Date of Award

Spring 2025

Project Type

Thesis

Program or Major

Biological Sciences

Degree Name

Master of Science

First Advisor

Brittany Jellison

Second Advisor

Elizabeth Harvey

Abstract

Oysters are known to provide ecosystem services such as improving water quality, and providing habitats to other organisms, in addition to their role as economically important organisms. Many of these services are tied to the gaping behavior oysters exhibit, opening their shells to filter water and grow. Oysters are known to be impacted by many biological and abiotic factors, including predators, biofouling, and handing stressors. Past work has investigated oyster mortality and growth relating to predation and implementation of different cage and bag cleaning frequencies on farms. However, there is limited research regarding how oyster gaping behavior changes in relation to long term exposure to these components. To further investigate influences to gaping behavior, we exposed oysters to non-lethal predator cues and various aquaculture bag cleaning implementations and flow restrictions. I expected to find significant relationships between gaping and predator presence and relationships with various flow rates and cleaning durations. In the chapter 1 experiment, I exposed eastern oysters (Crassostrea virginica) to three levels of non-lethal green crab cues: no crab cue, olfactory: exposure to crab scent, and tactile: exposure to physical interaction with crabs. Although treatment alone did not significantly change gaping there was significant difference between treatments when accounting for diurnal cycle and date of experiment. Oysters spent the greatest amount of time open in the tactile treatment suggesting that when protected from consumption crab presence leads to increased gaping. Farmed oysters are protected from consumption but they have to contend with cleaning stresses and biofouling competition. To assess cage related influences, I studied the impacts of bag cleaning and flow restriction on eastern oyster gaping behavior. We found that cleaning frequency (daily, bi-monthly, never) altered behavior, with oysters in bags that were never cleaned spending an average 9.9% more time open per day than those cleaned daily. We found no significant differences in gaping to flow restriction treatments. In both the cleaning and flow restriction experiments I found significant effect of experiment day on oyster gaping behavior. In the cleaning experiment, all oysters regardless of treatment experienced an average decline of 38% proportion of time spent open per day. In the flow restriction experiment all oysters experienced an average increase of 13.1% proportion of time spent open per day. From these two chapters we conclude that stimuli from predators and cleaning frequency influence oyster gaping behavior. These results are important for informing oyster restoration groups and oyster aquaculturists on the impacts oysters are experiencing outside of water quality and seasonal shifts. The influences seen in these studies can inform farmers and restoration groups alike on how oyster health may change with increased populations of green crabs and reduction in cleaning when not experiencing substantial biofouling. Understanding behavioral responses in oysters could provide wider knowledge of the bivalve’s health along with ecosystem health and sustainability in shellfish aquaculture.

Download

Share

COinS