Seasonality of phytoplankton community and dynamics of autotrophic carbon in a cold temperate port (Argentina)

The changes within and between seasons in phytoplankton composition and abundance determine the carbon biomass available for upper levels of the food web. Temporal changes in phytoplankton community and environmental parameters in a port in Puerto Madryn, Southwest Atlantic were analysed. During an annual period (2011-2012), samples of surface seawater were collected approximately monthly. We determined phytoplankton community structure (species composition and abundance) and biomass (determined by carbon content and chlorophyll a (Chl a)). Water temperature, salinity and transparency were measured when sampling the surface water and local meteorological data were considered. The main groups observed were diatoms (Bacillariophyta; the most abundant during the concentration peaks of Chl a), dinoflagellates (Dinophyta) and flagellates, which mainly included species of Cryptophyta and Chlorophyta. Diatoms exhibited blooms in March (summer-autumn) and September (spring), represented by Skeletonema costatum and Pseudo-nitzschia spp. respectively. Dinoflagellates contributed to the highest carbon biomass, with peaks in January (summer) and April (autumn), exemplified by Prorocentrum micans and Scrippsiella acuminata, respectively. Temporal differences in community composition were related to the seasonal changes in temperature, solar irradiance, precipitation, salinity and wind velocity. The environmental conditions seem not only to determine the species composition but also cell size distribution: nanoplanktonic (<= 20 mu m) species dominated mainly during late spring, summer and early winter while microplanktonic species (> 20 mu m) during late winter and early spring. Our results showed within-season changes and show that not only Chl a, but also carbon content can be considered, as the former is a biased estimator of phytoplankton biomass. This study provides the first seasonally resolved estimation in the area of the carbon biomass available for upper levels of the food web and a necessary information for future scenarios prediction. HIGHLIGHTS center dot Two diatom blooms were followed by an increase in dinoflagellate abundance.center dot Annual environmental conditions drive the phytoplankton community structure.center dot First seasonally estimation of autotrophic biomass availability for Patagonian trophic web.

Automated summary

The study investigates the temporal changes in phytoplankton community and environmental parameters in a port in Puerto Madryn, Southwest Atlantic. It found that diatoms exhibited blooms in summer-autumn and spring, while dinoflagellates contributed to the highest carbon biomass in summer and autumn. The environmental conditions drive the seasonally resolved estimation of autotrophic biomass availability for the Patagonian trophic web.