The effectiveness of overwintering Eastern oysters (Crassostrea virginica) in cold-dry storage

Jannine D Chamorro , Josephine C DeMerit, Andrew R Villeneuve, Selina L Cheng, Kaila J Frazer, Joseph A Rankin, Brittany M Jellison, Easton R White 

In the northernmost part of the Eastern oyster (Crassostrea virginica) range, oyster farmers face challenges of maintaining stock through freezing winters. To avoid exposing oysters to variable field conditions, many farmers overwinter oysters out of the water in cold-dry storage (CDS). Using two iterative experiments conducted over consecutive winters, we sought to add to the limited but growing empirical research on the effectiveness of CDS and factors contributing to oyster survival (i.e., size, storage orientation, and storage duration). Oysters were sourced from a local farm in the Great Bay Estuary (New Hampshire, United States) and overwintered in a temperature- and humidity-controlled chamber held at ~4.8 ºC and 82% humidity. In Experiment 1, we evaluated how oyster size and storage orientation influenced survival. To gain insight into oyster physiology during CDS and the transitions in and out of storage, we also monitored oyster cardiac activity over the course of the experiment. Mortality was not observed until oysters were re-immersed in seawater at the end of the experiment, despite monitoring during storage. We found high short-term survival (86.5%), with no significant impact of size or storage orientation.  Oyster heart rate decreased with time spent in CDS, with a periodic heartbeat becoming undetectable five weeks into CDS in live oysters. Building on findings from the first year’s study, our objective for Experiment 2 was to determine if the amount of time spent in CDS impacted long-term survival in the field. We did so by examining the survival of oysters redeployed into the field at staggered dates. Here, we found that oyster mortality increased with time held in CDS. Together, these findings advance our empirical understanding of oyster survival in CDS, offering farmers practical guidance for overwintering strategies while raising informed questions about the physiological processes that govern survival and determine optimal CDS in the Northeast.