EFFECTS OF LARVAL STARVATION AND DELAYED METAMORPHOSIS ON JUVENILE SURVIVAL AND GROWTH OF THE TUBE-DWELLING POLYCHAETE HYDROIDS ELEGANS (HASWELL)

Competent larvae of the serpulid polychaete, Hydroides elegans (Haswel l), were induced to metamorphose by either 10(-4) M 3-isobutyl 1-methy lxanthine (IBMX), adult homogenate, or 30 mM excess K+. Treatment with excess K+ had adverse effects (P < 0.05) on juvenile growth while IBM X and adult homogenate had no detectable effects (P > 0.1). Metamorpho sis was triggered using IBMX in subsequent studies. Competent larvae w ere 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 f ully 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 metam orphic pathway and that only part of the pathway degrades as metamorph osis is delayed. Metamorphic responses were not affected by starvation during the competent phase. Delaying metamorphosis significantly redu ced juvenile survival whether the larvae were fed or starved. However, there was no apparent effect of starvation on juvenile growth as juve niles developed from the larvae that were starved while delaying metam orphosis grew as fast as those developed from the larvae that were fed during the delay period. Our results suggest that Hydroides elegans c annot delay metamorphosis without measurable adverse effects on juveni le survival and growth. (C) 1998 Elsevier Science B.V. All rights rese rved.