MEPS prepress abstract  -  DOI: https://doi.org/10.3354/meps12435

Amino acid utilization by eukaryotic picophytoplankton in a coastal upwelling system

Marta Hernández-Ruiz*, Antero Prieto, Esther Barber-Lluch, Eva Teira

*Email: mhernandez@uvigo.es

ABSTRACT: The ability to combine autotrophic and heterotrophic nutritional modes by planktonic protists may significantly influence nutrient dynamics in the surface ocean. The extent and significance of organic resource utilization by small photosynthetic eukaryotes remain poorly explored. In order to evaluate the importance of autotrophy and heterotrophy within the most abundant pico-nanoeukaryotic phytoplankton groups in surface waters of a coastal upwelling area of NW of Spain we combined catalyzed reported deposition-fluorescence in situ hybridization and microautoradiography with radiolabeled bicarbonate or amino acids. Over an annual cycle in 2015, picoplanktonic taxa represented more than 55% of the pico-nanoeukaryotic cells. Ostreococcus dominated both in terms of abundance and activity during the nutrient-limiting spring-summer stratification period, when the utilization of amino acids was confirmed for dinoflagellates (range 22-33% of the dinoflagellate cells), haptophytes (range 23-88% of the cells) and the picoeukaryotic genera Micromonas (range 9-38% of the cells), Ostreococcus (range 10-38% of the cells) and Bathycoccus (range 19-22% of the cells). Our data suggest different nutritional strategies among the smallest plastidic protists, which likely implies contrasting functional roles and competitive abilities within the picoeukaryotic phytoplankton.