Laura C. Armendáriz

Macroinvertebrates associated with Limnoperna fortunei (Dunker, 1857) (Bivalvia, Mytilidae) in Rio de la Plata, Argentina

An analysis was made of specific richness (S), specific diversity (H), equitability (J), frequency (F), dominance (Dm) and density (D) of the macroinvertebrates associated with the invasive species Limnoperna fortunei (Dunker, 1857), was made.Limnoperna fortunei caused an increase in the specimen number on the rocky environment studied. The species richness and abundance of different taxa of macroinvertebrates, except mollusks was positively related to the presence and density of L.fortunei. Autochthonous gastropod species conversely, tended to be displaced.

Population dynamics of Stylaria lacustris (Linnaeus, 1767) (Oligochaeta, Naididae) in Los Talas, Argentina

Population dynamics of Stylaria lacustris were analyzed over 2 years in a pond located at Los Talas, Argentina. In both years, the peak in abundance, due to intense asexual reproduction, fell at the end of winter, and was followed by mature individuals. The species was not collected during summer. Temperature was the main factor regulating the population through both sexual and asexual reproduction. In the second year, density was lower and correlated with a lower water level and a reduced vegetation development. Individuals were randomly distributed in periods of high abundance and contagious when density was low. Generation time was 15 days.

The distribution and ecology of littoral Oligochaeta and Aphanoneura (Annelida) of the Natural and Historical Reserve of Isla Martín García Río de la Plata River, Argentina

The objective of this paper is to provide data on the distribution and ecology of oligochaetes and aphanoneurans occurring in the Rio de la Plata, Argentina, including details regarding, their densities, faunal characteristics, species richness, diversity and equitability. Between 1995 and 1997, a total of five stations on the Rio de la Plata were sampled on eight different occasions. The taxocenosis of Oligochaeta and Aphanoneura included 30 species belonging in six families: Naididae, Tubificidae, Narapidae, Enchytraeidae, Lumbricidae and Aeolosomatidae. The density varied between 44495 ind m−2 and 57 ind m−2. Species richness varied between 1 and 17, the diversity ranged from 0.07 to 2.55, and equitability varied between 0.08 and 0.64. According to dominance and frequency, the dominant, constant and widely distributed species were: Nais variabilis, Stephensoniana trivandrana, Amphichaeta leydigi, Chaetogaster diastrophus, Limnodrilus hoffmeisteri, Aulodrilus pigueti, Narapa bonettoi and the species of Enchytraeidae and Aeolosomatidae.

Manayunkia speciosa Leidy (Polychaeta: Sabellidae): introduction of this nonindigenous species in the Neotropical Region (Uruguay river, South America)

We report the migration of Manayunkia speciosa from its distribution in North America into the Neotropical Region (Argentina). We collected specimens from November 2007 to March 2009 in the lower Uruguay River-at 33° 5.01′S 58° 12′W, 33° 5.9′S 58°25.2′W from sediments reaching densities of 2,890 ind. m−2, at a mean abundance of 350 ind. m−2. Introductions of nonindigenous species, resulting intentionally or accidentally from anthropic activities, cause significant changes in ecosystems. In aquatic environments, polychaetes are a key invasive group that increases the geographical range of several species through human activities. M. speciosa may have reached the Río de la Plata Basin through a shipping vector and thereafter the Uruguay River by self-navigation.

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 microm 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 microm for embryos in the early stage of development and from 250 to 345 microm for those in mid-developmental stage, while in C. granulatus from 250 to 345 microm and from 260 to 365 microm 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.

An introduced Polychaete in South America - Ecologic Affinities of Manayunkia speciosa (Polychaeta, Sabellidae) and the Oligochaetes of Uruguay River, Argentina

Rivers are very dynamic and complex ecosystems. The elements forming their structure are the riverbed, the bank area and the alluvial valley. They can change in size and complexity according to their geological features and the climate of the region they cross. This variation in the horizontal axis, the flow regime, the physicochemical characteristics of the water and the type and density of the vegetation determine, in fluvial systems, a spatial heterogeneity, in agreement with the temporal dynamism (Sabater et al., 2009).

Efectos de la temperatura sobre el crecimiento individual y formación de zooides en Stylaria lacustris (Linnaeus, 1767) (Oligochaeta, Naididae)

Armendariz, L.C. Temperature effects on individual growth and zooids formation in Stylaria lacustris (Linnaeus, 1767) (Oligochaeta, Naididae) Biota Neotrop. May/Aug 2007 vol. 7, no. 2 http://www.biotaneotropica. org.br/v7n2/pt/abstract?article+bn00907022007. ISSN 1676-0603. The experiments carried out with S. lacustris showed that the temperature plays a role of importance in the rate of asexual reproduction, as for the number of zooids produced by individual, as well as to the size reached by them. On the other hand, it would regulate the rate of growth and the sexual reproduction, giving place to the maturity of the individuals when temperature increases. The life time of the immature individuals was estimated in 15 days, being this independent of the temperature used in the cultures. The mature individuals lived on the average 37 days. The survival in S. lacustris was falling gradually, following a curve of type lll. Life expectancy presented its major value at the age of 16 days and stayed approximately constant up to an age of 28 days, after then falled persistently until the last reached age. The individual growth according to von Bertalanffy equation, was estimated for the organisms maintained at 23 r 2 °C and at 14 r� 1 °C. Those individuals cultivated at higher temperature attained a bigger size, although their rate of growth was smaller than those maintained at 14 °C.