Spatial distribution of phytoplankton assemblages in the Nazaré submarine canyon region (Portugal): HPLC-CHEMTAX approach

The distribution and composition of phytoplankton assemblages were studied in the Nazaré submarine canyon, during an upwelling event, using high-performance liquid chromatography (HPLC) pigment analysis, complemented by microscopic qualitative observations. High chlorophyll a (Chl a) concentrations were recorded in the canyon head, near the coast, where values greater than 4 μg L− 1 were observed. In contrast, Chl a was relatively low in offshore regions, with values below 0.5 μg L− 1. The most abundant accessory pigments were fucoxanthin, peridinin, diadinoxanthin and 19′-hexanoyloxyfucoxanthin. Pigment data information was analyzed using the CHEMTAX software to estimate the contribution of different taxonomic groups to total Chl a. North of the canyon head, an area with high concentration of peridinin-containing dinoflagellates was identified (with presence of chain-forming toxic dinoflagellates). The presence of these organisms was associated with mixed water columns and phosphate values lower than the ones south of the canyon head, where a dominance of diatoms was recorded. The rest of the study region showed a dominance of prymnesiophytes and a significant contribution of cyanobacteria at oceanic stations. This study demonstrates the usefulness of using pigment analysis to study spatial distribution of phytoplankton groups in relation to a complex physical environment.

Research highlights
► Distribution of phytoplankton groups using HPLC pigment analysis.
► Submarine canyon as an important factor on nutrient input to the study region.
► Presence of toxic dinoflagellate species associated with a high N:P ratio.
► Diatoms associated with higher phosphorus Ks.