Hypoxia and reduced salinity exacerbate the effects of oil exposure on sheepshead minnow (Cyprinodon variegatus) reproduction

Abstract

Estuaries of the northern Gulf of Mexico are dynamic environments, with fluctuations in salinity and dissolved oxygen, including areas of seasonal hypoxia. Fish that reside and reproduce in these estuaries, including sheepshead minnow (Cyprinodon variegatus; SHM), were at significant risk of oil exposure following the Deepwater Horizon oil spill. It is poorly understood how differences in environmental conditions during oil exposure impact its toxicity. The present study investigated the effects of crude oil high-energy water accommodated fraction (HEWAF) on SHM reproduction in three environmental scenarios (normoxic, hypoxic, and hypoxic with low salinity) to determine if differences in salinity (brackish vs low salinity) and dissolved oxygen (normoxia vs hypoxia) could exacerbate the effects of HEWAF-derived polycyclic aromatic hydrocarbons (PAHs). We observed that HEWAF exposure significantly increased liver somatic index of SHM compared to control, but this effect was not exacerbated by hypoxia or low salinity. HEWAF exposure also significantly decreased egg production and egg fertilization rate, but only in the hypoxic and hypoxic with low salinity scenarios. A significant correlation existed between body burdens of PAHs and reproductive endpoints, providing substantial evidence that oil exposure reduced reproductive capacity in SHM, across a range of environmental conditions. These data suggest that oil spill risk assessments that fail to consider other environmental stressors (i.e. hypoxia and salinity) may be underestimating risk.Mississippi, Alabama, and Florida were all impacted by oil slicks that washed ashore (Nixon et al., 2016). In late April 2010, in an effort to limit the effects of oil on coastal habitats, the state of Louisiana initiated a massive diversion of freshwater from the Mississippi River into Barataria Bay and Breton Sound (Bianchi et al., 2011;Martínez et al., 2012). These freshwater diversions significantly reduced salinities in the estuaries of the northern GOM (Bianchi et al., 2011;Powers et al., 2017), but it is still undetermined if this effort was effective in reducing oiling to the Louisiana coast (Martínez et al., 2012).Estuaries of the northern GOM are dynamic environments, with constant fluctuations in salinity and dissolved oxygen. Freshwater inflow from the Mississippi River causes a saline gradient in the estuaries that contributes to water stratification, usually during summer months (USEPA, 1999). The combination of water stratification, excess

Transcriptome Profiling Reveals a Divergent Adaptive Response to Hyper- and Hypo-Salinity in the Yellow Drum, Nibea albiflora

“…Salinity is an inherent physicochemical property of seawater, and fluctuations in salinity can affect the growth, reproduction, feeding, endocrine, and metabolism of marine organisms [ 1 , 2 , 3 , 4 , 5 ]. Most marine fish are always immersed in seawater, and their behavior and internal physiological states are particularly sensitive to environmental salinity changes [ 6 ].…”

Exposure to Oil and Hypoxia Results in Alterations of Immune Transcriptional Patterns in Developing Sheepshead Minnows (Cyprinodon variegatus)

“…Previous research has demonstrated that co-exposure to oil and hypoxia impacts developing C. variegatus as well as Fundulus grandis [14][15][16][17] and can reduce egg production and fertilization in adults 18 . Despite the fact that both oil and hypoxia are known to affect developing C. variegatus, and that both stressors are known to affect fish immune systems, little is known about how these two stressors interact to impact immune system development.…”

A review of the toxicology of oil in vertebrates: what we have learned following the Deepwater Horizon oil spill

“…Carr et al (2018) suggested that exposure to oil and dispersants may therefore adversely affect testicular function in these fish. Experimental exposure of sheepshead minnows to HEWAF under different oxygen and salinity conditions demonstrated that HEWAF exposure significantly lowered egg production and egg fertilization rate, but only under hypoxic and hypoxic with low salinity scenarios, suggesting that environmental conditions might directly modulate reproductive toxicity of oil exposure in fish (Jasperse et al 2019a).…”