What lives in the bottom of lakes and streams in Cobb County Georgia- benthic organisms!

Benthic organisms are remarkably diverse and vary with habitat. They include protozoa (like amoebas), sponges, cnidarians, flatworms, nematodes, isopods, crayfish, amphipods, mollusks, gastropods, leaches and aquatic worms, pelecypods, insects, and fish. Benthic species I have observed in my area (Cobb County, Georgia) include the Asian Clam (Corbicula fluminea), larval brook salamanders (Eurycea sp.), common sunfishes (Lepomis sp.), the Chattahoochee Crayfish (Cambarus howardi), caddisfly larva (Order Trichoptera), damselflies and dragonflies larval (Order Megaloptera), mayfly larva (Order Ephemeroptera), dragonflies and damselfly larval (Order Odonata), aquatic worms (phylum Annelida), Eastern Dobsonfly larval (Corydalus cornutus), water snakes (Nerodia sp.), longjaw minnow (Ericymba amplamala), river Cooter (Pseudemys concinna), true bugs (Order Hemiptera), true flies larval (Order Diptera), beetles (Order Coleoptera) and stonefly larval (Order Plecoptera). It is worth noting some of these species may only occupy the benthos for a period.

Image of a Brook Salamander. Brook salamanders are a genus, Eurycea, image by Lauren Schramm

Image of a Brook Salamander. Brook salamanders are a genus, Eurycea, image by Lauren Schramm

In some streams, Asian clams, an invasive aquatic species, can be one of the largest components of the benthic invertebrate community (Poff et al.,1993), however this is not the case in all streams in Cobb County. Black et al. (2003) evaluated benthic macroinvertebrate populations of two local streams: Sope Creek and Rottenwood Creek. In Sope Creek they found Ephemeroptera and Diptera to be the dominant orders. In Rottenwood Creek they found Trichoptera and Diptera to be the dominant orders.

An Asian Clam (Corbicula fluminea). Image by Lauren Schramm.

Walters et al. (2005) determined that 70 percent of fish species found within the Etowah River Basin, which includes a portion of Cobb County, were the sunfish family (Centrarchids), darters (Subfamily Etheosomatidae) and Minnows and Carps (Family Cyprinid). The study also found that as urban land cover increased there was reduced species richness. Therefore, my local benthos has fewer species than would be found outside a metropolitan area. However, the watershed is home to 76 species of fish. Benton et al. (2008) determined the most common fish species were the large-scale stoneroller (Campostoma oligolepis), banded scuplin (Coitus carolinae), and bluegill (Lepomis macrochirus).

According to the Georgia Department of Natural Resources Environmental Protection Division’s biodiversity portal rarer benthic species in my county include Sculptured Pigtoe (Cyclonaias infucata), Bluestripe Shiner (Cyprinella callitaenia), Delicate Spike (Elliptio arctata), Cherokee Darter (Etheostoma scotti), Lined Chub (Hybopsis lineapunctata), Gulf Moccasinshell (Medionidus penicillatus), Shoal Bass (Micropterus cataractae) and Highscale Shiner (Notropis hypsilepis). 

While historically, Unionidae, or the freshwater pearly mussels dominated the benthos of eastern North America (Parmalee & Bogan, 1998) they are a rare find in Cobb County, Georgia today. Their declines are due to previous commercial harvesting, invasive species, sedimentation, declines in fish host species, urban development, disease, predation, poor water quality/eutrophication, dams resulting in habitat alterations, habitat destruction and channelization (Bogan, 1993; Williams et al., 1993; Howells, 1996; Lydeard et al., 2004; Allen & Vaughn, 2010).

Image of Lauren Schramm (that’s me!) and the only freshwater mussel I have found in Cobb County. Image by Lauren Schramm.

If the phototrophic zone (the zone of a body of water where light reaches) extends to the bottom of the water body, it is possible to also find a variety of phytoplankton living there. One of the most common groups includes Chlorophyta or green algae and Bacillariophyceae or diatoms. In addition, there has been some documentation that zooplankton will exercise diel (daily) mitigations from the benthos to the open water zone (Wetzel, 1975). As you can see there is a great diversity of benthic aquatic animals in Cobb County!



Allen, D. C., & Vaughn, C. C. (2010). Complex hydraulic and substrate variables limit freshwater mussel species richness and abundance. Journal of the North American Benthological Society, 29(2), 383-394.

Benton, P. D., Ensign, W. E., & Freeman, B. J. (2008). The effect of road crossings on fish movements in small Etowah Basin streams. Southeastern Naturalist7(2), 301-310.

Black, D. D., Hughes, W. B., & Gregory, M. B. (2003). Water-quality and ecological assessment of Rottenwood and Sope Creeks, Marietta, Georgia, 2002. Georgia Institute of Technology.

Bogan, A. E. (1993). Freshwater bivalve extinctions (Mollusca: Unionoida): a search for causes. American Zoologist, 33(6), 599-609.

Burkhead, N. M., Walsh, S. J., Freeman, B. J., & Williams, J. D. (1997). Status and restoration of the Etowah River, an imperiled southern Appalachian ecosystem. [Textbook].

Georgia Department of Natural Resources Environmental Protection Division’s biodiversity portal. https://gakrakow.github.io/

Howells, R. G., Neck, R. W., & Murray, H. D. (1996). Freshwater mussels of Texas. University of Texas Press.

Lydeard, C., Cowie, R. H., Ponder, W. F., Bogan, A. E., Bouchet, P., Clark, S. A., & Thompson, F. G. (2004). The global decline of nonmarine mollusks. BioScience, 54(4), 321-330.

Parmalee, P. W., & Bogan, A. E. (1998). Freshwater mussels of Tennessee. University of Tennessee Press.

Poff, N. L., Palmer, M. A., Angermeier, P. L., Vadas, R. L., Hakenkamp, C. C., Bely, A., & Martin, A. P. (1993). Size structure of the metazoan community in a Piedmont stream. Oecologia, 95(2), 202-209.

Walters, D. M., Freeman, M. C., Leigh, D. S., Freeman, B. J., & Pringle, C. M. (2005). Urbanization effects on fishes and habitat quality in a southern Piedmont river basin. In American Fisheries Society Symposium (Vol. 47, pp. 69-85).

Wetzel, R. G. (1975). Limnology. [Textbook].

Williams, J. D., Warren Jr, M. L., Cummings, K. S., Harris, J. L., & Neves, R. J. (1993). Conservation status of freshwater mussels of the United States and Canada. Fisheries, 18(9), 6-22.

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