Early detection of potentially invasive invertebrate species in Mytilus galloprovincialis Lamarck, 1819 dominated communities in harbours

Constan?a harbour is a major port on the western coast of the semi-enclosed Black Sea. Its brackish waters and low species richness make it vulnerable to invasions. The intensive maritime traffic through Constan?a harbour facilitates the arrival of alien species. We investigated the species composition of the mussel beds on vertical artificial concrete substrate inside the harbour. We selected this habitat for study because it is frequently affected by fluctuating levels of temperature, salinity and dissolved oxygen, and by accidental pollution episodes. The shallow communities inhabiting it are thus unstable and often restructured, prone to accept alien species. Monthly samples were collected from three locations from the upper layer of hard artificial substrata (maximum depth 2?m) during two consecutive years. Ten alien macro-invertebrate species were inventoried, representing 13.5% of the total number of species. Two of these alien species were sampled starting the end of summer 2010, following a period of high temperatures that triggered hypoxia, causing mass mortalities of benthic organisms. Based on the species accumulation curve, we estimated that we have detected all benthic alien species on artificial substrate from Constan?a harbour, but additional effort is required to detect all the native species. Our results suggest that monitoring of benthic communities at small depths in harbours is a simple and useful tool in early detection of potentially invasive alien species. The selected habitat is easily accessible, the method is low-cost, and the samples represent reliable indicators of alien species establishment.