Other marine invertebrates are obviously affected by diseases but on the whole these are very poorly documented except for economically significant taxa such as oysters and prawns. The Crown-of-Thorns starfish is affected by a poorly understood disease (see Section 6.8.2) and a disease wiped out large populations of diademnid urchins in the Caribbean in the 1970s-1980s (Lessios 1988). Trematode infection may have played a role in the mass mortality of two common soft-bottom invertebrates (a gastropod mollusc and an amphipod) on an intertidal mudflat in Denmark (Jensen and Mouritsen 1992).

Diseases attributable at least partly to human activity or to stresses directly resulting from anthropogenic environmental degradation have been reported in several taxa. For example, Aguado and Bashirullah (1996) recorded the incidence of shell diseases in wild penaeid shrimps in eastern Venezuela. Shell diseases - resulting in degradation of the exoskeleton - are commonly caused by bacterial genera such as Vibrio, Aeromonas, and Pseudomonas, but may also be associated with certain environmental parameters and be an indicator of a stressful environment (Aguado and Bashirullah 1996). Chu and Hale (1994) examined the relationship between pollution and susceptibility to infectious disease in the eastern oyster, Crassostrea virginica. The disease studied is caused by a protozoan parasite and results in significant oyster mortalities in the mid-Atlantic region of the United States. Exposure to pollutants was found to enhance pre-existing infections and increase the oysters’ susceptibility to experimentally induced infection in a dose-dependent manner (Chu and Hale 1994). In Norway, Bustnes and Galaktionov (1999) found that fishing industry complexes and fish farms appeared to be associated with a prevalence of trematode parasites in intertidal gastropods, due to the tendency of gulls (the final hosts) to concentrate in these areas to feed on offal.