Associate Professor
Department of Biological Sciences
Towson University
Towson, MD 21252 USA
Office: Smith 223
Phone: 410-704-4368
Fax: 410-704-2405
email: sgresens@towson.edu
Education:
Ph.D. University of Chicago
M.S. University of Wisconsin
B.S. S.U.N.Y. College at Oneonta
Courses Taught:
BIOL 208 - Biological Diversity
BIOL 402 - General Ecology
BIOL 406 - Limnology
BIOL 609 - Community Analysis & Bioassessment
Research Interests:
I study freshwater ecology, from the perspective of benthic invertebrates. Many of my research projects use chironomids, “non-biting midges”, as a model research system well-suited to studies of biodiversity. The Family Chironomidae includes thousands of species with an amazing range of ecological specialization. Chironomid larvae are abundant in many aquatic habitats, and thus are useful in studying the role of primary consumers in aquatic food webs. Three topics characterize my current research:
Species delineation and systematics of chironomids of the Genus Cricotopus, using analysis of DNA sequence data and morphological data: Worldwide, Cricotopus is a large genus with many undescribed and/or highly variable species. This project is being carried out in collaboration with Dr. Torbjørn Ekrem and Dr. Elisabeth Stur, of the Norwegian University of Science and Technology. We are using molecular genetic data to compare North American and European populations of nominal Cricotopus species, and to study their phylogenetic relationships.
Distribution of chironomid species along gradients of watershed urbanization: Collection of floating chironomid pupal exuviae (cast pupal exoskeletons) provides an effective means to compare species diversity among streams that are impacted by urban development. Since the chironomid species vary greatly in the sensitivity of their larvae to pollution, we are using samples of exuviae to develop statistical tools (metrics, tolerance values) which should provide improved resolution of changes in the ecological health of impacted streams, or streams undergoing restoration.
Periphyton (i.e., attached algae), provide important inputs to stream food webs, and are habitat for many aquatic invertebrates. Suspended silt-clay sediments are a widespread pollutant in streams and pose a major problem to the Chesapeake Bay. Production of stream algae is affected by grazing invertebrates and by fine silt-clay sediments, which are capable of binding and releasing phosphorus, a potentially limiting nutrient. We have developed laboratory microcosms to study the response of algal P-limitation and growth of chironomid larvae to different types and levels of suspended sediments.
Publications:
Karosas, A. and S.E. Gresens. 2010. Effects of silt-clay sediment and grazing chironomid(Diptera) larvae on physiological phosphorus limitation of periphyton. Hydrobiologia (submitted).
Gresens, S.E. 2010. Response of Chironomidae to multiple gradients of urban impact. Proceedings of the XVIIth Symposium on Chironomidae. X. Wang (ed.) Nankai University, Tianjin, China (submitted)
Stranko, S.A.., S.E. Gresens, R.J. Klauda, J.V. Kilian, P.J. Ciccotto, M.J. Ashton and A.J. Becker. 2010. The differential effects of
urbanization and non-natives on imperiled stream species. Northeastern Naturalist (in press).
Gresens, S.E. and L.C. Ferrington, Jr. 2009. Chironomid species assemblages of streams draining areas of serpentine vs.
non-serpentine bedrock. Proceedings of the XVth International Symposium on Chironomidae. (In press).
Kenney, M.A., A.E. Sutton-Grier, R.F. Smith and S.E. Gresens. 2009. Benthic macroinvertebrates as indicators of water quality: The intersection of science and policy. Terrestrial Arthropod Reviews 2:99-128.
Gresens, S.E. and L.C. Ferrington, Jr. 2008. Taxonomic distinctness provides an alternative view of the diversity of chironomid
(Diptera) assemblages. Boletim do Museu Municipal do Funchal Sup. No. 13: 101-108.
Sinclair, C.S. and S.E. Gresens. 2008. Discrimination of Cricotopus sp. (Diptera: Chironomidae) with mitochondrial gene
Cytochrome oxidase I sequence. Bulletin of Entomological Research 98:555-563.
Gresens, S.E., K.T. Belt, J.A. Tang, D.C. Gwinn and P.A. Banks. 2007. Temporal and spatial responses of Chironomidae
(Diptera) and other benthic invertebrates to urban stormwater runoff.Hydrobiologia 575:173-190.
Gresens, S.E. and L.C. Ferrington, Jr. 2007. Chironomid species richness in streams draining areas of serpentine vs.
non-serpentine bedrock. Proceedings of the XVth International Symposium on Chironomidae. (accepted).
Lawrence, J.M. and S.E. Gresens. 2004. Response of periphyton and grazers to nutrient enrichment in rural vs. urban streams.
Journal of Freshwater Ecology 19:375-385.
Gresens, S.E. 2001. Thermal sensitivity of ingestion and digestion in larvae of a eurythermal chironomid. Journal of the North
American Benthological Society 20: 68-83.
Gresens, S.E.1997. Interactive effects of diet and thermal regime on growth of the midge Pseudochironomus richardsoni.
Freshwater Biology 38:365-373.
Gresens, S.E. 1995. Grazer diversity, competition and the response of the periphyton community. Oikos 73:336-346.
Recent Graduate Student Theses:
Cory Lavoie, 2009: “Use of chironomid pupal exuviae in bioassessment of Baltimore County streams”
Megan Green, 2008: "Effects of suspended sediment on periphyton biomass accrual and phosphorus limitation"
Undergraduate Students: