Thomas Nalepa - NOAA GLERL (Emeritus)
Trends in benthic macroinvertebrate populations are an excellent indicator of ecosystem health in the Great Lakes. Presently, wide-scale population changes are occurring in many lake areas as a result of decreased nutrient loads and the introduction and spread of invasive species such as the Zebra and Quagga mussel.
Benthic macroinvertebrates, and particularly the amphipod Diporeia, play a major role in the cycling of materials (i.e., energy, nutrients, contaminants) through the food web. Populations are presently undergoing major changes in both nearshore and offshore regions of the Great Lakes. Most of these changes can be attributed to the widespread distribution and great abundances of dreissenid mussels (Zebra mussels and Quagga mussels). In this project, we examine spatial and temporal distributions in benthic macroinvertebrate populations, including dreissenid mussels, in various regions of the Great Lakes. These data will be used to determine trends in abundances and, in some cases, used to establish a baseline for future comparisons. Emphasis will be placed on Lake Huron since the last benthic surveys conducted in the main basin, Georgian Bay, and North Channel were in the early 1970s. Given the dramatic changes in benthic populations in Lakes Michigan and Ontario, similar changes are likely also occurring in Lake Huron. In addition, there is a renewed interest in the Lake Huron ecosystem (Lake Huron Initiative, Michigan Office of the Great Lakes)
Because mussel distributions are highly clumped, accurate density estimates are difficult to obtain using standard methodology such as grab samplers. Quantitative estimates of dreissenids are important in assessing impacts on macroinvertebrate populations and other food web components. In this project, we determine densities and distributions of dreissenids using traditional methods, side-scan sonar, and a benthic camera system. Each of these methods has its strengths and weaknesses, and data will be collected in a complimentary manner.
In August 2003, benthic samples were collected at 160 sites in the main basin of Lake Huron. The primary purpose was to examine changes in densities of Diporeia and Dreissena since 2000. A spreadsheet of data collected at 70 sites in the main basin in 2000 was completed. The file gives all organisms found in each of the replicate samples. Also, analysis of video tapes of Dreissena beds in Lake Michigan was completed. The tapes will be used to estimate areal coverage of mussels relative to coverages derived from side-scan sonar images and grab samples. Samples collected at 35 sites in the Straits of Mackinac in 2002 continue to be processed (e. g., organisms picked, counted, and sorted).
The work proposed in 2003 focused primarily on analyzing data collected in 2002: 1) pick and sort benthic samples in the Straits of Mackinac to assess trends in shallow water communities since 1997. This study is a joint effort between GLERL and USGS Great Lakes Science Center; 2) pick and sort benthic samples collected in North Channel and Georgian Bay. These samples will complete a benthic assessment of the entire lake that was initiated in 2000. Of greatest interest in these two regions is the distribution and abundance of Diporeia; 3) continue to analyze and interpret data collected in Lake Michigan to more accurately assess dreissenid abundances; 4) re-sample the open basin of Lake Huron to determine changes in Diporeia abundances.
The following surveys were conducted in Lake Huron as part of this project: Straits of Mackinac in 1997 and 2002 (35 sites); Lake Huron Main Basin in 2000 and 2003 (65 and 80 sites respectively); North Channel and Georgian Bay in 2002 (36 sites). The 2002 survey in the Straits of Mackinac and the 2003 survey in Lake Huron were designed to determine rates of population changes in Diporeia and Dreissena . All the surveys are in various stages of completion. Organisms collected in 2000 in the main basin have been counted, identified, and the data entered into a spreadsheet. The file gives the number of each species found in each of the replicate samples at each site. The samples collected in 2003 are being processed (animals picked and counted). Organisms in the samples from North Channel and Georgian Bay have been picked and counted and are in the process of being identified. Samples from the Straits of Mackinac are being processed by USGS Great Lakes Science Center.
