|An Island of Green from Space: Savannah River Nat'l Laboratory is just right of center, a circle of green forest surrounded by agriculture and suburban development. (from Google Maps)|
|Upper Three Runs Creek and Tributaries. The four sampling sites marked are the same as the previous study, all of them located downstream from a bridge crossing. (from Google Maps)|
|Site A, Upper Three Runs Creek, looking downstream. No rocks, but plenty of woody debris and aquatic plants.|
|Upstream, at Site B. Those rocks are part of the bridge stabilization structure and are not naturally occurring.|
In Fall of 2008, I had the opportunity to see for myself. My adviser, Dr. Morse, was contacted by Dr. J Vaun McArthur of Savannah River Ecology lab about a repeat of the 1978 survey. In particular, they were interested in adult caddisfly diversity. I had plenty of prior experience identifying the larvae, but almost none identifying the adults, so I knew this would be a particularly challenging project. In the previous survey and subsequent work, nearly ~160 species were found at these locations, some of which were new to science. We were also hoping to have a more complete sampling regime, with traps running at all four locations for the entire year. Since SRS is a high security government facility with high safety standards, we had to plan ahead for each of the collecting trips and could not stay with the traps overnight.
|Rube Goldberg Setup at Site A. This was taken in March, thus the early spring plant growth. By May they were as tall as the umbrella.|
|Less Rube Goldberg: This trap was under a bridge so it didn't need an umbrella.|
When I returned from a collecting trip, I would sort the caddisflies out the samples.
I also picked out a goodly portion of the other orders of aquatic insects for identification at some point down the line.
|A Really Good Day: This was the best (worst?) sample I ever sorted, and this is only the caddisflies, some of which had already been removed.|
|Oodles of Caddis: There are at least 7 genera in this shot, probably twice that number. Everything in view is less than 15 mm in length, most around 10.|
|Largest and Smallest: Hydatophylax argus, the largest caddisfly in North America, and Neotrichia falca, one of the smallest. Note: H. argus is not found in Upper Three Runs Creek.|
Despite the previous work, I was finding species not previously known from Upper Three Runs. But it wasn't until I saw these guys that I was stumped.
|Males of the mystery caddis, now known to be Oecetis parva Banks. Individuals are ~5 mm.|
Or...they sort of matched.
The first law of Biology is "variation exists". This is something every taxonomist must keep in mind during his or her work, or enter the folly of unnecessary junior synonyms. My specimens had the same general look, the same clasper shape, the same size and color, but there was something off about the tenth tergite. This part of male caddisfly genitalia is the last dorsal plate of the abdomen, often modified into various shapes. The shape of the male genitalia fits that of the female like a key in a lock, and it's thought this is one of the reasons there are so many species of insects.
|Left lateral view of O. parva male genitalia. Between the pad with hairs near the top is a long finger projection, and under that a pair of mebraneous hooks. Insect reproductive parts are complicated.|
There was also another issue with Oecetis parva. The only places this species was known from were 14 sites in Florida and the southern tip of Alabama. It was thought to be a far southeastern endemic, found only in forest pools. Aiken SC was two hundred miles outside its known range.
But as I sent for specimens from the Florida State Arthropod Collection, I soon found out my excitement was hubris. Variation exists, and there was variation in the Florida and Alabama specimens as well. Nothing quite as extreme, but intermediates between the reduced and elongate finger of the tenth tergite. Needless to say, I was a little crushed. This would have been my first species discovery.
There were still some interesting issues. Namely, why was Oecetis parva found so far outside of it's known range? And why was it found now, and not in the previous survey? Talking to other southeastern Trichopterists, I learned that O. parva had been collected recently at two other new sites, one in Georgia, and another near Columbia, South Carolina. So Dr Morse, Dr. McArthur, and I decided to publish this new information. This included new illustrations, of the variation seen in males from South Carolina, and of the female genitalia, which had not been previously illustrated.
|More genitalia. These are, however, much prettier, as this was after I learned how to use a vector image program. (Burington et al 2011)|
Recently, I gave a presentation on my master's research, including a segment on Upper Three Runs Creek and it's diversity. I was looking at my range map for Oecetis parva, and a little hypothesis started to form, and over a few days it got bigger and bigger, until I felt like I had to share it. So, please allow me a little speculation.
|Range map of Oecetis parva. Gray dots are those localities known previously. Black dots are new records. Red dot indicates unpublished previously unknown locality. Modified from Burington et al 2011|
So, back to the big question: Why Savannah River Site? Why the massive diversity at Upper Three Runs Creek? Savannah River Site is known locally as the "bomb shop", because it was used for weapons grade plutonium manufacture during World War II and the Cold War. During presentations about the original 1976 survey, some wise-cracker would get up and ask "Maybe it's the radiation?" And we laugh at that joke, except, we didn't really know why there was this high diversity just here, not in the surrounding stream systems.
But it now seems that there are few if any true site endemics. Nearly all the species of Upper Three Runs Creek have been found elsewhere, and some of them widely separated, like Cheumatopsyche richardsoni. This suggests an answer, and that is: Yes, Upper Three Runs Creek is a beautiful diverse gem, but it is not unique. The southern pine forests and their stream systems used to stretch in an unbroken chain across the entire sandhills and coastal plain region of the southeast US. This diversity was probably all over the place. When industrial agriculture arrived in the early 20th century, almost all these original forests were plowed into farm fields. And now, this original diversity only remains in a few well managed pockets with protected headwater streams. We could test whether this is isolation or recent dispersal by the methods of population genetics. Unfortunately, I don't have the resources to do this currently.
This also suggests a second idea. When aquatic entomologists and aquatic ecologists just look at blackwater streams like Upper Three Runs Creek, we expect them to be of low diversity. But the natural state of these streams is HIGH diversity, and it's only because of widespread agricultural impacts that we are inclined to think differently. We need to turn the idea of blackwater streams as species poor on it's head. There are species new to science still being found in these pockets, indicative of what was lost and what treasures still are left.
Afterword: This project is in no way finished. Identifications are ongoing, and the material left is huge. I am no longer directly associated with this project and I hope it will be completed. During a recent conversation with Dr. Morse, he told me he was working through a sample from May of our collecting year. So far, that single black light trap sample has yielded over 5000 individuals and 57 different species of caddisflies. I remember that night. That was a good night.
Burington, Z. L., Morse, J. C., & McArthur, J. V. (2011). Distribution and variation of Oecetis parva (Trichoptera: Leptoceridae). Entomological News, 122(1), 100–106. [ed.: unfortunately, this is not open access. Entomological News does not yet have this option, despite being one of the few publications which will publish these sorts of articles.]
Morse, J. C., Chapin, J. W., Herlong, D. D., & Harvey, R. S. (1980). Aquatic insects of upper Three Runs Creek, Savannah River plant, South Carolina. I. Orders other than Diptera. Journal of the Georgia Entomological Society, 15(1), 73-101.