First record of a brackish radiolarian (Polycystina): Lophophaena rioplatensis n. sp. in the Rý´o de la Plata estuary

BOLTOVSKOY DEMETRIO; KOGAN MARIELA; ALDER VIVIANA; MIANZAN HERMES

JOURNAL OF PLANKTON RESEARCH

OXFORD UNIV PRESS

Lugar: Oxford; Año: 2003 vol. 25 p. 1551 - 1559

0142-7873

Vertically stratified bottle plankton samples collected in the Río de La Plata estuary (Atlantic coast of South America at approx. 35°S), and in coastal waters off Mar del Plata (approx. 38°S) in December 1999 and November 2001 yielded up to 394 live cells per liter of a single new nassellarian species – Lophophaena rioplatensis sp. n. (family Plagoniidae). In estuarine waters the species was recorded at salinities as low as 15.4 PSU; densities in excess of 100 cells per liter were found at salinities ranging from 16.9 PSU. These extremely high concentrations (the highest ever reported in the literature), as well as the fact that over 90% of the individuals recorded are provided with cytoplasm, indicate that these are self-sustaining populations which thrive in the estuary (and in nearshore coastal waters) probably due to plentiful dissolved silica and an abundant food supply. L. rioplatensis is the first polycystine brackish-water species described. This finding shows that radiolarian fossils are not unequivocally associated with open-ocean conditions, but may also be useful indicators of coastal and brackish estuarine paleoenvironments.