A Rare Bloom of Leptocylindrus minimus Reveals Seasonal HAB Risk in the Southern Waters of Portugal.

This dataset provides the underlying quantitative data for the manuscript, documenting phytoplankton community dynamics off the Faro-Olhão inlet (FO) in the Algarve, Portugal from September 2020 to April 2021. The repository includes: Environmental Data: Chlorophyll a (Chl a) concentrations measured in mg m-3 and size-fractionated phytoplankton abundance. Phytoplankton Community Composition: Cell counts (cells L-1) for Nanophytoplankton (<10 µm), Cryptophytes, Diatoms, and Dinoflagellates. HAB Monitoring: Abundances for Harmful Algal Bloom (HAB)-related genera, specifically Prorocentrum spp., Dinophysis spp., Pseudo-nitzschia spp., and Dictyocha spp. Tidal and Seasonal Context: Seasonal categorisation (Summer, Autumn, Winter, Spring) and tidal regime details (Ebb/Flood) associated with each sampling event. Protocols used: Chlorophyll a Determination: Calculated using spectrophotometric equations as per Lorenzen (1967) and Parsons et al. (1984) Taxonomic Identification: Performed using the Utermöhl method (Utermöhl, 1958) for quantitative phytoplankton analysis.