While grade 3 and 4 lesions appeared to have more severe microbial infections, bacteria were
histologically visible in some examples of all grades. However, histological examination is an insensitive measure of the presence of bacterial infections and typically underestimates its prevalence. Even healthy blue crab carapace has a heavy bacterial flora (Noga et al. 1994), suggesting that the mere presence of bacteria is not solely responsible for lesion development. This is also suggested by the diverse species of bacteria isolated from these lesions (Table 1, Noga et al. 1998). Fungal infections were rarely seen in all but grade 1 lesions, suggesting that they were secondary to the initial damage. To our knowledge, fungal or oomycete infections have never been observed in adult blue crabs. Lagenidium callinectes, an oomycete, infects blue crab eggs and larvae (Noga, Sawyer & Rodo´n Naveira 1998). The width and the variability in width of hyphae in our lesions suggested that they might be an oomycete. Because of the rarity of this fungal infection, its culture and identification will require intensive sampling.