Influence of delayed metamorphosis on postsettlement survival and growth in the sipunculan Apionsoma misakianum

Certain stresses experienced by marine larvae from many groups can dramatic ally reduce aspects of juvenile performance. This study reports the effects of delayed metamorphosis and nutritional stress on survival and growth of the deposit-feeding sipunculan Apionsoma (= Golfingia) misakianum. Approxim ately 600 larvae collected from the Florida Current plankton were distribut ed among 3 treatment groups. Ninety larvae (controls) were offered sediment and adult-conditioned seawater 4 d after collection, to induce metamorphos is; larvae of this species could not be induced to metamorphose by increasi ng the K+ concentration of seawater. The remaining 500 larvae were kept swi mming for either 2 or 4 weeks, with or without phytoplankton (clone T-ISO). At the end of the periods of prolonged larval swimming, subsampled larvae (360) were induced to metamorphose as in the controls. Surviving individual s were retrieved 6 weeks after the addition of excess sediment in all treat ments, and weighed to document growth. Neither delayed metamorphosis nor st arvation influenced juvenile survival. However, starving larvae for 2 weeks significantly reduced mean juvenile growth rates relative to the mean grow th rate of control individuals (p<0.0001), while prolonging larval life by 4 weeks significantly reduced mean juvenile growth rates (p<0.05) whether o r not larvae were fed. Reduced juvenile growth rates may have been caused b y nutritional stress experienced by larvae in both the starved and fed trea tments. The rapid response of freshly collected larvae to sediment indicate s that competent larvae of this species routinely delay metamorphosis in th e field. The extent to which they also experience food limitation is not ye t clear. If competent larvae are food limited while delaying metamorphosis in the field, our results suggest that juveniles will grow more slowly and may thus exhibit reduced fitness.