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

Jannine Danielle 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 maintaining stock through freezing winters. To avoid leaving oysters exposed to variable field conditions, many farmers overwinter oysters outside of the water in cold-dry storage (CDS). Here, we sought to add to the limited but growing empirical research examining the effectiveness of CDS and factors contributing to oyster survival (i.e., size and storage orientation). 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 4.6 ºC and 81.8% humidity for four months (Nov – Mar). To gain insight into oyster physiology during CDS and the transitions in and out of storage, we monitored oyster cardiac activity over the course of the experiment. While oyster mortality was monitored throughout the storage period, it was not observed until oysters were re-immersed in seawater at the end of the experiment. We found high survival in CDS (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. 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.