First record of a Trichodesmium erythraeum bloom in the Mediterranean Sea

Abstract

Trichodesmium erythraeum is a species of marine cyanobacteria that forms extensive blooms in tropical and subtropical areas, predominantly in the Indian and Pacific oceans. An extensive bloom of this species, identified by microscopic and molecular analysis, is recorded for the first time at latitude greater than 30 degrees N in Lesvos Island, Aegean Sea, eastern Mediterranean. Analysis of climatological trends revealed that the September 2010 bloom followed an extended period of the highest sea surface temperature and lowest wind speed observed since 1955, leading to a shallow thermocline formation. These conditions are considered among the main prerequisites for T. erythraeum bloom development. Analysis of abiotic parameters showed that other important factors for Trichodesmium proliferations, such as iron availability, oligotrophic conditions, and salinity levels, typical for the eastern Mediterranean, were also favourable. These findings seem directly linked to climate change already reported for the Mediterranean Sea and provide further evidence of the "tropicalization" of the area. Expansion of Trichodesmium blooms to greater latitudes may have important regional and global implications potentially affecting the global nitrogen cycle, the biological carbon pump, productivity levels, and harmful algal bloom frequency.