Oyster reef community interactions: The effect of resident fauna on oyster (Crassostrea spp.) larval recruitment

During their transition from the pelagic larval form to the benthic adult form, larvae are likely to encounter a diverse assemblage of resident invertebrates on oyster reefs. 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.Native (Crassostrea virginica) and non-native (Crassostrea ariakensis) oyster larvae were exposed to reef-collected shells, each supporting a single species of reef-associated fauna, over a series of laboratory microcosm studies. The presence of adult bryozoans (Membranipora tenuis) had little effect on rates of larval settlement 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. In some trials, adult barnacle bathwater enhanced settlement of oyster larvae, highlighting the importance of waterborne cues. Barnacle bathwaters, adult clam worm (Neanthes succinea) bathwaters and bathwaters created using adult oysters were all found to cause oyster larval mortality. Predation by clam worms, which were observed at very high densities on field-collected oyster shells, caused significant oyster larval mortality in these experiments.The combined effects of positive and negative interactions between oyster larvae and resident invertebrate reef fauna require enumeration under field conditions. The results from this study highlight the need for a more thorough understanding of settlement behavior and mortality sources of recruiting oyster larvae.