The fisheries ecology group of the FSUCML is taking part in a long-term $20 million study being conducted by the FSU-led Deep-C Consortium, involving ten major institutions (http://deep-c.org/) that are focused on evaluating the deep-sea-to-coast connectivity in the northeastern Gulf of Mexico and the consequences of the Deepwater Horizon oil spill. Our group will specifically investigate the environmental consequences of petroleum hydrocarbon release in the deep Gulf on living marine resources and food web dynamics.
The dual pressures in the northeastern Gulf of Mexico of expanding oil exploration in the outer continental slope and burgeoning population growth along the coast increase the risk of catastrophic discharges of oil and gas, over-enrichment of nutrients, and habitat loss. The region is considered a hotspot of biological diversity and has the highest biological productivity in the Gulf of Mexico so it has tremendous economic value. The DwH accident revealed that oil exploration activities can cause oil spills that affect a substantial part of the Gulf, and that the confluence of petroleum hydrocarbon release and water quality deterioration can have synergistic and negative effects on seafloor and pelagic ecosystems. It also brought to light a profound lack of understanding of the consequences of petroleum hydrocarbon release to the deep and shallow Gulf ecosystems, a deficiency that impairs the effectiveness of disaster response and mitigation efforts. Specifically, processes controlling the spatial and temporal distributions of oil components and dispersants, and the pathways through which petroleum hydrocarbons and their decomposition products move through the ecosystem are poorly quantified.
The overarching goals of this project are (1) to generate quantitative data on the physical, chemical, and biological systems of the northeastern Gulf of Mexico including regions affected by the DwH spill such as the De Soto Canyon and the Florida Panhandle Bight; and (2) to integrate these data in both earth system and food web models that will improve prediction of the path, fate, and consequences of crude oil and gas released from the northeastern deep Gulf through natural or anthropogenic causes. This structure will ultimately allow the forecasting of changes in ecosystem services.
The ecological component of the study evaluates the biological diversity and trophic interactions among organisms ranging from primary producers to apex predators and from the deep-sea benthos to the coast. These data contribute to a food web model used to determine risks to ecosystem structure and function and regional economies following from extreme anthropogenic events (e.g., discharged and background hydrocarbon) and adaptive management strategies. This provides a powerful tool for investigating and assessing the influence of hydrocarbon releases on fisheries, tourism, and human health. Making the connection between the productivity of the region (including the impacts of hypoxia, harmful algal blooms, fishing, habitat loss, and other anthropogenic impacts) and the physical oceanography of the system, is a major outcome.
Studies of the biological diversity and trophic interactions of fisheries species of the West Florida Panhandle Bight are motivated by evidence that DwH oil reached the continental shelf from the deep sea via the De Soto Canyon. They also are based on anecdotal evidence from fishermen and scientists that this event had a significant effect on fish health and community composition, with dramatic population declines in areas once considered highly productive. Given the strong linkages between large-scale oceanographic features (e.g., the Loop Current, upwelling events), geomorphology (e.g., the De Soto Canyon, the Apalachicola River Delta), and fisheries productivity , we adopt an approach to evaluating post-spill impacts on the Gulf ecosystem that includes collaborations with geomorphologists, physical oceanographers, and biogeochemists, and will demonstrate the trophic linkages among these species.
The goal of this work is to survey fish assemblages of the region to determine the level and effect of exposure to PAHs on fish health, and to characterize areas most likely affected by the oil spill. We seek to answer three general questions.
- What are the spatial, temporal, and depth-mediated differences in the diversity, distribution, and abundance of fish assemblages in the deep sea, slope, and shelf edge of the region?
- What are the spatial, temporal, and depth-mediated differences in exposure to PAHs and does this correlate with any differences in fish health, based on age, size structure, and reproductive condition?
- What are the physical and trophic linkages of this assemblage?
