Size-fractionated phytoplankton chlorophyll in an Eastern Mediterranean coastal system (Maliakos Gulf, Greece)

Abstract

The dynamics of phytoplankton biomass were studied in an Eastern Mediterranean semi-enclosed coastal system (Maliakos Gulf, Aegean Sea), over 1 year. In particular, chlorophyll a (chl a) was fractionated into four size classes: picoplankton (0.2–2 µm), nanoplankton (2–20 µm), microplankton (20–180 µm) and net phytoplankton (>180 µm). The spatial and temporal variation in dissolved inorganic nutrients and particulate organic carbon (POC) were also investigated. The water column was well mixed throughout the year, resulting in no differences between depths for all the measured parameters. Total chl a was highest in the inner part of the gulf and peaked in winter (2.65 µg l–1). During the phytoplankton bloom, microplankton and net phytoplankton together dominated the autotrophic biomass (67.2–95.0% of total chl a), while in the warmer months the contribution of pico- and nanoplankton was the most significant (77.5–93.4% of total chl a). The small fractions, although showing low chl a concentrations, were important contributors to the POC pool, especially in the outer gulf. No statistically significant correlations were found between any chl a size fraction and inorganic nutrients. For most of the year, phytoplankton was not limited by inorganic nitrogen concentrations.