Spatial trends and β-diversity of tintinnid ciliates along a salinity gradient in a temperate estuary (Río de la Plata, South America)

Abstract

The response of tintinnids to frontal processes and to strong gradients of salinity and suspended particulate matter was studied in the Río de la Plata estuary, one of the widest and most turbid in the world, and characterized by a quasi-permanent salt wedge regime. The tintinnid community was explored at different depths under strong stratification conditions along the main axis of the estuary, covering from fluvial to marine coastal waters. A total of 21 taxa belonging to 10 genera (Amphorides, Climacocylis, Codonellopsis, Eutintinnus, Luminella, Nolaclusilis, Salpingella, Stylicauda, Tintinnidium and Tintinnopsis) were identified. The highest number of species was found at polyhaline waters. Species abundances varied within 4 orders of magnitude and allowed differentiating the tintinnid community into three main assemblages, Riverine, Mid-estuary and Marine Coastal, with highest, intermediate and lowest mean abundances, respectively. Discrepancies between ordination analyses based on environmental variables and species abundances were found in locations associated with salinity fronts. The Estuarine Turbidity Maximum matched with the highest tintinnid abundances, while the halocline hosted the highest number of species. A small variability of β-diversity and its components (Abundance Difference and Abundance Replacement) were explained by salinity, temperature and Suspended Particulate Matter. A significant correlation was found between species contributions to β-diversity and the mean Lorica Oral diameter of taxa, probably due to the influence of prey size on the spatial distribution of tintinnids. General results emphasize the importance of site-to-site physical and biological conditions in the distribution of tintinnids within the Rio de la Plata estuary.