia sp. (Saito et al. 2004). This study found that the concentration of renieramycin M was not equally distributed into the body parts of Jorunna funebris. The concentration of renieramycin M was decreased by increasing starvation periods. However the feeding deterrent activity was found in tissues of Jorunna funebris, as well as, the renieramycin M. In conclusion, Xestospongia sp. is a reef inhabitant that frequently coexists with Porites lutea and Palythoa ceasia. This sponge produces renieramycin M, the alkaloid substance and distributes it along its body. Although, renieramycin M did not show either allelopathic or anti-microbial effects, it exhibited anti-fouling and anti-feeding effects. Jorunna funebris was found to contain renieramycin M and Jorunnamycin in the mantle and foot muscle. The concentrations of these chemicals decreased when Jorunna funebris was starved.