Capture of conspecific planktonic larvae by the suspension-feeding gastropod Crepipatella peruviana: association between adult and larval size

ABSTRACT Free-living, planktonic larvae can be vulnerable to capture and ingestion by adult suspension-feeders. This is particularly the case for larvae that settle gregariously in benthic environments where suspension-feeders occur at high densities. Larvae of gregarious suspension-feeding species are at particularly high risk, as adults of their own species often serve as cues for metamorphosis. We conducted laboratory experiments to assess the extent to which adults of the suspension-feeding caenogastropod Crepipatella peruviana would capture and ingest their own larvae. Experiments were conducted with adults of different sizes, with larvae of different ages and sizes, and in the presence or absence of phytoplankton. Adults captured larvae in all experiments. The presence of microalgae in the water did not influence the extent of larval capture. On average, 39% of larvae were captured during the 3-h feeding periods, regardless of adult size. However, up to 34% of the larvae that were captured on the gill were later discarded as pseudofaeces; the other 64% were ingested. The extent of capture by adults was not related to adult size, or to larval size and, thus, to larval age. Our results suggest that the filtration of congeneric larvae by adult C. peruviana is a result of accidental capture rather than a deliberate feeding preference. Such ingestion could, however, still be an important source of larval mortality, especially when the advanced larvae of this species are searching for a suitable substrate for metamorphosis.

Modeling the life cycle of echinoderm larvae clones

Larval cloning occurs in echinoderm species and has been viewed as possibly adaptive. A species of Oreaster currently being described has linked a rare benthic stage with common planktonic larvae that clone, and this calls attention to questions in life stage linkages. Life cycle analysis shows that there are unresolved problems in our understanding of the dynamics of species with cloning larvae, in particular their survival and duration in the plankton. Possible solutions are (1) benthic adults that are rare are also very long-lived or (2) survival in the plankton is much higher than has been reported.

Life Cycle and Seasonal Migrations

Seasonal and life cycle migrations are mass movements in which individuals move horizontally for long distances to encounter favorable conditions for reproduction and development. Such migrations have been best studied in larger mobile decapod crustaceans, many of which are commercially important. Some decapod shrimps and brachyuran crabs are dependent on productive estuaries for completion of life cycles. In these species, planktonic larvae develop in oceanic waters. Postlarval stages utilize currents and appropriate behaviors to enter estuaries via selective tidal stream transport (STST). After growth, juveniles and subadults leave for the adult oceanic habitats, again using STST. Many subtropical and temperate zone neritic species make seasonal offshore migrations into deeper waters during the winter, with return nearshore in the spring; some high latitude species make these migrations but with seasons reversed. Numerous freshwater shrimps are amphidromic, that is, they live and reproduce in streams and rivers, but their planktonic larvae drift or are released directly into the sea for development and dispersal. Postlarvae find the mouths of streams, and then make spectacular mass migrations as juveniles back upstream to the adult habitat. Adults of terrestrial crabs live inland, but brooding females move into the littoral zone during new or full moon periods to hatch out larvae into high amplitude tides that carry the larvae out to sea for development and dispersal.