The occurrence of black necrotic disease in crab species from the West of Scotland

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Abstract
The incidence of Black Necrotic Disease affecting a) the carapace and other areas of the external skeleton, and b) the gills, was recorded for crab species from sites on the west coast of Scotland. The highest incidence of carapace infection was found in Cancer pagurus, with Carcinus mamas, Liocarcinus puber, L. corrugatus and L. depurator showing a lower incidence; other species of crabs, especially from sandy habitats, and species of Natantia showed no infection. The highest incidence of gill disease was in L. depurator and L. corrugatus, while L. puber and Hyas arenarius showed a lower occurrence; other species of crabs, and species of Natantia showed very low or zero incidence. The percentage incidence and severity of attack apparently was not dependent on depth of capture, nor was there any significant seasonal pattern of variation, but some species showed significant differences in percentage incidence between the sexes, and Carcinus mamas parasitised by the rhizocephalan Sacculina carcini showed a higher incidence than those which were not infested with this parasite.