Laminaria ochroleuca Bachelot de la Pylaie canopy effect on intertidal understorey benthic assemblages in northern Portugal

Dissertação de mest., Biologia Marinha, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2010

The canopy effect of the kelp Laminaria ochroleuca on the associated species assemblages was studied at a northern Portugal intertidal kelp bed, by doing a removal experiment of kelp individuals inside plots of 0.25 m2. The understorey assemblages in undisturbed plots with the same area were sampled for comparison as well as the assemblages inside the holdfasts from the removed kelps. A total of 238 taxa was identified, from which 77 belonged to macroalgae and 161 to invertebrate fauna. The holdfasts showed an average number of 35 epibiont species per holdfast, and several exclusive species when compared to the bottom samples. The understorey assemblage was composed essentially by highly branched red algae and Annelids, Nematods and Arthropods. There was a temporal variability in the assemblages from April to August and an interaction effect between factors time and canopy for algal biomass, but there was no significant interaction for these factors for invertebrate fauna. There was a significant effect of the factor canopy on algal total species, as well as for faunal biomass, faunal species richness and fauna total species. The removal of the canopy did not seem to produce an effect on the recruitment density of its gametophytes. The results seem to respond to changes in light availability and space, with an increase in coarsely and finely branched macroalgae, that represent an increase in habitable space for invertebrate fauna. There was an increase in the number of invertebrate fauna taxa after canopy removal, with an increase in filter and deposit feeding species. The removal of the dominant species in this ecosystem seems to influence the physical structure of the environment, with consequences on the composition of the associated community.