LB 31-302 - Meta-analysis reveals controls on oyster predation

Background/Question/Methods:

Predators can exert strong influence over the occurrence and distribution of foundation species. With the recognition that predators have important roles, research now focuses on quantifying the strength of predatory effects and relating variation in interaction strengths to ecological mechanisms. However, a barrier to evaluating how this variation mediates general predation patterns is inconsistency in methodology among studies. Manipulative experiments provide powerful tools to infer mechanisms, but are often limited to small spatial scales, few locations, and short durations. To resolve these challenges, we used meta-analysis to systematically quantify the magnitude and uncertainty associated with predator effects on oysters. Specifically, we (1) characterize geographic and temporal patterns in oyster predation experiments, (2) determine the overall strength and sign of predator effects on oyster mortality and recruitment, and (3) assess how predation varies among environmental conditions, predator characteristics; oyster attributes; and experimental design.

Results/Conclusions:

We synthesized 384 predator-exclusion experiments from 49 peer-reviewed publications published between 1977 and 2021. Most effect sizes (93%) were from studies along the U.S. Atlantic and Pacific Coasts. Studies meeting our criteria were rare or entirely absent outside of North America, except for Germany and Northern Ireland. Predators resulted, on average, in a 4.3-fold increase in oyster mortality and 46% decrease in recruitment. Across a range of global environments, our results indicate that oyster predation is heavily influenced by tidal zone, predator identity, and predator richness. Predators increased oyster mortality by 2.3-fold in the intertidal and 4.5-fold in the subtidal. Unexpectedly, we found no effect of salinity, water temperature, oyster species, or oyster size on predation strength. Stark differences in effect sizes between experiment types and oyster tethering methods revealed the importance of experimental design and being cautious when extrapolating results. Predators increased oyster mortality by 2.5-fold in field exclosures relative to the 5.6-fold increase in field and lab enclosures. Moreover, our review of the literature also uncovers relatively few studies that have quantified predation on oyster recruitment. Beyond improving our basic understanding of oyster predation patterns, our results also unveiled broad trends that inform decision-making about oyster restoration practices.