OCCURRENCE OF Nephtys fluviatilis (MONRO, 1937) AND Alitta succinea (FREY & LEUCKART, 1847) (ANNELIDA: POLYCHAETA) IN AN OLIGOHALINE ENVIRONMENT AT FAISQUEIRA RIVER, ANTONINA, PARANA

Abstract

Estuarine basins are known as ecosystems with a wide variation on some abiotic factors mainly due to the inflow of freshwater coming from the continent. Salinity is an example and variations on this environmental factor, from freshwater to ordinary salinity levels found in open seas, require certain physiological tolerance. Many species from several kinds of animals (crustaceans, mollusks, echinoderms, polychaetes) present this feature. Nephtys fluviatilis and Alitta succinea are two polychaete species that had already been reported in estuarine waters, but not yet formally reported in Faisqueira River (Paranagua Bay, southern Brazil) at salinity 0‰. Surveys were performed with plankton net in the same direction of the water flow during a crescent moon night. Current literature indicates that these species must certainly be tolerant to such salinity variations in the estuarine basins where they have already been observed; this fact might also be true at least for some of their close relatives, which have also been reported in places with similar abiotic conditions around the world. The presence of these polychaete worms suggest that they might occur in a wider range than currently known, including estuarine regions where water salinity reaches values close to 0‰.