The Use of Littoral Benthic Macroinvertebrates of the Martín Garcia Island Nature Reserve as Indicators of Water Quality

At Martín García Island—a Natural Reserve located at the confluence of the Paraná and Uruguay rivers—we used benthic-macroinvertebrate biotic indices to elucidate the structure and community parameters of the littoral benthos and their response to environmental variables and to evaluate the island's coastal water quality. Seasonal campaigns were carried out (March/1995-March/1996) at eight sites of the island's littoral sites, selected according to the substrate characteristics (fine sands, sandy-silty, reedbed, and silty with great hydrophyte development). From the sites with a soft substrate, triplicate samples were extracted using a 225-cm2 Ekman manual dredge. The relative abundances of 71 taxa were measured: Nematoda, Turbelaria, Oligochaeta (23 sps.), Mollusca (21 sps.), Crustacea (11 sps.), Insecta (12 families), and Tardigrada. Macroinvertebrate density: 15-58,800 ind.m-2. Analysis of variance revealed significant differences between the average annual macroinvertebrate-population densities among the five sites (F: 3.059; p<0.05). Site 7 exhibited the highest density at 38,700±19,000 ind.m-2 Community parameters: diversity (H'; 0.77-2.16 bits); equitability (J; 0.16-1.02), and species richness (S; 3-29). Canonical-correspondence analysis indicated the environmental variables experiencing the greatest fluctuation to be: dissolved-oxygen concentration, pH, temperature, and conductivity. The results of this analysis suggest that macroinvertebrate-species distribution involves the physicochemical conditions of the water. Of the correlation between species and environmental variables, 95.5% were distributed on the canonical-correspondence ordering diagram's Axis 1. Functional feeding groups: In all sites and seasons, the gathering collectors predominated, followed by the scrapers, filtering collectors, shredders, and predators. Macroinvertebrate Index of Pampean-Rivers: values generally ranged from weak to weak-to-very-weak to zero pollution, but there was a high degree of pollution (2.4 and 1.5) in the spring of 1995.

Biologic and Ecologic Aspects of Sinelobus stanfordi (Richardson, 1901) (Crustacea, Tanaidacea) in the Martín García Island Natural Reserve, Río de la Plata, Argentina

We investigated the biology and ecology of the tanaidacean Sinelobus stanfordi from the littoral water of Martín García Island at five sites along the coast chosen for their substrate characteristics, and classified the individuals according to size (mm) and ectosomatic characterinalysisstics as: manca III (0.60-1.19), juvenile male and female I (0.90-1.49), juvenile female II and copulatory male I (1.2-1.79), preparatory female I (1.8-2.39), preparatory female II (2.40-2.99), copulatory female I (2.40-2.69), copulatory female II (2.99-4.19), ovigerous female (1.80-3.59), copulatory male II (1.5-1.79), copulatory male III (2.10-2.69) and copulatory male IV (2.40-3.89). The smallest female with rudimentary ovisacs measured 1.84 mm. The tanaid density ranged from 0 to 10,548 ind.m-2. The average female-to-male sex ratio was 3.04:1. An abundance analysis indicated no significant differences among the sampling sites (X2 =4.037, p>0.001), while the fecundity (number of eggs) did not vary significantly with female size (r2 =0.2164, n = 19). The almost permanent presence of all developmental stages during every season of the year suggested a likely continuous year-long reproduction of S. stanfordi. Relationship between the water variables and S. stanfordi populations: The lower than optimal average electrical conductivity (160.24 μS.cm-1) for the species did not seem to limit the population-growth kinetics. The postmarsupial development throughout almost all the stages evidenced a significant positive correlation with pH. The soluble-reactive-phosphorus levels were within the low tolerance values as well as the NO-3 and the NH4 + and both close to optimal along with the near-optimal percent saturation of oxygen.

Fecundity of Uca uruguayensis and Chasmagnathus granulatus (Decapoda, Brachyura) from the "Refugio de Vida Silvestre" Bahía Samborombón, Argentina

The aim of the present work conducted at the Refugio de Vida Silvestre Bahía Samborombón is to analyse the most relevant aspects of the fecundity of Chasmagnathus granulatus and Uca uruguayensis. Samplings were carried out from March 2001 to February 2003. Ovigerous females of U. uruguayensis (N = 13) and C. granulatus (N = 25) were found during spring and summer, their sizes (CW) varied from 9.1 to 11.7 µm for the former species and from 22.8 to 32.4 mm for the latter. The egg diameter in U. uruguayensis ranged from 245 to 260 µm for embryos in the early stage of development and from 250 to 345 µm for those in mid-developmental stage, while in C. granulatus from 250t o 345 µm and from 260 to 365 µm respectively. Fecundity varied from 1126 to 6745 eggs/brood in U. uruguayensis and 15688-57418 eggs/brood in C. granulatus. For those females with broods in mid-developmental stage, several relationships were made. For U. uruguayensis the best correlation coefficients were obtained for the relationships: female weight vs. egg mass weight and carapace width vs. egg mass weight; for C. granulatus the best association was obtained between female size and the egg number and the egg mass weight.

