A comparative analysis of the phytoplankton from six pampean lotic systems (Buenos Aires, Argentina)

Phytoplankton, as well as physical and chemical variables of six lotic systems of Buenos Aires province, tributaries of Río de la Plata river (Rodríguez, El Gato, El Pescado, Buñirrigo and J. Blanco streams, Samborombón river) were analysed and results were related to the degree of anthropic pollution. Surveys were carried out seasonally from May 1997 to June 1998. Sample sites were stablished at 2 or 3 stations depending on the length of the systems, from the headwaters to the mouths. Specific composition, species richness, dominance, diversity and eveness were assessed. Diatoms and clorophytes presented the highest number of species. Cyanobacteria were dominant in 60% of the samples and diatoms were subdominant in 42% of them. Samborombón river showed minimun and maximun phytoplankton densities among the six systems (50 cell.ml^–1 and 188475 cell.ml^–1, respectively). Indexes values showed a non-defined pattern, increasing or decreasing in the most polluted sites. The first axis of the PCA which included the physical and chemical variables is characterized by the nutrient concentrations and it is related to the pollution of these systems, separating samples of Rodríguez and El Gato streams, which presented high positive scores, from the rest of them. The second axis is represented by variables which determine the water conductivity and separates samples from the mouths of Samborombón river and Buñirrigo stream, which presented high positive scores, from the rest of them. The species PCA indicate that its distribution is related to the first two components of the chemical data set PCA. The first axis separates species found in high-conductivity sites, such as the mouths of Samborombón and Buñirrigo systems (i.e. Cocconeis placentula, Aulacoseira granulata, Melosira varians, Actinocyclus normanii, Dictyosphaerium ehrenbergianum) from those registered in low-conductivity sites, such as J. Blanco stream (i.e. Pseudanabaena catenata, Nitzschia gracilis, Mallomonas sp.). The second axis separates and mesosaprobic species from polluted sites -Rodríguez and El Gato streams- (i.e. Gomphonema parvulum, Navicula cryptocephala, Nitzschia palea, N. umbonata, Oscillatoria amphibia, Lyngbya limnetica, Euglena acus) from those found in oligosaprobic non-polluted sites – J. Blanco stream – (Nitzschia gracilis, Pseudanabaena catenata, Gomphonema clavatum).     

Species richness in some Neotropical (Costa Rica) and afrotropical (West Africa) lotic communities of Chironomidae (Diptera)

Drift collections of pupal exuviae from 2nd–5th order streams of the Guanacaste National Park in Northwest Costa Rica and from 3rd–6th order streams of the West African countries of Guinea, Ivory Coast, Sierra Leone and Togo have revealed high community (alpha) and regional (beta) levels of species diversity.Samples have been processed from 13 streams of the Guanacaste N. P. including two, Quebrada Las Yeguitas (2 stations) and Rio Tempisquito, for which year-long series were available. A total of 266 species level taxa have been recognized from these streams and are distributed over the higher taxa as follows: Chironomini-73, Pseudochironomini-4, Tanytarsini-55, Orthocladiinae-92, Macropelopiini-5 and Pentaneurini-37. The two sites on the Q. Las Yeguitas have a combined total of 216 species, and together with R. Tempisquito a total of 238 species. The single richest sample (Q. Las Yeguitas, Orosi station, 1990-Jan.-9) contained 102 species.Samples have been processed from 31 West African Streams which, for the most part, are represented by single samples. A total of 299 species level taxa have been recognized from these streams which are distributed over the higher taxa as follows: Chrinomini-139, Tanytarsini-62, Orthocladiinae-56, Coelotanypodini-2, Macropelopiini-3 and Pentaneurini-37. The single largest collection, containing 175 species, was taken from the Upper Dion River, a 6th order stream in the Upper Niger basin of the Guinean highlands.The compositions of the two regional faunas show similarities in two general features: they are both taxonomically narrow (few subfamilies and tribes) and taxonomically deep (many closely related genera, often with a relatively large number of closely related species). The high alpha diversity values require an ecological explanation, most probably along the axes of resources (time, space and food). The high regional diversities require an historical explanation. It is proposed that great climatic variation during the Pleistocene coupled with great geographic alteration of the connection between North and South America may be responsible for both the taxonomic narrowness and depth seen in the chironomid faunas of West Africa and Costa Rica.     

