Meeting Abstract

71.9  Friday, Jan. 6  Why Marine Mollusks don't require larvae for dispersal HICKMAN, Carole S.; Univ. of California, Berkeley

Dispersal modes in marine mollusks are linked classically to larval life history. Taxa that lack a planktonic larval stage and larvae that do not feed in the plankton allegedly lack exposure to currents and prolonged opportunity for long-distance travel and establishment of broad geographic ranges. Because lecithotrophic larvae are characterized as poor dispersers, it has been difficult to explain how so many molluscan taxa with this mode of development have achieved broad geographic distributions. Rafting, transport on the feet of birds and successful passage through the guts of motile predators are entrenched in dispersalist folklore. However there are other dispersal mechanisms consistent with otherwise enigmatic distribution patterns. The following biological phenomena are proposed as a charter for an alternative body of biogeographic theory: (1) re-entry of adults into the water column to form pelagic spawning aggregations (2) byssus drifting of juveniles, (3) mucus thread kiting of juveniles and adults, (4) midwater metamorphosis, (5) gas flotation at the air-water interface, (6) adhesion to surface films, and (7) pelagic egg capsules and egg masses. Two additional phenomena that merit greater attention with respect to dispersal are ontogenetic migration of lecithotrophic larvae of deep-sea taxa and transport of larvae entrained in mesoscale parcels of water that form “dispersal units” during turbulent disturbance events. There are observational reports of all these phenomena in the literature and opportunities for rigorous study of the underlying structural, functional and behavioral biology.