Blue crabs (Callinectes sapidus) are an ecologically and economically important species in the Gulf of Mexico. In Chesapeake Bay and North Carolina, blue crabs have suffered from unexplained population crashes in recent years, purportedly due to increase fishing pressure and habitat degradation. Despite the importance of this species and the propensity for their stocks to crash, a realistic and predictive population model is still lacking for blue crabs.

This RAPID project will use a metapopulation approach to understand and predict the population dynamics of blue crabs. Blue crabs spend their initial, larval, life-stages in the ocean then recruit to estuaries for their juvenile and adult stages. In the metapopulation model to be used, local dynamics in a patch (estuary) will be described and parameterized using fisheries data, remotely-sensed habitat quality estimates, and results from field experiments estimating cannibalism rates. The PIs will estimate connectivity (dispersal of larvae between estuaries) of the population with a particle tracking approach using a fine-scale, spatially-explicit ocean circulation model.

When the Deepwater Horizon oil rig exploded on April 20, 2010, and began discharging several million gallons of oil into the Gulf, blue crabs were just beginning their spawning season. In this RAPID, the PIs propose to investigate the impacts of the oil and chemical dispersants on the larval stages, and ultimately on population dynamics, of blue crabs by sampling planktonic larvae at three ocean locations that vary in distance from the oil source. Results will estimate both lethal and sub-lethal effects of oil and dispersants on larvae. They will incorporate the extent and concentration of oil and dispersants into the particle-tracking model and use it to predict the effects of the oil spill on dispersal and recruitment for the entire Gulf of Mexico. To validate model results, the PIs will sample recruitment to estuaries over a wide stretch of the coastline, including areas unaffected, lightly affected and heavily affected by the spill. They will incorporate results into the metapopulation model to explore the long-term effects of the spill on the Gulf of Mexico blue crab population and its fishery.

Broader Impacts:

The PIs intend that results from this RAPID project will be used to inform fisheries policy so as to prevent collapses of blue crab fishery in the Gulf, especially in light of the recent oil spill. Dispersal information is lacking from current blue crab fishery assessments and may prove especially important now in helping to decide how to not exacerbate the effects of the oil spill. Their sampling will also be useful to document and consider the effects of oil and of dispersants on other commercially and ecologically important species with planktonic larvae, such as menhaden and shrimp. This project will provide interdisciplinary research experiences for several undergraduate and graduate students including field projects as well as computational experience.

Project Report

Blue crabs are an ecologically and economically important species in the Gulf of Mexico. This species supports a large recreational and commercial fishery and is a key predator and prey species in estuarine and marine habitats. When the Deepwater Horizon rig exploded, the blue crab was just beginning its peak-spawning season. Female blue crabs travel out to deep, high salinity, waters to spawn eggs and the quickly hatching larvae then spend 6-9 weeks traveling on ocean currents before settling back into estuaries where they spend the rest of their lives. With support from this grant, we have developed an oceanographic tracking computer model to predict movements of larval crabs between spawning and settlement. We are using this model to estimate rates of exposure to oil and other spill –related chemicals. We also conducted the largest ever field sampling of larval blue crabs. We collected larval crabs as they return to the estuary at 9 sites across the Gulf of Mexico, ranging from Galveston, TX to Apalachicola, FL. These sites spanned the area affected by the oil spill. We are testing the samples for evidence of exposure and examining them for any evidence of sub-lethal effects of the spill. The sampling will be repeated in 2011 with support from the Gulf Research Institute to provide a comparison. Preliminary analysis of the data gathered in 2010 show highly variable and episodic patterns of settlement and these data will be used to validate and check the results of the computer model. We also sampled plankton in the ocean to investigate the distribution of blue crab larvae and other species during the spawning season. This large and unique dataset is awaiting analysis and will also be integrated with the computer model. We discovered unusual coloration in many of the crab larvae that were collected and have been developing chemistry tests to determine whether this is related to the oil spill. All results are in the process of being integrated into predictive models that can be used to estimate the degree and geographic extent of the oil spill impacts on this key species.

National Science Foundation (NSF)
Division of Ocean Sciences (OCE)
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David Garrison
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Tulane University
New Orleans
United States
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