In the past, coastal environmental health has been analyzed through direct measurements of the sediment and the water. However, there is much evidence that certain species may serve as bioindicators, the ecological and morphological properties of which can predict the level of anthropogenic impact. The purpose of this study is to test the feasibility of utilizing Uca pugilator as a bioindicator of anthropogenic impact. In the field, three sites (Reference, Municipal, and Golf Course) were selected in Beaufort, South Carolina as examples of different types and levels of human impact. Crabs were sampled (n = 1164) for carapace width, dominant to subordinate claw ratio (males only), and population density; mating behavior was also observed. In the lab, four mesocosms were set up: one to simulate each impacted field site and one control for each. Carapace width and claw size ratio measurements were made before, during, and after treatments were applied. In the field, carapace width was found to be significantly reduced in the Golf Course crabs (p < 0.001), and these crabs exhibited increased claw wave behavior. The population densities were significantly greater at both affected sites (p < 0.001). The claw size ratios were significantly influenced by site, day, and the interaction of site and day (p = 0.005, 0.008, and 0.002 respectively), but there was no clear pattern in these influences. The mesocosm experiment resulted in no significant differences among crab groups. In conclusion the significant differences among crabs in the field are likely attributed to anthropogenic activity. This study supports the notion that Uca pugilator could be a valuable bioindicator of estuarine health, and shows that population density, carapace widths, and mating behavior of Uca pugilator are influenced by anthropogenic activity. Future studies should use Uca pugilator as a bioindicator of estuarine health.
Hometown: Farragut, Tenn.
Thesis Title: “Fiddler Crabs (Uca pugilator) as Bioindicators of Environmental Health in Coastal Estuarine Communities of Beaufort, South Carolina”
Advisor: Dr. Drew Crain, Professor of Biology
Exactly this time last year, Steven Giblock was starting to enjoy the sand and water of the South Carolina coastline, but he wasn’t on vacation.
Instead of an iPod, he packed a Vernier Caliper.
Instead of sand pails, he took five-gallon buckets.
And instead of a calm spot looking out on the Atlantic Ocean, he chose views of marshland, tidal pools and Spartina grass.
Giblock, then a rising senior at Maryville College, spent a month last summer in and around Beaufort, S.C., collecting data for his Senior Study on the Uca pugilator, which are better known as “sand fiddler crabs.”
When deciding on a topic for his Senior Study last year, Giblock thought he would like to involve marine invertebrates and ecology, since they are two strong interests of his.
“I never decided on a specific topic from the beginning. My topic started with a broad interest for marine invertebrates and with much research on sedimentation, pollution, and crabs,” Giblock explained. “After talking to [Professor of Biology] Dr. Crain for some time, it eventually evolved into what it is.”
What it is today is an exemplary Senior Study focused on the feasibility of utilizing sand fiddler crabs as an indicator of anthropogenic impact.
“Fiddler crabs are a good indicator of environmental quality for at least two reasons,” Giblock explained. “First, they are so reliably found in the salt marshes along the coasts of most continents; secondly, they are found whether or not there is pollution (which allows for impacted and nonimpacted comparisons).”
The undergraduate also felt confident in his topic selection because other studies had reported differences in populations that correlated with pollution.
Approved for funding through a congressional grant administered through the United States Department of Education and the Fund for the Improvement of Post-Secondary Education (FIPSE) program, Giblock received a stipend for two months and money for transportation to South Carolina and the supplies he would need to conduct the research.
The goal of his research was to examine the influence of various human-altered habitats on the morphological measurements, population densities and behaviors of the fiddler crab.
He selected three sites from which to collect, measure and study the crabs. One, the Lemon Island Preserve, served as a reference site because it is virtually undisturbed by human activity. The others – one on Parris Island and one near the Harbor Town Golf Course on Hilton Head Island – served as models of industrial and agricultural impact, respectively.
Would the crabs look different and behave differently because of effluent from a wastewater treatment plant or the presence of insecticides and fertilizers? What data would he need to answer the question?