An introduction to a special issue on lotic meiofauna

• 1 This special issue focuses on the meiofauna of lotic freshwater systems, providing a review of the biology and ecology of this relatively poorly studied constituent of the benthos in running waters.
• 2 Six papers review the biology and ecology of the major groups of lotic meiofauna: microturbellarians; rotifers and gastrotrichs; nematodes; water mites; microcrustaceans and tardigrades.
• 3 Current knowledge of the ecology of lotic meiofauna is presented further in six papers that also highlight important future directions for research.

     

The reproductive cycle in the population of Saccostrea cuccullatta (Born) from the coast of Karachi,Pakistan

Periphytic diatom communities on clay tile and sterilized rock substrates were compared with those on natural substrates. Clay tiles yielded diatom communities with the least variability between replicate samples, and the greatest similarity to the natural substrate assemblage. The advantages of utilizing introduced substrate communities and problems encountered with their simulation of the natural substrate community are discussed.     

A new species of Gyraulus (Gastropoda: Planorbidae) from Ancient Lake Lugu,Yunnan-Guizhou Plateau,Southwest China

A new aberrant species of the planorbid genus Gyraulus, Gyraulus luguhuensis n. sp., is described from Lake Lugu (Lugu-hu, in Chinese), Southwest China. The generic assignment with Gyraulus is based on features of the genital anatomy that are characteristic for members of that genus, in particular the presence of a chitinized penial stylet. Gyraulus luguhuensis n. sp. differs from most other congeners by its large, thick shell with an elevated spire. Similarly, aberrant shells are known from congeners in other Ancient Lakes worldwide indicating a potentially convergent evolution of shell characteristics in exclusively lacustrine species. Gyraulus luguhuensis differs from other lacustrine Gyraulus species with similarly large shells in having a sub-terminal penis pore and an unkeeled shell.     

Variation in nutrient limitation of lotic and lentic algal communities in a Texas (USA) river

Nutrient limitation of periphyton and phytoplankton was assessed in the Upper Guadalupe River, Texas USA. Nutrient-diffusing substrates with added nitrogen (N) and phosphorus (P) were used to identify the limiting nutrient for lotic algae at three river sites in summer, fall, and winter. Pots enriched with P had significantly higher chlorophyll a concentrations for 7 of 9 trials. Added N alone did not significantly increase algal standing crops, although it was found to be secondarily limiting on one (and possibly two) occasions. Flow-through enrichment experiments were conducted in order to quantify the concentration of P needed to significantly increase algal standing crops. Response to enrichment was rapid when ambient P concentration was low (< 0.010 mg L^–1), but more moderate when ambient P levels were higher (0.015–0.025 mg L^–1). Nutrient limitation of phytoplankton in small surface-release reservoirs varied throughout the study, but N was either primarily or secondarily limiting in 6 of 8 trials; shifts in the limiting nutrient were correlated with fluctuations in flow into the reservoirs. Our enrichment studies show that algal response to nutrient addition was unpredictable as phytoplankton tended to be N-limited while periphyton was mainly P-limited. Further, while discharge apparently dictated the nutrient-biomass relationship for phytoplankton in reservoirs, ambient nutrient level is an important determinant of lotic periphyton response to enrichment.     

Fish fauna and environments of the Pilcomayo-Paraguay basins in Formosa,Argentina

The ichthyofauna from subtropical (East) and tropical (West) areas in the Formosa province (Northern Argentina) is analyzed. An up-to-date list of fishes is provided, including 18 new reports for environments associated with the Pilcomayo and Paraguay rivers, considering the detailed distribution of the fishes. Dominant families in terms of number of species are Characidae, Pimelodidae, Loricariidae and Curimatidae. Percentage of individuals (about 5000 examined) were 66% for characoids and 25% for siluriforms, with less than 10% for other groups. Comparisons were made with other South American environments. Most frequent species were Psellogrammus kennedyi, Astyanax bimaculatus, Gymnocorymbus ternetzi, Hoplosternum thoracatum and Cichlasoma portalegrense. The predominant type of environment sampled, of small size and shallow depth, with extensive plant cover, and temporal level variations, explains the dominance of the above groups. This interpretation is supported by independent studies. Diversity values ranged between 0.71 and 3.92. A marked reduction in number of species from East to West was observed (79 and 41 species respectively, 31 shared). No species of Gymnotidae, Hemiodidae, Characidiidae, Trichomycteridae, Lebiasinidae nor Aspredinidae were captured in the West. The higher number of species in eastern environments is considered to be due to the influence of the Paraguay river and the complex hydrology of the area. Other factors, both historical and ecological are considered. A correlation between total phosphorous content in the water and fish richness is also suggested. Water chemistry is compared with near by environments. Sites studied showed pH values from 6.14 to 7.5. The dissolved solid contents ranged from 51.8 to 474.3 mg 1^–1, within the hypohaline level. Ionic composition differed somewhat between East and West, water in the East being mainly hypocalcic, as in the Paraguay river. Conductivity was rather variable and Secchi disk values similar to those in the Parana river.     

