Long-term monitoring of hydrological dynamics and phytoplankton biomass indicator in three shellfish ecosystems of the English channel (2000–2024)

Abstract. This data paper presents a harmonized and quality-controlled dataset resulting from 24 years (2000–2024) of monthly monitoring at three coastal stations in Normandy, France: Blainville-sur-Mer, Saint-Vaast-la-Hougue, and Utah Beach. The dataset includes measurements of key physico-chemical parameters (temperature, salinity, pH, dissolved oxygen), biogeochemical variables (dissolved nutrients: nitrate, ammonium, phosphate, and silicate), and biological indicators (chlorophyll a concentration). Sampling was conducted using consistent protocols across stations, allowing for long-term comparison. All data have undergone validation and standardization to ensure their usability for environmental assessment and modeling purposes. The dataset provides valuable insights into the evolution of coastal water quality under the influence of climate change and anthropogenic pressures. Notable trends include increasing winter temperatures (especially since 2010), progressive ocean acidification at Blainville-sur-Mer, and changing nutrient regimes across the region, with a marked phosphate decline and spatial contrasts in nutrient limitation (phosphorus-limited on the East coast, nitrogen-limited on the West coast). These long-term observations are critical for understanding ecosystem dynamics, supporting coastal management strategies, and informing sustainable aquaculture development. The dataset is openly available and intended to support further interdisciplinary research in marine science and environmental policy (SMEL, 2024, https://doi.org/10.5281/zenodo.15058835).