Ocean acidification and bivalve byssus: explaining variable responses using meta-analysis

Abstract

Numerous studies have documented weakened byssal attachment strength under ocean acidification (OA); however, a comparable number have reported no effect, even within the same species. We used meta-analysis to explore factors that could potentially explain observed effect size variation in byssal attachment strength following OA exposure. A systematic literature search uncovered 20 studies experimentally testing the impact of OA on byssal attachment strength (or some proxy thereof). Meta-analysis revealed body size (mean shell length) to be the strongest predictor of effect size variation, with a negative linear relationship observed between body size and effect size. Despite this relationship, no single study or experiment included body size as a moderating factor. Our finding that the byssal strength of larger bivalves is more susceptible to negative OA effects runs counter to prevailing wisdom that larger, older animals of a given species are more robust to OA than earlier life history stages. This result highlights that body size may be an important factor in moderating OA sensitivity in adult calcifiers; however, in stress response studies, variation in animal size is typically standardized methodologically rather than embraced and warrants further investigation for other taxa and biological traits. In addition to body size, our analysis also identified a suite of previously unconsidered factors that could influence byssal thread attachment strength, including aspects of thread morphology, animal nutritional status, and the impact of seasonality, which we highlight to provide suggestions for future research.