Meet Great Lake Researcher Tom Nalepa
Thomas Nalepa is an aquatic biologist with the National Oceanic and Atmospheric Administration’s Great Lakes Environmental Research Laboratory in Ann Arbor, Michigan. He has been a Great Lakes researcher for the past 37 years, and has served on various Great Lakes committees and panels, including being president of the International Association for Great Lakes Research. Nalepa’s research has focused on understanding changes in the structure, function, and relative health of benthic communities relative to natural and man-induced perturbations, and also on understanding the community’s role in nutrient cycling and food webs. His current research projects include identifying population trends in benthic macroinvertebrates in Lakes Huron and Michigan, and examining the importance of benthos in the diets of prey fish in southern Lake Huron. Additionally, he is leading efforts to determine why the benthic amphipod Diporeia spp. is disappearing throughout the Great Lakes. Results of Nalepa’s research are important for understanding connections between benthos, invasive species, and fish communities in both Lakes Huron and Michigan.
Current Projects on Lake Huron
- Trends in benthic macroinvertebrate populations in Lake Huron, including Saginaw Bay, Georgian Bay,
and North Channel.
This project examines trends in benthic populations over time, with particular emphasis on the amphipod Diporeia spp. and the dreissenid mussels, zebra and quagga mussel. A recently published paper documented large changes between the early 1970s and 2000, and between 2000 and 2003. Sampling efforts are continuing as populations change at a rapid rate.
- Diets and condition of forage fish in southern Lake Huron (with S. Pothoven).
Given the collapse of prey fish populations, this project examines the diet of prey fish in Lake Huron relative to what diet items are available. Both fish and potential prey (zooplankton, benthos, and Mysis) are being collected over a seasonal period along a nearshore-offshore transect during both day and night.
Other Current Projects
- Long term trends in macroinvertebrate populations in Lake Michigan.
This is an assessment program that began in 1980. Remarkable changes have been documented over this time period, including the disappearance of Diporeia, the increase of zebra mussels, and now the replacement of zebra mussels by quagga musssels. The simultaneous monitoring of populations in both Lakes Michigan and Huron allows us to compare and contrast changes in the two systems.
- Efforts to determine mechanisms for the decline of Diporeia in the Great Lakes.
While the decline of Diporeia in the Great Lakes is related to the introduction and spread of zebra and quagga mussels, the exact mechanism for the negative response in not entirely clear. Field and laboratory studies have and are being conducted to explore different hypotheses.
- Impact of hypoxia on macroinvertebrate populations in central Lake Erie
Low oxygen conditions prevail in late summer every year in central Lake Erie, and this project examines impacts on benthic populations. Emphasis is placed on the growth and physiological condition of chironomids since this taxonomic group is heavily fed upon by fish.
Past Projects in Lake Huron
- Impacts of zebra mussels on the Saginaw Bay ecosystem (with G. Fahnenstiel).
The impact of the zebra mussel on the Saginaw Bay ecosystem was studied between 1990 and 1996. This was during the period just before, during, and after the initial colonization period. Ecosystem components included nutrients, water clarity, bacteria, phytoplankton, zooplankton, macrobenthos, and macrophytes. The study consisted of researchers from many different agencies and universities, and resulted in a special issue of the Journal of Great Lakes Research.
- Ecology of lake whitefish and response to changes in benthic communities (with S. Pothoven)
The spread of zebra and quagga mussels has led to the disappearance of Diporeia, the primary food of lake whitefish. The loss of Diporeia in Lake Huron had led to a shift in the diet of lake whitefish to less energy-rich food sources, causing a decline in fish growth and condition.