Estuaries such as are present along Alabama's coastline represent important mixing zones for marine and fresh waters, typically containing extremely diverse species assemblages and providing critical nursery habitats for a wide variety of aquatic fauna. These areas can provide habitat for many species of fish and invertebrates during their larval and juvenile stages, with some that are commercially valuable (e.g., menhaden, drums and croakers, flounders, blue crabs, shrimp, etc.) entering estuaries as larvae or post larvae. Our previous work in these coastal systems has demonstrated the presence of complex food webs, with some of these migratory groups playing important roles.
The Deepwater Horizon incident may have as of yet undocumented effects on the offshore fauna, and the loss or reduction of these offshore life stages having effects on coastal food webs. For example, oil has been documented from larval blue crabs in the Gulf of Mexico, which may have effects on their survival and eventual migration to these coastal regions. Here we will use our experience with these coastal food webs to generate predictions as to the effects of oil as mediated through these indirect foodweb effects; we take this approach rather than stating explicit strawman hypotheses. Below we describe the data that we will collect, followed by how those data will allow us to address the questions and bullets listed above.
We will sample broadly across low salinity estuarine habitats from Perdido Bay to Grand Bay, and will coordinate our selection of sites with other investigators sampling other components of the near shore and marsh ecosystems (mostly from Theme I, Ecosystem Integrity). We will attempt to select sites that were likely contaminated with oil and dispersants and others with little or no direct exposure. Comparisons among sites and with previously collected data, including data collected by the Alabama Department of Conservation and Natural Resources, will allow us to explore potential impacts of the spill.
Our sampling will be approximately monthly from February through mid-June and then less frequently into September to capture the most important months for recruitment of larval and juvenile fishes in the estuaries. We will collect standard water quality information (DO, temperature, salinity and water clarity), zooplankton, and fishes. We will sample fishes using habitat appropriate gears.
Most adult fish taken with active gear will be measured, weighed, tagged (with a floy anchor tag), their diets removed (for key species), and then released in the field. Sub-samples of fish will be retained for tissue contaminant analysis, age and growth determination, and otolith microchemistry (to help determine any movement patterns). Given that other groups may have need for these fishes, we plan to team with others working in these habitats, and can retain these fish for their needs as well (e.g., to identify and quantify parasite load as a function of one of the other Theme I groups activities).
Juvenile and small-bodied fishes will be collected using habitat appropriate gears. These fish will be preserved in the field and returned to the lab. We will quantify diets of a subsample of these individuals from key species in the lab, and a subsample will also be used for otolith microchemistry to quantify their movement during early life. Larval fishes will be collected using both push net samples (0.5-m diameter net, 500-µm mesh) and quatrefoil light-trap samples at selected sites.
We have not included funds in this request for tissue analysis of fishes from these sample areas. Our expectation is that collaborative teams will be built among groups from with the Ecosystem Integrity group, as well as with individuals from other groups in Themes I and III, and because several groups may have need for fish tissue analysis data, this effort will likely be conducted by the broader group in the final developed proposal.
The samples we collect will allow us to address our target questions in the following way:
- general sampling will provide information to address Q2, B2
- larval fish sampling, age-0 fish sampling pertains to Q2, B3
- adult floy tag work and otolith microchemistry work with key species will get at Q2, B4
- diet analysis of adults and juveniles of key species will get at Q3, B4
Laboratory analyses will commence immediately after the first sample has been collected, and we anticipate doing some comparative work with baseline data immediately in an effort to have a paper submitted by mid-2011.