O objetivo do presente trabalho foi analisar os aspectos mais relevantes da fecundidade de Chasmagnathus granulatus e Uca uruguayensis no Refúgio da Vida Silvestre Bahia Samborombón. As amostragens foram realizadas de março de 2001 a fevereiro de 2003. As fêmeas ovígeras de U. uruguayensis (N = 13) e de C. granulatus (N = 25) foram capturadas na primavera e verão. A largura da carapaça (LC) de U. uruguayensis variou de 9.1 a 11.7 mm, e de 22.8 a 32.4 mm para C. granulatus. O diâmetro dos ovos de U. uruguayensis variou de 245 a 260 µm para embriões em estágio de desenvolvimento inicial e de 250 a 345 mm para aqueles em estágio intermediário; para C. granulatus as variações foram de 250 a 345 µm e de 260 a 365 µm, respectivamente. A fecundidade de U. uruguayensis variou de 1126 a -6745 ovos/desova e para C. granulatus de 15688 a 57418 ovos/desova. Para as fêmeas com massa de ovos em estágio de desenvolvimento intermediário foram efetuadas várias relações: para U. uruguayensis os melhores coeficientes de correlação foram obtidos nas relações: peso da fêmea vs. peso da massa de ovos, e largura da carapaça vs. peso da massa de ovos. Para C. granulatus, a melhor associação foi obtida entre o número de ovos e o peso da massa de ovos.

Secondary production of Chasmagnathus granulatus (Crustacea; Decapoda) in a Ramsar Site from Argentina

Secondary production of Chasmagnathus granulatus was calculated at the Refugio de Vida Silvestre Bahía Samborombón, Argentina (36° 16' S and 57° 06' W). Sampling was conducted on nine occasions between March 2001 and February 2003, crabs were collected by hand, physico-chemical variables, granulometry and organic matter contents of the sediments were registered. Crabs were classified as male, female and undifferentiated, measured (total carapace width: CW) and weighed (wet and dry weight: DW at 60 °C, during 48 hours). A correlation analysis between CW and DW was made. Morphometric growth of C. granulatus was by the application of the power function (y = a x b), where the carapace width (CW) was used as an independent variable. Males, females and undifferentiated individuals were analysed separately as well as all together as a group. The data were fitted indicating a positive allometry (constant of allometry b > 3), the males showing the greatest allometric value. The individuals (n = 957 juveniles and adults) were separated in cohorts by the polymodal width-frequency distribution converted into normal curves. Three cohorts were found during the whole study period, and two cohorts coexisting in each sampling date. Ovigerous females were caught on December 2001, 2002 and February 2003. The size-frequency method was used to estimate the annual production. The major contribution to production was carried out by the mature individuals, in particular those with size between 25 and 30 mm, but on the other hand, only few individuals measuring from 10 to 20 mm were collected. The annual production of C. granulatus was estimated in 7.76 g.m-2. The biomass (expressed as total dry weight) varied between 0.55 and 1.85 g.m-2, with the greater values being registered during autumn and spring, and the lower values during summer.

Foram calculadas as primeiras estimativas da produção secundária de Chasmagnathus granulatus no Refúgio da Vida Silvestre Bahía Samborombón, Argentina (36° 16' S e 57° 06' W). As amostragens foram realizadas em nove ocasiões, entre o período de março de 2001 a fevereiro de 2003. Os caranguejos foram coletados manualmente. Variáveis físico-químicas, granulometria e teor de matéria orgânica dos sedimentos foram analisados. O caranguejos (n = 957, jovens e adultos) foram classificados em: machos, fêmeas e indiferenciados; foram mensurados (Largura da Carapaça, LC) e pesados (peso úmido e seco, PS a 60 °C, 48 horas). Uma análise de correlação entre LC vs. PS foi efetuada. O crescimento morfométrico de C. granulatus foi analisado pela aplicação da função potencial (PS = a LC b), sendo que machos, fêmeas e indivíduos com sexo não diferenciado foram analisados separadamente e em conjunto. O ajuste dos dados indicou uma alometria positiva, com os machos apresentando o maior valor. Os indivíduos foram separados em coortes por meio da conversão de curvas de normalidade de uma distribuição de freqüência polimodal. Três coortes foram encontradas durante todo o período de estudo, e duas coexistindo em cada data de amostragem. Fêmeas ovígeras foram coletadas em dezembro de 2001 e 2002 e em fevereiro de 2003. Utilizou-se o método da distribuição de freqüência de tamanho para estimar a produção anual. A maior contribuição para a produção é dada pelos indivíduos sexualmente maduros, particularmente por aqueles com tamanhos entre 25 e 30 mm. A produção anual foi estimada em 7,76 g.m-2. A biomassa, expressa em peso seco, variou entre 0,55 e 1,85 g.m-2, com maiores valores registrados no outono e na primavera, e menores valores registrados no verão.