The goal of the proposed project is to address theme III. We will define ecologically relevant outcomes for the response of the early life history stages of GOM fish and invertebrate species to exposures of lethal and sub-lethal levels of oil under conditions that mimic natural scenarios in play during DWH. The objective is to provide a basis for better understanding impacts related to DWH for ecologically and economically important coastal species of nekton. It is likely that the most significant direct impacts of DWH oil releases for fisheries of the nGOM were impacts to the early life stages of spring and summer spawning fishes and invertebrates that reside in the offshore to inshore regions of Louisiana and Mississippi where the most abundant and valuable Gulf of Mexico fisheries exist. Many important species were affected because spring and summer is the principal spawning period for most species. In spite of the challenge of studying the ELH stages of fishes, it is critically important to understand environmental impacts to this life stage because embryonic and larval fish often exhibit greater sensitivity to xenobiotic compounds than do adult fishes.
The area most impacted by oil is also the most productive waters of the GOM and characterized by the very high primary productivity (i.e. the fertile-crescent) with coastal condition that range from oligotrophic (offshore bluewater) to eutrophic (inshore) plus high turbidity zones from river-borne sediments that are easily re-suspended by tides and wind in shallow coastal waters. Although larvae and juveniles were the most heavily impacted life stages of nekton they are also the most difficult to assess at the population level because of their naturally high mortality rates from predation and other factors. The backbone of modern toxicological methods is to focus on the repeatability, traceability of exposure levels and the ability for intra- and interspecies comparisons of the lethal toxicity of various toxic compounds including crude oil. While this provides a standard for comparisons of toxic compounds, it does not provide a means to easily account for specific environmental conditions or the behavioral effects that can alter larval survival under the real world conditions that occur during a spill.
During an oil spill exposure levels vary over a large part of the environment, many biota are exposed for short durations and many exposures are below lethal concentrations as toxicity is dispersed and oil degrades. Especially important ecologically relevant kinematics that can be affected by sub-lethal exposures include prey search behavior (swimming), prey capture and predator avoidance behaviors. Typical laboratory exposures also do not account for the effects of the presence of phytoplankton and suspended sediments on toxicity of oil and dispersant compounds. In order to get around some of these limitations, we are proposing site relevant studies with native species under conditions that mimic natural exposure scenarios to provide a better understanding of the effects of the oil spill on early life stages of marine organisms. We chose 4 prominent species for testing lethal and sub-lethal effects of oil on larvae: bay anchovy, spotted seatrout, blue crab and red snapper.
- We will first establish 24 hour LC50s with marine larvae exposed to WAFs (water accommodated fractions) of crude oil as a baseline for sub-lethal tests,
- We will conduct sublethal exposures of larvae to WAFs with different exposure durations at both lethal and sub-lethal concentrations,
- We will conduct experiments with aged (WAFs) and aged/dispersed oil (CEWAFs) and evaluate the degree that toxicity is moderated by aging at different salinities
- We will conduct separate toxicity experiments with and without phytoplankton added to the test waters to evaluate the effects of those on the toxicity of WAFs
- We will evaluate post exposure larval performance (feeding, growth, swimming, forage behavior) and use those performance responses to quantify sub-lethal effects to different crude oil concentrations, exposure durations and exposure conditions.
The array of experiments outline above are designed to provide a better basis for predicting impacts to larvae exposed to crude oil from DWH in the nGOM. We will synthesize the results and make projections of sub-lethal effects on the ELH stages of the studied biota based upon their performance in response to contact with crude oil. These results will allow managers to better assess impacts from DWH as well as develop strategies to reduce or minimize impacts to ELH stages of fish from future oil releases.