THE EFFECTS OF SEDIMENT GRAIN SIZE AND SHELL CONTENT ON THE BURIAL TIME OF THE COQUINA, Donax sp.
Bergquist, Derk C.
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Anthropogenic modifications of the coastal environment can significantly impact the physical characteristics and the biological communities of sandy beaches. This study examined how changes in the amount and the size of the shell in sediments affect the burrowing ability of <italic>Donax</italic>, an abundant and ecologically important genus of beach bivalves. Two laboratory-based experiments examining the burial behaviors of <italic>Donax</italic> sp. were performed: (1) a full factorial experiment utilizing four different grain sizes of sand (very coarse, coarse, medium, and fine) and four different percentages of crushed oyster shell (0, 25, 50, and 100%) and (2) a beach sediment experiment using sediment from two South Carolina beaches of differing grain size distributions along with shell mimicking those distributions and the shell grain size distribution found on the beach. In Experiment 1, increasing shell content increased time to complete burial, and the effect of percent shell varied by grain size. Shell had a significant effect on the burial time; the shortest burial times were in 0% shell and the longest were in 100% shell. Shell in fine and medium sand increased the burial time more than in coarse or very coarse sands especially at higher percentages of shell. Increasing the grain size distribution did not significantly increase the burial time. Coarseness due to shell increases the burial time more than coarse sand. This study may provide a mechanism behind some of the changes observed in the biological community as a result of changes in the physical characteristics of the beach sediment, particularly those following human impacts.