Fibrocapsa japonica (Raphidophyceae) occurrence and ecological features within the phytoplankton assemblage of a cyclonic eddy, offshore the Eastern Alboran Sea

Abstract The Raphidophycean Fibrocapsa japonica Toriumi & Takano was detected for the first time offshore in the Eastern Alboran Sea (Western Mediterranean) in October 2006. Its distribution appeared very localised and atypical, as it was abundant in the open waters of a cyclonic eddy. Microscope counts of the natural phytoplankton assemblages revealed that F. japonica was dominant in the microplankton, together with Dinophyceae, within and below the cyclonic nutrient-rich dome (25 - 30 m). Bacillariophyceae were the primary microplanktonic fraction in only a few samples on the edges of the eddy. Moderately high abundances of F. japonica (maximum of 60 cells ml-1), with preliminary cysts and many cells aggregated in mucous nets, indicated a senescent phase. Despite the Atlantic origin of the cyclonic water masses, the molecular identification and the water temperature of 15°C, which could have favoured pre-cyst formation, would suggest a Mediterranean source for F. japonica cells. Finally, we hypothesise that F. japonica , which is generally a coastal species, could have a coastal origin. In fact, F. japonica was mainly detected at a depth of 40-60 m at the coastal sites and at 25-30 m at the cyclonic dome. F. japonica generally being a coastal species, it can be hypothesised that it was entrapped by the cyclonic eddy, which typically detaches from the coastal waters, and thus carried offshore to the cyclonic waters.