Nutrient limitation study on marine microbial abundance and photophysiology in coastal and offshore waters of the Canary region

The waters of the Canary Islands region undergo chronic nutrient limitation, resulting in oligotrophy and predominance of picoplankton throughout the year. Situated between the North Atlantic Subtropical Gyre (NASTG) and the highly productive Northwest African coastal upwelling system, and influenced by the continuous Saharan dust deposition, this region experiences a uniquely transient oceanographic regime. To understand nutrient limitation and the potential for nutrient co-limitation in the region, full-factorial nitrate (NO3-), phosphate (PO43-), and dissolved iron (Fe) enrichment bioassay experiments were conducted in coastal and offshore waters east of Gran Canaria in late September 2024. The response of marine microbes to these nutrient additions was measured after 48 hours of incubation. The quantified variables include concentrations of inorganic nutrients (nitrate + nitrite, phosphate and silicate), dissolved organic carbon and nitrogen, total dissolved iron, as well as marine bacterial and phytoplankton abundance and community composition. Additionally, high-resolution photophysiological responses – including maximum photochemical efficiency (Fv/Fm) – were monitored. Measurements were obtained using flow cytometry and a Single Turnover Active Fluorometer (LabSTAF) instrument for bulk photophysiology. This dataset provides key empirical evidence of primary nitrogen limitation, with minimal secondary phosphate limitation, and the absence of iron limitation in the region, offering a distinct contrast to the broader NASTG and advancing our understanding of oligotrophic marine systems such as the Canary Islands region.