HOLDFASTS OF ADULT KELP ECKLONIA-MAXIMA PROVIDE REFUGES FROM GRAZING FOR RECRUITMENT OF JUVENILE KELPS

The distribution of young sporophytes (up to 0.25 m stipe length) of t he kelp Ecklonia maxima, on various substrata, at depths of 2.5 to 5.0 m, was studied at 8 sites on the southwest coast of South Africa. The most common substratum available was rock (bare or covered with encru sting coralline algae), followed by kelp holdfasts, and the ascidian P yura stolonifera at some sites. A disproportionately high ratio (relat ive to the available substrata) of young sporophytes grew on the holdf asts of mature kelps at most sites, but particularly where high densit ies of benthic invertebrate grazers were present (mainly the urchin Pa rechinus angulosus, also abalone Haliotis midae, limpets Patella spp, and gastropods Turbo spp, and Oxystele spp.). Jacobs' index of electiv ity was used an indicator of 'preference for' (interpreted as indicati ng survival on) the substratum type. This showed a statistically signi ficant 'negative selection' of rock as a substratum at sites where gra zers were numerous. The ratios of young sporophytes on holdfasts/young sporophytes on rock were directly proportional to grazer densities wh en sites were compared (r = -0.90, p = 0.002); supporting the hypothes is that mature holdfasts are an important refuge for recruitment of E. maxima sporophytes. There was an inverse relationship between percent age cover of understorey algae and grazer densities (r = 0.92, p = 0.0 01). In general, sites east of Cape Point (west coast/south coast tran sition zone) have far more grazers and reduced understorey algal bioma sses compared to west coast sites. There thus appear to be fundamental differences in some of the major ecological processes in kelp beds in these 2 areas, with important implications for commercial kelp harves ting.