NATURAL HISTORY OF THE SPONGE DISCODERMIA DISSOLUTA (PORIFERA: DEMOSPONGIAE: LITHISTIDA) IN SANTA MARTA, COLOMBIAN CARIBBEAN.

Abstract

The marine sponge Discodermia dissoluta is a source of the polyketide discodermolide, a potent antitumoral agent that has reached clinical trials in humans. In Santa Marta, where this species occurs at shallower depths than in other Caribbean areas, for the first time it was possible to study by SCUBA its ecological characteristics, distribution and abundance. By searching the base of the reefs (12-25 m in depth) it was found that this species is restricted to sites or bays with relatively low wave-exposure, dwelling predominantly in hard, horizontal to inclined substrata, generally exposed to light. Censuses carried out in 4 m-radius circles in sectors where this sponge occurs showed moderate densities (about 2-5 ind/50 m2) that, although not very low, do not support its commercial exploitation to obtain discodermolide. By locating individuals in the sampling space and using the point pattern distribution functions F, G and K, it was determined that individuals of D. dissoluta are aggregated in patches at scales from decimeters to a few meters. This pattern possibly arises from short-distance larval dispersal or fragmentation, both common in sponges. Size of censused individuals was estimated as projected area from digital photos, and expressed in volume by a regression calculated from the real volume of 30 collected individuals. In the population, small individuals (<50 mL) predominate, while several very large ones (reaching 2000 mL) persist, indicating high mortality in small and medium sizes. This population is viable for individual marking and follow-up studies and application of in situ and biotechnological cultures techniques in order to develop sustainable methods for production and supply of discodermolide.