Phytoplankton variability and oceanographic conditions at Condor seamount, Azores (NE Atlantic)

The variability of phytoplankton biomass (chlorophyll a as a proxy of biomass) and community structure was evaluated over and around the Condor seamount SW of Faial Island in the Azores Archipelago using data provided from five cruises (July and November 2009, and March, July and October 2010). Phytoplankton cell abundance, taxonomy and chlorophyll a concentration were related to both the physical–chemical conditions and to the main circulation patterns observed, bringing new insights into the temporal and spatial variability of phytoplankton. Only microphytoplankton and large nanophytoplankton were identified. Higher phytoplankton abundances were observed during 2010 with a maximum in October (1.3×105 cells.L−1), and higher biomasses were reported at sub-surface in March (0.43 mg Chl-a.m−3). Diatoms were the dominant group (e.g., Pseudo-nitzschia spp. and Chaetoceros spp.) except in November 2009 when coccolithophores dominated (e.g., Ophiaster spp.). Significant differences were found between seasons but not in space, and salinity appears to be an important factor contributing for this seasonal variation. The present study also provides, for the first time, a list of phytoplankton species for this seamount.