An unprecedented association of an encrusting bryozoan on the test of a live sea urchin: epibiotic relationship and physiological responses

Abstract

Although well known for their epibiotic relationship with many living substrates, records of bryozoans settling on echinoderms are uncommon. In the few recorded cases, most basibionts (hosts) are cidaroid sea urchins, and their primary spines seems to be the preferred place for bryozoa settlement. Here, an unprecedented epibiosis between a bryozoan and a non-cidaroid sea urchin is reported, in which the epibiont Schizoporella errata (Waters, 1878) was found attached to a living specimen of Echinometra lucunter (Linnaeus, 1758). Additionally, the total coelomocyte counts (TCC), the differential coelomocyte counts (DCC), and the wound healing dynamics of the bryozoan-encrusted sea urchin were observed and contrasted to a control group of healthy animals. Confidence intervals of the mean for TCC and DCC in the healthy animals were calculated and compared with the bryozoan-encrusted sea urchin. Only one bryozoan colony was found on the affected echinoid, covering a spineless area of 58.9 mm2. Consistent differences were observed in coelomocyte counts (TCC and DCC) for the bryozoan-encrusted echinoid when compared with the control group: 1.9-fold more coelomocytes and 4.7- and 2.75-fold more red and colorless spherulocytes, as well as 1.38 and 2.05 fewer phagocytes and vibratile cells respectively. An advanced inflammatory-like response on the wounded area after the careful removal of S. errata was also observed, suggesting that the healing process had started before epibiont removal. Thus, the integrated analyses of the results presented here indicate that the basibiont sea urchin was physiologically affected during epibiotic associations.