Spatial pattern of vertical zonation of rocky shore organisms and the influence of ocean exposure at the Islas Ces (NW Spain)

Abstract

A sampling was conducted around the intertidal coast of the Islas Cies, (NW Spain) with the goal of determining the variation of the shore landspace, based on vertical zonation profiles of sessile organisms in relationship with the Atlantic Ocean influence. The Western Coast is heavy wave beaten and the Eastern Coast is sheltered. Many species coexist in a limited intertidal space of the sheltered than in the exposed shores. The sheltered coast presents in this way, a mosaic structure of their organisms. On the other hand few species dominated the cliffs of the west coast. In this section, the upper intertidal limit of distribution was raised by the increased of humidity caused by the splash and spray. The winds also favoured the presence at the high littoral level of organisms such as brown algae, lichens and vegetation. Multivariate techniques detected differences in the communities between exposed and sheltered shores as well as between the two main islands. Distribution of species in the intertidal zone was related to the particular geomorphological feature of the coast, such as coves, points or exposed cliffs. Four different landscape intertidal patterns of vertical zonation were represented by each island face. The algae, Asparagopsis armata and Bifurcaria bifurcata characterized the sheltered North Island. Pelvetica canaliculata and Fucus spiralis had a greater presence in the sheltered side of the South Island. The fucoids were absent at the wave beaten shore. The lichens, Verrucaria maura and Caloplaca marina, and the Rhodophyta belt had a higher upper limit of distribution at the exposed sides of the North Island. Bare rock and the crust phase of Mastocarpus stellatushad a greater presence at the exposed side of the South Island. Key words: Intertidal ecology, Galician Coast, ocean exposure, sessile organisms, digital image analysis, multivariate analyses.