A Quest to Uncover the Extinction Event that Wiped Out Endemic Hawaiian Snails

HPU Master of Marine Science graduate student Samantha Arsenault is researching endemic Hawaiian land snails and their extinction event that may have been caused by climate change thousands of years ago. The Pleuropoma laciniosa snail once lived along the shoreline of Kaʻena Point on Oʻahu. The size of a pencil eraser, the once abundant Pleuropoma laciniosa flourished in Hawaiʻi by the millions, but after a climatic event after the Last Glacial Period this endemic land snail became extinct. Now, with innovative research technology at HPU and a new grant from the Society for Integrative and Comparative Biology Arsenault is set to uncover the events that led to the extinction of Pleuropoma laciniosa. 

“Today, Kaʻena Point is a hot, dry environment without many trees, and sparse vegetation. How could these native Hawaiian snails have lived in this very hot and dry environment?” said Arsenault, holding a dozen prehistoric shells in her hand “My hypothesis is Kaʻena Point was not always a very hot and dry environment. Thousands of years ago, it was most likely a forested, verdant habitat.”

Most native Hawaiian land snails can only thrive in forested environments with native vegetation. The snails will eat the microbial community that grows on the leaves. Some species of rare endemic snails can still be found in Hawaiʻi, but they are threatened and can only survive in protected areas with native Hawaiian vegetation. 

There were over 800 individual species of snails in Hawaiʻi, but today there are 80 to 300 species alive due to environmental condition changes, habitat loss, over collection, and invasive predators. There is currently a debate between scientists for the true number of remaining species.   

“Several predators eat endemic snails,” said Arsenault. “Rats. Jackson’s Chameleons. Rosy Wolf Snails. They all are introduced species to Hawaiʻi, and they play a role, along with climate change and deforestation, that threaten the remaining snail species.”  

Arsenault will use stable isotope analysis to do radiocarbon dating on the Pleuropoma laciniosa. “There is Carbon-12, the rarer Carbon-13, and Carbon-14, which is radioactive,” said Arsenault. “This is the method used to do radiocarbon dating. Carbon-14 decays at a steady rate at 5,730 years, so you can look at the amount of Carbon-14 in a remaining organism and date how long ago that organism lived.” 

Preliminary radiocarbon analysis was completed on six shells at the Lawrence Livermore National Laboratory. The analysis indicated the snails lived at Kaʻena Point between 30,000 to 46,000 years ago. 

Arsenault also plans to use Carbon-13 analysis to uncover the variety of vegetation that lived at Kaʻena Point when the snails flourished. 

“Plants go through many methods of photosynthesis,” said Arsenault. “There are C3 plants and C4 plants. C3 plants live in wet, cool environments; C4 plants live in hot and dry environments, like Kaʻena Point. When looking at Carbon-13 in an organism, we can tell if an animal was living off C3 or C4 plants, which in turn will tell us whether the environment was cool and wet, or hot and dry.” 

A minimum of 32 shells will be sent to the lab for analysis. Arsenault will look at oxygen isotope data in the snails. This will determine the amount of precipitation an area had at a particular time.  

“In addition to Pleuropoma laciniosa, I will also be examining several species from the genus  Leptachatina, a species from the genus Amastra, as well as a species from the genus Endodonta,” said Arsenault. “These species are undescribed and unfortunately don't have scientific or common names yet. 

“My primary goal is to reconstruct how the environment changed, and how that change affected Hawaiian snail populations. We want to use this information to conserve current populations. We do not want to see a repeat of what we saw at Kaʻena Point. I hope to get all the data back from the lab this summer to reconstruct exactly what happened to the Hawaiian land snails and what the climate was like thousands of years ago.”