Dr Iacopo Bertocci1, Dr Elena Maggi1, Miss Claudia Scirè Scappuzzo1, Dr Luca Rindi1, Prof Lisandro Benedetti-Cecchi1
1University of Pisa, Department of Biology, ,
Experiments indicated that effects of temporal variance of disturbance depend critically on how much time is available between subsequent events, this being associated with the recolonization ability of organisms. Nevertheless, a priori inclusions of varying recolonization ability of organisms in studies of recovery to disturbance are lacking. We examined the response of two high-shore rockpool taxa, namely epilithic microphytobenthos (EMPB) and green filamentous algae, known to have different growth rates, to regimes of disturbance varying for the time interval between consecutive events, while controlling for the overall frequency and intensity. Based on modelling and previous experimental evidence, we designed a field experiment involving three temporal patterns of physical disturbance all characterized by total 12 events over 9 months, but differing for the clustering degree: Low (20-day interval between consecutive events), Medium (40-d interval between paired events), High (80-d interval between groups of four events). Our hypotheses were: (1) 20 days between disturbances would be too short to allow recovery of both EMPB and filamentous algae; (2) 40 days between disturbances would still prevent the recovery of the taxon characterized by lower recolonization rate (filamentous algae), while they would allow the recovery of EMPB; (3) both taxa would recover effectively under events of disturbance separated by 80 days. Response variables were percentage cover and frond lenght of filamentous algae, then converted to biomass through regression, and the biomass of EMPB estimated with Diving-PAM. While EMPB could persist during the 40-d and the 80-d periods between disturbances, filamentous algae did not withstand even a regime characterized by 80 days between disturbance events. We point out that relatively small differences in growth rate can drive different responses of organisms to the same disturbance regime, suggesting that such responses would be even stronger when involving taxa with more markedly contrasting life-history traits.
Presentation Slides – Iacopo Bertocci
