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RESPONSE OF GHOST SHRIMP (NEOTRYPAEA CALIFORNIENSIS) BIOTURBATION TO ORGANIC MATTER ENRICHMENT OF ESTUARINE INTERTIDAL SEDIMENTS
DeWitt, T H. RESPONSE OF GHOST SHRIMP (NEOTRYPAEA CALIFORNIENSIS) BIOTURBATION TO ORGANIC MATTER ENRICHMENT OF ESTUARINE INTERTIDAL SEDIMENTS. Presented at 27th Annual Meeting of Pacific Estuarine Research Society, Port Townsend, WA, May 17-18, 2004.
Populations of burrowing shrimp (Neotrypaea californiensis and Upogebia p;ugettensis) are the dominant invertebrate fauna on Pacific estuarine tide flats, occupying >80% of intertidal area in some estuaries. Burrowing shrimp are renowned for their bioturbation of intertidal sediments, although little is known of the causes for variability in bioturbation rates for N. californiensis or other thalassinids. As human populations increase along Pacific coasts, anthropogenic nutrient loading to estuaries may increase, likely increasing organic matter (OM) production and its deposition on the seafloor. Burial of OM and enhancement of OM remineralization by bioturbation can reduce sediment organic matter (SOM) concentration at the sediment surface and thereby reduce the risk of adverse effects of elevated OM production. Because N. californiensis is a deposit feeder, its bioturbation rate may be affected by SOM concentration. An experiment was conducted to determine whether N. californiensis bioturbation rate was affected by SOM enrichment. Chopped green macroalgae was mixed with sediment from N. californiensis habitat and a dyed-sand tracer to create enrichment treatments of 1.5-50% macroalgae by wt (and a 0% macroalgae control), frozen into 20 cm x 2 cm discs, and buried flush with the sediment surface in intertidal habitats having no burrowing shrimp or high ghost shrimp density. Replicate plots were destructively cored to 30+ cm after 0, 14, and 28 d, and cores were sectioned at 1 to 4 cm intervals. Concentrations of dyed-sand tracer and total organic carbon (TOC) were measured in each core section. Sediment mixing was determined from vertical profiles of tracer and TOC. Dyed sand was observed in ghost shrimp fecal pellets in SOM-enriched plots within a few days of the start of the experiment, but not in the 0% macroalgae control. Preliminary analysis of the sediment cores suggests that sediment reworking was greatly increased in SOM-enriched treatments relative to 0% macroalgae control in shrimp-dominated habitat. Increased bioturbation by N. californiensis in response to SOM loading may be an important process to moderate adverse effects of anthropogenic nutrient loading to Pacific estuaries.