Rocky intertidal benthic systems in temperate seas: A synthesis of their functional performances

Species composition and values of diversity, biomass, quantities of chlorophylla and carotenes of 5 algal communities, located at different intertidal levels in northwestern Spain, were studied at monthly intervals. Productivity and loss of matter, as well as the production/biomass ratio in the same communities, are related to environmental stress (e.g. emersion, high temperature) and used to explain the dynamics of the system. Dynamic performances are also related to seasonal changes of patterns of zonation and special micropatchiness. High productivity values (computed values between 0.50 and 2.71 g C m^–2 day^–1) are ascribed to extra-energy inputs (not due to illumination) in terms of waves, tides and other water movements. The importance of such extra energy for productivity is discussed. Extra-energy is more important at low levels; at high levels its role is substituted by the ability of plants to photosynthesize during emersion periods. High intertidal communities are resistent to stress and hence, physically controlled; in contrast, low-level communities are biologically controlled. The former are more conservative, the latter less efficient. Based on all data obtained, a hypothesis is presented, regarding the general functioning of intertidal communities.