Abstract

In recent decades a decline in the foundation species Gelidium corneum (Hudson) J. V. Lamouroux has been detected along the Basque coast (northern Spain). This decline has been attributed to several factors, but recent studies have found a relationship between high irradiance and the biochemical and physiological stress of G. corneum. Since physiological responses to changes in light occur well before variations in morphology, the present study seeks to use a size-class demographic approach to investigate whether shallow subtidal populations of G. corneum off the Basque coast show different frond bleaching, density and biomass under different irradiance conditions. The results revealed that the bleaching incidence and cover were positively related to irradiance, whereas biomass was negatively related. The effect of the irradiance level on frond density was found to vary with size-class, i.e. fronds up to 15 cm showed greater densities under high light conditions (126.6 to 262.2 W m(-2)) whereas the number of larger fronds (>20 cm) per unit area was lower. In conclusion, the results of the present study suggest that irradiance might be a key factor for controlling along-shore bleaching, frond density and biomass in G. corneum. Further research should be carried out on the physiology of this canopy species in relation to its bed structure and on the interaction of irradiance and other abiotic (nutrients, temperature, wave energy) and biotic factors (grazing pressure). (C) 2017 Elsevier B.V. All rights reserved.