Meeting Abstract

S8.9  Thursday, Jan. 6  Plasticity in Stage at Hatching that Controls Pelagic Duration and Dispersal in Marine Invertebrate Larvae OYARZUN, F. X.*; STRATHMANN, R. R.; University of Washington rrstrath@u.washington.edu

Plasticity in hatching potentially adjusts risks of benthic and planktonic development for diverse benthic marine invertebrates. The proportionate effect on duration of larval swimming would be greatest for animals that brood or encapsulate offspring until hatching near metamorphic competence. Early hatching could extend larval durations from less than a day to days of obligate swimming as precompetent larvae. Two examples illustrate contrasting kinds of plasticity in hatching. In the nudibranch mollusk Phestilla sibogae, early hatching is stimulated when a predator feeding on the gelatinous egg ribbon scatters the encapsulated offspring. When egg ribbons are undisturbed, hatching is at or near metamorphic competence. Disturbance of an unguarded benthic egg mass can insert 4 or more days of obligate larval dispersal into the life history. In the spionid annelid Boccardia proboscidea, the mother broods capsules, each with both cannibalistic and developmentally arrested planktivorous siblings, plus nurse eggs. If a mother hatches capsules early, the developmentally arrested offspring hatch as planktonic larvae, feed on phytoplankton, and resume development and growth to metamorphic competence after a potentially dispersing period of 15 days. If a mother hatches capsules late, developmentally arrested larvae are consumed, along with the nurse eggs, by their adelphophagic siblings, which metamorphose with little or no period of swimming. In laboratory conditions, females varied their brooding period in response to food availability and environmental temperature, but hatching by mothers appeared to be unaffected by the stage of development of the offspring. The maternal control of stage at hatching appears to differ among species within the genus.