Phytoplankton along the coastal shelf of an oligotrophic hypersaline environment in a semi-enclosed marginal sea: Qatar (Arabian Gulf)

Phytoplankton biomass (chlorophyll a concentration), primary production, abundance, species diversity and species groupings were measured in the coastal waters surrounding Qatar (Arabian Gulf) at 13 stations in February 2010, July 2010, February 2011 and May 2011. In addition, a broad suite of physico-chemical characteristics were measured: temperature, salinity, pH, dissolved oxygen, turbidity, and nutrients (dissolved and particulate). Waters surrounding the Qatari peninsula were found to be highly diverse (125 species of diatoms, dinoflagellates and cyanobacteria were identified) but were low in both biomass (0.18–2.19 μg Chl a l−1) and productivity (0.14–0.97 mg C m−2 day−1). Phytoplankton physiology (Fv/Fm, σPSII, τQa, p) revealed acclimation strategies consistent with phytoplankton populations receiving ample light but insufficient nutrients. The finding of low primary production is consistent with water column nutrient ratios (DIN:P and DIN:Si ratios<1) and nutrient enrichment experiments in which the addition of nitrate or the addition of near-bottom waters stimulated biomass production of phytoplankton. This study in an oligotrophic, hypersaline semi-enclosed marginal sea is intended to contribute to the growing body of ecological information on this ecosystem functions.

Researchers at Qatar University (Environmental Studies Center), Texas A&M University at Galveston and Ministry of Environment would like to thank the Qatar National Research Fund (QNRF) for the support of Grant NPRP 08-497-1-086 . The captain and crew of the research vessel " Mukhtabar Al Bihar " who made the work at sea possible, and the Qatar University ESC laboratory staff and technicians where all chemical and biological analyses of the samples were accomplished in Doha, are thanked. The ideas and content of this paper do not reflect the views of QNRF but rather those of the manuscript authors. We thank the two anonymous reviewers and the editor for comments which enhanced the quality of the manuscript.

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