Temporal succession of tintinnids in the Northern Ionian Sea, Central Mediterranean

Vertical distribution, abundance, diversity and community structure of tintinnid assemblages were investigated at monthly intervals at one fixed station in the coastal Ionian Sea, Central Mediterranean, between March 2003 and May 2004. A total of 79 species belonging to 23 genera were identified; Dadayiella ganymedes, Steenstrupiella steenstrupii, Craterella torulata and Stenosemella nivalis contributed up to 50% of the tintinnid abundance. Two main changes in species composition as well as abundance were recorded, one in May and the other in November-December. In general, species richness remained unchanged along the water column (7 ± 1 species at each depth) while about 40% of the overall richness (31 species of 79) was represented by species that were found only once. H' ranged from 1.3 to 2.7, with the maximum values from September to January (H' 2.3-2.7) generally at the deep chlorophyll maximum depth. A cluster analysis showed that both abundance and diversity were strongly influenced by the hydrological characteristics of the site. Tintinnid diversity appeared to be positively linked to salinity (Spearman 0.47, P < 0.01) while negatively to chlorophyll. Our findings support the idea that the rapid shifts between the two dominant lorica oral diameter size-classes (29 and 34 ?m) could be considered a sensitive indicator of changes between coastal and pelagic ecosystems. Our data on tintinnid assemblages are coherent with those found along a longitudinal transect in the Mediterranean and contribute to the knowledge of tintinnid diversity and richness in a peculiar oceanographic coastal area of the Central Mediterranean Sea, a crucial point in the W- to E- tintinnid biogeography.