Species-specific transparent exopolymer particle (TEP) during three harmful algal blooms (2022–2024) in an upwelling-influenced coastal bay

Transparent exopolymer particles (TEP) are key components of the marine carbon cycle, coupling biological productivity with biogeochemical and operational processes in coastal environments. This study quantified ex-situ surface TEP concentrations during three harmful algal blooms (HABs) in Todos Santos Bay (Mexico) between 2022 and 2024, each representing a different bloom stage and dominated by a distinct species: Prorocentrum micans (2022), Pseudo-nitzschia cf. australis (2023), and Lingulaulax polyedra (2024). Surface TEP concentrations increased from 163 μg XG eq·L −1 in 2022 to 693 μg XG eq·L −1 in 2023 and 778 μg XG eq·L −1 in 2024. The highest TEP-to-biomass ratio occurred during the P. australis bloom, coinciding with low nutrients levels (PO₄ 3− = 0.4 μM; NN = 2.4 μM) and moderate upwelling conditions (BEUTI = 1.0 mmol m −3 s −1 ). The L . polyedra bloom developed under stratified, warm conditions (SST ≈ 18.5 °C), with high PO₄ 3− concentration (0.8 μM) and operational impacts including filter clogging at a desalination plant. In contrast, P. micans occurred under higher nutrient availability (PO₄ 3− = 2.46 μM; NN = 6.9 μM) and lower TEP levels. TEP-C contributed up to 87 % of the particulate carbon pool during the P. australis event, suggesting species-specific physiological control on exopolymer formation. Overall, each event represented a different bloom stage, underscoring how bloom progression, species dominance, and environmental forcing together shape TEP dynamics in coastal upwelling systems. • First quantification of TEP during three HABs in an upwelling-influenced bay. • TEP-C reached 87 % of particulate carbon during the Pseudo-nitzschia cf. australis bloom . • Distinct bloom stages and nutrient regimes shaped species-specific TEP dynamics.