cc-by-4.0Takolander, Antti2025-04-292022-08-232022-08-23https://datakatalogi.helsinki.fi/handle/123456789/6080This dataset contains ecophysiological measurements of brown algae Fucus vesiculosus and environmental variables, measured in different seasons in 2017 in the Northern Baltic Sea, SW Finland. More specifically, the measured parameters include in situ chlorophyll a fluorescence: Fv/Fm, maximum relative electron transport rate, and quantum yield of photochemistry. Carbon and nitrogen content, carbon:nitrogen ratio and chlorophyll a and c content were determined in the laboratory. Environmental parameters monitored include in situ irradiance, temperature, salinity, alkalinity, DIC, pCO2, HCO3-, CO32-, CO2, seawater nitrogen (NO2- and NO3-) and phosphorus (PO43-). Measurements were conducted in February, May, July, September and November in two sites, with additional three sites sampled in July. Irradiance was measured with 1 meter depth intervals from the surface. Irradiance values in the data are irradiances at F. vesiculosus sampling depths in each site, estimated with linear regression from the irradiance and depth data. Fv/Fm values for sites Spikarna, Ekö and Björnholmen in July were imputed from other variables using R package "Amelia". MacroalgaeBrown algaeChlorophyll fluorescenceSeasonalityEcophysiologydataset