Community-dependent variability in species composition and richness on rocky shores at a regional scale

Abstract

Identifying scales at which most of the spatial heterogeneity occurs is important to understand how ecological communities are structured. Rocky shore communities are distributed vertically as a response to environmental variables and mainly water availability gradients. There has been much debate about the relative importance of vertical and horizontal variation gradients in littoral community structure and richness. In this study we assessed if horizontal variability is responsible for changes in community structure at a regional scale (hundreds of Km) by restraining vertical variability. We studied ten different rocky shore communities from the upper mediolittoral to the upper infralittoral levels with different geographical distribution patterns. We aimed at assessing if structure and species richness are affected by their geographical position of each community. The results proved that horizontal variation in species composition and richness was community-dependent and there was no common pattern at a regional scale. Communities with a wide geographic distribution typically showed some variation, which was related to changes in the environmental factors across the geographical gradient. This study sheds light on the existence of latitudinal variability in species composition and richness at a regional scale in rocky shores. It also strongly supports the validity of littoral communities and habitats from conservation panels as consistent ecosystem subdivisions and reliable working units.