Abstract

Blue crab life history includes an offshore larval stage vulnerable to changes in environmental conditions in the Gulf of Mexico (GOM), particularly on the continental shelf adjacent to Mississippi and Louisiana. Blue crabs spawn from March through October in the northern Gulf of Mexico (nGOM). Hatching of eggs occurs near the barrier islands with zoeae immediately transported to surface waters of the open GOM. Toward the end of this planktotrophic phase, metamorphosis to the megalopal stage occurs and they recruit to estuaries across the nGOM. There is high spatial and temporal overlap between the occurrence of blue crab larvae offshore and the presence of oil and dispersant in offshore waters. Blue crab megalopal settlement is being measured daily using simple settlement collectors deployed in quadruplicate at six sites along the Mississippi coast. Deployment will occur from July 1 to October 31 with the collectors suspended from piers. Once each day the collectors will be removed from the water, and all blue crab megalopae and early crab stages present will be removed and preserved in ethanol for identification and enumeration. The seasonal pattern in daily counts of megalopae will be compared to similar data from previous years (1991 - 1999 and 2007). Loss of recruitment due to oil-induced larval mortality will radiate into the coastal food web, as blue crabs are a keystone species in northern Gulf estuaries. These data are critical to assessing ecosystem response to the oil spill and will provide an important baseline for measuring ecosystem recovery.

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