Phytoplankton major groups and harmful microalgae species in the Balearic Sea

Abstract

[eng] This work describes the seasonal pattern and composition of the phytoplankton community both in offshore and confined waters of the Balearic Sea. The dynamics of the phytoplankton community were investigated from April 2015 to February 2016 in the Mallorca and Ibiza channels, and from May to September 2019 in the Port of Mahón (confined waters). Phytoplankton in Mahón showed a peak of up to 3.9x106 cellsL-1 in September, this seasonal trend contrasts with the classical pattern of offshore blooms that occur regionally in mid-winter/early spring, as in the case of the Mallorca and Ibiza channels, reaching the maximum abundance of 2.1x106 cellsL-1 in April. Small flagellates (<10 μm) dominated the phytoplanktonic community in both confined and open waters, and dinoflagellates showed a common increase during the summer season. In contrast, the group of diatoms only showed large blooms in the Port of Mahón, the key factor supporting this high abundance seems to be the continuous availability of silicate through runoff events. Both in the channels and in the Port of Mahón, potentially toxic and bloomforming species were detected, some of them like Pseudo-nitzschia spp., Alexandrium spp. and Chaetoceros spp. reached high densities. However, a more frequent sampling throughout the year would allow a better understanding of the succession of the phytoplankton community and detect species that might bloom at a different time of the year