A paradoxical mismatch of fecundity and recruitment in deep-sea opportunists: Cocculinid and pseudococculinid limpets colonizing vascular plant remains on the Bahamian Slope

摘要

Between 1992 and 1994, palm fronds and bundles of fibrous material (rolled door mats of Chinese dragon grass) were deployed by submersible every 3 months at 520 m depth in the Tongue of the Ocean, Bahamas. Substrata were recovered after 3-month and 6-month exposure periods and searched intensively for invertebrate colonists. Recruitment surfaces were colonized during every exposure period by three species of cocculiniform limpets, Cocculina rathbuni, Cocculina emsoni, and Notocrater youngi. At least two species appeared in each season, but the relative numbers varied in a way that may indicate seasonal differences in reproduction. Gonad development could be observed through the transparent shell of C. rathbuni, which attained sexual maturity in less than 3 months and had a maximum instantaneous fecundity of 40 eggs. Growth rates (0.025-0.044 mm/day) were high when scaled to adult body size. We used current-meter data from the deployment site to calculate the fluxes of larvae that would be required to produce the measured levels of recruitment. Observed recruitment would require larval densities of hundreds of thousands to millions of larvae per km~3. Nevertheless, it is remarkable that these snails are able to succeed with an opportunistic strategy given their low fecundity and lecithotrophic development.