Diel density variation of amphipods associated with Sargassum beds from two shores of Ubatuba, Southeastern, Brazil

Abstract

ABSTRACT. Densities of mobile epifaunal assemblages associated with macrophytes are very variable during the day and the activity of visually-oriented predators is thought to have an important influence on this pattern. Here we compared densities of amphipods associated with a common brown alga, Sargassum stenophyllum (Phaeophyceae), at sites contrasting in water turbidity. We expected that diel variation of amphipods would occur in a shore with clear waters (Perequê), whereas no variation was expected in a shore with turbid waters (Lamberto). Amphipod density varied during the day at both shores, with no indication of a larger variation at Perequê. Most species showed two density peaks, one at night and the other in the afternoon. These peaks occurred close the times of high tide, suggesting that tidal rhythms could influence more amphipod densities than the activity of predators. Thus, more studies are necessary to understand factors that influence short-term variation of epifaunal assemblages. KEYWORDS. Diel variation, amphipods, Sargassum.RESUMO. Variação ao longo do dia na densidade de anfípodos associados a bancos de Sargassum em duas praias de Ubatuba, SP, Brasil. As densidades da epifauna móvel associada a macrófitas variam muito ao longo do dia, sendo a atividade de predadores visualmente orientados um dos principais fatores apontados para explicar este padrão. Neste estudo, comparamos as densidades de anfípodos associados a uma alga parda comum, Sargassum stenophyllum (Phaeophyceae), em praias contrastando em turbidez da água. Era esperada a ocorrência de variação ao longo do dia numa praia com águas claras (Perequê) e nenhuma variação na praia com águas turvas (Lamberto). A densidade de anfípodos variou ao longo do dia em ambas as praias, sem indicação de maior variação em Perequê. A maioria das espécies apresentou dois picos de densidade: um à noite e outro à tarde. Estes ocorreram próximos aos períodos de maré alta, sugerindo que o ritmo de maré poderia influenciar mais as densidades de anfípodos que a atividade de predadores. Assim, mais estudos são necessários para se compreender os fatores que influenciam a variação de curto prazo das comunidades epifaunais. PALAVRAS-CHAVE.Variação temporal, anfípodos, Sargassum.

Assessing habitat fragmentation on marine epifaunal macroinvertebrate communities: an experimental approach

“…Lamberto Beach is located in Enseada do Flamengo (23°30 0 S/45°07 0 W), and is classified as sheltered or semi-sheltered due to the barrier formed by Anchieta Island (Leite and Guth 2003;Leite et al 2007). The climate is tropical with rains distributed throughout the year (AF) and superhumid without dryness according to the Koeppen classification (SalatiFilho 2001).…”

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