Research

Distribution of picophytoplankton communities from brackish to hypersaline waters in a South Australian coastal lagoon

Mathilde Schapira^1,2 , Marie-Jeanne Buscot¹ , Thomas Pollet³ , Sophie C Leterme^1,4 and Laurent Seuront^1,4,5

¹  School of Biological Sciences, Flinders University, GPO Box 2100, Adelaide SA 5001, Australia

²  Southern Ocean Group, Department of Zoology & Entomology, Rhodes University, PO box 94, Grahamstown 6140, South Africa

³  UMR CARRTEL, Centre Alpin de Recherche sur les Réseaux Trophiques des Ecosystèmes Limniques, Station d'Hydrobiologie Lacustre, Université de Savoie, 75 avenue de Corzent, BP 511, 74203 Thonon les Bains Cedex, France

⁴  South Australian Research and Development Institute, Aquatic Sciences, West Beach SA 5022, Australia

⁵  Center for Polymer Studies, Department of Physics, Boston University, 590 Commonwealth Avenue, Boston, MA 02215 USA

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Saline Systems 2010, 6:2doi:10.1186/1746-1448-6-2

Published:	24 February 2010

Abstract

Background

Picophytoplankton (i.e. cyanobacteria and pico-eukaryotes) are abundant and ecologically critical components of the autotrophic communities in the pelagic realm. These micro-organisms colonized a variety of extreme environments including high salinity waters. However, the distribution of these organisms along strong salinity gradient has barely been investigated. The abundance and community structure of cyanobacteria and pico-eukaryotes were investigated along a natural continuous salinity gradient (1.8% to 15.5%) using flow cytometry.

Results

Highest picophytoplankton abundances were recorded under salinity conditions ranging between 8.0% and 11.0% (1.3 × 10⁶ to 1.4 × 10⁶ cells ml^-1). Two populations of picocyanobacteria (likely Synechococcus and Prochlorococcus) and 5 distinct populations of pico-eukaryotes were identified along the salinity gradient. The picophytoplankton cytometric-richness decreased with salinity and the most cytometrically diversified community (4 to 7 populations) was observed in the brackish-marine part of the lagoon (i.e. salinity below 3.5%). One population of pico-eukaryote dominated the community throughout the salinity gradient and was responsible for the bloom observed between 8.0% and 11.0%. Finally only this halotolerant population and Prochlorococcus-like picocyanobacteria were identified in hypersaline waters (i.e. above 14.0%). Salinity was identified as the main factor structuring the distribution of picophytoplankton along the lagoon. However, nutritive conditions, viral lysis and microzooplankton grazing are also suggested as potentially important players in controlling the abundance and diversity of picophytoplankton along the lagoon.

Conclusions

The complex patterns described here represent the first observation of picophytoplankton dynamics along a continuous gradient where salinity increases from 1.8% to 15.5%. This result provides new insight into the distribution of pico-autotrophic organisms along strong salinity gradients and allows for a better understanding of the overall pelagic functioning in saline systems which is critical for the management of these precious and climatically-stress ecosystems.