Type and timing of disturbance modify trajectories of recovery of rockpool assemblages at Aguda (NW Portugal)

Abstract

Patterns of recovery of rock pool assemblages were experimentally investigated along the rocky shore of Praia da Aguda (NW Portugal). The temporal variance in the structure of whole assemblages and abundance of individual algal and invertebrate organisms was examined after two experimental disturbances differing in intensity, i.e. one able to eliminate all the biota from the substratum, the other able to create a mosaic of bare patches interspersed within the remaining organisms. Two experimental trials were carried out (starting in March 2007 and July 2007, respectively), with a duration of the study of 13 months each. Multivariate results indicated a temporally consistent positive relationship between the intensity of disturbance applied and the temporal variance of the structure of assemblages. A similar response was documented at the univariate level by the encrusting coralline alga Lithophyllum incrustans and the foliose green algae of the genus Ulva, while both experimental disturbances decreased temporal fluctuations of the abundance of mussels, Mytilus galloprovincialis, compared to unmanipulated control. The present study has implications for understanding and predicting responses of intertidal assemblages to natural disturbances whose intensity is predicted to increase in the future, including climate events.