Shifts in Zooplankton Community Structure: Implications for Food Web Processes in the Upper San Francisco Estuary

Winder, Monika and Jassby, Alan D. (2011) Shifts in Zooplankton Community Structure: Implications for Food Web Processes in the Upper San Francisco Estuary Estuaries and Coasts, 34 (4). pp. 675-690. DOI 10.1007/s12237-010-9342-x.

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Zooplankton are an important trophic link and a key food source for many larval fish species in estuarine ecosystems. The present study documents temporal and spatial zooplankton dynamics in Suisun Bay and the Sacramento–San Joaquin Delta—the landward portion of the San Francisco Estuary (California, USA)—over a 37-year period (1972–2008). The zooplankton community experienced major changes in species composition, largely associated with direct and indirect effects of introductions of non-native bivalve and zooplankton species. A major clam invasion and many subsequent changes in zooplankton abundance and composition coincided with an extended drought and accompanying low-flow/high-salinity conditions during 1987–1994. In the downstream mesohaline region, the historically abundant calanoid copepods and rotifers have declined significantly, but their biomass has been compensated to some extent by the introduced cyclopoid Limnothoina tetraspina. The more upstream estuary has also experienced long-term declining biomass trends, particularly of cladocerans and rotifers, although calanoid copepods have increased since the early 1990s due to the introduced Pseudodiaptomus spp. In addition, mysid biomass has dropped significantly throughout the estuary. Shifts in zooplankton species composition have also been accompanied by an observed decrease in mean zooplankton size and an inferred decrease in zooplankton food quality. These changes in the biomass, size, and possibly chemical composition of the zooplankton community imply major alterations in pelagic food web processes, including a drop in prey quantity and quality for foraging fish and an increase in the importance of the microbial food web for higher trophic levels.

Document Type: Article
Keywords: Food Webs; Marine Biology; Zooplankton; Sacramento–San Joaquin Delta; Trophic interactions; Carbon biomass; Invasion; Copepods; Mysids; Limnoithona
Research affiliation: OceanRep > GEOMAR > FB3 Marine Ecology > FB3-EOE-N Experimental Ecology - Food Webs
Refereed: Yes
DOI etc.: 10.1007/s12237-010-9342-x
ISSN: 1559-2723
Date Deposited: 06 Dec 2010 09:44
Last Modified: 22 Dec 2016 09:44

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