The influence of the filter-feeding bivalve Cerastoderma edule L. on microphytobenthos: a laboratory study

Abstract

The effect of the filter-feeding bivalve Cerastoderma edule L. on microphytobenthos was investigated in three laboratory experiments. In the first experiment adult specimens of C. edule placed in flow-through aquaria containing sieved sediment were compared to aquaria without C. edule. The aquaria were incubated for 40 days, and sampled weekly for inorganic nutrient concentrations in the overlying water, sediment pigment concentrations and determination of benthic primary production. The presence of C. edule significantly increased the release of NH 4 + and PO 4 3− to the overlying water. The chlorophyll α concentration in C. edule treatments increased, and was significantly higher than in controls. The benthic primary production in C. edule treatments increased, reaching a mean maximum of 27.9 mg C·M −2·h −1, while the controls stayed at the initial mean level of 14.7 mg C·m −2·h −1 throughout the experiment. When the possible effect of fertilizing with faecal pellets from C. edule was tested in a second experiment, no differences were observed in nutrient fluxes, chlorophyll α concentration or primary production. In a third experiment, the effect of nutrients released by C. edule was investigated. Water from an aquarium containing a number of C. edule equivalent to the high natural density of cockles at the site of collection of the sediment was directed to four of the aquaria. The primary production was significantly higher in C. edule treatments than in controls. Thus the stimulating effect of C. edule on the microphytobenthos seems to be mediated by the release of nutrients, mainly NH 4 +, by the cockles themselves rather than through the deposition of faecal pellets.