In the shallow microtidal Patos Lagoon estuary, southern Brazil (32°07′ S-52°06′

A long-term study (monthly sampling, 1992 to 2007) was conducted in the surf zone of Cassino Beach, Southern Brazil, in order to detect possible natural and/or anthropogenic disturbances. Surface water temperature (6-29°C) was the only parameter with predictable seasonal variation; salinity (14-38) was inversely related to rainfall (3.1-485.2 mm month −1 ) and low values followed extreme precipitation periods in and 2002/2003. Asterionellopsis glacialis and chlorophyll a presented high concentrations and peak frequency until 1998, when an intense mud deposition occurred with concomitant extreme rainfall. It affected the surf zone and beach, changing the hydrology and dissolved inorganic nutrient availability. Six phytoplankton species groups were recognized with distinct responses to this mud deposition. We conclude that large-scale climatic changes, like El Niño Southern Oscillation, in conjunction with human activities significantly altered the phytoplankton ecology of the highly dynamic Cassino Beach surf zone.

A taxonomic survey of nanoflagellates in the extreme southern Brazilian coastal waters of the Patos Lagoon estuary and adjacent coastal shelf was undertaken using transmission electron microscopy. A total of 44 species was recorded including 42 nanoflagellates, one scale-bearing amoeba and two species incertae sedis. Scale-bearing haptophytes predominated (27 species), followed by prasinophytes (7), chrysophytes (6), pedinellids (2), incertae sedis (2) and one scale-bearing amoeba. Most of the species (42) are new records for Brazilian marine waters. Among the haptophytes, Chrysochromulina was the most species-rich genus, occurring mainly in high salinity waters, and C. simplex was the most frequent species. Scales of undescribed Chrysochromulina species were observed and documented. Other haptophytes present were Prymnesium parvum and Phaeocystis scrobiculata. Five scale-bearing prasinophytes of the genus Pyramimonas were observed including the uncommon species P. longicauda, in addition to Micromonas pusilla and Nephroselmis pyriformis. Among the chrysophytes, the scale-bearing Paraphysomonas species (4) and the loricate Dinobryon belgica were recorded. The pedinellids (Apedinella radians and Parapedinella reticulata), the amoeba Rabdiophrys sp. and the incertae sedis (Meringosphaera mediterranea, Thaumatomastix sp.) are all scale-bearing protists. The 44 taxa (mostly scale-bearing flagellate species) identified and the finding of further undescribed Chrysochromulina species indicate that only a fraction of the species present in the region are known, and that an effort must be made to increase general knowledge of biodiversity in these southern waters.

The biodiversity of marine heterotrophic protists is poorly known in the South Atlantic coastal zone (~32 °S) especially regarding the nanoflagellates. The presence of loricate choanoflagellates was reported for the first time in the Patos Lagoon estuary and the adjacent coastal zone. Seventeen species of eleven genera of loricate choanoflagellates were observed between October 1998 and May 2000 in fixed water samples (lugol's solution + glutaraldehyde) in a JEM 100-SX transmission electron microscope. Most species were recorded in euhaline and mixopolyhaline waters during the spring and summer, none in autumn and a few (four) in winter. The absence of choanoflagellates at the more sheltered inshore stations is due freshwater influence, and at the beach station, probably due the strong wave action. The probably cosmopolitan species Pleurasiga minima, Cosmoeca norvegica, C. ventricosa and Parvicorbicula circularis were present in spring or summer in the estuary channel and coastal area while Stephanoeca diplocostata which apparently prefers lower temperature, was recorded in winter. Calotheca alata and Campyloacantha spinifera are mainly temperate species and were present in spring. The new species Diplotheca tricyclica was recorded at the estuary channel in the summer 1999, in high salinity water.

We examined the morphology of Skeletonema species occurring in coastal waters of southern Brazil, on the basis of LM, SEM, and TEM analyses of six isolated strains and of 13 field samples from the Patos Lagoon estuary and the adjacent Cassino Beach. We concluded that the genus Skeletonema is highly diverse in coastal waters of southern Brazil, with the occurrence of four confirmed species: S. costatum, S. pseudocostatum, S. potamos, and S. tropicum. In addition, EM details must still be provided for S. menzelii, and genetic studies should be conducted to confirm the identity of S. cf. grethae and S. subsalsum. The high diversity in this geographic area can be attributed to the proximity of the Subtropical Convergence and to the freshwater ecosystems of Patos Lagoon and La Plata River that favor the presence of warm-, cold-, and brackish-water species.

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