Bivalve filter feeding revisited

Recent developments concerning the nature of bivalve filter feeding are reviewed and interpretations of data are examined. No convincing evidence was found for: (1) a function of mucus in the normal feeding mechanism; (2) sorting of suspended particles according to food value; (3) low rates of water processing in nature; (4) physiological control of water pumping and filtration efficiency according to nutritional needs. Recent findings are consistent with the view that the capacity for water processing is evolutionarily adapted to the concentrations of suspended food, primarily phytoplankton, that prevail in the biotope during the productive seasons of the year. 'Scope for growth', computed from measurements of the energy balance parameters, is extensively used to assess effects of environmental factors, including pollutants, on the physiology and energetics, particularly of mussels. Estimates tend, however, to underrate the values they are believed to reflect due to neglect of negative effects of the experimental conditions on the filter-pump. Possible effects of the experimental conditions on filtration rates should therefore be established before a calculated 'scope for growth' can be extrapolated to the habitat which the experiment simulates.