Effects of size and season of disturbance on algal patch recovery in a rocky intertidal community

Effects of gap size and the season of clearing on algal patch recovery were investigated in a high rocky intertidal shore of British Columbia, Canada, to understand community dynamics in relation to physical disturbance. The community studied contains 3 dominant perennial macroalgae, Mazzaella cornucopiae (= Iridaea cornucopiae, Rhodophyta), Fucus distichus and Pelvetiopsis limitata (Phaeophyta), and some ephemeral algae as well as barnacles and limpets. The experimental design comprised 3 gap sizes of clearing (5 x 5 cm, 10 x 10 cm and 20 x 20 cm) and 4 seasonal clearings (August 1991, October 1991, February 1992, April 1992). The recolonization rate of all algal species was fastest in the medium gaps, followed by the small and large gaps. Thus, medium gaps were filled by a relatively well-mixed combination of all algal species including M. cornucopiae (rare in large gaps) and F. distichus (low in small gaps). Responses of each alga to the different sizes of clearing were species-specific and related to the alga's reproductive characteristics. The results indicate that negative factors (e.g. whiplash, desiccation) were probably responsible for slow colonization in the 2 extreme sizes of gap. Different algal species responded differently to the gaps cleared in different seasons. New substrata created a short time (e.g. 2 mo) before the peak of fucoid recruitment in unmanipulated plots received a greater number of fucoid propagules, and this initial recruitment secured fucoid persistence in the later successional period. On the other hand, for M. cornucopiae, which propagates mostly vegetatively, the timing of clearing generally did not influence dominance of this alga in the patches. Barnacle densities during the experimental period were less in small gaps than in medium and large gaps, but limpet abundance was not significantly influenced by clearing size. The kinds of algal species which move in when a gap of a particular size is created in a particular season were predicted for this community using the interaction terms of size and season effects of disturbance.