Taxonomy and ecology of Synedropsis roundii sp. nov. (Bacillariophyta) from a tropical brackish coastal lagoon, south-eastern Brazil

A new Synedropsis species is described from a coastal tropical lagoon in south-eastern Brazil. This species has a single chloroplast in both views of the valve, apical pore fields composed of three slits, and uniseriate striae. It is planktonic and was found in brackish water. Synedropsis roundii is the eighth Synedropsis species to be described and the first to be found in a tropical region. We studied the seasonal dynamics of S. roundii, which can form blooms in the coastal Imboassica Lagoon, Rio de Janeiro state, Brazil. Continuous mixing of this shallow environment is suggested to be an important physical factor determining the success of the species. Availability of soluble reactive silicon is thought to be the main factor regulating the large biomass fluctuations. In the classification of Reynolds in 1997 (Vegetation processes in the pelagic: a model for ecosystem theory. Ecology Institute, Oldendorf, Germany, 371 pp.), S. roundii appears to belong to D-assemblage, a set of small and fast-growing diatoms, well represented in small, shallow and enriched waters. We also offer a tentative habitat template for S. roundii

Occurrence of anatoxin-a(s) during a bloom of Anabaena crassa in a water-supply reservoir in southern Brazil

Cyanobacterial blooms and the accompanying production of cyanotoxins are a serious global problem. Toxic blooms of Anabaena species are common in lagoons and reservoirs of southern Brazil. Worldwide, species of the genus Anabaena produce the majority of the known hepatotoxins (microcystins) and neurotoxins [anatoxin-a, anatoxin-a(s), and saxitoxins]. This report links a bloom of Anabaena crassa in the Faxinal Reservoir, the main water supply for the city of Caxias do Sul (400,000 inhabitants) in southern Brazil, to the occurrence of anatoxin-a(s) in the water. During the bloom period, the reservoir was strongly stratified, with higher temperatures and a deep anoxic hypolimnion. Two methods for sample concentration (direct and complete extraction) were tested, and direct extraction of samples proved to be more efficient. Water samples collected during the bloom showed 9% acetylcholinesterase inhibition at 50 mg mL−1, corresponding to 0.61μg of anatoxin-a(s) per gram of lyophilized powder. At these concentrations, symptoms of neurotoxicity and mortality were not observed in tests with Swiss albino mice. Although the concentrations of anatoxin-a(s) in the Faxinal Reservoir were low, these results are important because this is the first record of the toxin for A. crassa. Furthermore, this cyanotoxin is not yet included in Brazilian legislation for drinking-water monitoring, because of the lack of information about toxicity levels and risk calculation for oral doses. The data presented here contribute to the basis for the future inclusion of this toxin in Brazilian legislation for drinking-water quality control, and for the development of analytical methods for this toxin