Mytilus galloprovincialis (Lamarck, 1819) as host of Mytilicola orientalis (Mori, 1935) in the northern Adriatic Sea: presence and effect.
The transfer of mariculture bivalves into new areas is increasing the risk of spreading Mytilicola copepods in native bivalve populations. Mytilicola orientalis was spread from Japan to native oysters and mussels in the Mediterranean. However, the presence of M. orientalis and its effect on the Mediterranean mussel, Mytilus galloprovincialis, are so far under-investigated. Our study shows the first identification of M. orientalis in mussels from the northern Adriatic Sea. M. orientalis was detected in mussels, from the Lim Bay, around the mariculture area of M. galloprovincialis. The adult stages of the copepod occur in mussels from May to August. The mean intensity of infestation and prevalence reached the maximum in August and was positively related to seawater temperature and salinity. We found one to three parasites per host individual, and most of the infested mussels were infested by one single parasite. Using the condition index, we found a relation between mussel physiology and seasonal cycle. Number of parasites was not related to the applied condition index. Our study established no difference in M. galloprovincialis condition index between infested and uninfested individuals, suggesting that the presence of M. orientalis does not adversely affect the mussel physiology to a measurable extent. However, our study reports the first record in the Adriatic Sea for M. orientalis.