http://dx.doi.org/10.1590/1676-06032014011514Abstract: The phytal is characterized by the formation of seaweed beds and a great diversity of associated species, the malacofauna being one of its main components. Aiming to record the species of Gastropoda associated to the brown algae Sargassum sp. C. Agardh, 1820, this study was carried out in Sã o Sebastião Channel, northern coast of Sã o Paulo, and nearby areas. A total of 13945 individuals were identified, belonging to 35 families and 62 species. Cerithiidae, Phasianellidae and Columbellidae were the most abundant families, represented by 34, 33 and 17% of the total collected individuals, respectively. Bittiolum varium (Pfeiffer, 1840) (Cerithiidae) and Eulithidium affine (C. B. Adams, 1850) (Phasianellidae) are the dominant species, followed by the columbelids Mitrella dichroa (G. B. Sowerby I, 1844), Anachis fenneli Radwin, 1968 and Costoanachis sertulariarium (d'Orbigny, 1839). Among the least abundant species, some of them may be considered as of fortuitous occurrences, while others seem to be typical in those habitats, although rare. The presence of juvenile specimens was recurrent, this indicating that the algae can function as a nursery for most of these species. The expressive values found, for both abundance and number of species, illustrate the great ecological importance of the phytal habitats for the gastropod species.

Macrophytes provide a habitat for many species of marine invertebrates, the gastropods being one of the main components. This study provides new information about Sargassum-associated gastropod biodiversity, through characterization of the fauna from a highly impacted area of Brazil, investigating its variation at a small spatial scale and between two main seasons of the year, as well as its relationship with macroalgae parameters. Density of gastropods was higher during the warmest season and varied throughout sampling sites. A significant and positive, however weak, relationship between gastropod density and Sargassum dry weight was found in all localities. For all sites, a marked and unusual dominance of Bittiolum varium was observed. The high dominance of this species seems to be related to the impacts caused by shipping activities and highway construction in the 1970s and 1980s, which caused a decline in local species diversity that seems to have continued until now. Many species, both typical of these habitats and characteristic of other, nearby habitats, benefit from Sargassum sp. These macrophytes allow gastropods to establish and grow during their most vulnerable stages, as shown by the growth series and juvenile forms found for most species of gastropods. The present data highlight the importance of macrophyte habitats for gastropod biodiversity in coastal areas and call attention to the importance of raising knowledge on this fauna, especially in impacted areas, thus contributing to the conservation of these highly diverse and ecologically important macrophyte–gastropod systems.

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Among the rocky shores’ biota, the networks of interaction between macroalgae and associated organisms, especially gastropods, stand out. In order to contribute to the understanding of the ecology of rocky shores, this study aims to evaluate the relation between macroalgae and associated gastropods in Ribanceira Beach, Imbituba, Santa Catarina, Brazil. The survey of algae samples took place in a wet season, using 20 cm x 20 cm quadrants, allocated in 18 transects distributed equally in the infra and mesolittoral zones, with five points each. In the laboratory, algae were screened and associated gastropods identified. Concepts of network theory were applied for a better understanding of interactions among organisms, where connectance descriptors, niche overlap and centrality index for each species were calculated. Multivariate techniques were used to assess the significance of intertidal zones, morphofunctional group and other variables in the composition of the associated gastropods. The sampling resulted in a total of 1.466 gastropods, distributed in 14 species and nine families. In relation to the macroalgae, 14 species were identified, with seven presenting associated gastropods. The ecological network showed low connectance and niche overlap for both levels (gastropods and macroalgae), suggesting the existence of many specific interactions. The centrality values highlighted Eulithidium affine (C.B. Adams, 1850) and Sargassum cymosum C. Agardh as key species in the studied network. The mass and morphofunctional group of the macroalgae sampled showed influence in the composition of the associated community. Cortical algae, especially S. cymosum, stood out with high levels of species richness and species density of associated gastropods, suggesting importance in the structural complexity of macroalgae for gastropods. The non-significant effect of the tidal zone for the gastropod composition was highlighted, suggesting that the nesting and foraging stability provided by the macroalgae allows the same gastropod species to occur in both infralittoral and mesolittoral zones.

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The aim of this study is to investigate if Sargassum-associated herbivorous amphipods Cymadusa filosa Savigny, 1816 and Sunamphitoe pelagica (H. Milne Edwards, 1830) present differences in their population parameters at sites located at different distances from a state marina, which is the main source of pollution (especially heavy metals) in an impacted bay. The study was conducted at four beach sites within Flamengo Bay, Ubatuba municipality, northern coast of São Paulo State, Brazil. The beaches are Lamberto and Ribeira close to the pollution source and Flamengo and Santa Rita, which are more distant. We observed the predominance of juveniles in the populations of C. filosa and S. pelagica, followed by females, with the sex ratio for both species being favored toward females, and the highest densities of individuals were observed during the summer. Sunamphitoe pelagica presented lower density, smaller ovigerous females and egg volumes at Lamberto beach, indicating a possible higher sensitivity to metal pollution

A abundancia da fauna associada as macroalgas pode ser influenciada pela biomassa da alga hospedeira e de seus epibiontes. O objetivo do trabalho foi verificar se a biomassa de Sargassum e seus epibiontes influencia a abundancia de decápodes. Para isso foram feitas coletas mensais durante um ano em duas praias da Enseada do Flamengo, Ubatuba-SP. Somente Hyppolyte obliquimanus e Epialtus brasiliensis foram influenciados positivamente pela biomassa dos epibiontes, sendo que o primeiro teve relação negativa com Sargassum. Os demais decapodas não são influenciados pela biomassa de alga.

Este trabalho procura esclarecer possíveis relações entre a biomassa de Sargassum sp. e a abundância de anfípodes herbívoros da família Ampithoidae, assim como sua relação com a sazonalidade e temperatura.