Food intake of Macoma balthica (mollusca) in relation to seasonal changes in its potential food on a tidal flat in the Dutch Wadden Sea

Abstract

Food intake, absorption and presumed origin of the food were studied simultaneously throughout the year for a tidal flat population of Macoma balthica in the westernmost part of the Dutch Wadden Sea. The rate of food intake was calculated from the amount of chlorophyll a in the stomach and the rate of stomach evacuation. Highest rates of intake by Macoma were found during the first 4 hours of submersion and during the months April, May and June. During the emersion period and in winter the feeding activity was low. The total intake per submersion period was positively correlated with the concentration of chlorophyll a in the water, but not with that in the top layer of the sediment. Moreover, the season with high rates of intake coincided with the short maxima in spring for the concentrations of organic carbon and chlorophyll a in the water, but not with the longer seasonal maxima (from April to October) for these concentrations in the sediment. In the sediment mainly pennate diatoms were found, in the water centric diatoms. The algal species composition of the stomach content showed a strong resemblance to the composition of the water samples. Observations on siphon movements in the laboratory showed that Macoma spent more time with the siphon near the bottom than with the siphon extended into the water column. It is concluded that Macoma, although it behaves most of the time as a deposit feeder, depends for its food intake for the greater part on food present in the water column.