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

Abstract. Certain stresses experienced by marine larvae from many groups can dramatically 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. Approximately 600 larvae collected from the Florida Current plankton were distributed among 3 treatment groups. Ninety larvae (controls) were offered sediment and adult‐conditioned seawater 4 d after collection, to induce metamorphosis; larvae of this species could not be induced to metamorphose by increasing the K+ concentration of seawater. The remaining 500 larvae were kept swimming for either 2 or 4 weeks, with or without phyto‐plankton (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 individuals were retrieved 6 weeks after the addition of excess sediment in all treatments, and weighed to document growth. Neither delayed metamorphosis nor starvation influenced juvenile survival. However, starving larvae for 2 weeks significantly reduced mean juvenile growth rates relative to the mean growth rate of control individuals (p<0.0001), while prolonging larval life by 4 weeks significantly reduced mean juvenile growth rates (p<0.05) whether or not larvae were fed. Reduced juvenile growth rates may have been caused by nutritional stress experienced by larvae in both the starved and fed treatments. The rapid response of freshly collected larvae to sediment indicates that competent larvae of this species routinely delay metamorphosis in the field. The extent to which they also experience food limitation is not yet 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.