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

Abstract

Dentre a biota dos costoes rochosos, destacam-se as redes de interacao entre as macroalgas e os organismos associados, sobretudo gastropodes. Visando contribuir com o entendimento da ecologia dos costoes rochosos, avaliou-se a relacao entre as macroalgas e os gastropodes associados na Praia da Ribanceira, Imbituba, Santa Catarina, Brasil. O levantamento das amostras de algas ocorreu em estacao umida, utilizando quadrantes de 20 cm x 20 cm, alocados em 18 transectos distribuidos igualmente nas zonas infra e mesolitoral, com cinco pontos cada. Em laboratorio, as algas foram triadas e os gastropodes associados identificados. Foram aplicados conceitos de teoria de redes para entendimento das interacoes entre os organismos, sendo calculados os descritores de conectância, sobreposicao de nicho e indice de centralidade para cada especie.\xa0 Foram utilizadas tecnicas multivariadas para avaliacao da significância das zonas entremares, do grupo morfofuncional e outras variaveis na composicao dos gastropodes associados. A amostragem resultou no levantamento de 1.466 gastropodes, distribuidos em nove familias e 14 especies. Com relacao as macroalgas, foram identificadas 14 especies, com sete apresentando gastropodes associados. A rede de interacoes apresentou baixa conectância e sobreposicao de nicho para ambos os niveis (gastropodes e macroalgas), sugerindo a existencia de muitas interacoes especificas. Os valores de centralidade destacaram Eulithidium affine (C. B. Adams, 1850) e Sargassum cymosum C. Agardh como especies-chave na rede estudada. A massa e o grupo morfofuncional das amostras de macroalgas se mostraram influentes na composicao da comunidade associada. As algas corticadas, sobretudo S. cymosum , destacaram-se pela elevada riqueza e densidade de gastropodes associados, sugerindo importância na complexidade estrutural das macroalgas para a presenca de gastropodes. Destacou-se o efeito nao-significativo das diferentes zonas do costao na composicao de gastropodes associados, indicando que a estabilidade na nidificacao e forrageio proporcionada pelas macroalgas permite que ocorram as mesmas especies de gastropodes nas zonas infra e mesolitoral. ECOLOGICAL NETWORK OF GASTROPODS ASSOCIATED WITH MACROALGAE BEDS OFF RIBANCEIRA BEACH, SANTA CATARINA, BRAZIL: 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.