Environmental Monitoring & Assessment Program

Jan J.H. Ciborowski 1, David R. Barton 2, Kenneth A. Krieger 3, Timothy B. Johnson 4, and Stephen Lozano 4

1 Dept. of Biological Sciences , University of Windsor, Windsor, Ontario
2 Department of Biology, University of Waterloo, Waterloo, Ontario
3 National Center for Water Quality Research, Heidelberg College, Tiffin, Ohio
4 Ontario Ministry of Natural Resources, Picton, Ontario
5 Great Lakes Environmental Research Lab, NOAA, Ann Arbor, Michigan

Although lake-wide surveys have previously been conducted on Lake Erie, they typically lack either the intensity of sampling or the statistically robust framework needed to permit precise and unbiased estimation of basin-wide or whole lake benthic biodiversity and biomass. In 2004, a survey was conducted to generate a statistically valid estimate of lakewide and habitat-specific dreissenid abundance and biomass. These data are critical to understanding the mechanisms and magnitudes of benthic-pelagic fluxes of energy and nutrients of each basin.

The areal extent of the offshore zone of each of Lake Erie’s 3 basins was classified by depth (up to 4 classes) and substrate type (hard vs. soft). Fifty sampling locations were randomly apportioned across the classes in each basin, weighted by the estimated absolute abundance of dreissenids in each zone, and the inverse of variance of densities of dreissenids in habitat-specific samples collected during a 2002 study. Nearshore densities were estimated by sampling benthos at 2, 5 and 10-m depths along transects extending from shore at 20 stratified-randomly selected points per basin.

Benthic invertebrates, epipelic algae, sediments, and water for chemical measurements were collected at 283 stations between May and August 2004 by Canadian and US agencies (Environment Canada, Ontario MOE, Ontario MNR, NOAA, the USGS, several universities and other cooperators) using a total of 10 vessels. Hard substrates were sampled by divers operating air lift samplers. Soft substrates were sampled with a standard Ponar grab. All samples were preserved in the field and processed in the laboratory.

Approximately 75% of dreissenids by number (mostly quagga mussels) were located in the eastern basin, primarily on soft sediment of the deeper portions of the basin. The remainder were equally apportioned between western and central basins. Deepwater amphipods (Diporeia) were collected at only 4 stations. The total abundance of dressenids estimated from each basin differed considerably from the simulated abundance estimate that would have been derived had the 2004 survey resampled only at the locations used in 2002.