Effects of larval starvation and delayed metamorphosis on juvenile survival and growth of the tube-dwelling polychaete Hydroides elegans (Haswell)

Abstract

Competent larvae of the serpulid polychaete, Hydroides elegans (Haswell), were induced to metamorphose by either 10 −4 M 3-isobutyl 1-methylxanthine (IBMX), adult homogenate, or 30 mM excess K +. Treatment with excess K + had adverse effects ( P<0.05) on juvenile growth while IBMX and adult homogenate had no detectable effects ( P>0.1). Metamorphosis was triggered using IBMX in subsequent studies. Competent larvae were forced to delay metamorphosis for up to 12 days by preventing the formation of biofilm in glass beakers. Juvenile growth was assessed by increases in tube length and dry tissue weight. The larvae remained fully responsive to IBMX while delaying metamorphosis up to 11 days but lost the ability to respond to adult homogenates within only 3 days, suggesting that the two chemicals act at different points in the metamorphic pathway and that only part of the pathway degrades as metamorphosis is delayed. Metamorphic responses were not affected by starvation during the competent phase. Delaying metamorphosis significantly reduced juvenile survival whether the larvae were fed or starved. However, there was no apparent effect of starvation on juvenile growth as juveniles developed from the larvae that were starved while delaying metamorphosis grew as fast as those developed from the larvae that were fed during the delay period. Our results suggest that Hydroides elegans cannot delay metamorphosis without measurable adverse effects on juvenile survival and growth.