Fragmentation, re-attachment ability and growth rate of the Mediterranean black coral Antipathella subpinnata

Cnidarians are known for their simple body plan and their complex life cycles, involving high regenerative and asexual-reproduction potential. In particular, several asexual reproductive strategies are known for anthozoans, including fragmentation, carried out by tentacles, by groups of polyps or by portions of colonies. Here, we report the first observation of an extensive event of fragmentation in the Mediterranean black coral species Antipathella subpinnata (Antipatharia: Myriopathidae) in rearing conditions. Once detached, fragments lose their polarity and new anchorages are rapidly created with polyps and cnidocysts participating in the adhesion phases. Multiple attachments are frequently observed, with new skeletal plates produced through the expansion of spines. Dendritic spines gradually arise on these new plates. Fragments start to generate numerous new branchlets orientating upward and with a fixed arrangement. In 7months of monitoring, fragments revealed fast growth rates, up to 1.85 and 1.58cmmonth(-1), for the whole fragments and new branchlets, respectively. Attachment of black coral fragments has never been recorded in the field; nevertheless, frequent adhesions observed in aquaria suggest that fragmentation could be a successful reproductive strategy in these anthozoans.