We will draw on existing fishery-independent and fishery-dependent databases to determine historical distribution, abundance, and biological diversity of key species, including top level benthic predators (e.g., reef fish, sharks, hake), pelagic species (e.g., mahi mahi, tunas, mackerel), and forage species (e.g., basslets, herbivorous snapper) that contribute to biodiversity and fisheries productivity. We will then establish current distributions and abundances for select species in this study. Further, we will determine the extent to which exposure to PAHs influences condition using standard tissue (e.g., gonad, muscle, gills, liver) and length- weight analyses. PAHs, the most toxic of the hydrocarbons, are metabolized primarily in the liver and excreted through the kidneys. Because they are lipophilic, they accumulate in ovaries, primarily in oil deposits in the developing eggs. By examining them during the reproductive season, we can identify cryptic effects on productivity, including the effect on gametogenesis, gonad size, fecundity, hatching success, and pelagic larval survival.
Methodology – We draw on our previous work over the past 10-15 years in De Soto Canyon, Madison Swanson Marine Reserve, Steamboat Lumps Marine Reserve, and in other sites along the WFS. We are particularly interested in identifying species that serve as indicators of the effects of the oil spill on productivity by drawing from species found across a broad depth range, from the deep sea and slope waters (~200 to 2014 m depths) to the continental shelf (40-200 m depths), and across trophic levels. We will concentrate on such mid- to upper-level predators as hakes (Urophycis cirrata and U.floridana), golden tilefish (Lopholatilus chamaeleonticeps), Cuban dogfish (Squalus cubensis), and red grouper (Epinephelus morio); scavengers, the hagfish Eptatretus springeri and E. minor, and prey species such as damselfish, small basses, and vermillion snapper.
An important aspect of our study is characterizing habitat in cooperation with geomorphologists. Against the geomorphological backdrop, we determine the distribution and abundance of key species, and overall biodiversity using a combination of actual capture techniques using long lines and traps, and virtual capture techniques using video and still cameras on sleds and ROVs to run quantitative transects through significant habitat. Using this approach, we can develop benchmark estimates of community demographics following work we’ve been conducting over the last 20 years.
Each long-line sampling event (=set) includes 50 hooks of four sizes and multiple temperature-depth recorders attached at intervals to provide accurate profile data. At depths > 150 m, this method will likely result in high mortality in teleost fishes, but virtually no mortality in fishes lacking air bladders, such as the sharks and rays, which can be tagged and released from deep captures. At shelf edge depths (< 150 m), fish experience very low mortality when captured in chevron traps (2 m x 1.5 m x 1m). At time of capture, trapped fish are raised from the bottom to midwater, where a diver purges gas from the fish’s air bladder in situ before traps are hauled aboard the vessel.
Once onboard, fish are identified, measured, and tagged with dart tags, passive integrated transponder tags, and/or acoustic tags. Tag returns are obtained through video surveys, scientific recaptures, and fishery captures (the latter reported either directly to us or to the Florida Fish and Wildlife Conservation Commission Hotline, with whom we’ve collaborated for 15 years). Acoustic returns are archived on in situ receivers deployed in the surrounding habitat, which are retrieved and downloaded regularly.
We take tissue biopsies from each captured fish to determine their age (from fin rays), sex and reproductive condition (from gonad tissue), and exposure to PAHs (from muscle, liver, and other tissue when possible). Our methods have been scientifically validated and proven to be reliable. Fin rays provide a reliable means of determining age because they have annular rings (like a tree) that can be counted under magnification. Radiocarbon and stable isotope analysis will determine the level of exposure to petroleum products. Following these procedures (all of which take only minutes to perform), captured fish are returned to the seafloor in a specialized trap that opens upon making bottom contact. All these techniques are non-consumptive. That is, fish are not killed. We operate under the premise that we get far more information from recapturing fish than we do by sacrificing them at first capture. This method has proven quite effective at maximizing survival overall and preventing mid-water predation by pelagic sharks when fish are released.
What we are developing is: (1) a meta-analysis of spatial and temporal changes in the distribution, abundance, size structure, and biological diversity of fish communities throughout the WFPB; (2) an integrated condition, stomach content, and isotopic analyses (e.g., 13C, 15N and 34S) of key species to delineate the trophic structure, exposure to PAHs, and patterns of biomagnification of lipophilic oil component; and (3) a food web models that includes elements of both biogeochemical and trophic characteristics (e.g., Atlantis) that can help us forecast ecological problems from oil spills and other extreme events, identify critical data gaps in our knowledge, and suggest experimental approaches for obtaining targeted ecological information to improve the model.