MEPS 551:141-154 (2016)  -  DOI: https://doi.org/10.3354/meps11684

ABSTRACT: We developed and tested a method to field test fertilization success, measured as the proportion of eggs fertilized, in the giant sea scallop Placopecten magellanicus, a commercially valuable and sedentary broadcast spawner in the northwest Atlantic. A laboratory sperm dilution series determined maximum fertilization success expected in the field and assessed gamete longevity. We also developed and flume-tested a fertilization chamber to assess ambient water-column sperm loads near field populations. We then conducted a series of dockside field trials using these chambers over the course of the late summer spawning season in coastal Maine, USA. Chambers were deployed among manipulated populations of scallops to assess effects of local spawner abundance and location on time-integrate fertilization success. In dilution-series experiments, maximum fertilization success occurred at sperm concentrations >10⁷ sperm ml^-1. Egg longevity fell to zero between 8 and 24 h at ambient temperatures of 12°C, and sperm half-life shortened from 2 h to 9 min with a 10-fold dilution from a sperm concentration of 10⁷ cells ml^-1. Flume trials demonstrated chamber artifacts: fertilization was lower inside the chamber and the effect was greater at higher flow rates, but chamber orientation to flow had no effect. Increasing the numbers of eggs tended to reduce fertilization efficiency. In dockside tests, a 30-fold difference in spawner numbers had a significant effect on fertilization success. Notwithstanding acknowledged chamber artifacts due to flow impedance, this study establishes the feasibility of time-integrated fertilization experiments with scallops and sets the stage for further investigations of fertilization dynamics in natural scallop populations.

KEY WORDS: Giant sea scallop · Placopecten magellanicus · Fertilization success · Fertilization ecology · Population density effect · Allee effects · Fisheries · Depensation