Northward establishment of the mediterranean mussel Mytilus galloprovincialis limited by changing climate

Throughout Europe the blue mussel Mytilus edulis is dominant in the north while the Mediterranean mussel Mytilus galloprovincialis prevails in the south. Studies from the 1970s to the late 2000′s documented the northward range expansion of M. galloprovincialis in Europe and predicted this trend to continue with climate change. The objectives of this study were to sample predominantly wild mussels (n = 1459) at twenty-four Irish intertidal sites over a seven year period and at three Welsh sites to investigate (a) the abundance and distribution of Mytilus spp., identified molecularly by polymerase chain reaction (PCR), and (b) compare with historical observations, at Irish sites where M. galloprovincialis was observed to be more abundant than M. edulis. Mussels were sampled more than once at certain sites to investigate if there was a temporal effect. The findings of this study indicated that M. edulis was consistently the most abundant species, followed by hybrids and M. galloprovincialis. At certain sites, hybrids were detected while M. galloprovincialis was absent. This finding may indicate transient M. galloprovinicialis populations or input from individuals subtidally. One factor that may be of importance was the anomalous cold winter “polar snaps” (2010 and 2011) that occurred during this study. In addition, heavy precipitation events and subsequent increased freshwater loading in bays and estuaries also occurred during this time period. Future warming climate scenarios have been predicted to facilitate the northwards establishment of M. galloprovincialis, however, nearshore meteorological extremes may have an impact in its larval settlement, establishment and subsequent reproductive output.