Emersion and relative humidity control resettlement success of juvenile marine mussels

Abstract

The successful resettlement of marine mussels is an essential but overlooked process in their early life. A major challenge facing the mussel aquaculture industry is the extreme inefficiency of the seeding process, with most mussels being lost soon after seeding due to mortality or secondary settlement behaviour. Extended periods of nursery culture have been proposed as a method to reduce these losses by culturing juveniles to a larger size. The ability of mussels to resettle to suitable aquaculture structures is critical to the success of nursery culture. This study assessed the ability of juvenile mussels (Perna canaliculus) to resettle to a commonly used aquaculture substrate (coir ropes) following emersion (0−20h) and variations in relative humidity (RH), stressors that are intrinsic to the transfer of mussels among aquaculture sites. Across the experiments, increased emersion time either reduced or slowed resettlement success. Increases in RH had strong positive effects on the resettlement success of juvenile mussels even at long emersion durations (20h). Low (~ 40%) and mid (~ 60%) RH reduced resettlement to <7.1% ± 3.5 SE after a 5-h emersion compared to 61.7% ± 3.2 SE in samples held at high (>90%) RH. Staining procedures indicated that mussels failing to resettle after longer emersion and low RH treatments were non-viable. Aquaculture operators should strive for high RH conditions and shorter emersion durations whenever their juvenile mussels are emersed. If these conditions can be achieved, the results of the study suggest that juvenile mussels can be successfully resettled for use in aquaculture, representing a first step toward extended nursery culture and a more efficient use of juvenile mussel resources.