COUPLING OF NAUPLII RELEASE IN BARNACLES WITH PHYTOPLANKTON BLOOMS - A PARALLEL STRATEGY TO THAT OF SPAWNING IN URCHINS AND MUSSELS

We examined the coupling between the release of nauplii in Semibalanus balanoides and phytoplankton blooms, and compared it with the mechanism synchronizing spawning with phytoplankton abundance in green sea urchins (Stronglyocentrotus droebachiensis) and blue mussels (Mytilus edulis). Close contact with phytoplankton cells is required to stimulate the release of nauplii in Semibalanus, whereas spawning in urchins and mussels is triggered by an extracellular metabolite of phytoplankton. The response is concentration dependent and positively correlated with the frequency of moulting. The moulting rate in Semibalanus is reported to be directly correlated with food intake and thus larval release should be proportional to feeding activity. The release of Semibalanus nauplii is more strongly stimulated by the diatom Skeletonema costatum than by Phaeodactylum tricornutum, whereas the highest response is obtained in treatments with nauplii of Artemia salina. We suggest that these differences are related to size of the planktonic particles (Artemia nauplii > Skeletonema > Phaeodactylum). Exposure to air, as occurs in the intertidal zone, does not influence significantly larval release. Larval release in other crustacea may similarly be coupled to phytoplankton abundance.