(From Fall 2014 Newsletter) Dr. Joseph Neigel from University of Louisiana at Lafayette answered a few questions about his RFP-II project, The Environmental Effects of an Oil Spill on Blue Crabs in the Gulf of Mexico and the Dynamics of Recovery: Integrating Oceanography and Molecular Ecology, below.
1. Tell us a bit about your research. What are the goals of your project?
Together with my colleagues at Tulane, we are investigating how the blue crab, Callinectes sapidus, was affected by the Deepwater Horizon Oil spill, and more generally, how species like the blue crab respond to environmental change. This is a complex problem because along with the direct effects of a historically unprecedented oil spill there were the indirect effects of an unprecedented fisheries closure.
2. What has your research found with respect to oil spill impacts on blue crab larval dispersal and rates of larval settlement?
Perhaps surprisingly, we did not see a big change in blue crab settlement during 2010, the year of the spill. Indeed, some of the fisheries data that we have examined suggest that the following year was one of unusually high levels of recruitment to the juvenile stage. This may have been a consequence of the fisheries closures.
We do not yet know how patterns of dispersal were affected, this will require the larger population genetic data set that we are presently assembling. We are particularly interested in testing the hypothesis that loss of larvae from the oil spill was offset by larvae arriving from more distant sources. Our initial genetic analysis did show a shift in genetic structure that occurred between 2010 and 2011. It remains to be seen whether this is an unusual occurrence or how it might relate to the oil spill.
3. How have you used population genetics to look at connectivity among blue crab populations in the northern Gulf?
What we have found using nuclear gene sequences is that genetic connectivity is high among northern Gulf populations of blue crabs. This makes sense in terms of the life-cycle of blue crabs, which includes offshore spawning followed by a planktonic stage of a month or two. It also matches earlier studies that were conducted with other types of genetic markers. However, we also have evidence that the environment acts as a filter on recruitment, favoring some genotypes over others depending on local environmental conditions. This could mean that although larvae arrive from many different sources, only larvae with genotypes that are suited to the local environment are successful.
4. What are some of the most significant or exciting findings so far in your work?
Some of the most exciting findings come from the work of Bree Yednock, who was first a graduate student and then later a post-doc on the project. She showed that genetic variation in blue crab stress-response genes is adaptive, and she identified the genes that are regulated in response to oil exposure that we are now studying. Some of these oil-response genes are similar to human genes that are involved in metabolism of pharmaceuticals and other foreign chemical compounds.
5. What are the broader implications of your research and how might your findings inform the management of blue crab fisheries?
We know very little about how marine species adapt to environmental change and the role that genetic variation plays in this process. We are finding that genetic variation could be very important for the blue crab, which lives in coastal marshes where it must tolerate a broad range of environmental conditions. Maintaining genetic variation depends on a large and diverse breeding stock, which is vulnerable to a range of threats including loss of critical habitats, overfishing, excessive bycatch, oil spills, and other forms of pollution. The blue crab is nearly an ideal model for addressing these questions because so much prior work has been done on its biology and management. What we learn will have broader implications for many other species about which we know less.
6. Can you tell us more about your research collaboration with fellow GoMRI researchers?
I have some great collaborators. My Co-PI is Caz Taylor at Tulane. Her lab is using a particle-tracking model that is based on oceanographic data to predict blue crab larval dispersal trajectories. This complements our genetic analysis of dispersal and helps us determine where larvae that were exposed to oil and dispersant eventually settled. The Taylor lab is also looking at the sub-lethal effects of exposure to oil, dispersants, and other chemicals on blue crab larvae and juveniles, which ties in with our gene expression studies. We are also working with Ed Chesney at LUMCON, who is funded by a separate GoMRI RFP-II grant. Ed and his post-doc, Tara Duffy, are interested in how oil exposure effects fish and invertebrate larvae. We are helping look at this from a biochemical perspective by characterizing the transcriptomes (expressed genes) of larval Bay Anchovy exposed to oil and dispersant.
7. If funding were not an issue, what would add to your project?
Our ongoing research will fill in some important pieces of the puzzle, but there are others that we urgently need if we are to have a complete picture of how blue crab populations function. I say urgently, because what we learn now about healthy blue crab populations will be our only baseline for understanding changes in the future. In the early 1980’s as a graduate student, I was studying two of the most common corals in the Caribbean: Elkhorn and Staghorn coral. At the time, we had no inkling that they were about to begin a steep decline that would lead to them being listed as threatened under the Endangered Species Act. This was a lesson that I will never forget. For blue crabs, I would focus on three things: 1) We need to know more about what is happening offshore, to females that are spawning and to larvae from the time they are released to the time they settle as post-larvae. Although every stage of the blue crab life cycle is vulnerable, spawning females and larvae are especially so. We also need to integrate laboratory work with extensive field work, including plankton sampling and tracking of female crabs. 2) With the blue crab transcriptome now available, along with the tools made possible with it, we have the opportunity to gain a better understanding of how blue crabs respond not only to oil and dispersant, but also to other chemicals. Fertilizer, pesticides, detergents, and other chemical pollutants constantly flow into the Gulf, and we need to better understand how blue crabs and other species are affected. 3) We know that pathogen outbreaks can have sudden and severe impacts on marine species, but we seldom pay much attention until after an outbreak occurs. I would like to work at better characterization of pathogens carried by blue crabs in the Gulf, along with experimental investigations of what causes pathogens that are normally tolerated to suddenly cause disease outbreaks.