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

1. Many bivalve molluscs settle and attach to surfaces using adhesive byssal threads – proteinaceous fibers that together form a network known as the byssus. Since these bivalves rely on byssus for survival, strong byssal attachment promotes a myriad of broad ecological services, including water filtration, nutrient extraction, sediment stabilization, and enhancing biodiversity through habitat creation.

2. Numerous studies have documented weakened byssal attachment strength under ocean acidification (OA); however, a comparable number report no effect, even within the same species. Consequently, whether elevated CO2 levels expected under near-future OA will affect byssal attachment strength in nature remains hotly contested.

3. We used a systematic literature search and meta-analysis to explore factors that could potentially explain observed effect size variation in byssal attachment strength following OA exposure.

4. A systematic literature search uncovered 20 studies experimentally testing the impact of OA on byssal attachment strength (or some proxy thereof). Meta-analysis revealed that body size (mean shell length) was the strongest predictor of effect size variation, with no significant effect of climate, species, year, study temperature, study location, exposure time, food amount, and pH offset. Functionally, a negative linear relationship was observed between body size and effect size.

5. 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.

6. This highlights that body size and age may be important factors that determine OA sensitivity in adult calcifiers. In addition to body size, a critical review of each study revealed commonly neglected factors that could influence byssal thread attachment strength which we highlight to provide suggestions for future research in this area.

Supplementary materials

Clements J. C. & George M. N., 2021. Ocean acidification and bivalve byssus: explaining variable responses using meta-analysisis. EcoEvoRxiv Preprints. Article.

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