GEOGRAPHIC CONSISTENCIES OF EFFECTS OF EXPERIMENTAL PHYSICAL DISTURBANCE ON UNDERSTOREY SPECIES IN SUBLITTORAL KELP FORESTS IN CENTRAL NEW-SOUTH-WALES

Experimental physical disturbances on the assemblages of understorey species living in sublittoral kelp forests in central New South Wales were examined across several spatial and temporal scales. Experimental clearing of kelp canopies (mimicking damage done during storms) and subsequent macro- and microscopic sampling of cleared areas, edges of clearings and uncleared, control areas of natural kelp forest were done over a 14-month period across several spatial scales: three replicate patches of clearings and controls (3-5 m apart) in each of two sites (10-20 m apart) in each of two kelp forests (0.2-5 km apart) in each of four locations (20-140 km apart). Despite large variations in abundances and temporal fluctuations, there were some similarities in responses to disturbance by several taxa in most locations. The covers of holdfasts of Ecklonia radiata and encrusting algae decreased in the centres of most clearings in most kelp forests as plots became overgrown, first by microscopic filamentous algae and then by macroscopic foliose algae. While these changes occurred, a layer of sediment increased in cover in clearings and the species richness of the assemblage declined. Assemblages on the edges of clearings often showed effects intermediate between those in the centres of clearings and those under the natural canopy. In some forests, juveniles of Ecklonia radiata recruited, but this tended to occur toward the edges of clearings where the covers of microalgae, turf and sediment were least. The presence of turfing species in the centres of clearings also seemed to preclude the successful establishment of some sponges and an ascidian during their periods of recruitment. The microscopic and turfing algae which colonized clearings were different in different places, as were the periods after clearing before they colonized. Species that were fairly uniform in their responses to disturbance were common, occurring in similar abundances in most places. Temporal variability showed that some fluctuations occurred over a matter of weeks (e.g. the microscopic organisms), others occurred over several months (foliose algae), whilst the largest time-scale involved the recovery of the disturbed kelp canopy over the full duration of the experiment. Despite significant small-scale spatial patchiness in the responses of taxa to disturbances, these effects were fairly consistent within a particular forest. The results are discussed in terms of current theories of patch dynamics, as they apply to our understanding of kelp systems.