María Cristina Claps

Zooplankton diversity of a protected and vulnerable wetland system in southern South America (Llancanelo area, Argentina)

In arid regions, climatic conditions exert a great control on the aquatic systems present, but recent changes in climate have produced an enhanced salinization of the aquatic environments located there. Consequently, a major reduction in biodiversity would be expected in those wetlands that were originally fresh water. Salinity is a principal cause of reduced biodiversity particularly in zooplankton because few of those species can adapt to the salt pressure of saline environments. Therefore, the aim of this study was to gain essential information on the diversity of aquatic invertebrates in Llancanelo basin by focussing the analysis on the zooplankton community and exploring seasonal and spatial differences in the zooplankton assemblages of this vulnerable wetland system within an arid region of Argentina. Seasonal samples were taken at nine sites in the basin (a shallow lake, 4 springs, streams, and the Malargüe River). A total of 45 species were identified. The zooplankton abundance in the lake displayed a clear seasonal contrast and was higher than that recorded in the springs and lotic environments. Boeckella poopoensis, Fabrea salina, and Brachionus plicatilis predominated in the lake, indicating their halophilia. The presence of the crustaceans Alona sp., Macrocyclops albidus, and Paracyclops fimbriatus was restricted to the springs; whereas Notholca labis and Notholca squamula were found only in running water. The zooplankton species richness in the Llancanelo area is low because of both the salt content in the lake and the irregularity of freshwater entry in all locations during the annual cycle.

Pelagostrobilidium wilberti n. sp. (Oligotrichea, Choreotrichida): Morphology and Morphogenesis

ABSTRACT. Morphology, infraciliature, morphogenetic features, and some ecological data for Pelagostrobilidium wilberti n. sp. are described. This new species was collected from a temporary pond in Magdalena, Buenos Aires province, Argentina, which was sampled monthly from August 2003 to July 2005. The species was found in autumn and winter. Observations were made in vivo and after staining with protargol. Pelagostrobilidium wilberti n. sp. measures 63–84 × 42–49 μm in vivo and is conical in shape, with a posterior spine‐like cytoplasmic process. It possesses 6 somatic kineties, with kinety 2 sinistrally curved and shorter than the others. The oral apparatus is composed of 25–32 external and two internal membranelles. The macronucleus is horseshoe‐shaped and located beneath the oral apparatus; two or three spherical micronuclei lie dorsally. There is a posterior contractile vacuole. Morphogenesis is hypo‐apokinetal and begins dorsally between the curved kinety 2 and kinety 3. After the discovery of this new species, the diagnosis of the genus Pelagostrobilidium was amended.

Morphology and Notes on Morphogenesis during Cell Division of Deviata polycirrata n. sp. and of Deviata bacilliformis (Gelei, 1954) Eigner, 1995 (Ciliophora: Kahliellidae) from Argentina

ABSTRACT. Described herein are the morphology and certain morphogenetic stages of a new freshwater ciliate species, Deviata polycirrata n. sp., and of Deviata bacilliformis recorded in the soil of a dried temporary pond from Argentina. Ciliates were studied alive and after silver impregnation with Protargol. Deviata polycirrata n. sp. measures 130–180 × 45–70 μm in vivo. The species possesses 8–9 long cirral rows on the right and 9–13 on the left of the oral zone, and 3 dorsal rows of dikinetids. The adoral zone is composed of 39–48 membranelles. There are four macronuclear nodules and usually two micronuclei. A single contractile vacuole is located equatorially on the left body margin. This new species mainly differs from its congeners in having a higher number of cirral rows, the three long dorsal rows of dikinetids (vs. usually one to two dorsal rows of dikinetids), and a higher number of adoral membranelles. The other species reported here, D. bacilliformis, is recorded for the first time in Argentina. Unlike previous observations on this species, on the dorsal surface there are cirral rows that are preceded by cilia (combined cirral rows), and stomatogenesis begins with the proliferation of non‐ciliferous basal bodies some distance posterior to the buccal vertex.

Phytoplankton chlorophyte structure as related to ENSO events in a saline lowland river (Salado River, Buenos Aires, Argentina)

We analyzed the phytoplankton present in the lower sector of the Salado River (Buenos Aires, Argentina) for 10 years (1995–2005) and detected significant changes occurring in chlorophyte abundance and species richness during La Niña event (1998–1999), which period was analyzed throughout the entire basin (main stream and tributaries). We compared the physicochemical and biologic variables between two El Niño–La Niña–Southern Oscillation (ENSO) periods – El Niño (March 1997–January 1998) and La Niña (May 1998–May 1999) – to identify possible indicators of a relationship between climatic anomalies and chlorophyte performance. Chlorophyte density increased during the La Niña. Under normal or extreme hydrologic conditions, mobile (Chlamydomonas spp.) and nonmobile (Monoraphidium spp.) chlorophytes codominated. These species belonged to Reynoldss functional groups X1 and X2, those typical of nutrient-enriched environments. Comparative analyses between El Niño and La Niña periods indicated significant differences in physicochemical (K+, dissolved polyphenols, particulate reactive phosphorus, alkalinity, pH) and biologic (species diversity and richness, phytoplankton and chlorophyte total densities) variables between the two periods at all basin sites. During the La Niña condition, species richness was greater owing to interconnected shallow lakes and drainage-channel inputs, while the Shannon diversity index was lower because of the high abundance values of Monoraphidium minutum. A detailed analysis of the chlorophytes in the entire basin, indicated that changes in density and species dominance occurred on a regional scale although diverse chlorophyte assemblages were identified in the different sectors of the Salado River basin. After La Niña event, the entire basin had the potential to revert to the previous density values, showing the resilience to global environmental changes and the ability to reestablish the general conditions of stability.

