Date of Award

Winter 1995

Project Type

Dissertation

Program or Major

Zoology

Degree Name

Doctor of Philosophy

First Advisor

Michelle P Scott

Abstract

Processes that limit the distribution arid abundance of marine species may affect larvae, juveniles, or adults. I focus on larval and early benthic phases of reef corals as determinants of spatial pattern. In CHAPTER I examine larval behavior during dispersal and settlement as a mechanism for aggregated spatial pattern in two corals. A short swimming period and non-selective settlement behavior explains the highly aggregated spatial pattern in Favia fragum. Spatial pattern in Agaricia agaricites probably reflects larval behavior at settlement and post-settlement mortality. These larvae had a longer planktonic period and were selective in settlement surfaces.

In CHAPTER II, I examine potential mechanisms that lead to shallow-water zonation in F. fragum. Adult survivorship was similar over the range of the vertical distribution, however larval production was 3$\times$ higher in shallow-, compared to deep-water habitats. I examined sperm limitation as a mechanism for high larval production in shallow water. Experimental manipulation of colony density had no effect on larval production. Larvae also settled in greater numbers on substrata from shallow water than from deep habitats. Given that dispersal is philopatric, increased larval production and larval behavior largely explain F. fragum's shallow distribution.

CHAPTER III examines vertical patterns of larval recruitment in agaricid and poritid corals. I found spatial patterns of Larval recruitment to correlate with juvenile and adult patterns. I discuss potential mechanisms for this pattern, and suggest that competition between coral recruits and cryptofauna for space best explains recruitment patterns on Guana Island and perhaps elsewhere. CHAPTER IV synthesizes results of CHAPTERS I-III. I suggest that larval behavior is important in the small scale distribution of corals. Large scale patterns (i.e. zonation) probably reflect interactions between larval supply and post-settlement mortality.

In CHAPTER V I present a model which predicts larval behavior given the ecological constraints of dispersal. In non-feeding competent larvae, the model predicts an increase in the probability of settlement and metamorphosis as larval mass declines. Feeding competent larvae may delay metamorphosis longer and settle at smaller sizes. Specific intraspecific and interspecific predictions are discussed in the context of larval energetics.

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