Surface Microplankton Composition at a Hyper Saline Oligotrophic Environment of Bitter Lake on the Suez Canal, Egypt

摘要

The Bitter Lake is the central and most important water body of the Suez Canal as it contains 85% of the water of the canal system. This study reports the microplankton found occurring in the surface water of the Bitter Lake at monthly intervals from November 2008 until November 2009. A total of 130 taxa were identified, among which 67 taxa were of Bacillariophyceae, 15 Dinophyceae, 11 Chlorophyceae, 11 Cyanophyceae, 1 Euglenophyceae, 18 Tintinnidae, 4 Foraminiferidae, as well as 3 of Rotifera. Species diversity, numerical abundances and dynamics were analyzed for each taxon at three sites inside the Bitter Lake. At each of these sites Bacillariophyceae were predominant in the standing crop forming 67.2% of the total microplankton community with an average of 11,594 ind. L-1. The Dinophyceae occupied the second rank constituting about 16.5% of the total microplankton. Increase of microplankton abundance started in spring with maximum values being attained in late summer and early autumn (August ), with an average of 37,498 ind. L-1, while January was characterized by the lowest density (9,251 ind. L-1). Relatively higher diversity values were recorded at the northern part of the lake and a progressive decline in diversity was observed southward. Nutrient concentrations in the lake waters were very low, with silicate varying between 0.52-1.34 μM, phosphate between 0.14 and 0.55 μM and nitrate between 0.82-3.16 μmol L-1. Moreover, chlorophyll a fluctuated between 0.4 and 0.89 μg L-1. Data from microplankton analyses, nutrient (P) and chlorophyll a concentrations and transparency measurements were used to assess the ecosystem health of the Bitter Lake according to OECD, Canadian, and Quebec classification criteria, and it is concluded that the Bitter Lake be classified as an ultraoligotrophic lake.