As part of an effort to assess distributions of Zebra and Quagga mussels on the east and west side of Lake Michigan; a benthos camera system and side-scan sonar were used to estimate areal coverage of mussels along transects near Port Washington and Sheyboygan (west side), and Little Sable Point and Muskegon (east side). Depths were 10, 20, 30, and 40 m along each transect. Grab samples were also taken at each depth to estimate densities of Diporeia. Since previous whole lake surveys in 1994/95 and 2000 showed that Diporeia was far more abundant on the west side of the lake than the east side, we were interested in determining the distribution of mussels in these two areas. In 2003, all side-scan images have been digitized and areal coverage by mussels defined. Video images taken with the camera system have also been digitized. The images were grabbed randomly and areal coverage defined.
Video images of Zebra mussels on Lake Michigan bottom sediments: note the patchy distribution of the mussel beds (darker areas) in the sand
All organisms in the samples collected at 70 sites in Lake Huron in 2000 were sorted and counted. All amphipods were identified, and chironomids and oligochaetes were mounted on microscope slides for identification.
Benthic samples were collected at 160 sites throughout Lake Michigan in summer 2000 to determine the lake-wide distributions of Diporeia and other taxa. Many of the sites sampled were also sampled in 1994/95, so changes over this 5-year time period will be assessed. Also, many of the sites were located in areas where whitefish populations are showing a decline in condition. This fish species feeds heavily on Diporeia.
Benthic samples were collected at 70 sites throughout Lake Huron in summer 2000. A lakewide survey of benthic populations in Lake Huron has not been conducted since the early 1970s;
Benthic samples were collected at 120 sites in Lake Ontario in 1999. Densities of Diporeia will be examined relative to densities found in 1997 and 1998.
Nalepa, T. F., Fanslow, D. L., and Lang G. 2009. Transformation of the offshore benthic community in Lake Michigan: recent shift from the native amphipod Diporeia spp. to the invasive mussel Dreissena rostriformis bugensis. Freshwater Biology 54: 466-479.
Zhulidov, A. V., Pavlov, D. F., Nalepa, T. F., Scherbina, G. H., Zhulidov, D. A., and Gurtovaya, T. Y. Relative distributions of Dreissena bugensis and Dreissena polymorpha in the lower Don River, Russia. Internat. Rev. Hydrobiol. 83: 326-333.
Cavaletto, J. F., Nalepa, T. F., Fanslow, D. L., and Schloesser, D. W. 2003. Temporal variation of energy reserves in mayfly nymphs (Hexagenia spp.) from Lake St. Clair and western Lake Erie. Freshwater Biology 48: 1726-1738.
Nalepa, T. F., Fanslow, D. L., Lansing, M. B., and Lang, M. A. 2003. Trends in the benthic macroinvertebrate community of Saginaw Bay, Lake Huron, 1987 to 1996: responses to phosphorus abatement and the Zebra mussel, Dreissena polymorpha. J. Great Lakes Res. 29: 14-33.
Schloesser, D. W. and Nalepa, T. F. 2002. Comparison of 5 benthic samplers to collect burrowing mayfly nymphs (Hexagenia spp.:Ephemeroptera:Ephemeridae) in sediments of the Laurentian Great Lakes. J. N. Am. Benthol. Soc. 21: 487-501.
Vanderploeg, H. A., Nalepa, T. F., Jude, D. J., Mills. E. L. Holeck, K. T., Liebig, J. R., Grigorovich, I. A., Ojaveer, H. 2002. Dispersal and emerging ecological impacts of Ponto-Caspian species in the Laurentian Great Lakes. Can. J. Fish. Aquat. Sci. 59:1209-1228.
Nalepa, T. F., Hartson, D. J., Fanslow, D. L., and Lang, G. A. 2001. Recent population changes in Unionidae and Dreissena polymorpha (Zebra mussel) in Lake St. Clair. Amer. Malacol. Bull. 16: 141-145.
Lozano, S. J., Scharold, J. V., and Nalepa, T. F. 2001. Recent declines in Lake Ontario populations of benthic macroinvertebrates. Can. J. Fish. Aquat. Sci. 3: 518-529.
Schloesser, D. W. and Nalepa, T. F. 2001. Changing abundance of Hexagenia mayfly nymphs in western Lake Erie of the Laurentian Great Lakes: impediments to assessment of lake recovery? Internat. Rev. Hydrobiol. 86: 87-103.