Microzooplankton (tintinnid ciliates) diversity: Coastal community structure and driving mechanisms in the southern Tyrrhenian Sea (Western Mediterranean)

To examine patterns and diversity of tintinnid assemblages, samples were collected twice a month from March 2003 to May 2004 at a coastal site in the Southern Tyrrhenian Sea (Western Mediterranean). Dynamics of tintinnid assemblage tracked the changes in hydrographical conditions and the rapidly varying meteo-oceanographic conditions. Two main assemblages were found: a neritic one characterized by Stenosemella nivalis and a pelagic one characterized by Dadayiella ganymedes. A total of 67 species were found; taxonomic diversity (Shannon H') ranged between 1.5 and 2.3 for most of the year. In summer, H' dropped to 0.2 due to a monospecific bloom of Tintinnopsis beroidea. Clear oscillations were present in spring 2004. Morphological diversity was examined based on lorica oral diameter (LOD). Median LOD of the community varied between 21 and 40 ?m and the number of LOD size-classes occupied by the species pool was 14. Morphological diversity as H'-LOD was ~25% less than taxonomic H'. Species abundance distribution (SAD) of the tintinnid community showed the common left-skewed overall pattern (with 14 singletons on a total of about 1700 specimens) associated with a general log-normality thus suggesting the influence of non-neutral processes such as competition and niche partitioning. Hence, the structure and dynamics of the coastal tintinnid community in the Southern Tyrrhenian Sea seemed to be driven by the underlying environmental conditions rather than by neutral dispersal of species. SAD deconstruction indicated that 56 species with occurrence lower than 8 times during the study can be considered as "occasional". Among the remaining 11 "core" species, 8 were cosmopolitan, 2 were neritic, S. nivalis and Tintinnopsis sp. and one a warm-water pelagic species, D. ganymedes.