Feeding activity of scallops and mussels measured simultaneously in the field: Repeated measures sampling and implications for modelling

Abstract

Many studies on the biology of bivalves have focused on identifying the importance of various environmental factors in regulating feeding behaviour in order to predict ingestion and growth responses in a variety of habitats. When taking into consideration the diversity of studies undertaken and the variety of methodologies employed, it is perhaps not surprising that there have been inconsistencies in both interspecific and intraspecific comparisons. In order to compare and contrast the way in which feeding activities of a mussel species ( Mytilus edulis) and a scallop species ( Placopecten magellanicus) respond to environmental factors and seston characteristics, we exposed both species simultaneously to a fluctuating assemblage of natural particles found in their local environment. Similar sizes of mussels (40–73 mm) and scallops (40–88 mm) were held in flow through chambers at two different sites in Atlantic Canada on four separate occasions, during which environmental conditions, including seston characteristics, were monitored and individual clearance rates were measured. Because the same individuals were measured over time, repeated-measures statistical procedures were used to analyze the data. Results indicate that weight standardized clearance rates of mussels were significantly higher than those of scallops only at the highest concentration tested (12.8 mg l − 1 ), which translates into almost 3 times more material being filtered. Scallops appeared to respond to fluctuations in environment parameters and suspended food particles more consistently than mussels. These data suggest that the feeding behaviour of these two species is mediated differently by the same environmental parameters. Our study also demonstrates the importance of selecting appropriate statistical tests (e.g., repeated measures) for the analyses of data obtained from repeated sampling of the same individuals over time, and the need to consider species-specific feeding responses when developing models that predict the influence of bivalve feeding on ecosystem function.