Connectivity and patch area in a coastal marine landscape: Disentangling their influence on local species richness and composition

Abstract

Landscape ecology emerged as a terrestrial discipline to evaluate the effect of spatial configuration of natural systems on ecological patterns. The advances in marine systems have been comparatively scarce perhaps as a consequence of a long-standing view about the greater dispersal potential of marine species and its effect on the spatial homogenization of marine landscapes. Herein we used an intertidal rocky system as a model to analyse the effect of landscape attributes on local species richness and composition. We evaluated the effect of patch area, landscape connectivity and salinity gradient on local species richness of macro-invertebrates, and the effect of geographic distance on species similarity. We sampled 19 rocky patches along the Uruguayan Atlantic coast one time during the spring of 2003. The relative contribution of the variables assessed on specific richness of sessile, mobile and total macrofauna was analysed with a stepwise multiple linear regression. For the mobile macrofaunal richness, we also incorporated the sessile macrofaunal richness as another independent variable. The effect of geographic distance on biological similarity was assessed by a Mantel test. We showed that landscape connectivity, as a descriptor of the average physical isolation of a biological community in the landscape, is an important factor explaining the community species richness for sessile macrofauna, what indirectly increases the mobile macrofaunal richness. The geographic distance between sites was negatively related to species similarity. We suggest that at the landscape scale, connectivity among sites can be important to understand the local structure of marine communities, particularly in rocky intertidal systems. Also the distance-decay of similarity in community composition provides a useful descriptor of how biological composition varies along a physical gradient. Our results contribute to reinforce the view that mesoscale connectivity (101–2 km) in coastal marine landscapes plays a more important role in local community structure than previously assumed.