Do large seston particles contribute to the diet of the bivalve Cerastoderma edule?

Abstract

The vertical distribution of suspended cellulose particles in the size range 60 to 500 μm was studied with artificial bivalve siphons in flume flow for a range of flow speeds and degrees of bed roughness. Significant vertical concentration gradients with an increase in particle concentration of 200 to 300% compared with their near-bed values were found for some combinations of flow speed and particle size in a 6 cm layer above the bed, which was an effect of flow velocity. In a second series of experiments, artificial siphons were replaced by the infaunal bivalve Cerastoderma edule (L.), and filtration was studied for large particles (60 to 500 μm). Corresponding experiments in a static system were also performed. C. edule readily ingested particles up to a maximum size of ca. 500 μm, and calculations of clearance for sizes between 60 and 300 μm were in the range of 0.5 to 3 l h-1 g-1 dry weight, which is close to rates measured for microflagellates. Field studies on large particles in the near-bed layer (0 to 10 cm) show that this fraction contributes significantly to total seston. It is concluded that large particles like plant detritus, benthic diatoms and invertebrate larvae may accumulate in the near-bed layer and form a significant food source for benthic bivalves.