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Marine Ecology Progress Series

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MEPS 378:81-92 (2009)  -  DOI:

Effects of disturbance on marginal populations: human trampling on Ascophyllum nodosum assemblages at its southern distribution limit

Rita Araújo1,*, Stefano Vaselli1, Mariana Almeida1, Ester Serrão2, Isabel Sousa-Pinto1,3

1Centre of Marine and Environmental Research, University of Porto (CIMAR-Porto), Rua dos Bragas, 289,
4050-123 Porto, Portugal
2Centre of Marine Sciences, University of Algarve (CIMAR-Algarve), Campus of Gambelas, 8005-139 Faro, Portugal
3Department of Botany, Sciences Faculty, University of Porto, Rua do Campo Alegre 1191, 4150-181 Porto, Portugal

ABSTRACT: The negative effects of disturbances on the long-term persistence of populations may be more severe in marginal populations, i.e. those occurring at the boundaries of geographical and ecological distribution ranges. Human trampling is an important source of anthropogenic disturbance for intertidal assemblages. Effects of human trampling on intertidal rocky shore assemblages dominated by Ascophyllum nodosum (L.) Le Jol. at its southern distributional limit in Europe were tested experimentally. Four different intensities of trampling disturbances were applied to experimental areas, over a period of 5 mo. Percentage cover of A. nodosum and associated organisms was quantified during the disturbance period and for a recovery period of 1 yr. The 2 highest trampling intensities drastically reduced the cover of A. nodosum. Trampling also negatively affected Fucus vesiculosus and understorey species, while indirectly allowing colonisation by ephemeral green algae. One year after the end of disturbance, A. nodosum assemblages in the highest disturbance intensity areas were still significantly different from assemblages in the control and lowest disturbance intensity areas. These results were mainly driven by a switch in the dominant canopy species, from A. nodosum to F. vesiculosus. Results obtained in this study show that disturbance by human trampling negatively affects A. nodosum assemblages and that the effects are dependent on trampling intensity. These findings highlight the risk of local extinction imposed on these populations by anthropogenic disturbance, and the consequent need for protection measures for such sensitive populations.

KEY WORDS: Ascophyllum nodosum · Trampling disturbance · Distributional range limits · Macro-algal communities · Resilience · Portuguese biogeography

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Cite this article as: Araújo R, Vaselli S, Almeida M, Serrão E, Sousa-Pinto I (2009) Effects of disturbance on marginal populations: human trampling on Ascophyllum nodosum assemblages at its southern distribution limit. Mar Ecol Prog Ser 378:81-92.

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