Effects of the duration of larval life on postlarval stages of the demosponge Sigmadocia caerulea

Abstract

Variability in the duration of the free-swimming period of lecithotrophic larvae of the demosponge Sigmadocia caerulea (Hechtel, 1965) was assessed in the laboratory in the absence of metamorphic inducers and inhibitors. The free-swimming period in three clutches of larvae ranged from 8 to 70 h and the cumulative settlement curve was sigmoid, with settlement peaking between 20 and 28 h after release. There were significant differences among clutches in the time to reach 50% settlement. Within each clutch, small percentages of larvae (<25%) were short-lived (settled less than 12 h after release) or long-lived (settling more than 32 h after release). Juveniles originating from short-lived larvae survived better, grew faster and were more regular in shape than those originating from long-lived larvae. In additional laboratory experiments, we examined the consequences of feeding during the early postsettlement period. Size differences between fed and starved juveniles became apparent 5 days after osculum formation, suggesting that the filter-feeding ability does not begin immediately after osculum formation. Our results are consistent with the hypothesis that long-lived larvae bring fewer reserves to the postsettlement period than do short-lived larvae, thereby experiencing nutritional stress prior to the onset of feeding that can reduce the vigor of the juveniles. Although larvae delaying metamorphosis should theoretically be important in colonizing new habitats and increasing gene flow, low postsettlement survival of such individuals may reduce the evolutionary importance of variability in the duration of the larval period.