The effect of long‐term alteration of in situ currents on the growth of Mercenaria mercenaria in the northern Gulf of Mexico

Abstract

Water currents were experimentally manipulated for 3 months in a shallow subtidal sandflat through a series of nine channels with diverging, parallel, or converging walls (7 m long, 1.2 m high). Three treatments were chosen to bracket the ambient flow rates; vertically averaged velocities were reduced by 40%, reduced by 2%, or increased by 65%. Within the center of each channel, six Mercenaria mercenaria [shell length, 36.9±2.2 mm (mean ± 1 SD)] were placed haphazardly in 0.25‐m2 plots. Although water‐column chlorophyll a levels declined near the substratum, concentrations did not differ among channel flow treatments. Mean clam lengths increased 19% during the study, but growth rates did not differ significantly among channel flow treatments. These results suggest that the natural range of flow rates (up to 27 cm s−1), in the absence of local food depletion, does not alone alter growth of this active suspension feeder.