Epibiont―basibiont interactions: examination of ecological factors that influence specialization in a two-sponge association between Geodia vosmaeri (Sollas, 1886) and Amphimedon erina (de Laubenfels, 1936)

Issue Title: Ancient animals, new challenges: developments in sponge research 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 Gv tissue for consumption. In caging experiments, predator exclusion had no effect on Gv tissue loss. Amphimedon erina may benefit from the vertical substrata represented by Gv colonies because Ae grown in a vertical orientation experienced less tissue loss compared to Ae grown horizontally. Taken together, our results provide empirical support for the hypothesis that Gv is afforded chemical protection from predators through Ae and some evidence that Ae benefits from growing on Gn substrata.[PUBLICATION ABSTRACT]