Rack n’ Roll: Assessing the effects of acute and chronic mechanical agitation on farmed eastern oysters (Crassostrea virginica)

Abstract

Oyster aquaculture is economically and ecologically important across much of the Southeastern United States, but unusual summer mass-mortality events are threatening farmer livelihoods and reducing water filtration through the death of oyster crops. Prior research indicates that oysters are negatively impacted by mechanical stress on both acute and chronic time scales, as evidenced by hormonal changes and increases in mortality. Exposure to these forces are tied to farming practices such as tumbling on the acute level and to culture gear selection and site-specific wave action on the chronic level. However, the specific mechanisms and impact of these forces on oyster health and mortality have not been studied directly. In order to investigate how oysters respond to mechanical disturbance on both acute and chronic time scales, I performed a series of field and laboratory experiments on triploid eastern oysters (Crassostrea virginica) in coastal North Carolina. Eastern oysters were found to experience increased mortality when exposed to excessive mechanical stresses on both acute (hours-days) and chronic (weeks-months) timescales. Acute mechanical stress was found to be associated with increased expression of the interferon-induced protein 44 (IFI44) and interleukin 17 (IL17) genes. Fixed aquaculture gear is shown to reduce chronic oyster G-force exposure, but only at sites with high ambient wave action. This study suggests that sites with abnormally high wave energy, as well as culture practices that expose oysters to high levels of agitation, can trigger stress pathways and potentially leading to reduced growth and performance. Replacing floating aquaculture gear with fixed gear at high-energy farm sites may improve oyster resilience in these locations by limiting exposure to mechanical stress.