The Abundance and Distribution of Gelatinous Zooplankton in the San Francisco Estuary

Until recently, gelatinous zooplankton were not considered important components of the San Francisco Estuary (SFE) foodweb. However, anecdotal evidence, ongoing research, and a few published reports and papers suggest an increase in their abundance over the last 10 to 20 years. Of particular interests are three species of introduced hydromedusae (Blackfordia virginica, Maeotias marginata, and Moerisia lyonsi). All three inhabit the fresh to brackish regions of the estuary, including Suisun Bay, the channels of Suisun Marsh, and the western Sacramento-San Joaquin Delta, and are seasonally abundant throughout late summer and fall. As a result, they overlap both spatially and temporally with several species of planktivorous fish, including delta smelt. Changes in the abundance and distribution of these species may strongly influence interactions between fish and jellyfish, both directly through consumption and indirectly through competition. Here, we report the distribution and abundance of gelatinous zooplankton at 9 stations throughout the upper SFE during late summer and fall of 2010 and 2011. Gelatinous zooplankton and their prey were sampled monthly. While work in four smaller tributaries (see oral presentation by Donald et al.) reports high abundances (\u3e100 m-3) of two species (B. virginica and M. lyonsi), abundances of these species in the larger bays (San Pablo and Suisun) and rivers (Sacramento and San Joaquin) were significantly lower (\u3c1 \u3em-3). Most of the previous work to define the habitat range (salinity and temperature) of these species has occurred within Suisun Marsh. Extending this work into the open bays will help provide a more accurate habitat description. Additionally, information on the distribution and abundance of gelatinous zooplankton and how these vary with X2 will provide insight regarding the potential for interactions between gelatinous zooplankton and protected fish species within the SFE