SELECTIVE FEEDING ON ALGAL CELLS BY THE VELIGER LARVAE OF NASSARIUS OBSOLETUS (GASTROPODA, PROSOBRANCHIA)

¹ Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543

Planktotrophic veliger larvae of the prosobranch gastropod Nassarius obsoletus (Say) are able to feed selectively. Presented with a mixture of Dunaliella tertiolecta, Phaeodactylum tricornutum, and Cyclotella nana, they exhibit a definite order of preference in the number of cells of each algal species they ingest. Dunaliella is clearly the last choice for veligers of all sizes. Early larvae choose Cyclotella in preference to the other two species, but with increasing veliger size and age, ability to discriminate between Phaeodactylum and Cyclotella diminishes while the selection of Phaeodactylum in preference to Dunaliella increases. However, in recently emerged and intermediate stage veliger larvae the relative cell volume of Dunaliella consumed is approximately equal to that of Cyclotella, whereas that of Phaeodactylum is substantially less than that of either of the other two algal species. In older larvae the relative volume of Cyclotella eaten exceeds the volumes of both other species, whereas the volumes of Phaeodactylum actylum and Dunaliella become approximately equal.