Physical disturbances in an Australian kelp community. I. Temporal effects

Physical disturbances leading to clearances of kelp canopies were investigated for their effects on understorey species.First, frequencies and types of natural dsturbances in a kelp forest were quanhf~ed from data on s t o m activity and undenvater surveys.Storms removed parts of kelp plants, whole plants and groups of plants.The latter led to cleanngs and Increased the quanhty of light reachlng the substratum.Second, manipulative experiments throughout l yr determined temporal vanation in the effects of canopy removal on the understorey assemblage.Replicate areas in the kelp forest were cleared and others left as controls.The microscopic assemblage of species was sampled as well as macroscopic plants and anlmals On substrata cleared in spring, summer and autumn, turf dominated after initial increases in the covers of microalgae and microinvertebrates This turf inhibited kelp recrmtment during dense recruitment in wlnter and persisted for up to 2 yr, unhl kelps encroached into clearings from the edges.In areas cleared d u ~i n g dense kelp recruitment (in winter), kelp colonized the substratum together with filamentous and turf algae.The kelp quickly developed a canopy, leadlng to the decline of turf species.These results demonstrate inhibitoqr successions: kelp canopies and areas of turf both occupied the substratum and inhibited the establishmcnt of the other.The type of vegetation found in any place at any hme depended on the timing of, and bme since, the last removal of kelp.