Graduate Faculty Memberships
Ecology, Water Resources Science
Limnology; photosynthetic activity of algae; abundance and spatial distribution of zooplankton.
I am fascinated by plankton, amazed by the number of ways these small organisms interact with each other and with the other kinds of organisms in their liquid environment. It's a challenge to understand how the abundance and spatial distribution of these organisms are controlled. As a graduate student, I studied the fossils of planktonic animals preserved in lake sediments, primarily to gain information about climatic change during lake history. This led to postdoctoral studies here at the University of Minnesota, in which I analysed the microfossils in sediment cores we obtained in western Iran to reconstruct the history of climate in the Middle East during the time that primitive agriculture developed in that region.
Planktonic algae are much more abundant in some lakes than others. There are practical reasons for understanding these variations, because extremely abundant algae often degrade aquatic environments. I have studied phytoplankton fluctuations and environmental conditions in a number of lakes, with special attention to the effects of light intensity and phosphorus on the rate of algal photosynthesis. Somewhat paradoxically, the studies of underwater light in inland lakes, where the water is often turbid with abundant algae, led to optical studies of the eastern Mediterranean Sea, where the water is extremely transparent and there are very few phytoplankton.
During the past decade I have studied the spatial distribution of zooplankton in lakes. For these studies, I assembled a high-frequency (192 kHz) sonar system that consists of a microcomputer connected to a commercial echo-sounder and a Loran navigation receiver. The sonar system records acoustic backscattering by zooplankton aggregations located at various depths continuously. The aggregations also are displayed instantaneously on a computer screen so they can be sampled precisely with plankton nets.
In Lake Superior, we have found that almost all mesozooplankton (Copepoda and Cladocera) are aggregated in the surface layer during spring and summer, in relatively shallow water within and above the thermocline. Consequently, the spatial distribution of these planktonic animals is very dependent on temperature-density stratification and other physical attributes such as coastal upwelling. Because of the close association with lake stratification, almost all mesozooplankton in Lake Superior occur in the upper 40 meters of water during summer; they are nearly absent in deeper water.
Megard, R.O. 2000. Diagnosis of light attenuance with Secchi disks. Arch. Hydrobiol. Spec. Issues. Advanc. Limnol. 55: in press.
Megard, R.O., M.M. Kuns, M.C. Whiteside, and J.A. Downing. 1997. Spatial distributions of zooplankton during coastal upwelling in western Lake Superior. Limno. Oceanogr. 42:827-840.
Ross, M.J., J.W. Curtsinger, and R.O. Megard. 1996. Development of population structure in Daphnia clones in a stratified lake. Heredity 77:292-302.
Dean, W.E. and R.O. Megard. 1993. Environment of deposition of CaCO3 in Elk Lake, Minnesota, pp. 97-113. In Elk Lake, Minnesota: Evidence for Rapid Climate Change in the North-central United States. J.P. Bradbury and W.E. Dean, eds. Geol. Soc. Amer. Special Paper 276.
Megard, R.O., J.P. Bradbury, and W.E. Dean. 1993. Climatic and limnologic setting of Elk Lake, pp. 19-36. In Elk Lake, Minnesota: Evidence for Rapid Climate Change in North-central United States. J.P. Bradbury, and W.E. Dean, eds. Geol. Soc. Amer. Special Paper 276.
Megard, R.O. and T. Berman. 1989. Effects of algae on the Secchi transparency of the southeastern Mediterranean Sea. Limnol. Oceanogr. 34:1640-1655.
Megard, R.O., K.A. Pearson, and D.A. Larsen. 1989. A microprocessor based sonar data acquisition system for fish and plankton research. Proc. Inst. Acoustics Symposium (Edinburgh) 11:141-148