Oysters may offer insight into environmental threats

Over the last two decades, mangrove habitats have seen a loss of 35% of their area due to global climate change. This is more than the losses that have been observed for coral reefs and tropical forests.

In an effort to illuminate the mechanisms that underlie environmental responses to climatic changes in mangrove ecosystems, students working in the Environmental Epigenetics Laboratory took to the ocean for some field work. Victoria Suarez-Ulloa and Michelot Michel, under the guidance of Dr. Jose Eirin-Lopez, explored North Biscayne Bay and collected samples from flat tree oysters to assess stress exposure.

Man in water holding oyster

Flat tree oysters are an important sentinel species for monitoring mangrove health. The oysters can provide advance warning for potential health risks in the water. The researchers analyzed DNA methylation in oyster samples taken from different sites across the bay. Methylation can modify the function and activity of genes without altering the actual DNA sequence. 

“If we can establish a molecular baseline of DNA methylation patterns across time, then later on this data could be used to develop some type of biomonitoring tool. Theoretically, the oysters’ methylation profile would be altered because of a specific pollutant. Having this information can alert us as to what might be in our water. Knowing this is important for the oysters, of course, but it’s also really important for the environment they live in,” Michel explained. 

Ulloa and Michel’s study is the first to observe DNA methylation over time and across different locations. They sampled five adult oysters over a period of two years every couple of months and at six different sites in the bay, collecting more than 350 samples. The samples gave a glimpse of seasonal patterns and location-based changes that the oysters are experiencing.

“We can’t yet make definitive links to different events, like red tides or hurricanes, but now that we have an idea of what things look like over time and space, we can begin to understand seasonal patterns and how to attribute them to different things. Looking for seasonal variations, like weather, temperature and salinity (which are abiotic factors that change with the seasons) did show us differences in gene expression,” said Michel. 

The changes that the researchers observed in the oysters can eventually act as a solid baseline for expectations in terms of “normal” patterns and variations. Using this foundation, further research can now be done to identify unexpected changes in genetic makeup, which could eventually lead to a method for monitoring disaster or pollution events in our oceans.

If researchers can tell that a specific event or pollutant leads to a specific change in the oysters’ DNA, then they can alert experts and the public about such an activity and begin addressing it immediately and preventing any potential damage associated with it. 

This research was published in the Journal of Shellfish Research in April. The full paper can be found here.