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The suspension-feeding mud shrimp, Upogebia pugettensis, is a common inhabitant of intertidal mudflats in estuaries throughout the Pacific Northwest, where it develops extensive burrows. Also inhabiting the shrimps' burrow is the commensal bivalve, Cryptomya californica. Filtration by dense populations of the shrimp and its commensals may have a negative impact on phytoplankton abundance within these estuaries. The presence of the shrimp introduces three possible sinks for phytoplankton: filtration by the shrimp, filtration by the commensal bivalve, and removal of phytoplankton by the burrow itself. Together, the shrimp, commensal bivalve, and burrow, comprise the shrimp-burrow complex. Laboratory feeding experiments were conducted to measure particle removal rates of the shrimp-burrow complex, and to determine the relative importance of each of the three components of the complex in particle removal. For comparison, the same experiments were conducted with the Pacific oyster, Crassostrea gigas, Retention efficiencies were determined for particles in the size range from 2 to 10 1m in an effort to determine whether shrimp utilize the same size range of particles as other suspension feeders. Using data from our filtration experiments, a simple box model was developed to predict the proportion of the total volume of water in the lower Yaquina Bay, Oregon, that is filtered by shrimp-burrow complexes over a 24-hour period. Results indicate that the burrow wall may be an important factor in removal of phytoplankton (expressed as suspended POC), potentially accounting for 0.7 that removed by the shrimp alone. The model predicts that, for the phytoplankton concentrations tested, the shrimp-burrow complex may potentially remove 0.152-1.667 times the total amount of phytoplankton found in the lower Yaquina each day, depending on tidal-flow dynamics. We conclude that the shrimp-burrow complex is capable of removing large proportions of available phytoplankton, and may potentially deplete phytoplankton in some areas of the lower Yaquina Bay. |
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