Crayfish and DNA

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.

Procambaru petersi, Photo by Chris Lukhaup

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.

RELEASE: Applications For $25,000 Fellowship At Ogeechee Riverkeeper Open

09/14/2022
Ogeechee Riverkeeper
Contact: Meaghan Gerard
Communications and Administrative Director
meaghan@ogeecheeriverkeeper.org

APPLICATIONS FOR $25,000 FELLOWSHIP AT OGEECHEE RIVERKEEPER OPEN
The annual fellowship provides research opportunities in the watershed

Ogeechee Riverkeeper (ORK) is accepting applications for the annual research fellowship through October 15, 2022. The fellowship, which runs through the 2023 calendar year, is designed to support research activities for graduate students conducting work in the Ogeechee River Basin as part of their degree program. The $25,000 fellowship will be awarded to a single student. 

“Research is important to our mission to protect the waterways in our basin,” said Damon Mullis, executive director and riverkeeper of ORK. “This fellowship will spur more interest in our basin and result in more academic research projects.”

In January 2022, ORK launched a new research fellowship to be filled each year. The 2022 fellowship focused on different native crayfish species, including Procambarus petersi, an endemic species commonly called the Ogeechee Crayfish. The fellowship is underwritten by investments secured from the 2011 fish kill settlement. 

Students can find guidelines and application details at ogeecheeriverkeeper.org/fellowship.

About Ogeechee Riverkeeper: Ogeechee Riverkeeper 501(c)(3) works to protect, preserve, and improve the water quality of the Ogeechee River basin, which includes all of the streams flowing out to Ossabaw Sound and St. Catherine’s Sound. The Canoochee River is about 108 miles long and the Ogeechee River itself is approximately 245 miles long. The Ogeechee River system drains more than 5,500 square miles across 21 counties in Georgia. More at ogeecheeriverkeeper.org.

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ORK at Joint Aquatic Sciences Meeting

The Grand River in downtown Grand Rapids, just outside of the convention center

This past week, Dr. Checo Colon-Gaud’s research lab and I were able to attend the Joint Aquatic Sciences Meeting (JASM) in Grand Rapids, Michigan, to share our research with the broader scientific community!

Scientific conferences are one of the best ways for scientists to connect with the larger research community to enhance and spread our research impact. JASM was certainly no exception, as it is the premier aquatic sciences conference in the world. In addition to seeing lots of fascinating talks in our field and great conversations with colleagues, I was able to share a poster presentation on the research efforts that we have been conducting on crayfish of the Ogeechee basin.

Brian presents his research poster on crayfishes of the Ogeechee basin.

Lots of people walked by my poster and talked with me about their experiences working with crayfish and coastal plains organisms, and I certainly think I learned immensely from conversations with other scientists I interacted with. Certainly the most common comment on my research was related to how little we know about crayfish of the coastal plains.

Moving forward from this amazing experience, I hope to utilize the knowledge I gained as well as the connections I forged to help me tackle my research in the best way possible. This is not only done by using the best methods or researching the most important topic, but also by collaborating with a diverse group of scientists and the broader public to have the most prominent impact.

The next big aquatic sciences meeting is in Australia next summer, so we’re already looking forward to expanding our connections on a global scale!

What kinds of crayfish might you expect to find in the Ogeechee?

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.

Procambarus pygmaeus

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.

Cambarus latimanus

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.

Procambarus troglodytes

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)

Why should we care about freshwater organisms?

Why should we care about freshwater organisms? This is an incredibly common question directed towards freshwater ecologists like myself, and it’s completely valid. Why spend all the time and effort to study things that appear to have little to no impact on human welfare? While the ultimate answer to this question is nuanced, one of the most important reasons why we as scientists care about them is their use as bioindicators.

The concept of a bioindicator is fairly straightforward, generally referring to the use of a living thing (bio-) as an indicator for the health of the ecosystem it lives in. For example, let’s say that there’s a rare crayfish species that is known to only occur in pristine habitat with very clean water, and has no tolerance for pollution of any kind. Therefore, if that species is found, scientists can use it as evidence that the stream it was found in is very healthy. On the flip side, if the only species that are found in a specific stream are fairly common and can tolerate a large range of conditions, then these species might indicate that that stream has poor water quality.

Female Red Swamp Crayfish from 15 Mile Creek, with young on the abdomen. Image by Ray Chandler.

Beyond being good “tools” for humans to assess the health of our ecosystems, different freshwater organisms serve distinct purposes in the aquatic food web. This is especially true of crayfishes, which are commonly viewed as “keystone” species. A keystone species is one that performs such an important role in an ecosystem that without it, there would be a large-scale detrimental effect on the rest of the ecosystem.

The crayfish is a keystone species for a variety of reasons. Firstly, crayfish are omnivorous, eating all kinds of different things in stream ecosystems, from other smaller insects to plant matter. Secondly, crayfish are important food sources for larger predators, like sport fish and amphibians. This combination of  eating and being eaten by so many different things make crayfish an integral part of aquatic food webs. 

Thirdly, crayfish act as “ecosystem engineers” through the creation of burrows. Many of you may be familiar with crayfish burrows that you see on land (check out this article), but what many people don’t realize is that all crayfish burrow to some extent. In stream ecosystems, these underwater burrows act as key habitat for other freshwater organisms, and therefore harbor the diversity of life that is important for healthy streams.

A crayfish burrow found in the field in southern Georgia.

With spring already in full swing, I’m sure many of you will be seeing crayfish a lot more often, and I’m excited to write more about what you may see out in the watershed.