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.

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The in situ primary production of three common under‐story members of the Rhodophyta in South African west coast kelp beds was determined monthly for a year using dissolved oxygen techniques. Strong seasonal patterns of photosynthesis and respiration were evident in all three species. Net photosynthesis of all three species was greatest in spring (October) and lowest in winter (June). Increasing photosynthesis in late winter coincided with increasing ambient irradiance and photoperiod, whereas decreasing photosynthesis in summer was not explained by changes in the environmental parameters measured. We suggest that this may he due to an innate pattern related to some other seasonal plant activity such as reproduction. Seasonal Pmax and Ik values reveal that the obligate understory species, B. prolifera and E. obtusa, are shade‐adapted whereas G. radula, a low intertidal and shallow subtidal dominant, is sun‐adapted. Low C: X ratios consistent with a high nutrient environment and high rates of productivity were found in all three species. Net photosynthesis to respiration (Pn:R) ratios were fairly constant for B. prolifera and E. obtusa, implying that then photosynthetic processes were governed more by seasonal variations in irradiance than by instantaneous light availability. The Pn: R ratio of G. radula was variable, suggesting that this species is more responsive to rapid fluctuations in irradiance and may therefore be adapted for rapid growth during periods of high irradiance.

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