Low serum antibacterial activity coincides with increased prevalence of shell disease in blue

We provide epidemiological evidence that shell disease, a very common problem of crustaceans in polluted environments, coincides with low serum antibacterial activity. In commercially important blue crabs Callinectes sapidus from the Albemarle-Pamlico Estuary, North Carolina, USA, we identified potent antibacterial activity which was active against most of the bacteria inhabiting the shell of both clinically normal crabs as well as those with shell disease. Clinically normal blue crabs from riverine sites, presumed to be at high risk for developing shell disease, had as little as one-fifth the antibacterial activity of crabs from more oceanic control sites, which had low prevalence of shell disease. Crabs with shell disease had lower serum antibacterial activity than cohorts without shell disease from the same geographic site. This antibacterial activity may be an important mechanism protecting crabs against shell disease and may be a useful biomarker of blue crab health.