The Cooperative Institute for Climate, Ocean, and Ecosystem Studies

Greetings! My name is Ryan and I am an Environmental Science major at Virginia Tech. This summer I worked alongside Dr. Craig Norrie in the School of Aquatic and Fishery Sciences and at Baywater Shellfish Farm in the Hood Canal. Our research was focused on assessing whether farmed oyster valve behavior (how much and how often an oyster is open or closed) offered a viable physiological proxy for documenting and comparing heat-related stress across ploidies. That was a lot, so let me explain…

Standard diploid oysters carry two sets of chromosomes and spend their summer reproducing, leaving their meat thin and unappealing to consumers. Conversely, triploid oysters that are bred with an extra set of chromosomes skip reproduction entirely. This makes them plump and market-ready when regular oysters aren’t. This should be great news for farmers, but summer is also when the water gets hottest, and triploid oysters seem to be much more vulnerable to heat-related die-offs than diploid oysters. The exact window when they’re most valuable is also the time when they’re most likely to die.

We wanted to find a warning sign that farmers could watch for. Oysters open and close their shells constantly to eat, breathe, and keep their body chemistry balanced. So, we looked at how the opening-and-closing behavior changes when both oyster ploidies are struggling, and whether farmers could ultimately use this data as an early alert that their stock is at risk before a die-off happens.

In order to do this, we spent a few days every low tide cycle in the field attaching and deploying sensors on both diploid and triploid oysters in the tidal zone. We also used environmental sensors to collect information on a myriad of variables. Back in the lab, we compared changes in these variables (temperature, salinity, dissolved oxygen) to changes in whether the oysters were opened or closed to see if there was any association. Additionally, we compared the times that diploid oysters were opened to the times that triploid oysters were open to see if valve behavior was a good way to track differences in the ways they experience heat stress.

We found that differences in ploidy did not offer a solid explanation for any variation in valve behavior. It is important to emphasize that the key takeaway here isn’t that diploid and triploid oysters don’t experience varying degrees of temperature stress, it is that valve behavior does not sufficiently capture the difference. Hopefully in the future, we will be able to identify a more informative behavior metric for quantifying oyster stress.

Project Introduction

Research Poster