Phytoplankton types and primary production in the Argentine Sea

Abstract

Several satellite models classify phytoplankton functional types (PFT) based on cell size. In this study we used field data from the Argentine Sea on both the photosynthetic and the bio-optical properties of phytoplankton to distinguish photosynthetic and bio-optical phytoplankton types (PBPT). Cluster analyses were run using data from 70 stations sampled during 3 periods to distinguish different PBPT, and principal component analysis was used to describe them. We examined the main taxonomic composition and percentage of chl a in the <5 µm size fraction found within the PBPT. The distribution of PBPT in relation to hourly primary production and environmental conditions was also investigated. The results showed a high degree of variability in biooptical and photosynthetic properties, e.g. the specific absorption coefficient of phytoplankton, aBph(440), varied between 0.015 and 0.067 m2 (mg chl a)−1, and the maximum production at light saturation, PB m, varied between 0.68 and 10.05 mg C (mg chl a)−1 h−1. This resulted in the discrimination f 11 PBPT. Some had similar average cell sizes but differed in their bio-optical or photosynthetic characteristics, e.g. PBPT1 (with diatoms <5 µm and Emiliania huxleyi 2–5 µm) and PBPT6 (with diatoms <5 µm and coccal cells ~2 µm) had markedly different PB m values (PBPT1: 1.20 mg C (mg chl a)−1 h−1 and PBPT6: 6.71 mg C (mg chl a)−1 h−1). This variability in the bio-optical and physiological properties is most likely the result of adaptation by phytoplankton communities to the high heterogeneity in environmental conditions in this region. These results indicate that satellite models describing the distribution of PFT based on cell size alone will not provide a realistic representation of the phytoplankton composition in this highly productive and heterogeneous area.