MEPS

Marine Ecology Progress Series

MEPS is a leading hybrid research journal on all aspects of marine, coastal and estuarine ecology. Priority is given to outstanding research that advances our ecological understanding.

Online: ISSN 1616-1599

Print: ISSN 0171-8630

DOI: https://doi.org/10.3354/meps

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Volume contents
Mar Ecol Prog Ser 159:265-273 (1997)

Holdfasts of adult kelp Ecklonia maxima provide refuges from grazing for recruitment of juvenile kelps

ABSTRACT: 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 wasrock (bare or covered with encrusting coralline algae), followed by kelp holdfasts, and the ascidian Pyura stolonifera at some sites. A disproportionately high ratio (relative to the available substrata) of young sporophytes grew on the holdfastsof mature kelps at most sites, but particularly where high densities of benthic invertebrate grazers were present (mainly the urchin Parechinus angulosus, also abalone Haliotis midae, limpets Patella spp. and gastropods Turbospp. 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 selection' of rock as a substratum atsites where grazers were numerous. The ratios of young sporophytes on holdfasts/young sporophytes on rock were directly proportional to grazer densities when sites were compared (r = -0.90, p = 0.002), supporting the hypothesis that mature holdfasts arean important refuge for recruitment of E. maxima sporophytes. There was an 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 coasttransition 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, with importantimplications for commercial kelp harvesting.

KEYWORDS

R. J. Anderson (Co-author)

  • Sea Fisheries Research Institute, Private Bag X2, Roggebaai, 8012 Cape Town, South Africa

P. Carrick (Co-author)

  • Department of Botany, University of Cape Town, Rondebosch 7700, South Africa

G. J. Levitt (Co-author)

  • Sea Fisheries Research Institute, Private Bag X2, Roggebaai, 8012 Cape Town, South Africa

A. Share (Co-author)

  • Sea Fisheries Research Institute, Private Bag X2, Roggebaai, 8012 Cape Town, South Africa