Lípidos en el anfípodo Talorchestia margaritae (Amphipoda: Talitridae) y su relación con la ecología de la especie

Lipids in the amphipod Talorchestia margaritae (Amphipoda: Talitridae) and its relationship with the ecology of the species. T. margaritae, an endemic species inhabiting Venezuelan coasts, plays an important ecological role in plant and animal decomposition. To understand this issue in some animal groups, especially small ones, lipid composition analysis has been an interesting tool to describe their trophic relationships and food preferences. In order to assess this and visualize the components of their diet, we determined the lipid composition differences between males and females and among age classes in this species. Two sandy beaches were selected: Mangle Quemao and Las Mercedes de Paparo, from which sand samples of known volume were collected at the supralittoral area in 2007. Organisms were separated by age and sex classes, and their size, weight, density, biomass, total lipids (TL), lipid classes and fatty acid markers present in their tissues were determined. The sizes were similar for all age classes between the two locations, while the weights were higher for Mangle Quemao. The TL and lipid classes showed similar proportions between sexes, age classes and locations (TL: 3-5%; Phospholipids: 20-30%; Glycolipids: <1%; sterols: 4%). On the other hand, Triglycerides (TAG) were higher in Mangle Quemao, which may be related to the difference between the weights of two locations. The most abundant fatty acid biomarkers in the two studied sites were 16:0 and 18:1(n-9); this last one is characteristic of a carnivorous diet. The other nine markers were identified with changes in their distribution in organisms at Mangle Quemao and between males and females of both populations. Based on observed fatty acids markers we can assume T. margaritae as a generalist carnivore. Those populations were influenced by available food; inducing differences in weight, TAG proportion and markers diversity. Rev. Biol. Trop. 58 (3): 841-855. Epub 2010 September 01.

T. margaritae cumple un papel importante en la descomposición de restos vegetales y animales en las costas venezolanas. El objetivo fue determinar las diferencias en la composición lipídica entre sexos y talla de la especie. Para esto, especímenes de T. margaritae fueron recolectados en la zona supralitoral de dos playas arenosas: Mangle Quemao y las Mercedes de Paparo. Posteriormente se separaron por talla y sexo determinándoles su peso, densidad, biomasa y perfil lipídico. Todas las categorías presentaron tallas similares entre localidades. Los pesos fueron superiores en los organismos de Mangle Quemao. Los lípidos totales presentaron proporciones similares entre sexos, talla y localidad (3-5%), al igual que los fosfololípidos (20-30%), glicolípidos (<1%) y esteroles (4%), exceptuando los triglicéridos (TAG), siendo estos superiores en Mangle Quemao. Esto último pudiendo estar relacionado con la diferencia de pesos entre localidades. Los ácidos grasos más abundantes en ambas localidades fueron 16:0 y 18:1(n-9). Se identificaron otros 9 marcadores con variaciones en su distribución. Con base en los biomarcadores se puede catalogar a T. margaritae como una especie carnívora- generalista, siendo sus poblaciones influenciadas por la disponibilidad de alimento que a su vez, podría inducir diferencias de peso, TAG y biomarcadores.

Biodiversity of the Gammaridea and Corophiidea (Crustacea: Amphipoda) from the Beagle Channel and the Straits of Magellan: a preliminary comparison between their faunas

Gammaridea and Corophiidea amphipod species from the Beagle Channel and the Straits of Magellan were listed for the first time; their faunas were compared on the basis of bibliographic information and material collected in one locality at Beagle Channel (Isla Becasses). The species Schraderia serraticauda and Heterophoxus trichosus (collected at Isla Becasses) were cited for the first time for the Magellan region; Schraderia is the first generic record for this region. A total of 127 species were reported for the Beagle Channel and the Straits of Magellan. Sixty-two species were shared between both passages (71.3 % similarity). The amphipod species represented 34 families and 83 genera. The similarity at genus level was 86.4 %, whereas 23 of the 34 families were present in both areas. For all species, 86 had bathymetric ranges above 100 m and only 12 species ranged below 200 m depth. In the Beagle Channel, only one species had a depth record greater than 150 m, whereas in the Straits of Magellan, 15 had such a record. The Beagle Channel and the Straits of Magellan contain 57.5 % of the species, 71 % of the genera and 77.3 % of the families of Gammaridea and Corophiidea from the entire Magellan region.

