Particle removal rates by the mud shrimp Upogebia pugettensis, its burrow, and a commensal clam: Effects on estuarine phytoplankton abundance

Abstract

The burrowing shrimp Upogebia pugettensis is an abundant intertidal invertebrate of Pacific Northwest, USA bays and estuaries where it lives commensally with the bivalve Cryptomya californica. Suspension-feeding activities by the shrimp and by its commensal clam, as well as particle settlement within the burrow, represent 3 different components that could remove phytoplankton from water drawn into shrimp burrows. These 3 components together comprise what we call the 'U. pugettensis shrimp-burrow complex'. In laboratory experiments, we measured particle removal by each of these components. Our results indicated that U. pugettensis itself is responsible for filtering the majority of phytoplankton removed by the U. pugettensis shrimp-burrow complex at phytoplankton concentrations of 0.12 mg C l-1, with filtration by C. californica becoming increasingly important at phytoplankton concentrations of 0.48 mg C l-1. Particle settlement in the burrow and adhesion to the burrow wall may also be responsible for removal of substantial proportions of phytoplankton. Using results from both laboratory and field experiments, we developed a population filtration model to examine the potential impacts of U. pugettensis shrimp-burrow complexes on phytoplankton in the Yaquina estuary, Newport, Oregon, USA. We showed that U. pugettensis shrimp-burrow complexes in this estuary may be capable of daily filtering the entire body of overlying water. We also examined the potential for food competition between U. pugettensis and other suspension feeders that are found in shrimp habitats, represented in this study by the Pacific oyster Crassostrea gigas. Comparison of retention efficiencies of shrimp and oysters indicated that they are both capable of utilizing phytoplankton-sized particles with similar efficiencies and, therefore, may compete for food when phytoplankton abundance is growth-limiting.