Fitoplâncton na Baía do Almirantado, Ilha Rei George, Antártica: frações de tamanho, diversidade e traços funcionais

Abstract

The western shelf of the Antarctic Peninsula has experiencing increasing air temperatures while the climate is transitioning to a warm-humid subAntarctic-type of climate. As a consequence, abiotic changes are leading to alterations in the trophic web. In this sense, taxonomic composition, abundance and size class of phytoplankton community of Admiralty Bay, King George Island, Antarctic Peninsula were analyzed during the austral summer from 2009 to 2011 and from 2013 to 2015, across environmental gradients of sea surface temperature, salinity, Meltwater percentage (% MW), nutrient availability and Functional Diversity (FD), whose indices were calculated based on species traits. A broad range of nutrients was recorded, followed by a trend of increasing concentrations over the years analyzed. Two sampling periods (2013/14 and 2014/15) were influenced by Meltwater (> 2.25% MW); this parameter associated with nutrient availability and top-down control drives the community size structure. There was a dominance of the pico (0.2 - 2 µm) and nanoplankton (> 2 - 20 µm) classes, 1010 Cell.L-1 and 106 Cell.L-1, respectively; resulting a greater contribution of carbon biomass of these fractions (maximum of 1.61 x 103 µgC.L-1) indicating the importance of smaller fractions and the presence of a microbial trophic web in this region. In scenarios under influence of Meltwater, the microphytoplankton fraction was grouped into communities according to ecological and physiological tolerances, thus leading changes in the community-specific composition (e.g. diatom and dinoflagellate co-dominance) and greater FD. An increase in the dinoflagellate fraction of microplankton, notably with mixotrophic nutrition mode, as well as the dominance of smaller-sized classes can be considered triggers for changes in the structure of the Antarctic trophic web. Our results suggest using Admiralty Bay as a model for studies on changes in phytoplankton community structure, composition and Functional Diversity.