Collaborating with Crain, his advisor, before he left for South Carolina and while he was in the field, Giblock decided he would compare and contrast the populations of crabs at each site, collecting data specifically on their carapace (the widest point of its chest), differences in males’ dominant and subordinate claw lengths, population densities, and the frequency of the “claw wave,” which the males exhibit to attract a mate. Giblock also collected environmental data to ensure that any differences noted between the crabs at the three sites could not be attributed to temperature, salinity and turbidity.
“Steven and I stayed in contact throughout his study,” Crain said. “Upon his arrival on the South Carolina coast, we would communicate daily, with Steven providing me a daily update and me providing him some guidance for the following day. After Steven had the plots identified and the techniques worked out, we would communicate every few days.
“The distance between us did not inhibit the research at all, mainly a result of Steven’s stellar work ethic and meticulous nature,” he added.
Armed with a Vernier Caliper to do the measurements and a Sharpie pen to distinguish recaptures, Giblock collected approximately 390 crabs at each site for a total of 1,164 crabs.
He said planning the research and organizing the experiments were the biggest challenges for him in the study.
“I am a disorganized person,” he said. “This study certainly stretched my planning skills, as I needed to plan the trip to Beaufort, where I was going to live for that month, where I was going to sample, how I was going to catch the crabs, what equipment I needed, what data to sample from the crabs.
“Additionally, this study stretched my organization skills. I had to keep tabs on five variables for more than 1,000 crabs, so I got organized really fast!”
Crain said he was stretched by Giblock’s focus on invertebrates.
“I normally study vertebrates, so the selection of an invertebrate model organism caused me to learn a great deal about using invertebrates as bioindicators,” the professor said. “This certainly stretched my perspective on sentinel species.”
Giblock’s results from the field yielded significant differences in carapace widths and population densities. The ratio of dominant claw size to subordinate claw size in males was not significantly different at the three sites, but regarding mating behavior, Giblock observed the crabs near the golf course to be much more active than at the other two sites.
But he wasn’t finished. Back at Maryville, Giblock needed to conduct four mesocosm experiments with 203 fiddler crabs to see if he could replicate what he saw in the field by using the chemical agents that he thought were the most likely agents present in pollution.
(Giblock and Crain theorized that nitrogen fertilizer, pesticides and herbicides would be present at the golf course; and BPA and EE2 would be present at the municipal site.)
“Ideally, the mesocosm results would have mirrored the results found in the field, but they did not – most likely because of limitations in scale and length of time,” Giblock said. “It may have yielded superior results if I had one or two years to carry it out rather than a couple of months.”
Both Giblock and Crain expect that other students will want to pick up where the MC senior-now-graduate left off. Future studies could involve water analyses, which would provide useful data. Giblock described his Senior Study as a “foundation” for future studies.
Looking back on his summer in South Carolina, Giblock said he had “a blast.”
“I certainly had a lot of fun with this project, despite the rigor it demanded,” he added. “Dr. Crain was a huge help, and I cannot thank him enough.”
Giblock hopes to become a field biologist and believes that his Senior Study was the “perfect hands-on” experience for showing him what the career would be like.
Crain said he has no doubts about Giblock’s preparation and promise as a field biologist.
“Steven had shown all the signs of a stellar scientist in his coursework at Maryville College, but a successful scientist is able to work through unforeseen obstacles,” the professor pointed out. “Steven worked through many difficulties very well. Examples include estimating populations of crabs during different tidal flows and marking crabs so that recaptures can be documented. Steven’s focus and persistence at overcoming obstacles allowed him to mature as a scientist.”
And whether or not future MC students choose to build on Giblock’s findings, Crain said he believes the Senior Study is worth sharing. He recommended it for presentation at the 2012 Southeastern Ecology and Evolution Conference at Clemson University this past Spring, and he recommended it for Maryville College’s permanent library collection.
“Steven did a stellar job, start to finish,” Crain said. “From generating a novel question to conducting one of the most thorough studies I have seen, Steven Giblock’s Senior Study is the kind of study that all science students should aspire to conduct.”