Date of Award

Fall 1996

Project Type

Dissertation

Program or Major

Zoology

Degree Name

Doctor of Philosophy

First Advisor

Peter F Sale

Abstract

This dissertation examined the ecological constraints during the early life history of the bicolor damselfish, Stegastes partitus Poey (Perciformes, Pomacentridae). A series of studies, conducted in Teague Bay, St. Croix and Discovery Bay, Jamaica between 1991 and 1996, determined the cause of variation in length of the planktonic larval period, the effect of larval history on settlement success and examined the causes behind the patterns of distribution and population structure seen throughout its geographic range. Variable growth rates in early-stage larvae established a canalized trajectory toward larval competence and provides a mechanism for determining planktonic duration. Using otolith microstructure I determined that larvae with the fastest growth rates during the first 10 days post-hatching had planktonic durations up to 15 days shorter than larvae with the slowest growth rates. Moreover, there was a positive correlation between pre- and post-settlement growth. With a series of experiments, I determined that larval settlement behavior of S. partitus was most important in determining small-scale (10's of meters) distribution patterns and that differential survival after settlement enhanced these initial patterns. Survival was related to the structural architecture of different substrates which determined refuge suitability and predation risk. During ontogeny, juvenile bicolor damselfish can increase their overall fitness by selecting small rubble substrates at settlement then switching to adult substrates at maturity. Juveniles selecting this strategy had a 50% increase in survivorship over larvae which settled directly to the adult coral substrate. I interpret these results with a graphical model and discuss its relevance to identifying trade-offs and predicting habitat shifts during ontogeny. At larger spatial scales (100's of meters) larval recruitment was of minor importance in structuring adult populations in St. Croix. The additive effects of interspecific competition, food supply, and the physical and biological features of various reef habitats significantly affected juvenile growth. A prolonged juvenile period, due to reduced growth, indirectly affected mortality and thus adult abundance. These effects were nearly identical on St. Croix and Jamaican barrier reefs and were altered only by site-specific predation intensity. The relative importance of these various ecological constraints on life history patterns is discussed.

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