Persistence and stability of lotic invertebrate communities in New Zealand

1. Persistence and stability of lotic invertebrate communities were determined at an annual time scale over a 9‐year period (1990–98) at 26 river sites over the northern half of New Zealand. In addition, a number of water quality variables were measured monthly and flow information collected continuously over the same period at each site. 2. The aim of the study was to describe the levels of interannual variability in invertebrate communities, and relate community changes to variability in environmental conditions. The consequences of this temporal variability for the sensitivity of predictive models were also investigated. 3. Levels of change in environmental conditions varied significantly between years, but were relatively similar across sites. In contrast, community persistence (similarity between years in species assemblage composition), and stability (similarity between years with respect to relative abundance of species in the community) both varied significantly between sites, but changes between years were similar. Community stability was highest at sites with relatively harsh flow conditions (high coefficient of variation, high relative size of floods), and was also greater in communities dominated by Ephemeroptera. 4. Relationships between change in environmental conditions and changes in community composition and structure were relatively weak for most individual sites. However, when average levels of change for each of the 26 sites were used, communities showed greater persistence under conditions where flow conditions remained relatively constant. Water quality changes had no significant effect on community persistence when assessed for all 26 sites combined. 5. Results from this study suggest that lotic invertebrate communities fluctuate around a relatively stable state, at least over a 9‐year period. However, the extent of interannual variation in community composition and structure observed, along with the relatively low degree of cluster fidelity observed within a single region, suggests that predictive models based on reference site conditions extrapolated over several years should be applied with caution in New Zealand streams.     

A portable pump sampler for lotic periphyton

A sampling technique for collecting lotic periphyton on sedimentary substrates using a peristaltic pump is described. Quantitative samples of periphyton standing crop and colonization rate are collected by the same procedure. The technique eliminates human disturbance problems associated with floating artificial samplers by establishing permanent sampling sites directly on submerged substances.     

Evaluation of the meiobenthic copepod Bryocamptus zschokkei (Schmeil) as an ecologically-relevant test organism for lotic freshwaters

Despite proven utility as ecotoxicological testorganisms in marine systems, harpacticoidcopepods have not been used in freshwaterbiomonitoring. Here we assess the value ofBryocamptus zschokkei, a common member ofmeiofaunal stream communities, as a testorganism for lotic systems by measuring theeffects of copper on acute (survival ofovigerous females) and sub-lethal (offspringproduction, juvenile [i.e. naupliar andcopepodite] development times) end points. Allovigerous females survived exposure atconcentrations <180 µg Cu l^–1, butat >180 µg Cu l^–1, mortalityincreased with exposure times up to 72 h;seventy-two and ninety-six hour LC50s wereidentical (290 µg Cu l^–1). After sixtydays, total offspring production per femaledeclined with increasing copperconcentration; no offspring were producedat 150 µg Cu l^–1 and significantlyfewer offspring were produced at 100 µg Cul^–1 compared with the control. In thejuvenile development tests, nauplii andcopepodites did not survive at 150 µg Cul^–1, but there was no significant effecton development times at lower Cu concentrations(0–100 µg Cu l^–1). Comparison oflaboratory-derived, toxicity end points withdata for B. zschokkei populations incopper-contaminated streams in south-westEngland, demonstrated that significant declinesin the number of surviving offspring closelymatched concentrations of copper across whichdeclines in field populations occurred. Theseresults indicate that B. zschokkei haspotential as an ecologically-relevant testorganism for lotic systems.     

The responses of a lotic mayfly Nousia sp. (Ephemeroptera: Leptophlebiidae) to moving water and light of different wavelengths

1. Although laboratory studies of the behaviour of aquatic macroinvertebrates are common, there has been little critical evaluation of the importance of test conditions to them. We used a common Australian leptophlebiid mayfly, Nousia sp., to investigate responses to light, wavelength of light, presence or absence of cover and still or flowing water.
2. Nousia sp. showed substantial qualitative differences in behaviour, as measured by movement, when there was no refuge (in the form of a crevice beneath a tile) present in the experimental arena.
3. We found no evidence of diel periodicity in activity in Nousia sp.
4. Nousia sp. did not respond to infra-red, red or green light at a flux density of 18–19 μmol m^–2 s^–1.
5. Nymphs were three times more likely to remain stationary in flowing water (mean velocity 0.10 m s^–1) than in still water.
6. We conclude that generalized assumptions about test conditions for experiments designed to quantify laboratory behaviour in benthic macroinvertebrates are unjustified and that evaluation of the individual requirements of test species should be conducted routinely.     

