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Survival and Growth of Eastern Oyster Spat, Crassostrea virginica, when Exposed to Low Salinity for Prolonged Periods with Short Intervals of Recovery at Higher Salinities

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Date Issued:
2020-12-08
Summary:
The Caloosahatchee River and Estuary in Southwest Florida has a history of human driven alterations by dredging, channelization, construction of several lock and dams, and an artificial connection to Lake Okeechobee. Water management has changed the quality and quantity of discharges into the river and the ecological health of the estuary. The artificial connection to Lake Okeechobee sometimes requires large freshwater releases into the Caloosahatchee River. The euryhaline species in the Caloosahatchee River face osmotic challenges from these freshwater inputs. The eastern oyster, Crassostrea virginica, is a keystone species that can provide an indication of estuary response to freshwater inflow and the resulting salinity fluctuations. A valued ecosystem component, the eastern oyster, helps sustain the ecological structure and function of the estuary by providing food, living space, and foraging sites for other estuarine species. Oyster spat, newly settled oysters <25mm, have an optimal salinity range of 15‰ to 22.5‰ and exposure to low salinity levels for long periods of time causes mortality. High temperatures (300C), which occur during the summer and rainy season, have a synergistic effect on low salinity stress. As part of a larger study to investigate how to improve water management to sustain oyster reefs in the Caloosahatchee River while managing the lake levels, this project examined oyster spat survival and growth during exposure to low salinity levels with intermittent recovery periods at higher salinity. This study carried out iterative bioassays to determine the longest duration (i.e., consecutive days) that oysters can be exposed to some minimum salinity (0‰-5‰, where valves will likely remain closed) with the shortest periods of recovery (10‰) to survive and grow. The results of this study clearly show that Crassostrea virginica spat exhibited improved survival rates and growth when given periods of recovery at a tolerable salinity after being stressed by prolonged low salinity conditions both with and without thermal stress. Spat reach greater than 50% survival when stressed at 5‰ for less than seven days and are allowed periods of recovery at a salinity of 10‰ or higher under thermal stress. Without thermal stress 50% survival was observed in spat that were stressed for less than 14 days at a salinity of 5‰ and allowed periods of recovery at a salinity of 10‰ or higher. The longer the recovery period at both 25oC and 30oC, the better the results tended to be in matching or exceeding growth in the negative stress controls held at 25‰. A ≥14-day period of recovery should always be targeted regardless of exposure duration in order to ensure oyster spat growth.
Title: Survival and Growth of Eastern Oyster Spat, Crassostrea virginica, when Exposed to Low Salinity for Prolonged Periods with Short Intervals of Recovery at Higher Salinities.
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Name(s): Hans, Samuel, Author
College of Arts & Sciences, Degree granting institution
Type of Resource: text
Genre: Thesis
Issuance: single unit
Date Issued: 2020-12-08
Extent: 39 pgs.
Language(s): English
Summary: The Caloosahatchee River and Estuary in Southwest Florida has a history of human driven alterations by dredging, channelization, construction of several lock and dams, and an artificial connection to Lake Okeechobee. Water management has changed the quality and quantity of discharges into the river and the ecological health of the estuary. The artificial connection to Lake Okeechobee sometimes requires large freshwater releases into the Caloosahatchee River. The euryhaline species in the Caloosahatchee River face osmotic challenges from these freshwater inputs. The eastern oyster, Crassostrea virginica, is a keystone species that can provide an indication of estuary response to freshwater inflow and the resulting salinity fluctuations. A valued ecosystem component, the eastern oyster, helps sustain the ecological structure and function of the estuary by providing food, living space, and foraging sites for other estuarine species. Oyster spat, newly settled oysters <25mm, have an optimal salinity range of 15‰ to 22.5‰ and exposure to low salinity levels for long periods of time causes mortality. High temperatures (300C), which occur during the summer and rainy season, have a synergistic effect on low salinity stress. As part of a larger study to investigate how to improve water management to sustain oyster reefs in the Caloosahatchee River while managing the lake levels, this project examined oyster spat survival and growth during exposure to low salinity levels with intermittent recovery periods at higher salinity. This study carried out iterative bioassays to determine the longest duration (i.e., consecutive days) that oysters can be exposed to some minimum salinity (0‰-5‰, where valves will likely remain closed) with the shortest periods of recovery (10‰) to survive and grow. The results of this study clearly show that Crassostrea virginica spat exhibited improved survival rates and growth when given periods of recovery at a tolerable salinity after being stressed by prolonged low salinity conditions both with and without thermal stress. Spat reach greater than 50% survival when stressed at 5‰ for less than seven days and are allowed periods of recovery at a salinity of 10‰ or higher under thermal stress. Without thermal stress 50% survival was observed in spat that were stressed for less than 14 days at a salinity of 5‰ and allowed periods of recovery at a salinity of 10‰ or higher. The longer the recovery period at both 25oC and 30oC, the better the results tended to be in matching or exceeding growth in the negative stress controls held at 25‰. A ≥14-day period of recovery should always be targeted regardless of exposure duration in order to ensure oyster spat growth.
Identifier: fgcu_ETD_0350 (IID)
Degree Awarded: Master of Science
Department: Marine & Earth Science
Committee Chair: David Rumbold, Ph.D.
Committee Member: David Fugate, Ph.D.; Aswani Volety, Ph.D.
Subject(s): Crassostrea virginica
Eastern oyster
Salinity
Caloosahatchee River (Fla.)
Persistent Link to This Record: http://purl.flvc.org/fgcu/fd/fgcu_ETD_0350
Use and Reproduction: Creator(s) holds copyright.
Use and Reproduction: http://rightsstatements.org/vocab/InC/1.0/
Host Institution: FGCU