Marginal populations under pressure: spatial and temporal heterogeneity of Ascophyllum nodosum and associated assemblages affected by human trampling in Portugal

Abstract

Anthropogenic disturbances are major threats to coastal biodiversity and may exert drastic effects on natural populations occurring at the borders of the geographical distribution of species, which are thus already experiencing sub-optimal environmental conditions. In this paper, we examined the effects of experimental intensities of human trampling on temporal and spatial variance of the brown seaweed Ascophyllum nodosum and associated organisms in north Por tugal. This is the southernmost population of A. nodosum in Europe and shows morphological and demographic traits that are different from those of populations from more central locations within its range of distribution. Results indicated that high trampling intensity reduced the smallscale spatial heterogeneity in the abundance of A. nodosum, whose cover was stabilized around relatively low values, and of the associated red algae Polysiphonia lanosa and Rhodothamniella floridula; however, it increased the spatial variance of limpets and green foliose macroalgae of the genus Ulva. Idiosyncratic responses in temporal patterns were also documented, with high trampling intensity causing relatively larger fluctuations in the structure of whole A. nodosum associated assemblages and in the abundance of Ulva spp., and smaller fluctuations in the cover of Fucus vesiculosus. The present findings are key to predicting the relatively unstudied responses of coastal populations of A. nodosum to increasing anthropogenic disturbance and have important implications for the management and conservation of the examined population, which represents a relevant component of the biodiversity of European rocky shores.

Climate change impact on seaweed meadow distribution in the North Atlantic rocky intertidal

“…1), whose distribution limits coincide with phytogeographic boundaries (Van den Hoek 1975), Fucus serratus, Fucus vesiculosus, and Ascophyllum nodosum (L€ uning et al 1990;Chapman 1995;Wahl et al 2011). Along the Northeast-Atlantic coast, the three species reach their northern distribution limit at the 10°C summer isotherm (upper limit of the cold-temperate province) in the White Sea with F. vesiculosus extending south to the Canary Islands (Haroun et al 2002) (20°C winter isotherm and lower limit of the warmtemperate province) and both F. serratus and A. nodosum south to North-Portugal (Arrontes 1993;Ara ujo et al 2009;Pearson et al 2009;Bertocci et al 2011;Viejo et al 2011;Mart ınez et al 2012b). In the Northwest-Atlantic, A. nodosum extends from Southern Newfoundland (Canada) to Long Island, NY and F. vesiculosus extends from Southern Newfoundland (Canada) to Beaufort NC (Adey and Hayek 2005;Keser et al 2005;Muhlin and Brawley 2009;Olsen et al 2010).…”

Central-marginal population dynamics in species invasions

“…Variations within and among populations are critical for understanding species-range structure and dynamics (Storey et al, 2007;Bertocci et al, 2011;Guo, 2012). Both population size and density are main elements reflecting population structure and dynamics.…”

Effect of Disturbance Regime on Alpha and Beta Diversity of Rock Pools

“…For clarity in this paper, alpha diversity is defined as the diversity in taxa of individual rock pools and beta diversity refers to the variation in community structure (quantitative taxa abundance data) among rock pools, based on definitions given by Legendre et al [10]. Several authors underlined that changes in alpha diversity following disturbances received much more attention [11][12][13][14][15]. Firstly, high temporal variance of population abundance can often mask the occurrence of anthropogenic disturbances.…”