Effects of flow velocity, food concentration and particle flux on growth rates of juvenile bay scallops Argopecten irradians

Abstract

Feeding rates, and hence growth, of suspension-feeding organisms are determined by many interacting factors including efficiency of particle capture, food-particle concentration, and ambient flow regimes. Studies in a recirculating seawater flume were conducted to examine the growth rates of juvenile bay scallops Argopecten irradians irradians (L.) (3–10 mm in shell height) in four flow velocities (0, 1, 6, and 15 cm · s −1) over a range of food concentrations (0–75 000 cells · ml −1) in a four-by-four factorial design. Particle flux (algal cells · cm −2· s −1) encountered by the scallops is the product of food concentration (cells · ml −1) and flow velocity (cm · s −1). The experimental levels of food concentration and flow velocity were chosen to produce a wide range of fluxes. Several treatments with equal flux derived from different flows and food concentrations were used to decouple the effects of each factor. Within a given flux of particles, growth rates were not significantly different between flows or particle concentrations. Growth was only weakly correlated to flux of particles over the range of fluxes tested. The effects of algal concentration were more pronounced than the effects of flow velocity suggesting that differences in growth were a result of differences in algal concentrations. Additional experiments were run to determine the clearance rates of scallops at different food concentrations. These experiments support the findings of the flume experiments; clearance rates were seen to decrease with increasing food concentrations. Flux of food particles is not a predictor of growth, rather it is the combination of the effects due to food concentration and flow velocity which determine the response of the individual juvenile bay scallop.