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.

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Bentic Macroinvertebrates

Does the title of this post sound like Greek to you? Simply put, benthic macroinvertebrates are little tiny bugs that live in our waterways, but you are able to see them with your naked eye. They are often the larvae of insects that we are more familiar with like blackflies, mayflies, and more! While ponds and lakes do have some, there is a higher number of species found in running waterways. And they can actually tell you a lot about the water that they live in! Many agencies use them as a measure of water quality. In a nutshell, some species are more tolerant of pollution than others. So you collect insects for a certain amount of time, count how many are pollution tolerant, pollution sensitive and pollution intolerant, and then do some easy math! You can also calculate what is called an EPT index. This is based on how many mayflies (Ephemeroptera), stoneflies (Plecoptera), and caddisflies (Trichoptera). This is great if you have a stream running on your property and want to know more about its health.

Because there are so many species, typically macroinvertebrates are broken down into families or orders. A dichotomous key is very helpful in their identification. In West Virgina alone, there are 538 species that the state has identified! This level of identification is hard without breaking out a microscope. In high school, I volunteered with a stream team that was partnered with a local university. We would go out and collect the samples and analyze them. While the EPA does have an SOP for sampling macroinvertebrates most state agencies have their own SOP which can be found by simply googling XYZ State macroinvertebrate sampling. I’m basing the rest of this information on the Georgia EPD SOP. These SOPs are similar to the EPA’s SOP but are adapted to be more effective based on the eco-region. I will detail how to conduct surveys in a future post but for now, let’s look at the different groups of macroinvertebrates.

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