Disturbance type and intensity combine to affect resilience of an intertidal community

Differing disturbance agents may vary in the local spatial pattern of their effects, which may in turn influence the resilience of communities, particularly if ecologically important species are affected variably. Here, we investigated the effects of disturbance type on the ecologically important intertidal alga Hormosira banksii and its understory community at 2 sites in southeastern Australia. Replicate 60 x 40 cm plots containing dense H. banksii canopies were disturbed with 11 treatments that varied the severity and type of the disturbance, and included 0 and 100% removal controls, plus a factorial array of 3 disturbance types (cropped, clumped and haphazard removals) crossed with 3 severities of removal (25, 50, and 75% of biomass removed). H. banksii cover, sediment loads and understory community were monitored 7 times over 25 mo. H. banksii recovery (and thus, resilience) was relatively high and was consistent across sites, but both the type and severity of disturbance had effects. Cropped treatments recovered quickly compared to clumped and haphazard treatments, which took up to 6 mo longer to recover as the severity of disturbance increased. Clumped and haphazard removals also produced varied responses in some understory species. This experiment demonstrates that disturbance type, as well as the more commonly explored disturbance severity, may be an important component of the disturbance-resilience relationship.