Title: Water quality parameters and total aerobic bacterial and vibrionaceae loads in eastern oysters (Crassostrea virginica) from oyster gardening sites Authors
|Fay, Johnna -|
|Ozbay, Gulnihal -|
Submitted to: Archives of Environmental Contamination and Toxicology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 25, 2011
Publication Date: January 1, 2012
Citation: Fay, J., Richards, G.P., Ozbay, G. 2012. Water quality parameters and total aerobic bacterial and vibirionaceae loads in eastern oysters (crassostrea virginica) from oyster gardening sites. Archives of Environmental Contamination and Toxicology. 64:628-637. Interpretive Summary: Oyster gardening is a method to restore water quality and marine habitat utilizing floating aquaculture baskets to grow oysters along coasts and estuaries. These gardens provide habitat for fishes and shellfish as well as improving water quality through increased filtration. Oyster gardening efforts have improved waters in areas such as the Chesapeake Bay and may be essential in restoring shellfish habitat in other areas. This study investigated the relationship between water quality, total bacteria, and Vibrio concentrations in Eastern oysters (Crassostrea virginica) located at two oyster gardening sites in the Delaware Inland Bays. One site was located at the end of a man-made canal and experienced low levels of flushing, whereas the other was located in an open location within Little Assawoman Bay and experienced high levels of flushing. Measured water quality parameters included temperature, dissolved oxygen, salinity, pH, total nitrogen, nitrate, nitrite, total phosphorus, and total suspended solids. A method developed by the USDA’s Agricultural Research Service, known as the colony overlay procedure for peptidases or COPP assay for short, was used to determine the total count of vibrios in the oysters. Total bacteria and Vibrio levels increased over the summer months at both sites. Total phosphorus levels consistently exceeded State-recommended levels at both sites while dissolved oxygen levels were below the state-recommended thresholds for attaining healthy aquatic life in marine waters for four out of the five sampling months at the canal site. Nitrogen levels occasionally exceeded the state’s recommendation at both sites. Overall, we conclude that the waters at the Bay and Canal sites are degraded in regard to high phosphorous, nitrogen, and total suspended solids as well as from low dissolved oxygen levels. Because the Delaware Inland Bays are subjected to high nutrient inputs from agricultural practices, they are at risk for algal blooms and possible Vibrio blooms. Additional monitoring of total Vibrio levels is needed to expand the database and to identify changes in Vibrio populations over time. It was previously proposed that total Vibrio levels, as detected by the COPP assay, may serve a regulatory role for monitoring the safety of shellfish growing areas. The information obtained from this study contributes to the development of a predictive index for when conditions are favorable for vibrio outgrowth.
Technical Abstract: Oyster gardening is a practice designed to restore habitat for marine life and to improve water quality. This study determined physical and chemical water quality parameters at two oyster gardening sites in the Delaware Inland Bays and compared them with total aerobic bacteria and Vibrionaceae concentrations in Eastern oysters (Crassostrea virginica). One site was located at the end of a man-made canal, whereas the other was located in an open bay. Measured water parameters included temperature, dissolved oxygen (DO), salinity, pH, total nitrogen, nitrate, nitrite, total phosphorus, and total suspended solids. The highest Vibrionaceae levels, as determined by the colony overlay procedure for peptidases, were at the Canal site in September (3.5 x 10e5/g) and at the Bay site in August (1.9 x 10e5/g). Vibrionaceae levels were significantly higher over the duration of the study at the Canal site (P = 0.01). This study provides the first baseline levels for total Vibrionaceae in the Delaware Inland Bays. Minimum DO readings at the Bay and Canal sites were 3.0 and 2.3 mg/liter, respectively, far less than the state-targeted minimum threshold of 5.0 mg/liter. Total phosphorus levels exceeded recommendations of less than or equal to 0.1 mg/liter at the Bay and Canal sites for all monthly samplings, with mean monthly highs at both sites greater than or equal to 0.68 mg/liter in August. Nitrogen occasionally exceeded the recommended level of 1.0 mg/liter at both sites. Overall, waters were highly degraded from high phosphates, nitrogen, and total suspended solids, and from low DO.