Date Awarded


Document Type


Degree Name

Master of Science (M.Sc.)


Virginia Institute of Marine Science


The behaviors of oyster larvae are difficult to monitor or experimentally manipulate, especially in field conditions. As a result, little is known of the fate of oysters in the larval portion of their life cycle, prior to recruitment. At the transition from pelagic larvae to benthic adults, larvae are likely to come into contact with many invertebrates resident on oyster reefs. Of these, fouling epifauna are generally believed to reduce the settlement of interspecific larvae through competitive exclusion and predation. Studies of these interactions, however, often utilize artificial settlement panels, which can exhibit different recruitment patterns to those observed on natural substrates. I therefore investigated the interactions between reef-associated fauna and settling oyster larvae on natural shell substrates.

Over a series of laboratory microcosm studies, native (Crassostrea virginica) and non-native (Crassostrea ariakensis) larvae were exposed to reef-collected shells, each supporting a single species of reef-associated fauna. The presence of adult bryozoans (Membranipora tenuis) had little effect on either larval settlement rate or mortality. The boring sponge (Cliona sp.) significantly decreased oyster larval settlement, and generally increased oyster mortality. Barnacles (Balanus improvisus) typically facilitated settlement. Barnacle molds and empty barnacle tests, intended to mimic the surface area and rugosity of live barnacles, did not significantly affect settlement. However, in some trials, adult barnacle bathwater enhanced settlement of both oyster species, implicating the role of waterborne cues. Such bathwaters were found to cause oyster larval mortality, as were bathwaters created by adult clamworms or even adult oysters. Predation by clamworms (Neanthes succinea), which were found at very high densities on field-collected oyster shells, caused significant oyster larval mortality in these experiments.

The combined roles of both positive and negative interactions between oyster larvae and reef fauna require enumeration under field conditions. The results from this study highlight the need for clarification of these roles in order to optimize shell supplementation restoration efforts, and to more thoroughly understand the settlement behaviors and mortality sources of recruiting oyster larvae



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