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

A Rattray,E Cebrian,M Andrello,J Evans,A Terlizzi,G Guarnieri,M Chiantore,V Asnaghi,F Bulleri,S Bevilacqua,Pj Schembri,J Claudet,L Benedetti-Cecchi,S Fraschetti,S Deudero,L Mangialajo

doi:10.3354/meps11783

Abstract

Ecological connectivity is important for effective marine planning and biodiversity conservation. Our aim was to identify factors important in influencing variation in benthic community structure on shallow rocky reefs in 2 regions of the Mediterranean Sea with contrasting oceanographic regimes. We assessed beta (β) diversity at 146 sites in the littoral and shallow sub-littoral from the Adriatic/Ionian Seas (eastern region) and Ligurian/Tyrrhenian Seas (western region) using a null modelling approach to account for variation in species richness. The distance decay relationship between species turnover within each region and geographic distance by sea was determined using generalised linear models. Mantel tests were used to examine correlations between β diversity and connectivity by ocean currents, estimated from Lagrangian dispersal simulations. Variation in β diversity between sites was partitioned according to environmental and spatial components using a distance-based redundancy approach. Species turnover along a gradient of geographic distance was greater by a factor of 3 to 5 in the western region than the eastern region, suggesting lower con-nectivity between sites. β diversity was correlated with connectivity by ocean currents at both depths in the eastern region but not in the western region. The influence of spatial and environmental predictors of β diversity varied considerably between regions, but was similar between depths. Our results highlight the interaction of oceanographic, spatial and environmental processes influencing benthic marine β diversity. Persistent currents in the eastern region may be responsible for lower observed β diversity compared to the western region, where patterns of water circulation are more variable.

Highlights

Elucidating the mechanisms that control patterns of diversity is a central objective of community ecology (Hubbell 2001, Leibold et al 2004), and has been the focus of considerable research across terrestrial (Tuomisto et al 2003, De Cáceres et al 2012), freshwater (Maloney & Munguia 2011, Angeler 2013) and marine systems (Watson et al 2012, Moritz et al 2013)
Species turnover along a gradient of geographic distance was greater by a factor of 3 to 5 in the western region than the eastern region, suggesting lower connectivity between sites. β diversity was correlated with connectivity by ocean currents at both depths in the eastern region but not in the western region
A better understanding of these mechanisms is critically important for conservation planning, which has historically focussed on prioritizing protection of areas containing high species richness and threatened or endemic species, but often failed to incorporate underlying variation in regional species assembly driven by ecological connectivity, spatial processes and environmental heterogeneity (McKnight et al 2007)

Summary

Introduction

Elucidating the mechanisms that control patterns of diversity is a central objective of community ecology (Hubbell 2001, Leibold et al 2004), and has been the focus of considerable research across terrestrial (Tuomisto et al 2003, De Cáceres et al 2012), freshwater (Maloney & Munguia 2011, Angeler 2013) and marine systems (Watson et al 2012, Moritz et al 2013). There are a multitude of approaches to defining and measuring β diversity, it is generally recognised as the change in species composition among sites in a geographic area of interest (Koleff et al 2003, Legendre et al 2005, Anderson et al 2011). 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). Patterns of β diversity provide a measure of ecological connectivity that can be related to broader environmental, spatial and temporal gradients and used to untangle drivers behind patterns of community assembly (Borcard et al 1992, Thrush et al 2010)

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