MEPS 152:175-186 (1997)  -  doi:10.3354/meps152175

The suspension-feeding activity of Cerastoderma edule (L.) was investigated in response to a wide range of experimental seston concentrations which approximated the changes in seston quality and quantity found in the natural environment over tidal cycles of sediment resuspension. The different seston concentrations were produced by adding increasing quantities of resuspended fine sediment to a relatively low and constant algal concentration (0.59 mg dry wt l^-1). The total seston concentrations (total particulate matter) varied over a wide range from 1.6 to 570 mg l^-1, and the organic fraction (particulate organic matter) between 0.62 and 79.8 mg l^-1. The organic content of the diets decreased with the increasing seston concentration, from 38.8% at the lowest concentration to 14% at the highest concentration. A significant negative relationship was found between clearance rate of C. edule and seston concentration, with very low values at 570 mg l^-1 of total seston. Filtration rate increased with seston concentration from a minimum value of 2.67 mg h^-1 at the lowest concentration to a maximum of 84.0 mg h^-1 at a concentration of 300 mg l^-1. Above 300 mg l^-1 there was an abrupt decline in filtration rate. Pseudofaeces production started at a concentration of 4.8 mg l^-1, showing its highest values at around 300 mg l^-1. The organic content of pseudofaeces was significantly lower than the organic content of the seston, suggesting that C. edule is able to preferentially select organic particles for ingestion instead of inorganic particles. Selection efficiency was maintained at a high and constant level at seston concentrations between 4.8 and 97 mg l^-1, declining at the highest seston concentrations with the lowest organic content. Thus the physiological sorting and selection mechanism appears to be very effective at seston concentrations below 100 mg l^-1, this ability declining abruptly at higher concentrations. Ingestion rate was constant in the lower range of seston concentration (1.6 to 34 mg l^-1), increased at concentrations around 250 mg l^-1, and declined abruptly at the higher food rations. Absorption efficiency appeared relatively independent of seston concentrations over a large range, but it was reduced at concentrations above 250 mg l^-1. We found a very effective digestive mechanism to regulate absorption rate at seston concentrations between 1.6 and 250 mg l^-1. The results suggest that C. edule can compensate efficiently for a decrease in seston quality over a wide range of seston concentration (1.6 to 300 mg l^-1) by maintaining an effective preingestive mechanism of selection for organic particulate matter, as well as increasing filtration and rejection rates. As a consequence, this species is well adapted to living in turbid environments, such as intertidal mudflats, which are characterised by marked fluctuations in seston quality and quantity, caused by resuspension of fine sediments during periods of high current velocities on the flood or ebb tides.

Feeding behaviour · Preingestive selection · Seston load · Diet quality · Cerastoderma edule