Seasonal succession of tintinnids in the Nervión River estuary, Basque Country, Spain

Abstract

The seasonal succession of tintinnids was examined in the outer part of the Nervión River estuary. Sampling was carried out at monthly intervals from March 2000 to March 2002. In this period, 21 species, belonging to 12 genera, were recorded, among which Tintinnopsis was the most abundant genus, contributing up to 86% of the total ciliate abundance. The maximum abundance was recorded in summer, with 7.4 x 103 individuals L-1 in July 2001, while the lowest value occurred in winter. A significant and positive correlation was found between temperature and tintinnid abundance. Most of the species showed a distinct seasonal occurrence and on this basis five different groups were differentiated. Two main changes in the species composition were recorded, one in March-April and the second in October-November. In this paper, the seasonal dynamics and the spatial distribution, as well as remarks on the morphology and ecology, of the most important tintinnid species in the estuary are given.