Associations and interactions between gorgonians ... - Porifera Brasil

446species are equivalent to their relative abundances in thestudy site. This result indicates that the number of coloniesof the gorgonian species associated with sponges are mostlydetermined by the abundances of the gorgonian species.Associations between sponges and gorgonian species can bedescribed as random in this respect. A notable exception tothis overall random pattern was Briareum, which was foundhighly associated with sponges relative to its low abundance.Most interactions with sponges had negative effects ongorgonians as observed in the overgrowth (smothering) ofvarious gorgonian species by sponges such as Desmapsammaanchorata, Dysidea janiae and Iotrochota birotulata.Smothering could be ‘direct’ in the sense that the spongeadhered directly to the tissue/skeleton of the overgrownorganism (i.e., direct smothering, Fig. 2) or ‘indirect’ wherelethal or non lethal effects occurred without the adherenceof the sponge tissue (i.e., indirect smothering). These andother interactions are given in Table 3. These interactionswere often species-specific. For instance, Desmapsammaanchorata usually outcompeted Pseudopterogorgia spp.by direct overgrowth but tissue discoloration of Gorgoniaventalina adjacent to the growing edge of Desmapsamma(Fig. 3) indicated the presence of allelochemicals.A notable exception to the negative interactionswith gorgonians was observed between Briareum andDesmapsamma anchorata, Amphimedon compressa, andMycale carmigropila. In these cases, Briareum and spongecolonies were intertwined and no indications of negativeinteractions were observed.DiscussionWe stress that the results of this study are preliminary inthe sense that future observations will increase the numberof sponges and associated species as well as species-specificinteractions. Nevertheless, some general inferences can bemade about Caribbean sponges and the biodiversity of coralreefs. As in the case of tropical rainforests where the treecanopy accounts for much of the biodiversity, the gorgonian‘canopy’ serves as a habitat for many sponge species. Ourresults thus indicate that the high biodiversity of sponges ispartially attributable to their ability to circumvent substratespace limitation in coral reefs (Connell 1978) by growingepibiotically on other sessile organisms (Rützler 1970). Inturn, sponges harbor numerous invertebrate species (Nevesand Omena 2003, Ribeiro et al. 2003).The associations and interactions of sponges with otherspecies also affect the biodiversity of sponges. Our resultssuggest that, with the exception of Briareum, the relativeabundance of gorgonian taxa largely determines theirassociations with sponges. This pattern represents a randomassociation in the sense that the probability of a gorgoniancolony being associated with sponges is equal amongindividuals of all gorgonian species. In contrast to patternsof associations, interactions between sponges and gorgoniansare often species-specific. Depending upon the speciesinvolved negative interactions may involve direct or indirectsmothering or allelochemicals. Also, in addition to negativeinteractions, the intertwined growth morphology observedbetween Briareum and various sponges may be indicativeFig. 2: Adherence of Dysidea janiae to Pseudoplexaura spp. Directsmothering of the tissue of Pseudoplexaura spp. caused by theovergrowing Dysidea janiae.Table 3: Sponges associated with gorgonians and their modes ofinteraction.SpeciesAmphimedon compressaAmphimedon erinaCallyspongia vaginalisDesmapsamma anchorataDysidea janiaeIotrochota birotulataIrcinia strobilinaMonanchora arbusculaMonanchora unguiferaMycale laevisMycale microsigmatosaNiphates erectaScopalina ruetzleriXestospongia caycedoiInteractionsovergrowth, smothering andintertwined growthsmotheringsmotheringovergrowth, smothering andintertwined growthovergrowth, smotheringovergrowth, smotheringovergrowth, smotheringovergrowthsmotheringsmotheringintertwined growthovergrowth, smotheringsmotheringsmothering