Category: Fellowship

I am Valeria Ensenat Rivera, an undergraduate researcher in the freshwater lab at Georgia Southern University and I am studying population genetics of crayfish native to south Georgia. Crayfish are also known as crawfish or crawdads, and they are invertebrate crustaceans that spend their lives at the bottom of lakes, rivers, and streams, eating just about anything they can get their claws on. Crayfish are also a vital part of the food web providing a tasty snack for birds, raccoons, fish, otters, and are delicious in a low country boil.    

The state of Georgia ranks fourth in crayfish diversity in the country, with more than 70 different species, and I am interested in deciphering how those species are related. One characteristic of crayfish is that they all look very similar to one another, and even experts can have difficulty identifying them and telling species apart. To solve this problem, I am using their DNA to determine the species and see what other information their genetics can tell us.

The Ogeechee crayfish, or Procambarus petersi, is one of the crayfish species that has only been found in the Ogeechee River and other nearby waterways.Not a lot is known about the Ogeechee crayfish due to limited population counts and the small area in which they historically have been found. Surprisingly, we were able to obtain one individual from the Canoochee River.

How can you really know that you actually have the Ogeechee crayfish in your hands, when there are so many crayfish that look similar?  I extracted DNA from this individual crayfish (which was named Eleven, like in Stranger Things) and compared it with the DNA of all of the other crayfish samples in our collection. 

The DNA from this Ogeechee crayfish was different from the other ones, but that was not the surprising part. Rather, the species was “nested” inside the population of Procambarus spiculifer, or the white tubercled crayfish. The white tubercled crayfish is found more commonly than the Ogeechee crayfish, having populations all along Georgia, Florida, and Alabama. 

Southern Georgia, the Ogeechee River, and other nearby river basins, may have more crayfish species than originally thought, and many of those species could be in danger of going extinct. It is important to obtain more information about them in order to conserve species diversity and protect the beautiful waterways of Georgia.

What kinds of crayfish might you expect to find in the Ogeechee?  With so much aquatic diversity in the basin, what you might see in the upper part of the basin can be completely different from what you might see near the coast. That’s because, even though the river is well connected from top to bottom, the habitats found in the upper part of the basin are completely different from the coastal habitats.

The headwaters of the Ogeechee form on the far extent of the Piedmont (the geographic region separating the coastal plain from the Appalachian mountains) making for clearer and swifter flowing water. But as the Ogeechee slowly snakes its way towards the coast, the water starts to move slower and slower, becoming much darker due to the leaching of tannins. Understandably, these stark differences result in differing crayfish fauna.

In the upper part of the basin, the Variable crayfish (Cambarus latimanus) and the Brushnose crayfish (Procambarus pubsecens) are two commonly found species that are strongly associated with this part of the basin, and are rarely if ever found downstream of Millen, Georgia. The Variable crayfish is one of only a couple of species within the genus Cambarus found within the Ogeechee basin, with the vast majority of other species belonging to the genus Procambarus. This is because, in general, Cambarus species are strongly associated with more rocky streams, like those found in the Piedmont. The Brushnose Crayfish is very similar to other Procambarus species found throughout the basin, with the namesake difference being dense hairs along the rostrum (nose area) of the crayfish.

Some species that can be found in both the upper and lower sections of the basin are the Ogeechee crayfish (Procambarus petersi), Blackwater crayfish (Procambarus litosternum) and Red Swamp crayfish (Procambarus troglodytes). The Ogeechee crayfish, though not common, can be found from the headwaters almost to Savannah. The Blackwater crayfish is incredibly common, and can be found in small streams all over. Chances are, if you’ve seen a small crayfish poking around in a stream in the basin, it was a Blackwater crayfish. The Red Swamp crayfish is one most people are familiar with – it is what people commonly catch for food, and they are easily distinguishable by their large, tubercle-covered red claws.

Lastly, you might see as the Ogeechee is flowing into the ocean would be the Hummock crayfish (Procambarus lunzi), and the Christmas Tree crayfish (Procambarus pygmaeus). Both of these species are more associated with slower, stagnant water; but the Christmas Tree crayfish has one particularly interesting adaptation. The bright colors of the Christmas Tree crayfish are thought to be used as camouflage, as it is almost always found in dense mats of lush aquatic vegetation. 

Hopefully this brief introduction to some of the crayfish found within our basin encourages you to get out and explore some of the novelties that make this basin a special place!

(All photos courtesy of Chris Lukhaup and Chris Skelton)