| Summary: | Phylum Mollusca is a large and diverse group of invertebrate protostomes of over 85,000 species including gastropods, cephalopods and bivalves. Molluscs are the largest marine phylum. Marine molluscs are economically important as a high protein food source for humans and provide ecosystem services including nutrient recycling, carbon sequestration, sediment stabilisation and bioturbation. Molluscs are harvested by traditional fishing but are increasingly cultured in many coastal communities worldwide. Hence most information on pathogens and disease is known in molluscs of commercial significance. Bivalves (oysters, mussels, clams, scallops, cockles) are susceptible to a wide range of diseases caused by viruses (e.g. ostreid herpes virus-1 and variants) bacteria (e.g. Vibrio spp., Nocardia crassostreae, Roseovarius spp., rickettsia and Mycobacterium spp.), microsporidians (e.g. Steinhausia spp.), paramyxids ( Marteilia refringens and M. pararefringens ), haplosporidans (e.g. Haplosporidium nelsoni, Minchinia spp., and Bonamia ostreae ) and macroparasites (e.g. trematodes, copepods and nematodes). The gastropod abalone are susceptible to viruses (e.g. Abalone Viral Ganglioneuritis) and bacteria (Rickettsiales-like organism). Of particular importance is Pacific oyster mortality syndrome (POMS) that is polymicrobial in nature with initial infection by ostreid herpesvirus with subsequent bacterial infections by a variety of vibrios, and marteiliosis. In North America, since the early 1950’s there have been episodes of diseases including Dermo disease, caused by Perkinsus marinus , and MSX disease caused by H. nelson in Crassostrea spp. Globally, it is recognised that marine diseases including those that impact molluscs are becoming more frequent and severe due to climate change, in particular increasing seawater temperature, and human activities.
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