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The aim of the present work conducted at the Refugio de Vida Silvestre Bahı´a Samborombo´n, Argentina, is to analyse the most relevant aspects of the life cycles of Chasmagnathus granulatus and Uca uruguayensis: their abundance, size distribution and sex ratio in order to be used for make management purposes. A total of 1200 individuals of U. uruguayensis (megalopae, juveniles and adults) and 957 individuals of C. granulatus (juveniles and adults) were collected

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The biogeography and ecological preferences of Neotropical freshwater ostracods are poorly known, and more so the dynamics of populations and habitat selection of species living in pleustonic environments of temporary ponds. In the present survey we analyze the population changes of ostracods living in pleustonic environments of small freshwater bodies on Martín García Island (Río de la Plata, Argentina). Between June 2005 and June 2007, monthly samples of floating vegetation from eight different ponds on the island were collected, and limnological parameters were measured in situ. The results of multivariate logistic regression showed that the presence of ostracods was significantly related to high dissolved oxygen content and high water temperature. In addition, multivariate regression analysis indicated that, when ostracods were present, their total abundance was negatively related to floating vegetation dry weight. Four ostracod species were found: Strandesia bicuspis, Chlamydotheca incisa, Cypridopsis vidua, and Bradleytriebella trispinosa. The seasonal variation in abundances indicated that populations of the most common species, S. bicuspis and C. incisa, were denser during the summer and autumn months. The results of canonical correspondence analysis showed that individuals of S. bicuspis were more abundant at higher temperatures and lower conductivity than C. incisa. Further research is needed to clarify the observed negative correlation between floating vegetation dry weight and ostracod density and the possible differential thermal preference of the two species studied.

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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 mm 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 250 to 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.Keywords: fecundity, Uca uruguayensis, Chasmagnathus granulatus, Argentina. Fecundidade deUca uruguayensis e Chasmagnathus granulatus (Decapoda, Brachyura) no "Refúgio de Vida Silvestre" Bahía Samborombón, Argentina Resumo 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 µm 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.

Deroceras reticulatum is a misanthropic European species spread widely throughout South America. At the moment this species is considered a 'pest' in direct sowing such as maize, soybean, sunflower, wheat, alfalfa and clovers, among others. The aim of this paper is to report the first record of D. reticulatum in the Reserva de Usos Multiples Isla Martín García, Buenos Aires province and to provide information about this species distribution in five Argentina provinces.Keywords: Deroceras reticulatum, distribution, pest, exotic species, Argentina. Distribução de Deroceras reticulatum (Müller, 1774) (Pulmonata, Stylommatophora) na Argentina com primeiro registro na Reserva de Usos Múltiplos Ilha Martín García, Río de la Plata superior ResumoDeroceras reticulatum é uma espécie sinantrópica oriunda da Europa e com grande dispersão na América do Sul. Esta espécie é considerada atualmente praga dos cultivos de semeadura direta de milho, soja, trigo, girassol, alfafa e trevos, entre outros. O presente trabalho tem por objetivo comunicar o primeiro achado do agriolimácido D. reticulatum na Reserva de usos múltiplos Ilha Martín García, província de Buenos Aires e proporcionar informação sobre a distribuição desta espécie em cinco províncias argentinas.Palavras-chave: Deroceras reticulatum, distribuição, praga, espécie exótica, Argentina.

Freshwater amphipods of the genus Hyalella have a great importance in aquatic ecosystems due to their role in matter and energy cycling and its utilization as bioindicators of environmental health. The aim of this work was to analyze relevant population parameters of Hyalella pampeana, such as population density and structure, individual body size, sex ratio, fecundity and recruitment, and to study the possible relation of these parameters to variations in environmental variables. Samples were taken monthly during a one-year period (2006) at three small ponds in the Natural Reserve Island of Martín García, Argentina. The inland aquatic environments showed distinctive physicochemical characteristics, mainly related to pH and conductivity values. Amphipod population density varied among sites and throughout the year, with population peaks during spring, positively correlating with pH values. The operational sex ratio of the total population was almost equal to 1 male: 1 female, displaying seasonal variation. Mean fecundity and mean size of ovigerous females were higher during winter and early spring months than in summer months. The presence of ovigerous females and juveniles in all months indicated that reproduction is continuous during the year for Hyalella, in its natural environment.