Introduction of microscopic non-indigenous species through ballast water in Arzew Gulf (SW Mediterranean Sea): the case of the harmful raphidophyceae Fibrocapsa japonica S.Toriumi et H.Takano, 1973 (Chattonellaceae).
The transfer of non-indigenous species (NIS) into the marine environment is mainly carried out by maritime transport (biofouling or ballast water). Ports are therefore the gateway to NIS, which can alter local biodiversity. In this study, the port of Arzew and Bethioua (Algeria, south-western Mediterranean) were studied for the presence of NIS by taking the case of the harmful Raphidophyceae Fibrocapsa japonica. Seawater samples were collected following a comparative sampling strategy between Arzew Gulf (AG region: presence of two hydrocarbon transport ports) and Ain Temouchent (AT region: absence of transport port - reference area). The Almeria-Oran front separates the two regions. The AT and AG regions generally have the same temperature, salinity and chlorophyll characteristics. The phtyhoplankton population showed a homogeneous quantitative distribution between the AT and AG regions. Diatoms and dinoflagellates have an equal density in both regions, nevertheless diatoms are more abundant in each region, (diatoms 6950 ind/l in AT 6380 ind/l in AG, dinoflagellates 1920 ind/l in AT and 1770 ind/l in AG). The specific assessment of the phytoplankton population revealed the presence of F. japonica at around 110 ind/l in the AG region in one station across the ports of Arzew and Bethioua and near the coast, and its absence in the reference area AT. Despite its presence in low density in a single station, this species remains harmful and presents a real danger if it is transported by the Algerian current along the coast to other places, in particular fisheries and aquaculture production areas. This study is part of a prevention process, is the first signaling of microscopic non-indigenous species on the Algerian coast, and contributes to establish a database for future assessments of microscopic NIS in Algerian ports.