Growth of Ligia exotica (Isopoda: Oniscidea: Ligiidae) in two estuarine regions of Patos Lagoon, Rio Grande do Sul, Brazil elis r. lopes-leitzke, luiz f.c. dumont and fernando d'incao FURG, Laboratório de Crustáceos Decápodos, Instituto de Oceanografia, CP: 474, CEP: 96201-900, Rio Grande, RS, BrazilThe aim of this study was to estimate growth parameters of two populations of Ligia exotica inhabiting discrete estuarine areas of Patos Lagoon, Rio Grande do Sul, Brazil. Sampling was performed fortnightly at two different estuarine zones, named Leonideo Island and West Breakwater, to detect different growth patterns for this species by using the von Bertalanffy growth model (VBGM). The VBGM estimated were as follows: TL mm ¼ 34.57 (1 2 e 20.012(t 2 2.93) ) (males in Leonideo Island), TL mm ¼ 35.61(1 2 e 20.009(t 2 5.87) ) (males in West Breakwater), TL mm ¼ 30.11(1 2 e 20.009(t 2 5.84) ) (females in Leonideo Island) and TL mm ¼ 29.65(1 2 e 20.01(t 2 4.87) ). Significant sexual dimorphism was observed, since males reach larger TL (mm) by higher k value (day) and consequently a faster growth pattern. Different growth patterns of males were also detected comparing both populations, in such a way that the West Breakwater individuals are larger than those from the Leonideo Island. One possible explanation is the higher food availability observed in the former site, as well as favourable environmental parameters, providing better conditions for individual growth. Briefly, two different populations of L. exotica were detected in the studied area, presenting discrete growth parameters highly influenced by environmental factors.

To date the genus Atlantoscia Ferrara and Taiti, 1981 includes two species, A. floridana (van Name, 1940) and A. rubromarginata Araujo and Leistikow, 1999. The species Atlantoscia petronioi sp.n. is described on the basis of material collected in a coastal dune forest area of the southern Rio Grande do Sul state, Brazil. This new species is characterized by antenna with accentuate setose sulcus from the peduncle to the distal article of the flagellum, outer endite of maxillula with slender seta among the outer group teeth and accessory tooth, one trifid tooth in the inner group, and male pleopod 1 endopod with distal part pointed and subapically not swollen.

RESUMODieta natural de Ligia exotica (Crustacea, Isopoda, Ligiidae) em duas regiões do estuário da Lagoa dos Patos, Rio Grande do Sul, Brasil Isópodos são exemplos da transição evolutiva dos crustáceos do mar para terra, existindo formas tipicamente aquáticas e formas tipicamente terrestres. Ligia exotica é dominante na região intertidal do Estuário da Lagoa dos Patos, tendo um importante papel na reciclagem de nutrientes e na cadeia trófica. A área de estudo compreendeu o Molhe Oeste de Rio Grande e a Ilha do Leonídeo. O conteúdo alimentar foi estudado sazonalmente, através da captura manual de indivíduos em Outubro/2003, Janeiro, Abril e Julho/2004. Após capturados, os indivíduos foram fixados imediatamente em formol 4% durante 24 horas e conservados em álcool 70%. Os tubos digestivos foram pesados e o grau de repleção foi estimado. O conteúdo de cada tubo digestivo foi diluído em 1 ml de água destilada. Para quantificação dos itens, o conteúdo foi colocado em uma lâmina de contagem graduada. Cada item identificado foi quantificado pela contagem do número de ocorrência nos quadrados da lâmina. Para testar a possível diferença entre a frequência dos itens consumidos por machos e fêmeas, foi utilizado o quiquadrado. Análises qualiquantitativas foram realizadas segundo os métodos de freqüência relativa de ocorrência, freqüência relativa dos pontos. Um total de 912 tubos digestivos foi analisado: 426 indivíduos no Molhe Oeste e 485 indivíduos na Ilha do Leonídeo. Seis itens alimentares foram identificados e diferenças significativas foram observadas nos itens consumidos por machos e fêmeas de ambas as populações. Os itens alimentares mais importantes para a dieta natural de Ligia exotica foram: detrito vegetal, areia e a alga Polysiphonia sp. Desta forma, em ambas as regiões do estuário, a espécie pode ser considerada generalista. PALAVRAS CHAVE: Oniscidea, Ligia exotica, alimentação, dinâmica populacional, Estuário da Lagoa dos Patos ABSTRACTIsopods are examples of the evolutive transition of the crustaceans from sea to land, inhabiting aquatic and terrestrial environments. Ligia exotica is dominant in the intertidal region of the of Patos Lagoon estuary, playing an important role in recycling nutrients and in the trophic web as a whole. The study area was the West Breakwater of Rio Grande Channel and Leonideo Island. The natural diet was analyzed through standardized one hour manual sampling performed in October/2003, January, April and July/2004. After collected, individuals were immediately fixed in 4% formalin during 24 hours and conserved in 70% ethanol. The guts were weighted and repletion degree was estimated. Each gut content was diluted in 1 ml of distilled water. To quantify the items, content was placed in a graduated slide for counting. Each identified item was quantified by the number of occurrences in the slide squares. To test significant differences between the frequencies of items consumed by males and females, a chi-square test was used. Qualiquantitative analysis was performed following the met...

. A abundância de isópodos terrestres foi estatisticamente diferente entre as estações do ano (p = 0,00), mas não entre as marismas (p = 0,86). Na Torotama/Inverno, a abundância de isópodos é significativamente maior do que nas demais estações e locais, exceto na Barra/Primavera (p = 0,14); Barra/Inverno (p = 0,20) e Pólvora/Primavera (p = 0,38). A salinidade é inversamente proporcional ao número de indivíduos coletados na Barra e na Pólvora. Na Torotama, o número de isópodos cresce com o aumento do nível da água e do detrito depositado sobre o terreno. A distribuição e abundância de isópodos terrestres são fortemente influenciadas por fatores ambientais. PALAVRAS-CHAVE: marismas, ecologia, Oniscidea, estuário, abundânciaABSTRACT Saltmarshes are abiotically stressful habitats, but highly productive. Most of this production is consumed by detritivorous such as Oniscidea. The study focused on the abundance and distribution of terrestrial isopods in the saltmarshes of the Estuary of the Patos Lagoon, Brazil. Three saltmarshes were sampled in spring/2007, summer, autumn and winter/2008. In each saltmarsh, a transect of 10m was set, where 10 squares of the 20x20cm were placed and all material removed. The variation of species abundance was compared between the saltmarshes through Manova. Two species were identified in each saltmarsh: Balloniscus sellowii and Atlantoscia floridana in West Breakwater of Rio Grande Channel and in Polvora Island and B. sellowii and B. glaber in Torotama Island. The mean density of isopods was 6.9 ind/m 2 (West Breakwater), 5.0 ind/m 2 (Polvora) and 6.1 ind/m 2 (Torotama). The abundance of terrestrial isopods was statistically different between the seasons (p = 0.00) but not between the saltmarshs (p = 0.86). In Torotama/winter, abundance of isopods is significantly higher than in other seasons and sites, except in the West Breakwater/spring (p = 0.14), West Breakwater/winter (p = 0.20) and Polvora/Spring (p = 0.38). The salinity is inversely proportional to the number of individuals in West Breakwater and Polvora. In Torotama, the number of isopods increases with the increase in the level of water and detritus deposited on the ground. The distribution and abundance of terrestrial isopods are strongly influenced by environmental factors.