External morphological variations and temporal distribution of the dinoflagellate Ceratium hirundinella in two dam reservoirs in the Tigris River basin (Turkey)

Seasonal distribution, abundance, and external morphological changes of Ceratium hirundinella in the Kralkizi and Dicle dam reservoirs on the Tigris River were investigated during 1 year (February 2008 to January 2009). This species was present in both dam reservoirs during all 4 seasons. The highest mean density of C. hirundinella in Kralkizi Dam Reservoir was recorded in December, while in Dicle Dam Reservoir it was highest in June. C. hirundinella cells had a fourth horn in both dam reservoirs during the study period, and morphologically they showed the highest relative standard deviation in the fourth horn. In addition, a new fifth horn occurred on some cells, always between the antapical and postequatorial horns. Total length, length of antapical horn, and length of the fourth horn of C. hirundinella displayed significant seasonal variations (P < 0.05). The total cell length showed significant correlations with the length of the apical horn and the length of the antapical horn.