Seston variability and daily growth in Mercenaria mercenaria on an intertitla sandflat

We conducted observations of weather and water column parameters to determine the scope and persistence of seston vanability on an intertidal sandflat (Cape Henlopen, Delaware, USA) and the effects of this variabhty on the daily growth rate of the hard clam Mercenaria mercenana. Wave-induced resuspension of bottom sediments was found to increase the quantity of particulate matter in the water column by an order of magnitude. At high suspended loads, the quality of the seston, measured as the percent organic matter, was reduced by a factor of 5 due to the dilution of the organic matter with inorganic particles. The seston parameters (suspended solids, particulate organic matter and percent organic) responded quickly to changes in the weather, showing no significant autocorrelations at lags greater than 1 or 2 d. Daily shell growth increments of M. mercenana were measured using shell microgrowth techniques. The daily growth rate was compared to the seston parameters and the water temperature. For 2 independent implantations, the dally mean ensemble and individual clam shell growth increments were s~gnificantly correlated to the quality of the seston The composition of the seston was demonstrated to be more important to clam growth than the concentration alone. Shell growth responded to changes in the percent organic matter on a daily time scale, with no lag or memory to previous seston parameters. These results provide direct, field evidence for the influence of particle quality on clam growth on a daily time scale.