Seasonal Prevalence of Hematodinium sp. Infections of Blue Crabs in Three South Carolina (USA) Rivers
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Blue crab, Callinectes sapidus, commercial landings in the USA have been declining at an alarming rate. In South Carolina, these declines are significantly correlated with years of decreased rainfall and elevated salt marsh salinity. Previous studies suggest that higher salinity increases the risk of infection by Hematodinium sp., a dinoflagellate parasite of blue crabs, C. sapidus. A 4-year survey (June 2008 to March 2012) of blue crabs in the ACE Basin National Estuarine Research Reserve documented (1) the temporal and spatial patterns of Hematodinium sp. infection in relation to salinity, (2) some environmental correlates of disease prevalence, and (3) the characteristics of infected blue crabs. Sampling was conducted four times a year in March, June, September, and December in the South Edisto, Ashepoo, and Combahee rivers beginning in June 2008. Crab hemolymph samples were collected and preserved and DNA was successfully amplified for 2,303 individuals. Hematodinium sp. infection was evaluated by PCR amplification of its 18S rRNA gene and adjacent regions. Prevalence was highest in December 2008 in the Combahee River at sites closest to St. Helena Sound. The spatial and temporal pattern of Hematodinium sp. infection was correlated with several environmental parameters. Infected crabs exhibited differences in carapace shape and body condition compared to uninfected crabs. Overall, these results suggest that blue crabs in regions of higher salinity are at greater risk of infection by Hematodinium sp. and infected individuals exhibit sub-lethal effects of the disease.
KeywordsHematodinium sp. Blue crab Salinity Infection pattern Morphology
We would like to thank Margaret Ptacek, Tim Jordan, Joe Bisesi, and Aaron Lauritson. We thank Daniel Barrineau and Dr. Al Segars for assistance with logistics and use of the McKinzie Field Station. Karrie Brinkley and Dr. Dick Lee provided valuable reference samples and guidance during development of our PCR protocols. Kristine Moody and Dr. Margaret Ptacek graciously shared their time, expertise, and laboratory equipment. This field work was conducted with the permission of the ACE Basin National Estuarine Research Reserve and the SC Department of Natural Resources (permit # EX09-0004, EX10-0076, and EX11-0068). This article is a result of work sponsored by the South Carolina Sea Grant Consortium with support from NOAA National Sea Grant College Program, U.S. Department of Commerce, Grant No. 2010-R/CF 15 (MJC). Student participation was supported by a Clemson University Creative Inquiry Grant (MJC), a Calhoun Honors Research Grant (CKM and JAM), and a Wade Stackhouse Graduate Fellowship (KJP). This research was conducted under an award from the Estuarine Reserves Division, Office of Ocean and Coastal Resource Management, National Ocean Service, National Oceanic and Atmospheric Administration.
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