Fragilariopsis species composition and abun-

SUMMARY Species of the marine dinophycean genera Azadinium and Amphidoma (Amphidomataceae) mostly attract attention because of their production potential of the lipophilic polyether phycotoxin azaspiracid (AZA). The genus Azadinium probably has a very wide geographical distribution. Blooms of Azadinium from the continental shelf off Argentina have been observed back in the early 1990, but were just recently published, and the causative species, identified at that time as Azadinium cf. spinosum, could not unequivocally be determined. Here we retrospectively analyzed old archived samples of one of the South Atlantic Azadinium bloom from 1991 with electron microscopy. It turned out that the dominant nanoplanktonic dinophycean species in fact represent a new species which we describe here based on the morphology. Azadinium luciferelloides sp. nov. is a small (approximately 9–14 μm cell length) thecate dinoflagellate with the dominant plate pattern of the genus (Po, X, 4′, 3a, 6″, 6C, 5S, 6″′, 2″″), and with a small antapical spine. Azadinium luciferelloides differed from all other described species of Azadinium by the position of the ventral pore, which was located on the right ventral side in a notch of an otherwise symmetric pore plate. In addition, we recorded and documented the presence of other similar sized species of the Amphidomataceae in the samples. Our finding of Az. spinosum, Az. dalianense, Az. dexteroporum, and Amphidoma languida are the first record for the South Atlantic and thus describe an important range extension of these species. The diversity and importance of the Amphidomataceae for South Atlantic spring bloom plankton is now known and taxonomically documented, but cultures and/or analysis of AZA in field samples of the area are needed to clarify the AZA production potential of the local species and populations in order to finally evaluate the risk potential of AZA for AZA shellfish contamination in the Southwestern Atlantic region.

In Argentina, as in other countries of Latin America, cholera has occurred in an epidemic pattern. Vibrio cholerae O1 is native to the aquatic environment, and it occurs in both culturable and viable but nonculturable (VNC) forms, the latter during interepidemic periods. This is the first report of the presence of VNC V. cholerae O1 in the estuarine and marine waters of the Río de la Plata and the Argentine shelf of the Atlantic Ocean, respectively. Employing immunofluorescence and PCR methods, we were able to detect reservoirs of V. cholerae O1 carrying the virulence-associated genes ctxA and tcpA. The VNC forms of V. cholerae O1 were identified in samples of water, phytoplankton, and zooplankton; the latter organisms were mainly the copepods Acartia tonsa, Diaptomus sp., Paracalanus crassirostris, and Paracalanus parvus. We found that under favorable conditions, the VNC form of V. cholerae can revert to the pathogenic, transmissible state. We concluded that V. cholerae O1 is a resident of Argentinean waters, as has been shown to be the case in other geographic regions of the world.Cholera reemerged in Latin America in 1991 after being absent from the continent for nearly a century. In Argentina, there have been seven epidemics since 1992, all of which were caused by El Tor biotype Vibrio cholerae O1. These cholera outbreaks occurred mainly during the summer months, and, consistent with reports from other geographic regions of the world, strains of V. cholerae O1 were isolated from water samples collected from rivers during epidemic periods. However, the microorganism could not be recovered from the environment during interepidemic periods (12).V. cholerae is a natural inhabitant of aquatic environments, and it has been found to survive for extended periods in estuarine and brackish waters (12,13,15). Furthermore, in response to extreme environmental conditions, the bacteria may enter a dormant state (7, 30), which has been designated the viable but nonculturable (VNC) state, since the organism cannot be recovered by using traditional culture media. It has been hypothesized that it is in the VNC state that V. cholerae survives in the environment during interepidemic periods. Also, interaction with plankton appears to play an important role in the ecology of the microorganism and to facilitate persistence, mainly in response to low temperatures and reduced nutrient concentrations (12,13,14,19,21).In Argentina, V. cholerae non-O1 was isolated from samples collected from the Río de la Plata in previous studies (5). Several facts, such as the seasonality of the outbreaks most likely associated with temperature shifts and plankton blooms, suggested that there are environmental reservoirs of V. cholerae. Additionally, in a recent study in which the genetic diversity of V. cholerae O1 strains isolated during the seven outbreaks that occurred in this country was analyzed, most of the cholera toxin (CT)-producing strains were found to belong to a single clonal group already recognized as the Latin American epidemic stra...

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