Mussel seed is highly plastic to settling conditions: the influence of waves versus tidal emergence

Phenotypic plasticity is important for organisms to adjust to a new environment. Therefore, the transplantation success of an organism to a new environment can be increased with knowledge of its capacity for phenotypic plasticity in different life stages, and the phenotypic adjustments it needs to make in specific environmental situations. Both the capacity for phenotypic plasticity and the necessary phenotypic adjustments for transplantation were tested in a mesocosm experiment using blue mussels Mytilus edulis as a model organism. This study tested (1) to what extent mussel seed coming from collectors in the water column are still capable of adjusting their phenotype, and (2) whether exposure to air or wave action is more important as a driver of phenotypic adjustments for mussels living in intertidal conditions. We found that mussel seed had a high capacity for phenotypic plasticity, and were capable of adjusting their morphology to accommodate different intertidal hydrodynamic conditions. Exposure to air influenced the shell shape, condition, byssal attachment strength and aggregation behaviour, but exposure to waves played the most important role in determining the phenotype of mussels. Wave-exposed mussels grew bigger, rounder, had thicker shells and a stronger byssal attachment strength than mussels exposed to either calm tidal or calm submerged environments. This knowledge is important for selecting a suitable source population and transplantation location.