Co-occurring morphologically distinct algae support a diverse associated fauna in the intertidal zone of Araçá Bay, Brazil

Abstract

Co-occurring morphologically distinct algae support a diverse associated fauna in the intertidal zone of Araçá Bay, Brazil. Biota Neotropica. 18(1): e20170464. http://dx.doi.org/10.1590/1676-0611- BN-2017-0464 Abstract: Species diversity is regulated by historical, neutral and niche processes, with species tolerance, dispersal and productivity guiding diversity at larger scales, while habitat heterogeneity and biotic interactions acts in smaller scales. In rocky shores, several organisms provide secondary substrates for mobile fauna, with macroalgae being the most abundant and diverse ones. The patchiness promoted by different macroalgae hosts enhances small-scale heterogeneity and may increase and maintain the diversity of the mobile organisms, since there is a close relationship between the associated fauna and its hosts. In this study we selected three morphologically different macroalgae that coexist in the same rocky shore height in the Araçá Bay, an area under the threat of the nearby harbor expansion, and evaluated the fauna associated to each algal host. Even under similar abiotic pressure (same rocky shore height), the associated fauna of each algal host varied in number and composition, revealing a close relationship. The poorly branched foliose Ulva lactuca sustained a lower density of organisms and was dominated by isopods, while the heavily branched turf and Bostrychietum community showed a high density of organisms, with a dominance of peracarid crustaceans and annelids on the turf and more resistant groups, such as bivalves, acaris and terrestrial insects on the Bostrychietum. Previous studies in the Araçá Bay already revealed a large spatial heterogeneity in the processes and sessile organisms distribution, and here we highlight that this heterogeneity can be observed in an even smaller scale, with different algal hosts mediating the turnover of species in a scale of centimeters and meters, resulting in diversity maintenance of the associated fauna. Since the harbor expansion may prevent the occurrence of macroalgae as a result of light limitation by suspended platforms, we may expect not only a decrease in algal cover but also in the total diversity of the associated fauna in the Araçá Bay. Keywords: rocky shore, phytal, peracarids, structural complexity, spatial heterogeneity Algas co-ocorrentes e morfologicamente distintas suportam uma diversa fauna associada na zona entremarés na Baía do Araçá, BrasilResumo: A diversidade de espécies é regulada por processos históricos, neutros e de nicho, com a tolerância das espécies, dispersão e produtividade do sistema guiando a diversidade em grandes escalas, enquanto a heterogeneidade do habitat e as interações bióticas atuam em escalas menores. Em costões rochosos uma série de organismos funciona como substrato secundário para a fauna móvel, sendo macroalgas o tipo mais abundante e diverso de substrato. O mosaico formado pelas diferentes macroalgas hospedeiras aumenta a heterogeneidade em pequena escala e pode aumentar e manter a diversidade dos org...

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“…In addition to the ecological questions, our study will help to support a discussion regarding anthropogenic impacts at the bay. Araçá Bay is under the threat of the eminent expansion of the port of São Sebastião, which will cover 75% of the bay with a structure suspended by pillars, potentially reducing the occurrence of macroalgae [24], which host diverse associated fauna [25].…”

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