Se confeccionó el primer listado de anfípodos Gammaridea y Corophiidea del Canal Beagle y del Estrecho de Magallanes, y se compararon, en forma preliminar, sus faunas con base en información bibliográfica y material recolectado en una localidad del Canal Beagle (Isla Becasses). Las especies Heterophoxus trichosus y Schraderia serraticauda (recolectadas en Isla Becasses) son citadas por primera vez para la región magallánica; Schraderia representa el primer registro genérico para dicha región. Un total de 127 especies fueron registradas para el Canal Beagle y el Estrecho de Magallanes, compartiendo entre ambos 62 especies, lo que representa una similitud del 71.3 %. El total de las especies pertenece a 34 familias y 83 géneros. La similitud a nivel genérico fue del 86.4 %, mientras que 23 familias estuvieron presentes en ambos pasajes. Del total de especies, 86 presentaron rangos de profundidad menores a los 100 m y sólo 12 especies superaron los 200 m. Sólo una especie tuvo un registro superior a los 150 m de profundidad en el Canal Beagle, mientras que 15 superaron dicha profundidad en el Estrecho de Magallanes. En el Canal Beagle y el Estrecho de Magallanes se registró el 57.5 % de las especies, 71 % de los géneros y 77.3 % de las familias conocidas para la región magallánica.

Structural variation in the brown alga Sargassum cymosum and its effects on associated amphipod assemblages

The presence of diverse biological substrates adds complexity to coastal landscapes and increases the number of ecological niches that can be used by the mobile epifauna. Studies on the influence of structural complexity have focused mainly on algal host species, but there is little information about the influence of intraspecific structural variation on the associated mobile epifauna. In this work, we examined whether intraspecific variation in the brown alga Sargassum cymosum influenced the structure of amphipod assemblages on two shores with different wave exposure. At least 15 fronds were randomly sampled at Fortaleza and Perequê-Mirim beaches, on the Atlantic coast of São Paulo state, southeastern Brazil, and 12 variables were measured for each alga. The amphipods were identified and counted. The greatest structural variation in S. cymosum occurred within shores, whereas the differences between shores were mainly related to algal size. These characteristics influenced amphipod assemblages differently on each shore, with the greatest effects being associated with variables related to morphological complexity, such as holdfast size, the number and size of branches, and the extent of cover by sessile colonial animals. These findings show that monospecific algal banks are not homogeneous, and that morphological differences and interactions with other biological substrates can influence the mobile epifaunal assemblages.

A presença de substratos biológicos aumenta a complexidade dos ambientes costeiros, proporcionando maior número de nichos ecológicos para a epifauna vágil. Estudos sobre os efeitos da complexidade estrutural das algas têm enfocado principalmente as espécies presentes entre os seus ramos, porém há poucos dados sobre a influência da variação estrutural intra-específica sobre essa fauna. Neste trabalho, foi analisada a influência da variação da alga parda Sargassum cymosum sobre a estrutura da assembléia de anfípodes entre duas praias com diferentes graus de exposição às ondas, e em cada uma delas, no SE do Brasil. Pelo menos 15 frondes foram individualmente coletadas aleatoriamente nos costões das praias de Fortaleza e Perequê-Mirim, e diversas variáveis (12) foram medidas para cada fronde de alga. Os anfípodes foram identificados e contados. As maiores variações nas características de S. cymosum foram obtidas em cada praia, enquanto que diferenças entre as praias foram principalmente relacionadas ao tamanho das algas. Estas características influenciaram as assembléias de anfípodes de maneira diferente em cada praia, sendo que os maiores efeitos foram atribuídos a variáveis relacionadas com a morfologia das algas como o tamanho do apressório, o número e tamanho dos ramos e a cobertura por organismos coloniais sésseis. Portanto, bancos monoespecíficos de algas não são homogêneos e tanto as diferenças morfológicas como as interações com outros substratos biológicos podem influenciar as assembléias da epifauna vágil.

Composition and seasonality of an amphipod community associated to the algae Bryocladia trysigera

The monthly fluctuations of amphipods associated to the algae Bryocladia trysigera was described from March 1997 to February 1998 at the rocky shore known as Poço de Anchieta in the Peruíbe Beach, Itanhaém, Southeastern Brazil. A total of 75,344 individuals were sampled, belonging to 10 species and 9 families. Three species dominated the phytal in number: Hyale nigra, Caprella danileviskii and Caprella penantis. Despite the alternation in dominance of the 3 most abundant species, the amphipod species composition remained generally unchanged, so that the majority of the species were observed in all sampling months. The temporally changing pattern of the community structure, with a decline in amphipod abundance in winter followed by an increase in spring, was probably due to a higher predation pressure in winter period