Salinity and temperature effects on Hematodinium sp in the blue crab Callinectes sapidus

The parasitic dinoflagellate Hematodinium sp. infects and causes mortalitie s in blue crabs Callinectes sapidus Rathbun 1896 from high salinity coastal embayments. The seasonal infection cycle and apparent salinity and tempera ture requirements for infections reported from wild crab populations indica te that environmental factors influence the parasite's ability to prolifera te within crab hemolymph. A series of experiments held crabs at various wat er temperatures and salinities to assay infection intensity and crab surviv al. There was a significant increase in mean intensity in infected crabs he ld in ambient 15-9 degrees C seawater for 32 days; at temperatures below 9 degrees C, mean intensity diminished. Mean intensity decreased significantl y in infected crabs held in 10% or 29% artificial seawater at 9 degrees C f or 73 days; the decrease was significantly greater at 10% than at 29%. Mean intensity increased in infected crabs held in 22% seawater at either 12 or 16 degrees C. Presumably uninfected crabs held at 22 degrees C presented i nfections after 14 days. No infections were transmitted by exposure of unin fected crabs to infected crabs after 85 days. Low water temperature and sal inity appear to limit the proliferation of Hematodinium sp. in blue crab he molymph. Apparently uninfected crabs from endemic areas can carry pre-paten t or latent infections.