Description of Deviata rositae n. sp., a new ciliate species (Ciliophora, Stichotrichia) from Argentina

ABSTRACT. Soil samples were taken from a temporary pond located in Buenos Aires province, Argentina, during the dry phase in the summer of 2005. The ciliates were studied alive and after staining with protargol. Deviata rositae n. sp. measures 112–154 μm in length and 21–28 μm in width in vivo and has a vermiform body. The contractile vacuole is located in the mid‐body on the left. The macronucleus is moniliform and there are 1–3 micronuclei. The oral apparatus is composed of 14–18 adoral membranelles and straight paroral and endoral membranes that never intersect each other. The somatic ciliature is arranged in four frontal cirri, one buccal cirrus, six long and slightly spiraled rows of cirri with the first right row extending up to the equatorial or sub‐equatorial region, and two dorsal rows of dikinetids. This new species of Deviata primarily differs from its congeners by the number of macronuclear nodules and the number and disposition of the dorsal rows of dikinetids.

Long-term study of plankton in Río Tercero Reservoir (Argentina) in relation to a nuclear power plant operation

The Río Tercero Reservoir was built for hydroelectric purposes in Córdoba Province, Argentina in 1936. Since 1983 the reservoir has been regulated by the requirements of a nuclear power plant of 600 MW; which uses the water for cooling, resulting in large water-level fluctuations. The warmer water (about + 7 •q is restricted to a sector in a bay. The aim of this study was to examine the plankton structure related to the functioning of the nuclear plant, based on data collected during 1977-2000, in the form o f Technical Reports (BoLTOVSKOY et al. 1979, 1981, MARIAzzi et al. 1994), papers (MA!uAzzi & CONZONNO 1980, MAiuAzZI et al. 1983, BOLTOVSKOY & FoGETIA 1985, EsCALANTE 1988, GOMEZ 1988, CoNZONNO & MARIAzzi 1991) and results of previous investigations by the current aurhors (MAluNELARENA et al. 1996, 1998, 1999, 2000).

A revised and updated checklist of Monogononta rotifers from Argentina

We provide here a checklist of species of Monogononta rotifers from lentic and lotic environments in Argentina, 25 years after the initial catalogue compiled by Susana B. Jose de Paggi. This new inventory now includes the reports on rotifers documented in 93 studies produced after 1990. The majority of the investigations were carried out in three of the 24 Argentine provinces. In addition, the presence of 13 species in samples from three water bodies within Buenos Aires province are now cited here for the first time in Argentina. In this updated checklist, a total of 351 species are catalogued, the majority being representatives of the Lecanidae, Brachionidae, and Lepadellidae.

Influence of temperature and conductivity on the life-history characteristics of a pampean strain of Brachionus plicatilis

In the present work, we provide the first approach about the life-history of Brachionus plicatilis in South America. We tested with laboratory experiments the response of the pampean strain of B. plicatilis for two of its main stressors (conductivity and temperature). We evaluated the effects of eight conductivity values from 1 to 17 mS.cm-1 and two temperatures (15 and 25 °C) to compare its abundance with those obtained in the pampean lotic and lentic environments, where this rotifer is frequent or dominant. The results demonstrated that the increase in population-growth rate and the peak of abundance occurred at the highest temperature and at medium conductivity. Minimum values were obtained at the lowest temperature and conductivities analyzed, but the final density attained was nevertheless similar to those recorded in the pampean environments at the optimum conductivity and during the spring and summer seasons. Males, mictic females, and resting eggs were observed at the minimum and maximum conductivities, revealing the strategy of this species for maintaining dominance in environments with fluctuating salinity. The experiments also indicated the possible behavior of this relevant member of the zooplankton community within a scenario of increasing temperature and salinity related to the climate changes occurring in the pampean region.

Phytomicrofauna of pampasic lotic environments (Argentina)

During 1985–1986, twelve rivers and streams belonging to the Delta Sub-basin (Río de la Plata estuary Basin, Argentina) were sampled for microfauna associated with fifteen species of aquatic macrophytes. A total of 171 species were determined. Ciliates and rotifers were most abundant. Dissimilarities in the colonization of the macrophytes were demonstrated. Water level and current influenced the periphyton community and contributed to the differences observed.