Short-term low salinity mitigates effects of oil and dispersant on juvenile eastern oysters: A laboratory experiment with implications for oil spill response activities

Abstract

Following the Deepwater Horizon oil spill, eastern oyster (Crassostrea virginica) reefs in the northern Gulf of Mexico were exposed to oil and various associated clean-up activities that may have compromised oyster reef health. Included in the exposure was oil, dispersant, and in some locales, atypical salinity regimes. Oil and dispersants can be detrimental to oysters and the effects of salinity depend on the level. In addition to these extrinsic factors, genetic diversity of oyster populations may help the oysters respond to stressors, as demonstrated in other systems. We used a 3×3×2 factorial design to experimentally examine the effects of oil/dispersed oil, intraspecific genetic diversity, and salinity on juvenile (ca. 25 mm shell height) oyster survivorship and growth during a 21-d exposure in a closed, recirculating system. The genetic effect was weak overall, oil and dispersed oil negatively affected juvenile oyster survivorship, and low salinity mitigated mortality in oil and dispersed oil treatments. Survivorship was about 40% greater in low-salinity than in mesohaline water for both oil and dispersed oil treatments, bringing survivorship in low salinity oil-only treatments to a similar level with low salinity controls (no oil). Oyster growth was minimal after 21 d but appeared to be negatively affected by oil and dispersed oil, and had a significant interaction with salinity. Our results may be informative for future decisions regarding oil spill response activities and suggest that a pulse of low salinity water may be a viable short-term mitigation option for oysters if filtration characteristics, exposure time, and water temperatures are all considered, in addition to weighing the costs and benefits of this type of response on other organisms and habitats.

A Synthesis of Deepwater Horizon Impacts on Coastal and Nearshore Living Marine Resources

“…While oysters have substantialtolerance for varying salinity and temperature regimes (Sehlinger et al, 2019), prolonged exposure to low salinities of <5 ppt will eventually result in death (Powers et al, 2017a). Schrandt et al (2018) in fact demonstrated that in laboratory conditions, short-term episodes of low salinity water may mitigate effects of oil/dispersant exposures. However, longterm fresh water conditions persisted in Breton Sound/Black Bay and Barataria Bay in much of the spring and summer of 2010, likely resulting in excess mortalities of 1.16-3.29 billion market sized oysters due to low salinity stress (Powers et al, 2017a).…”

Prospects for Gulf of Mexico Environmental Recovery and Restoration

“…The summer release of large quantities of freshwater from the Mississippi River through the Caernarvon and Davis Pond diversion structures as the State of Louisiana moved to protect marsh ecosystems from the inflow of oil in 2010 resulted in the loss of 2-3 billion market-sized oysters from subtidal areas of Barataria Bay and Black Bay/Breton Sound estuaries (Grabowski et al, 2017;Powers et al, 2017b). Mesocosm experiments funded by GoMRI indicated that exposing oysters to short periods of low salinity could help them combat oil contaminant effects; however, this must be balanced by heavy expected mortality resulting from extended periods at very low salinity (Schrandt et al, 2018). Oysters near the shoreline (fringing oyster reefs) suffered injury from direct oiling as well as from oil removal efforts (Powers et al, 2017a).…”

Metaplasia of respiratory and digestive tissues in the Eastern oysterCrassostrea virginicaassociated with the Deepwater Horizon oil spill

“…It is made The copyright holder for this preprint this version posted February 15, 2021. ; https://doi.org/10.1101/2021.02.15.431248 doi: bioRxiv preprint public leases were delayed east of the Mississippi River in 2010 due to a depressed spat set and oyster mortalities [16]. In addition, dramatic density decreases of oysters in areas affected by freshwater diversion efforts have been documented [17,18], although in experimental work, Schrandt et al [19] found that lower salinity conditions (5-10 ppt) led to increased survival of juvenile C. virginica exposed to oil and dispersed oil. In addition, Dietl and Durham [20] did not detect any significant difference of adult shell size between a baseline of pre-spill historical specimens and those collected in the years 2011 to 2013.…”