Culicidae (Diptera) selection of humans,chickens and rabbits in three different environments in the province of Chaco, Argentina

Studies were conducted to determine the selection of humans, chickens and rabbits by Culicidae in three different environments in the province of Chaco, Argentina. Mosquitoes were collected fortnightly using cylindrical metal traps containing animal bait (chickens and rabbits). The mosquitoes were collected between June 2001-May 2002. During the same period and with the same frequency, mosquitoes biting the human operators of the traps were collected during the first 15 min of exposure within different time intervals: from 09:00 am-11:00 am, 01:00 pm-03:00 pm, 05:00 pm-07:00 pm and 09:00 pm-10:00 pm. A total of 19,430 mosquitoes of 49 species belonging to 10 genera were collected. Culex species mainly selected chicken bait and Wyeomyia species selected rabbit bait. Ochlerotatus and Psorophora species were more abundant in rabbit-baited traps. Anopheles triannulatus, Coquillettidia nigricans, Ochlerotatus scapularis, Mansonia titillans and Psorophora albigenu showed a strong attraction for human bait. The Anopheles, Coquillettidia, Culex and Mansonia species were more active between 05:00 pm-09:00 pm, while Ochlerotatus, Psorophora, Haemagogus and Wyeomyia were most active from 09:00 am-07:00 pm. This study provides additional information about the biology and ecology of arbovirus vectors in Chaco.     

Rotifers from Saladillo river basin (Santa Fe province,Argentina)

Seventy two taxa of rotifers, belonging to 24 genera, are recorded from Saladillo river basin for the first time. Among them twelve are new for Argentina. These especies are described and illustrated. Ecological and biogeographical information is also given.     

Yeast diversity in the acidic Rio Agrio-Lake Caviahue volcanic environment (Patagonia, Argentina)

The Rio Agrio and Lake Caviahue system (RAC), in Northwestern Patagonia, is a natural acidic environment. The aims of this study were to characterize the yeast community and to provide the first ecological assessment of yeast diversity of this extreme aquatic environment. Yeast occurrence and diversity were studied at seven sites where the water pH varied between 1.8 and 6.7. Yeast CFU counts in the river ranged from 30 to 1200 CFU L⁻¹, but in the Lake the values were lower (30–60 CFU L⁻¹). A total of 25 different yeast species were found, 11 of which belonged to undescribed taxa. Among these was an unusual strongly acidophilic Cryptococcus species. The RAC yeast community resembles that of acidic aquatic environments resulting from anthropic activities such as the São Domingos mines in Portugal and the Rio Tinto in Spain, respectively. The isolated yeast species were organized into different grades of adaptation to the RAC aquatic system. Based on the proposed grades, Rhodotorula mucilaginosa , Rhodosporidium toruloides and two novel Cryptococcus species were the most adapted species. These Cryptococcus species are apparently specialists of acidic aquatic environments, and might bear physiological features that possibly account for their ability to thrive in such extreme environments.     

Description of the larva of Kempnyia colossica (Navás) (Plecoptera: Perlidae) with biological notes

In this paper, the larva of Kempnyia colossica (Navás 1934) is described based on material collected in Parque Estadual Intervales, São Paulo State, and biological notes are presented.     

The genus Dyschoriste (Acanthaceae) in Bolivia and Argentina

Recent field work in Bolivia has resulted in the recognition of new species ofDyschoriste (Acanthaceae). These novelties are introduced here for the convenience of other taxonomists prior to the publication of a treatment of the Acanthaceae of Bolivia. Three new Bolivian and one new Argentinean species ofDyschoriste,D. axillaris, D. boliviana, D. ceciliae, andD. prostrata are described, illustrated, and compared to their closest relatives.     

