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THE IMPACTS OF UPOGEBIA PUGETTENSIS POPULATIONS ON ORGANIC MATTER AND NUTRIENT CYCLING IN PACIFIC NORTHWEST ESTUARIES
Citation:
D'Andrea, A. F. AND T H. DeWitt. THE IMPACTS OF UPOGEBIA PUGETTENSIS POPULATIONS ON ORGANIC MATTER AND NUTRIENT CYCLING IN PACIFIC NORTHWEST ESTUARIES. Presented at Benthic Ecology Meetings, Orlando, FL, March 21-24, 2002.
Description:
The burrowing thalassinid shrimp, Upogebia pugettensis, is a major ecosystem engineering species of Pacific estuaries and can structure the physical, chemical, and biotic properties of benthic habitats. This study utilized incubations, benthic chambers and porewater peepers to quantify the role of U. pugettensis on OM remineralization processes in Yaquina Bay, Oregon. In Upogebia-dominated habitats, the flux of reactive OM into sediments was ~2-4 times greater than areas lacking shrimp. Sediment oxygen uptake was 2-7 times greater in the presence of shrimp and increased linearly with shrimp burrow density (R2 = 0.8). Similarly, the dissolved inorganic nitrogen (NH4 and NO3) flux from the sediments to overlying water increased with burrow density (R2 = 0.66) and was ~2-12 times greater than "no shrimp" habitat. At mid- and high shrimp densities (55 and 130 burrow openings 0.25 m-2, respectively), nitrate became proportionally more important to DIN efflux from the sediments indicating a potential density-dependent increase in nitrification and subsequent denitrification in Upogebia burrow walls. Porewater concentrations of ammonium and phosphate in the top 30 cm of the sediment column were reduced at mid- and high shrimp densities relative to sediments with few shrimp, presumably due to bioirrigation. In contrast, porewater profiles in sediments with low shrimp density (20 burrow openings 0.25 m-2) or "no shrimp" suggested solute advection was dominated by diffusive transport. Shrimp bioturbation results in the rapid burial of OM, leading to a large inventory of reactive OM in sediments dominated by burrowing shrimp relative to no-shrimp habitats. The high flux of DIN in shrimp-dominated habitats ensures that products of decomposing OM are recycled back to the overlying water, rather than accumulating in the sediments as appears to occur in habitats lacking burrowing shrimp.