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Changes in Benthic Macroinvertebrate Communities along the Northern Gulf of Mexico Coast Following Hurricane Katrina: A Comparison Using Pre-hurricane EMAP/NCA Data

Virginia D. Engle 1, Jeffrey L. Hyland 2, and Cynthia L. Cooksey 2

1 U.S. Environmental Protection Agency, ORD/NHEERL Gulf Ecology Division, Gulf Breeze, Florida
2 National Oceanic and Atmospheric Administration, National Ocean Service, Charleston, South Carolina

A study was initiated in October 2005 to assess potential effects on benthic fauna and habitat quality in coastal waters of Louisiana, Mississippi, and Alabama following Hurricane Katrina (August 29, 2005). Samples for analysis of macroinfauna, chemical contamination of sediments, and other general habitat characteristics were collected at 30 sites in Lake Pontchartrain, Louisiana and 30 sites in coastal waters of Lake Borgne and Mississippi Sound. Comparisons to pre-hurricane conditions were made using EMAP/NCA data collected from the same areas in 2000-2004 with similar indicators and protocols. There were notable changes in several benthic community characteristics suggestive of storm-related effects in both coastal systems. These included shifts in the composition and ranking of dominant taxa and reductions in number of taxa, H' diversity, and total faunal abundance. A benthic condition index in general did not reveal such effects, though there was a slight decline in the percentage of Lake Pontchartrain waters with healthy benthic assemblages after the hurricane in comparison to average pre-hurricane periods. Observed changes in the benthos did not appear to be linked to chemical contamination, organic enrichment of sediments, or hypoxia as major causes. Storm-related changes in salinity were a more likely cause in both survey areas. The salinity change was particularly pronounced in Lake Pontchartrain, which shifted from a predominantly oligohaline system before the hurricane to mesohaline after, due to storm surge and the intrusion of saltier coastal waters. Storm-induced scouring of sediments and localized increases in contaminants could have contributed to such effects as well.

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