Dating clams to study pollution history on St. Croix, US Virgin Islands

By Stephen Durham

Underwater seagrass meadows are disappearing fast, Dr. Kelsey Feser investigates why with the support of the Paleontological Research Institution (PRI). 

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Dr. Kelsey Feser

The Paleontological Research Institution (PRI) in Ithaca, New York, USA is currently running a campaign to support its new dating laboratory.  Before you jump to conclusions, this is not a lab taking the likes of tinder to a new scientific level, it is a lab for gauging the ages of biominerals such as seashells and bones using a technique known as amino acid racemization (AAR) geochronology (for info on how this works see PRI’s project page).  The dating of biominerals and seashells has many applications in research. Fields such as paleontology, tectonics and marine conservation all benefit from accurate dating methods that can help scientists put their samples in temporal context and form a clearer understanding of what has been going on over a period of time.

We spoke with Dr. Kelsey Feser, a paleontologist from Cornell College in Iowa, USA, who is visiting PRI’s AAR lab to date seashells from St Croix, U.S. Virgin Islands. Dr. Feser collected the shells from sediment cores and is using them to investigate the history of seagrass meadows that are threatened by pollution.  During her visit to Ithaca, we took the opportunity to ask her a few questions about her research and why AAR dating is an important tool for her project…

How did you collect the seashell samples and what can they tell us about human impacts on the spectacular marine environments of St. Croix?

I collected the seashells by digging sediment cores while SCUBA diving in shallow seagrass meadows just off the coast.  The cores were 40cm deep, and contained all of the sand and seashells that have accumulated on the seafloor for hundreds, or even thousands of years.  By picking out the shells of thousands of clams and snails from several depths in the cores we were able to construct a record of how the abundances of these animals have changed over time. 

Dr. Feser coring a seagrass bed in St. Croix

Dr. Feser coring a seagrass bed in St. Croix

Clams and snails are very sensitive to environmental changes, particularly those imparted by human activity, so through this research we hope to determine whether the population changes we found were  caused by nearby sources of pollution.

The sorts of pollution sources that we think could be impacting marine clams and snails in St. Croix include runoff during heavy rains and contamination from a power plant and a large, unregulated dump.

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Human impacts on the coast of St. Croix are not hard to find—Dr. Feser photographed this decaying barge not far from the island’s main power plant.

Why is AAR dating important for your research on St. Croix? What do you hope to learn from the data you are collecting at PRI?

I’ve been working in St. Croix for six years, and the question that keeps popping up is “how old are these shells?”  And it’s not a trivial question.  I am interested in the effects of human impacts on populations of marine clams and snails through time, so it is incredibly important to know how recently these population changes took place.  If they happened 5,000 years ago, humans were likely not the cause!  By sampling in seagrass beds, where a thick root mat anchors the sand and prevents it from getting mixed up by waves, we are hoping to find that the deeper the shells are buried, the older they are. 

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The clam shells being dated are tiny—smaller than a fingernail!

This would help us better interpret the changes we see in clam and snail populations through our cores.  By collecting lots of shell ages throughout a given core, we can answer this question. 

Finally, we want to know how long-lived seagrass beds are through time; this is especially pressing given the alarming declines in seagrass meadows around the world. 

By combining our knowledge of change in seagrass-indicating mollusks, and the ages represented through the core, we can determine over what timescales seagrass beds have remained stable around St. Croix and hopefully improve our understanding of what the human impacts on these ecosystems have been over time. The results of this research could have important implications for the conservation of other types of marine life that rely on seagrass, such as sea turtles. 

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A sea turtle foraging in seagrass, a habitat which, sadly, is in decline worldwide

 AAR is the best option for me because I can date far more shells than I could using a more expensive technique like radiocarbon dating, and quantity is crucial for answering these questions

What have been the benefits of running your samples at PRI?

I was thrilled when I found out PRI was getting an AAR lab! By visiting the PRI lab, I have learned the AAR process first-hand and am processing my own samples. This has provided me with invaluable insight into the steps required to date a shell and has also brought down the cost of sample processing considerably. I also was able to bring along one of my undergraduate students, John Lewis, who is participating in a faculty-student summer research program with me. Neither of us could have gained this “insider’s insight” had we elected to mail our samples to a lab to have them run for us. Additionally, working with PRI researchers like Greg Dietl and Steve Durham has been valuable and hopefully will lead to new collaborations beyond my short stay here in Ithaca.

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Dr. Feser and her undergraduate student, John Lewis, at work in the AAR lab last week

A big thanks to Kelsey for answering our questions. You can learn more about her research on St. Croix in the video below.

Please support our campaign to fund the AAR lab at PRI so that we can continue contributing to important projects by researchers like Dr. Feser!

You can also help us by spread the word about the project! Share on Facebook or tweet about it! 

 

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