REDE ECOLÓGICA DOS GASTRÓPODES ASSOCIADOS AO BANCO DE ALGAS DA PRAIA DA RIBANCEIRA, SANTA CATARINA, BRASIL

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.

Importance of biogenic substrates for the stone crab Menippe nodifrons Stimpson, 1859 (Brachyura: Eriphioidea)

In order to better understand the ecology of the different growth phases of the stone crab, Menippe nodifrons, and provide information for conservation of the natural stocks, this study describes the utilization of different biogenic substrates by this species in the intertidal zone. Sampling was carried out by hand at Ubatuba, State of São Paulo, Brazil. Crabs were captured among rocks or in association with three different biogenic substrates: Phragmatopoma lapidosa, Sargassum cymosum and Schizoporella unicornis. In the laboratory, the substrates were sorted and scanned for specimens of M. nodifrons, which were separated and measured at their maximum carapace width (CW), and classified as juvenile or adult specimens. Sex ratio and size distribution of crabs were analyzed for each of the substrate types. A total of 686 specimens of M. nodifrons were obtained during the sampling, ranging in size between 2.4 and 82.5 mm CW. Different mean sizes were recorded in the different substrates (P < 0.05). The high prevalence of juveniles in the samples suggests that these microhabitats are fundamental for the juvenile development of M. nodifrons, as they provide refuge, protection and probably food for juveniles.