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Occurrence of toxic blue‐green algae in the Kucukcekmece lagoon (Istanbul, Turkey)

The concentration of microcystin (MC) in the Kucukcekmece Lagoon, Istanbul, Turkey, and the physicochemical and biological parameters of water quality were investigated from October 2000 to June 2003. Water samples were collected from surface waters at three sites. Most bloom samples were dominated by Microcystis aeruginosa. The major microcystin variants detected by HPLC‐PDA were microcystin‐YR and microcystin‐LR. Microcystin concentration increased dramatically from early summer to early autumn and thereafter tended to decrease. The toxin concentration found in the filtered samples from surface waters varied between 0.06 and 24.2 μg L−1 microcystin‐LR equivalents. Each year extensive fish mortality was recorded between mid‐June and early October, coinciding with heavy algal blooms. A comparison of the conditions associated with cyanotoxin episodes in 2000, 2001, and 2002 showed that the microcystin increase was related to temperature, high concentration of dissolved nutrients, high light intensity (PAR). The highest MC concentrations were recorded at temperatures between 24°C and 28.5°C. Field data showed that the highest MC concentration (>3 μg L−1) and the highest cyanobacterial biomass (>30 mg L−1) corresponded to a total nitrogen:total phosphorus ratio greater than 7:1. The highest concentrations of M. aeruginosa biomass (173 mg L−1) and MC (24.2 μg L−1 MC‐LR equiv.) and the highest salinity (8.8%) were measured concurrently in the lagoon. To our knowledge, this is the first evidence of cyanobacterial toxins in the Kucukcekmece Lagoon. © 2005 Wiley Periodicals, Inc. Environ Toxicol 20: 277–284, 2005.