PARENT SESSION
Poster Session 3: Aquatic Ecology
Monday, August 8, 5:00 PM - 6:30 PM, Exhibit Hall 210 D, Level 2, Palais des congrès de Montréal
Blueback herring trophic responses to zebra mussels and range expansion in the Hudson River watershed, New York.
Limburg, Karin*,1, Caraco, Nina2, Harvey, Rodger3, Ju, Se-Jong3, Schmidt, Robert4, 1 SUNY Coll. Environmental Science & Forestry, Syracuse, NY, USA2 Institute of Ecosystem Studies, Millbrook, NY3 Chesapeake Biological Laboratory, Solomons, MD4 Hudsonia Ltd., Annandale-on-Hudson, NY
ABSTRACT- Blueback herring (Alosa aestivalis), an anadromous herring native to the Hudson River estuary, is a key intermediate member of the food web. In the 1980s its diet was quantified and found to be heavily dependent on pelagic organisms, primarily the cladoceran Bosmina freyi. With the invasion of zebra mussels (Dreissena polymorpha) in this system, and subsequent dramatic declines in phytoplankton and microzooplankton, we hypothesized that trophic flows to blueback herring would have altered considerably, with changes in growth and condition as fish would be forced to consume less favorable prey. However, blueback herring have also expanded their range into the Hudson's major tributary, the Mohawk River, where food web relationships were unknown. We quantified diet and food web relations (via stable isotope and fatty acid analyses) in 1999, with additional sampling through 2003. Blueback herring growth and relative condition declined dramatically in the tidal freshwater Hudson in 1999 compared to 1987. In 1987, B. freyi composed 16.7 to 92.5% of the diet by weight, but in 1999 this had fallen to 0 to 33.3% over the period July - September. The pelagic-based diet was replaced by a taxonomically broader diet dominated by littoral-epibenthic organisms, with the exception of early season dominance of daphnid cladocerans in the Mohawk. Stable isotopic ratios of N and C reflected the broad diets. Fatty acid profiles showed strong linkages between phytoplankton-copepods-Hudson herring (especially herring larvae) on the one hand, and seston-Bosmina and seston-invertebrates-Mohawk herring on the other. We hypothesize that the zebra mussel invasion caused a trophic shift in Hudson herring toward prey more enriched in highly unsaturated fatty acids than in the past, but not in the Mohawk River. These results represent some of the clearest impacts of zebra mussels on fish in this watershed documented to date.
Key words: blueback herring, zebra mussels, food web analysis