The distribution of young sporophytes (up to 0.25 m stipe length) of the 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 encrusting coralline algae), followed by kelp holdfasts, and the ascld~an Pyura stolonlfera at some sites. A disproportionately high rat10 (relative to the available substrata) of young sporophytes grew on the holdfasts of mature kelps at most sites, but particularly where hlgh densities of benthic Invertebrate grazers were present (mainly the urchin Parechinus angulosus, also abalone Haliotis mjdae, limpets Patella spp. and gastropods Turbo spp. and Oxystele spp.). Jacobs' index of electivity was used an indicator of 'preference for' (interpreted as indicating survival on) the substratum type. This showed a statistically significant 'negative select~on' of rock as a substratum at sites where grazers were numerous The ratios of young sporophytes on holdfasts/young sporophytes on rock were directly proport~onal to grazer d e n s~t~e s when sites were compared (r = -0.90, p = 0.0021, supporting the hypothesis that mature holdfasts are an important refuge for recruitment of E. maxlma sporophytes. There was a n inverse relationship between percentage cover of understorey algae and grazer densities (r = 0.92. p = 0.001). In general, sites east of Cape Point (west coast/south coast transition zone) have far more grazers and reduced understorey algal biomasses 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. w~t h important implications for commercial kelp harvesting.
In South Africa, more than 7000 t (f wt) of kelp (Ecklonia maxima) fronds are harvested annually to feed cultured abalone. Carpoblepharis flaccida, Gelidium vittatum and Polysiphonia virgata are conspicuous red algal epiphytes on older kelps and provide habitat and food for numerous animals. Over 4.5 y, we examined the effects of one destructive harvest of E. maxima on these 3 epiphytes. Two 20 × 20 m plots of kelp with similar epiphyte loads were demarcated. In one, all E. maxima sporophytes with stipes longer than 50 cm were harvested. The other plot served as a control. After 2.5 y the biomass of E. maxima in the harvested plot had recovered to control levels, but the epiphyte load (g epiphytes. kg kelp −1 ) was statistically lower in the harvested plot after 2.5 and 3.5 y, and only recovered after 4.5 y. While most commercial harvesters cut through the "heads" (primary blades) of the kelp, effectively killing them, a new, non-lethal method removes secondary blades 20-30 cm from their bases, leaving the meristems and primary blades intact. At 5 sites studied, G. vittatum and P. virgata were found almost entirely on stipes and primary blades, and harvesting only distal parts of secondary blades limited losses to about 50% of C. flaccida biomass. To protect epiphytes, non-lethal harvesting is recommended and permanent non-harvest zones have been established in addition to limiting kelp yields and disallowing harvesting in Marine Protected Areas.
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