No abstract

Under the risk of predation, the first response of bivalves is to close their shells. The strength and duration of valve closure can influence the probability of predator-related mortality. The behavioral ecology of valve closure responses, however, is understudied and the effects of global change stressors on these responses are unknown. We exposed two size classes of blue mussels (Mytilus edulis × trossulus) to different combinations of temperature 15 and 19 °C) and pH (8.2 and 7.5 pHT) for three months and subsequently measured individual time to open (i.e., startle response) following a tactile cue over a series of four consecutive trials. Time to open was highly repeatable on the short-term (adjusted R = 0.56) and decreased across the four trials from an average of 390.0 ± 493.6 secs in Trial 1 (mean ± SD) to 252.6 ± 421.4 secs in Trial 4. On average, individuals from the larger size class had a shorter time to open (154.1 ± 236.0 secs) than their smaller-sized counterparts (453.4 ± 449.9 secs). High temperature significantly increased time to open by 230%, on average, compared to low temperature, while pH had no effect. These results suggest that bivalve time to open is repeatable, related to relative vulnerability to predation, and affected by temperature. Given that increased closure times impact feeding and respiration, the effect of temperature on closure duration may play a role in the sensitivity to ocean warming in this species and contribute to ecosystem-level effects.