Sponges belonging to the genus Cliona are common inhabitants of many coral reefs, and as bioeroders, they play an important role in the carbonate cycle of the reef. Several Cliona species maintain intracellular populations of dinoflagellate zooxanthellae (i.e., Symbiodinium spp.), which also form symbioses with a variety of other invertebrates and protists (e.g., corals, molluscs, foraminifera). Unlike the case of coral symbioses, however, almost nothing is known of the metabolic interaction between sponges and their zooxanthella symbionts. To assess this interaction, we performed a tracer experiment to follow C and N in the system, performed a reciprocal transplant experiment, and measured the stable carbon isotope ratio of Cliona spp. with and without zooxanthellae to study the influence of environment on the interaction. We found strong evidence of a transfer of C from zooxanthellae to their sponge hosts but no evidence of a transfer of N from sponge to zooxanthellae. We also saw significant influences of the environment on the metabolism of the sponges. Finally, we observed significant differences in carbon metabolism of sponge species with and without symbionts. These data strongly support hypotheses of metabolic integration between zooxanthellae and their sponge host and extend our understanding of basic aspects of benthic-pelagic coupling in shallow-water marine environments.
The ecological and evolutionary forces that shape interactions between marine sponges and their symbiotic microbiota remain poorly understood. Considerable work has been done to characterize the sponge microbiome, and this research has shown that there are two distinct types of sponges: those with high microbial abundances (HMA) and those with low microbial abundances (LMA). There is no clear evolutionary driver for this distinction, and we have only a limited understanding of how HMA or LMA status affects host phenotypes (e.g. feeding behavior, capacity for nutrient cycling). We had two primary goals with the present study. First, we used a variety of microscopic techniques to compare aspects of host biology (e.g. choanocyte chamber morphology and density) in the context of symbiont status. Secondly, we used molecular approaches to uncover components of ecological structure of bacterial communities in HMA versus LMA sponges (e.g. species richness, evenness). We found that choanocyte chamber density is greater in LMA sponges than in HMA sponges. We also found distinct patterns of organization for bacterial communities in HMA and LMA sponges, although environmental factors, to a lesser degree, also influence community structure in the Floridian sponges we examined. These results suggest that the large bacterial communities found in HMA sponges may allow the host to decrease their heterotrophy versus that of LMA sponges with minimal bacterial communities.
The objective of this study was to determine what ecological benefits Geodia vosmaeri (Gv) and Amphimedon erina (Ae) gain from their symbiosis. The prevailing, though untested, hypotheses are that Ae protects Gv from predators through chemical defenses and that Gv provides Ae access to substrata. Data from our experiments support these hypotheses. During field surveys, Ae was never found growing without Gv in this habitat. Ae was the only epibiont on 81% of the Gv surveyed. Field feeding assays using chemical extracts indicated that Ae is less palatable than Gv. Laboratory feeding assays using sponge tissue demonstrated that spongivorous sea stars avoided contact with Ae tissue and frequently accepted
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