Spatiotemporal variation of the epifaunal assemblages associated to Sargassum muticum on the NW Atlantic coast of Morocco

Epifaunal assemblages inhabiting the non-indigenous macroalga Sargassum muticum (Yendo) Fensholt were investigated on two physically distinct intertidal rocky (S1) and sandy (S2) sites along the Atlantic coast of Morocco. The objective of this study was to test whether the habitat-forming marine alga S. muticum invasive in these sites supported different epifaunal assemblages under different environmental conditions and through time. The gastropods Steromphala umbilicalis, S. pennanti, and Rissoa parva and the isopod Dynamene bidentata were the most contributive species to the dissimilarity of epifaunal assemblage structure between both sites throughout seasons. SIMPER analysis showed a dissimilarity of 58.3-78.5% in the associated species composition of S. muticum between study sites with respect to sampling season. Species diversity and total abundance were significantly higher at the rocky site compared to the sandy site. PERMANOVA analyses showed significant differences of associated epifaunal assemblage structure for the season and site interaction. Accordingly, site and season were determinant factors conditioning the role of habitat in structuring epifaunal assemblages.info:eu-repo/semantics/publishedVersio

Porifera from the Argentine Sea: diversity in Patagonian scallop beds

The Patagonian scallop Zygochlamys patagonica (King & Broderip 1832) is distributed in the Magellanic Biogeographical Province. Its southern limit is Tierra del Fuego whereas the northern range extends to 42u S in the Pacific Ocean and to 35uS in the Atlantic Ocean (Waloszek 1984; Waloszek & Waloszek 1986; Ciocco et al. 1998). The commercial fishery started in 1996 in the Argentine continental shelf where it is performed by bottom otter trawls mainly at a depth range of 67\u2013108m (Lasta & Bremec 1998; Gutie\ub4rrez & Defeo 2003). Porifera are a frequently collected taxon in the invertebrate by-catch of the Patagonian scallop fishery (Bremec et al. 1998, 2000; Bremec & Lasta 2002). Sponges, being sessile and relatively fragile organisms, are very sensitive to pollution and mechanical stress produced by trawling (Muricy 1989; Wassenberg et al. 2002). Porifera from different Patagonian scallop beds in the Argentine Sea accounted for approximately 5\u201310% of total biomass of invertebrate by-catch during 1995, when commercial fishery started, and proved to be more sensitive to the fishing effort than other taxa (Bremec & Lasta 2002; Bremec et al. 2000). In these beds, the sponge contribution represented an average of 0.3 kg 100m22 (wet weight) between 1998 and 2001 (Schejter 2004). Consequently, studies on their diversity and distribution in areas subjected to trawling are important to assess the impact of fishery disturbances. Thirteen species of Demospongiae (four of which are new records for the Argentine Sea) have been identified, confirming the importance of this phylum as a major component of the scallop bed community

From coexistence to competitive exclusion: can overfishing change the outcome of competition in skates (Chondrichthyes, Rajidae)?

Competition for food could be a major force driving changes in the community structure of skates (Rajidae) subjected to fishing exploitation. Under this hypothesis, small skates are released from competition with larger skates after fishing has depleted the larger species. Here, we compare the abundance patterns of two sympatric skates with similar niches but different life histories, Bathyraja albomaculata (larger and slow-reproducing) and Bathyraja macloviana (smaller and faster-reproducing), before (1971, 1978) and after (1998-2004) a 108% increase in industrial bottom trawling on the southeastern South American shelf in order to test the prediction that B. macloviana should competitively exclude B. albomaculata after the increase in fishing mortality. In 1971 and 1978, there was no relationship between the abundance of both species, indicating that they coexisted over large scales. In 1998-2004, the relationship between the abundances of these skates was bell-shaped, indicating that both species increased in abundance at low densities until peaking, after which B. albomaculata decreased when B. macloviana became more abundant, consistent with resource competition. We tested whether food may be a potential limiting resource by comparing the diet of both species. The two species consumed mostly polychaetes, differing only in the consumption of polychaetes from the family Nephthyidae, which was much higher for B. macloviana. Bathyraja macloviana could replace B. albomaculata at high densities when food resources may become scarce. These results support the hypothesis that competition release is an important factor explaining the changes in skate communities in overexploited areas

Rio de la Plata (La Plata River) and Estuary (Argentina and Uruguay)

The La Plata River system can be defined as a funnel coastal plain tidal river with a semi-closed shelf at the mouth. La Plata River is both the world’s widest freshwater system and an estuary that drains the second largest basin in South America and the fifth largest in the world. The Rio de la Plata system is shared by Argentina and Uruguay and has an area of 38,000 km2, extends almost 300 km in length, and widens from about 40 km at the inner freshwater part to 227 km at the Atlantic Ocean boundary. The system is mainly formed by the Paraná and Uruguay rivers that provide 97 % of the water discharge contributing with a mean annual flow of 16,000 and 4,000 m3/s, respectively. The Rio de la Plata comprises three well-defined areas: the internal zone that starts at the end of the Parana Delta and is characterized by only freshwater, an intermediate or mixing zone, and an external or marine zone.Fil: Baigún, Claudio Rafael M.. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín. Instituto de Investigación en Ingeniería Ambiental; ArgentinaFil: Colautti, Dario César. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; ArgentinaFil: Maiztegui, Tomás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentin