Abstract
Juvenile edible crabs, C ancer pagurus L., were surveyed from M umbles H ead and O xwich B ay in S outh W ales, UK , and the number of heterotrophic bacteria and vibrios in the hemolymph was determined. The percentage of crabs with hemolymph containing bacteria was variable over the survey with higher numbers of animals affected in summer than in winter. Post‐moult crabs contained significantly higher numbers of heterotrophic bacteria in the hemolymph than pre‐ and intermoult animals. Crabs with cuticular damage to the gills also had significantly higher numbers of bacteria in the hemolymph. Crabs were found to have a high prevalence of infection by the dinoflagellate, H ematodinium . Such animals had significantly fewer bacteria in the blood in comparison with H ematodinium ‐free animals. Of the 463 crabs surveyed, only 3 individuals had hemolymph containing 2000 + CFU mL −1 . Based on 16S r RNA gene sequences, two of these crabs contained a V ibrio pectenicida ‐like isolate, while the other had a mixed assemblage of vibrios. Although 59% of the crabs surveyed had culturable bacteria in the hemolymph, the majority only had small numbers ( −1 ), suggesting that such infections may be of limited importance to the sustainability of the crab fishery in this region.