Counting on β-Diversity to Safeguard the Resilience of Estuaries

Abstract

Coastal ecosystems are often stressed by non-point source and cumulative effects that can lead to local-scale community homogenisation and a concomitant loss of large-scale ecological connectivity. Here we investigate the use of β-diversity as a measure of both community heterogeneity and ecological connectivity. To understand the consequences of different environmental scenarios on heterogeneity and connectivity, it is necessary to understand the scale at which different environmental factors affect β-diversity. We sampled macrofauna from intertidal sites in nine estuaries from New Zealand’s North Island that represented different degrees of stress derived from land-use. We used multiple regression models to identify relationships between β-diversity and local sediment variables, factors related to the estuarine and catchment hydrodynamics and morphology and land-based stressors. At local scales, we found higher β-diversity at sites with a relatively high total richness. At larger scales, β-diversity was positively related to γ-diversity, suggesting that a large regional species pool was linked with large-scale heterogeneity in these systems. Local environmental heterogeneity influenced β-diversity at both local and regional scales, although variables at the estuarine and catchment scales were both needed to explain large scale connectivity. The estuaries expected a priori to be the most stressed exhibited higher variance in community dissimilarity between sites and connectivity to the estuary species pool. This suggests that connectivity and heterogeneity metrics could be used to generate early warning signals of cumulative stress.

Temporal variability of biodiversity patterns and trophic structure of estuarine macrobenthic assemblages along a gradient of metal contamination

“…Box plots representing different beta-diversity metrics, namely Sorensen (b Sor) , Lennon (b Len) and Raup-Crick (b RC) indices, among the different sampling areas (SC e slightly contaminated; MC e moderately contaminated; HC e highly contaminated) and periods. anthropogenic disturbances (Magurran and Henderson, 2010;Bevilacqua et al, 2012;De Juan et al, 2013). An increase of these measures with increasing distances from the metal contamination source was expected, however this was not confirmed in the present study.…”

“…Biological communities in disturbed areas are expected to display lower regional (gamma) and local (alpha) diversity values when compared with less disturbed areas (Pearson and Rosenberg, 1978;Olden and Rooney, 2006;Bevilacqua et al, 2012;De Juan et al, 2013). The present results show that the least contaminated area cannot be considered a reference area.…”

“…Given the renewed interest in beta-diversity measures and their potential to provide complementary information to the alphadiversity measures (Terlizzi et al, 2009;Carvalho et al, 2013;Legendre and De C aceres, 2013), this component of diversity was also analysed. Beta-diversity helps to detect possible losses of ecological heterogeneity, which can be affected by anthropogenic disturbances (Magurran and Henderson, 2010;Bevilacqua et al, 2012;De Juan et al, 2013). Therefore, classical and multivariate measures of beta-diversity will be applied in order to better understand the variability in macrobenthic patterns in response to metal contamination.…”

Geographic distance, water circulation and environmental conditions shape the biodiversity of Mediterranean rocky coasts

“…In order to reduce pairwise dissimilarities to a single measure of β diversity for each site, the average Jaccard dissimilarity was calculated among all pairs of sites (Anderson et al 2013, de Juan et al 2013. That is, the β diversity for a given focal site was computed as the mean of all the pair-wise dissimilarities between the focal site and each of the other sites.…”

“…It can act as a measure of the change in species identities between 2 or more local assemblages, or the relationship between the diversity of the species pool for a given geographic region (γ diversity) and community diversity at local scales (α diversity) (Whittaker 1960). In each case, it reflects the range of processes acting on regional metacommunities that create and maintain patterns of biodiversity within them (de Juan et al 2013). Anderson et al (2011) identified 2 broad approaches to distinguishing β diversity: (1) turnover in species identities among sites along predefined spatial, environmental or temporal gradients or (2) variation in species identities among sites without reference to any specific gradient, both of which are useful for conservation planning (Legendre et al 2005, Smith & Lundholm 2010, Legendre & De Cáceres 2013.…”