ABSTRACT
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.
ABSTRACT
The present work analyses the individual growth of Heleobia piscium in natural conditions in coastal drainage channels of the Multiple Use Natural Reserve Isla Martín García, Buenos Aires, Argentina. Isla Martín García is located in the Upper Río de la Plata, to the south of the mouth of the Uruguay river (34° 11' 25" S and 58° 15' 38" W). Monthly collections were made from July 2005 to July 2006 in the eastern part of the island (Arena Beach). The population of H. piscium showed a complex and dynamic structure of sizes during a long period of the annual cycle. Two cohorts could be detected. The Bertalanffy growth equation was: Lt = 6 (1-e -1.85 (t+0.38)) and Lt = 3.9 (1-e -0.19 (t+4.84)) for cohorts 1 and 2, respectively. The pattern of population growth displayed a staggered model, where the greatest growth is observed during the summer. The reproductive period occurred during six months, from the beginning of summer to middle of fall. Based on only one reproductive effort, this pattern is not similar to that of other cogeneric species already studied.
O presente trabalho analisa o crescimento individual de Heleobia piscium em condições naturais em poças costeiras da Reserva Natural de Usos Múltiplos Ilha Martín García, Buenos Aires, Argentina. A Ilha Martín García está localizada no Rio da Prata superior, ao sul da desembocadura do rio Uruguai (34° 11' 25" S e 58°15' 38" W). Amostras mensais foram analisadas entre os meses de julho de 2005 e julho de 2006, no setor este da ilha (Praia de Arena). A população de Heleobia piscium se caracterizou por uma complexa e dinâmica estrutura de talhas ao longo de grande parte do ciclo anual. Duas cohortes puderam ser detectadas. A equação de von Bertalanffy para a cohorte 1 foi: Lt = 6 (1-e -1.85 (t+0.38)). Para a cohorte 2: Lt = 3.9 (1-e -0.19 (t+4.84)). O padrão de desenvolvimento da população mostra um modelo escalonado, estendendo-se o período de maior crescimento durante toda a estação do verão. A temporada reprodutiva se manifestou durante seis meses, desde o princípio do verão até meados do outono. Este padrão baseado em um único esforço reprodutivo não se assemelha ao de outras espécies congenéricas já estudadas.
Subject(s)
Animals , Fresh Water/analysis , Gastropoda/growth & development , Argentina , Gastropoda/classification , Population Density , Population Dynamics , Reproduction/physiology , SeasonsABSTRACT
The radula of five species of South American Ampullariidae was analysed by Scanning Electron Microscope (SEM) with the purpose of enlarging new studies on the systematic of this family. The studied species were Pomacea -canaliculata (Lamarck, 1822), Pomacea scalaris (d'Orbigny, 1835), Pomella (P.) megastoma (Gray, 1847), Asolene (A.) platae (Maton, 1809) and Felipponea neritiniformis (Dall, 1919). The central tooth shows different attributes which provide the means for generic determination; the analysis of the central tooth, the lateral and marginal ones by SEM adds further information for species differentiation.
A rádula de cinco espécies sul-americanas de Ampullariidae é analisada ao microscópio eletrônico de varredura com objetivo de fornecer novos subsídios à sistemática desta família. As espécies estudadas são Pomacea canaliculata (Lamarck, 1822), Pomacea scalaris (d'Orbigny, 1835), Pomella (P.) megastoma (Gray, 1847), Asolene (A.) platae (Maton, 1809) e Felipponea neritiniformis (Dall, 1919). O dente central apresenta novos subsídios à determinação genérica, o estudo ao microscópio eletrônico os dentes central, laterais e marginais acrescentam novos subsídios na determinação das espécies.