Mass mortality of farmed mussels – a phenomenon without explanation?

First mass mortality event of farmed mussels (Mytilus galloprovincialis Linnaeus, 1758), took place in the area of the Boka Kotorska Bay (southern Adriatic Sea) in the period from June to September 2020. The mortality caused a loss of production in the range of 80-90%. Possible ecological and environmental causes of this phenomenon were analyzed by the analyses of mussel cultivation technology, basic physico-chemical parameters of sea water, sanitary water quality analyses, condition index, analysis of the presence of the ectoparasite Stylochus mediterraneus Galleni, 1976 and temperature and salinity values on the farms during the last decade. The occurrence of mass mortality in farmed shellfish is a phenomenon that in most investigated cases has no concrete and clear explanation. It is most likely that this event is the consequence of cumulative impact of several different factors: changes in the marine ecosystem that affect the health of the coastal ecosystem, climate change, the impact of pathogens, genetic mutations or abnormalities, water quality and food availability, characteristics of the location where the farm is located, geographical origin of spat, i.e. procedures for planting and translocation spat from one location to another, the impact of various pollutants originating from land.