Estimating long-term trends in populations of two ecosystem engineering burrowing shrimps in Pacific Northwest (USA) estuaries

Temporal variation in the density and distribution of the burrowing shrimps, Neotrypaea californiensis and Upogebia pugettensis, were compared in two estuaries along the West coast of the United States (USA) where they are recognized as important ecosystem engineers. Since these shrimp construct deep burrows in the sediment, we quantified the relationship between burrow openings and shrimp density (1.5 and 1.7 burrow openings per shrimp for N. californiensis and U. pugettensis, respectively) to permit population abundance estimates to be made over broad landscape scales. Neotrypaea californiensis populations estimated from burrow counts collected using a gridded survey design across representative tide flats declined by 25% between 2008 and 2010 in Yaquina Bay, Oregon and by 67% in Willapa Bay, Washington from 2006 to 2011, but increased again in Willapa Bay by 2014. Upogebia pugettensis had mostly disappeared from Willapa Bay by 2006 and declines were observed in Yaquina Bay, but the magnitude and long-term trajectory of U. pugettensis in this estuary was less clear. These species population fluctuations mirrored those observed in density collected at discrete sampling locations over the same period, equate to large changes in secondary production, and have likely resulted in substantial changes to estuarine habitat and food webs.

Impact/Purpose

Research conducted collaboratively by USDA and USEPA estuarine ecologists documented large declines in the population size and spatial distribution of two native species of burrowing shrimps in Pacific Northwest estuaries. These population declines occurred in two estuaries, Willapa Bay (WA) and Yaquina Bay (OR), separated by >100 miles, over less than five years. These shrimps play major roles in the ecology of these estuaries, determining the composition and structure of invertebrate communities, pumping oxygen deep into the sediment and thereby increasing the rate of organic matter decomposition and cycling of carbon and nitrogen, filtering prodigious amounts of phytoplankton from the water column, and determining the structure of the food web and transfer of energy within the ecosystem. For these reasons, these shrimps are considered to be ecosystem engineering species for Pacific northwest estuaries. The declines in both species’ populations were apparent from single monitoring stations as well as estuary-wide population mapping surveys. The former afforded more frequent sampling of the populations, and were less expensive to conduct, but the population maps provided greater confidence of the magnitude and specific locations of the population changes. Failure of larval recruitment from offshore is believed to have been one cause of the declines of both shrimp species, suggesting that oceanographic conditions offshore can have major indirect impacts on the ecological dynamics of adjacent estuaries. Additionally, an invasive species of parasitic isopod, thought to have been introduced by ship transport from Japan or China, is believed to have contributed to the population decline of the mud shrimp Upogebia pugettensis. The population monitoring methods demonstrated here are useful tools to track those changes and help forecast changes to estuarine ecosystem structure, function, and production of valued ecosystem services.

Citation

Dumbauld, B., L. McCoy, Ted DeWitt, AND J. Chapman. Estimating long-term trends in populations of two ecosystem engineering burrowing shrimps in Pacific Northwest (USA) estuaries. Springer, New York, NY, 848(5):993-1013, (2021). [DOI: 10.1007/s10750-021-04544-7]

DOI: Estimating long-term trends in populations of two ecosystem engineering burrowing shrimps in Pacific Northwest (USA) estuaries