Association of Southeastern Biologists

Robert P. Creed
Associate Professor
Ph.D., Michigan State University

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I have two major areas of research, stream ecology and the biological control of introduced aquatic plants. Historically, streams have been considered communities that are structured by abiotic factors, i.e., droughts and floods. My work in various streams has demonstrated that members of the stream biota, primarily large invertebrates like crayfish, can also have very important influences on stream community structure. My research in Michigan streams demonstrated that crayfish can have dramatic impacts on the abundance of a dominant filamentous alga ( Cladophora glomerata ). By reducing the abundance of this filamentous alga crayfish indirectly facilitated smaller benthic algae (e.g., diatoms) and the invertebrates that fed on these smalllgae. In this stream crayfish were acting as keystone species. Research that I have conducted with students in Maryland and North Carolina streams demonstrated that crayfish can also accelerate leaf decomposition rates and have impacts on sediment accumulation in streams. In these streams crayfish were acting as ecosystem engineers, i.e., they were influencing habitat quality and resource abundance (availability of fine particles of detritus) for coexisting taxa. Most recently, my students and I have begun investigating the factors that influence the distribution and abundance of different crayfish species throughout watersheds, i.e., from small headwater streams to larger rivers.

My research in biological control has focused on the impact of a native insect on an introduced aquatic plant (Eurasian watermilfoil). Watermilfoil was introduced into North America about 60 years ago. Since then it has spread throughout much of the continent and is a considerable nuisance in hundreds of lakes and several rivers. Management of this nuisance plant has relied on the use of herbicides or mechanical devices that cut or uproot the plant. Beginning about 25 years ago watermilfoil populations began to decline on their own. An herbivorous weevil (a type of beetle) was found associated with these declining watermilfoil populations. Research that I have conducted (alone and in collaboration with other ecologists) has determined that the weevil can cause watermilfoil declines. Other research groups have reached similar conclusions. As a result, this native insect is being considered for use as a biological control agent for watermilfoil. In addition, with its switch to the introduced watermilfoil the role of this weevil in aquatic communities has changed. It has gone from being a relatively unimportant member of the communities it inhabits to playing an important role in structuring many communities. In a recent paper I have argued that this weevil should be considered a new keystone species in North American freshwater communities.

Selected Publications Creed, R.P., Jr. (1994) Direct and indirect effects of crayfish grazing in a stream community. Ecology 75:2091-2103. Creed, R.P., Jr., and Sheldon, S.P. (1995) Weevils and watermilfoil: Did a North American herbivore cause the decline of an exotic plant? Ecological Applications 5:1113-1121. Sheldon, S.P., and Creed, R.P., Jr. (1995) Use of a native insect as a biological control for an introduced weed. Ecological Applications 5:1122-1132. Creed, R.P., Jr. (2000) Is there a new keystone species in North American lakes and rivers? Oikos 91: 405-408. Brown, B.L., R.P. Creed Jr. and W.E. Dobson. 2002. Branchiobdellid annelids and their crayfish hosts: are they engaging in a cleaning symbiosis? Oecologia 132:250-255. Creed, R.P.,Jr. 2006. Predator transitions in stream communities: a model and evidence from field studies. J. of the North American Benthological Society 25:533-544 Back to Top