Efectos de la destrucción del estrato de Himanthalia elongata en la vegetación cespitosa del sistema intermareal de la ría de Vigo

Abstract

The evolution of some variables of a macrophytic intertidal community in which Himanthalia elongata was eliminated, are compared with unmanipulated vegetation growing in the same environmental conditions. The elongation of Himanthalia was prevented, since February, and samples of experimental surfaces were taken in August, September, November and January. Number of species remain constant, and no uncommon species were found. Whole biomass was lower in communities without Himanthalia, but the biomass of the cespitose species increases in experimental surfaces suggesting a competitive interaction between Himanthalia and canopy algae rather than a protective shelter effect. The winter dominant species, whren Himanthalia was degaged, were present earlier in experimental surfaces that in control ones, this fact is related with the mentioned competition for space, light and nutrients. Diversity increases when dominant species was eliminated, but in control surfaces, canopies are more diverse than in control cespitose communities. The concentration of chlorophyll a per biomass unit is higher, after manipulation, than in undisturbed communities, and the ratio between absortions of methanolic extracts at 430 and 665 nanometers is lower in experimental samples. Both figures suggest an increase of energy flow through manipulated communities. Low level communities, growing in Vigo intertide, present two phses considered cyclic in previous papers, present data suggest that the end of succession is archieved when Himanthalia elongata was dominant and the winter diversification phase, highly diverse, is only a transiet phase equivalent to an overlap between channeling phase and the end phase of succession with an Himanthalia dominated community