Abundance and diversity of tintinnids (planktonic ciliates) under contrasting levels of productivity in the Argentine Shelf and Drake Passage

The relationship between the abundance and diversity of tintinnids and the concentration of chlorophyll a (Chla) was contrasted between neritic and oceanic waters of the SW Atlantic during autumn and summer. Chla and tintinnid abundance and biomass reached maximum values (17.53 μg L− 1, 2.76 × 103 ind. L− 1, and 6.29 μg C L− 1, respectively) in shelf waters during summer, and their mean values generally differed by one order of magnitude between environments. Peaks in species richness (13) and Shannon diversity index (2.12) were found in the shelf–ocean boundary, but both variables showed nonsignificant differences between areas. Species richness correlated significantly with both Chla and abundance. Such relationships, which followed a negative linear or quadratic function in the shelf and a positive linear function in oceanic waters, are thought to reflect either the competitive dominance of one species or a relatively wide spectrum of tintinnid size-classes, respectively.