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

Abstract

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.Keywords: Sargassum cymosum, amphipods, structural variation, morphology.Variação estrutural da alga parda Sargassum cymosum e seu efeito sobre as assembléias dos anfípodes associados Resumo 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 morf...

Characterization of macrofauna associated with articulated calcareous algae (Corallinaceae, rhodophyta) occurring in a hydrodynamic gradient on the espírito santo state coast, brazil

“…The growth of epiphytes on calcareous algae also seems to have favored the settlement of organisms with different feeding habits, such as the Crustacea H. media, H. nigra and E. brasiliensis. Studies in the State of São Paulo, Brazil, have concluded that, despite the potential harm of epiphytes to substrate algae, they lead to an increase in the abundance of Amphipoda and in the species richness of other invertebrates in that region (see JACOBUCCI et al, 2006;LEITE et al, 2007).…”

“…In the case of sudden changes, whether climatic or of seasonal characteristics. the macrofauna associated with these algae, of which Crustacea and Mollusca are the main representatives also undergoes changes in its composition (LEITE et al, 2007). Besides the hydrodynamic characteristics, this ecosystem is also influenced by biotic and abiotic variables, the oscillations in water temperature, salinity, and water quality being particularly relevant (TÂMEGA; .…”

Variation of amphipod assemblage along the Sargassum stenophyllum (Phaeophyta, Fucales) thallus

“…The basal portion of Sargassum has more branches and higher structural complexity (herein, measured as biomass) than the distal portion, offering more space for the establishment of the associated fauna. Also, the holdfast is colonized by sessile organisms, which can function as a second biological substrate for mobile species (Leite et al, 2007). An increase in habitat complexity of a biological substrate (e.g.…”

“…The holdfast, at its basal portion, allows the fixation of sessile organisms (e.g. sponges) that can function as a second biological substrate for mobile fauna (Leite et al, 2007). In addition, the amount of branches, which can shelter the fauna, is higher at the basal portion than the distal portion.…”

Dimensão fractal e métodos quantitativos aplicados ao estudo de comunidades do macrobentos marinhos

“…Tais estudos utilizavam apenas a biomassa da macroalga (peso seco ou peso úmido) para mensurar a complexidade das macroalgas para evidenciar como essa variável influenciava a estruturação das referidas comunidades (WAKABARA et al, 1983;LEITE et al, 2007;CUNHA et al, 2008;JACOBUCCI et al, 2009a;JACOBUCCI et al, 2014). O uso da dimensão fractal como medida de complexidade morfológica em macroalgas é uma abordagem importante que tem sido foco de muita pesquisa no mundo todo (GEE & WARWICK, 1994a, b;McABENDROTH et al, 2005;DIBBLE & THOMAZ, 2009;FERREIRO et al, 2011).…”