Mitigation of Negative Effects of Ocean Change on Oysters by Eelgrass and its Implications for Aquaculture in Midcoast Maine

Species interactions are important to organisms and to the ecosystems they inhabit. These interactions, sometimes facilitations, can result in increased resiliency for both species. When facilitation occurs, organisms co-assist with physiological and environmental stressors. As anthropogenic impacts become more stressful for modern organisms, these interactions could offer a solution for many species. Ocean acidification has been shown to be detrimental to many calcifying organisms including oysters. More acidic conditions can slow the process of shell calcification, which can slow growth rates. This effect could directly impact the robust oyster farming business in Midcoast Maine. Because of its possible importance to oyster crops, we assessed the potential of Zostera marina, or eelgrass, to ameliorate the stresses of ocean acidification on farmed Eastern Oysters (Crassotrea virginica). Photosynthesizing organisms such as seagrasses have been shown to locally raise pH, which could create growth refugia for calcifying organisms. While eelgrass has the potential to enhance oyster growth rates, its meadows could also be influencing food availability. To better understand these dynamics, we grew C. virginica in two locations in Harpswell, ME. Crassostrea virginica were split into three habitats at each location: seagrass, fringe, and mudflat, and placed on surface or benthic arrays. We found that seagrass presence and depth interacted to increase shell growth rate. Similarly, Z. marina improved condition index of C. virginica. As ocean acidification worsens, oyster farmers might have to turn to mitigation strategies to ensure profit yield from their labors. Zostera marina could be the solution to their future problems.