The prevalence and severity of shell disease in the edible crab Cancer pagurus (L.) was investigated in animals collected from Langland Bay, Gower, South Wales, UK, at monthly intervals from 1997 to 1998. Shell disease is the progressive degradation of exoskeletal chitin accompanied by melanisation of the affected region. Over 50% of the crabs sampled had 1 or more black-spot lesions. The proportion of exoskeleton affected increased with the size of the crab. Male crabs showed significantly higher levels of the disease than females, a higher prevalence of black-spot lesions (63% in males, 40% in females) and a higher mean percentage of body covered by lesions (1 % in males, 0.2% in females). This difference between the sexes corresponded to an increase in ventral surface and chela infection in males. For both sexes, the dorsal carapace was the area most affected by the disease. Dorsal carapace regional breakdown revealed the areas most commonly affected were located to the posterior of the crab. Lesion location patterns suggested that sand abrasion injuries during back-burrowing behaviour of C. pagurus lead to the formation of shell disease lesions. Seasonal trends in shell disease were seen to be dependent on the onshore migration patterns of the different size classes and sexes over the sampling period.

With 1 plate and 2 figures in the text) Mites of the genera Halolaelups and Phaulodinychus (Gamasida), together with Hisriosfoma (Acaridida) (Acarina: Chelicerata), occur amongst tidal debris strandlines on the sandy shores of' the South Wales coast. Phoretic deuteronymphs of all three mites are dispersed between strandlines via talitrid amphipods (Talitridae: Amphipoda: Crustacea) which provide two principal advantages over the insect hosts used by most other phoretic Acarina. First, amphipods migrate between strandlines throughout the year allowing continual phoretic mite dispersal, and second, even juvenile Talitridae are sufficiently large to transport several mites. The highly aggregated populations of all three mites are distributed independently of amphipod age, sex and species, suggesting that host selection is primarily influenced by other factors. The most likely factors are those related to host behaviour and, in particular, monthlyidiurnal quiescence when the mites encounter, and are boarded by, the desiccation-sensitive phoretic mites. The discrete site selection exhibited by each mite species is at least partly influenced by attachment mechanisms.

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