UPPER AND LOWER LIMITS OF ROCKY SHORE ORGANISMS AT DIFFERENT SPATIAL SCALES AND WAVE EXPOSURE (ISLAS CIES, NW SPAIN)

A photographically sampling was conducted at Islas Cies, NW, Spain with the goal of determinate the upper and lower limits of vertical distribution of sessile organisms on the intertidal rocky shore of this National Park. The response of the species to different Atlantic Ocean exposure was tested at west coast (exposed) and east coast (sheltered) of Islas Cies. The sampling was made following a hierarchical spatial design. The contribution in the variation around the mean of the intertidal limits of each organism at diverse spatial scales in the rocky shore was estimated with Linear Mixed Effects Model with software R. The majority of the species were found to increase their upper limits in the exposed coast of the two islands. Several intertidal algae, mainly the fucoids, were absent at the exposed shore and this pattern could be influenced by excessive turbulence. The variation at large spatial scales was related to changes in the degree of exposure between islands. Physical characteristics and biological interactions accounted for the variability observed on the intertidal. The spatial heterogeneity introduces variability from very small to mid spatial scale. The species presented in the low intertidal have more variation at small scale (meter to tens of meters), and the organisms in the high intertidal vary their limits at medium scale (tens to hundreds of meters). The life cycle, adaptations, ecology and natural history of the intertidal organisms described in previous studies of Galician, Portuguese, and the British shores may explain the patterns found in Islas Cies.