A new species of Ilyocryptus (Anomopoda: Macrothricidae) from Argentina

I. elegans n.sp. from the Parana River, northeastern Argentina is proposed and its morphological features are compared with those of the apparently related I. agilis. Its outstanding characteristics are the long 2rd to 5th setae of ventral margin of the valves, the rudimentary nature of defensive setae, the low number of spines in the preanal lobe of postabdomen and the unequality of the length of the setae in the outer distal lobe of first trunk limbs.Finding of this new species suggests that I. agilis would be a complex of species and its records should be revised.     

Variations in the periphytic community structure and dynamics of Lake Nahuel Huapi (Patagonia,Argentina)

Little is known about periphyton community in Patagonia and the influence that urban development has on a particular water body. Lake Nahuel Huapi is located in a National Park with little industrial or agricultural activity in the basin, but it is influenced by urban discharges from San Carlos de Bariloche, a town of 80000 inhabitants located on its south shore. Variations in structure and dynamics of the periphyton community in Lake Nahuel Huapi were studied during 1 year, to examine the influence of urban discharges on this community. Periphyton samples were collected on the shoreline of the lake and evaluated for biomass (as chlorophyll a concentration) and cell density of the main algal groups, at sites with and without urban influence. Results indicated the major influence of pollution from urban sources on periphyton at the most impacted sites, as well as the effect of different local events at each site (degree of contamination, type of coast, wind exposure, etc.). Higher biomass and cell densities at contaminated sites were evident, but the variation of main algal groups through the year was similar in all the sites. Periphyton in Lake Nahuel Huapi proved to be an important bioindicator of urban impacts on this water body.     

Bionomics of Aedes aegypti subpopulations (Diptera: Culicidae) from Argentina

Differences in biological features of immature and adult Aedes aegypti, as well as variability in vector competence, seem consistent with the existence of genetic variation among subpopulations and adaptation to local conditions. This work aims to compare the bionomics of four Ae. aegypti subpopulations derived from different geographical regions reared under temperate conditions. Life statistics of three Ae. aegypti subpopulations from the provinces of Córdoba, Salta, and Misiones were studied based on horizontal life tables. The Rockefeller strain was used as a control. The development time required to complete the larva and pupa stages varied from 6.91 to 7.95 and 1.87 to 2.41 days, respectively. Significant differences were found in mean larval development time between the Córdoba and Orán subpopulations. The larva‐pupa development time was similar in all the subpopulations. However, survival values varied significantly between the Orán and San Javier subpopulations. The proportion of emergent males did not differ from females within each subpopulation nor among them. Adult longevity was similar among the subpopulations. The average number of eggs laid by each female was significantly different. The Rockefeller strain laid a significantly greater number of eggs (463.99 eggs/female) than the rest of the subpopulations. Moreover, differences in the demographic growth parameter R_o were detected among the four subpopulations. The differences obtained in larval development time, larva‐pupa survival values, and net reproductive rates among the subpopulations might reflect underlying genetic differences as a result of colonization from different regions that probably involve adaptations to local conditions.     

Molecular characterization of carotenogenic yeasts from aquatic environments in Patagonia, Argentina

Fifteen aquatic environments (lakes, lagoons and rivers) of glacial origin in the northern Andean Patagonia (Argentina) were surveyed for the occurrence of red yeasts. Subsurface water samples were filtered and used for colony counting and yeast isolation. A preliminary quantitative analysis indicated that total yeast counts ranged between 0 and 250 cells l⁻¹. A polyphasic approach including physiological and molecular methods was used for the identification of 64 carotenogenic yeast strains. The molecular characterisation of the isolates was based on the mini/microsatellite-primed PCR technique (MSP-PCR) employing the (GTG)₅ and the M13 primers. Comparison of representative fingerprints of each group with those of the type strains of pigmented yeasts allowed the expeditious identification of 87.5% isolates. The sequence analysis of the D1/D2 domains of the 26S rDNA was employed to confirm identifications and in the characterization of the unidentified MSP-PCR groups. Teleomorphic yeast species were detected by performing sexual compatibility assays. The isolates corresponded to 6 genera and 15 yeast species, including four new yeast species of the genera Cryptococcus (1), Rhodotorula (1) and Sporobolomyces (2). Rhodotorula mucilaginosa was found in the majority of the samples and represented ca. 50% of the total number of isolates. However, this yeast was not detected in aquatic environments with very low anthropic influence. Other frequent yeast isolates were teleomorphic yeast species of Rhodosporidium babjevae, R. kratochvilovae and Sporidiobolus salmonicolor. This study represents the first report on red yeast occurrence and biodiversity in northwestern Patagonia. This revised version was published online in June 2006 with corrections to the Cover Date.