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The gracilarioids in South Africa: long-term monitoring of a declining resource

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Abstract

In South Africa, gracilarioid red algae have been collected as wash-up to be dried and sold for agar extraction for at least 50 years. Despite much research, there is currently no commercial mariculture of the algae locally although this has been carried out in neighboring Namibia for a number of years. The industry is traditionally confined to Saldanha Bay on the west coast, although small wash-ups of Gracilariopsis longissima have been collected in nearby St Helena Bay. In Saldanha Bay, wash-ups of Gracilaria. gracilis have been very sporadic over the last few decades, with human alteration of the bay configuration possibly responsible for an initial major decline in 1974. This unpredictability in the amounts of wash-up has made the industry unstable and increasingly unprofitable. We compiled the results of previous surveys (some unpublished) of gracilariod populations in St Helena Bay and the Saldanha-Langebaan sytem, and re-surveyed these populations to examine long-term fluctuations. In Saldanha Bay and Langebaan Lagoon, standing stock of G. gracilis was estimated at 538 tons fresh weight and 71 tons fresh weight respectively. Less than 4 tons of gracilarioids are estimated to remain in St Helena Bay. We discuss the fluctuations in biomass and distribution of these South African gracilarioid populations.

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Acknowledgements

We thank Marine and Coastal Management (Department of Environmental Affairs and Tourism) and the University of Cape Town for funding this project and the use of its facilities. Thank you to Messrs G. Fridjhon, N. vd Heever, CM Muller, G. Levitt, B. Anderson, AJ Smit, L. Kruger and A. West who assisted with the diving work.

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Authors and Affiliations

  1. Marine and Coastal Management, Private Bag X2, Rogge Bay, South Africa, 8012

    M. D. Rothman, R. J. Anderson, C. J. T. Boothroyd & F. A. Kemp

  2. Botany Department, University of Cape Town, Private Bag, Rondebosch, South Africa, 7701

    R. J. Anderson & J. J. Bolton

Authors
  1. M. D. Rothman
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  2. R. J. Anderson
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  3. C. J. T. Boothroyd
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  4. F. A. Kemp
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  5. J. J. Bolton
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Correspondence to M. D. Rothman.

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Rothman, M.D., Anderson, R.J., Boothroyd, C.J.T. et al. The gracilarioids in South Africa: long-term monitoring of a declining resource. J Appl Phycol 21, 47–53 (2009). https://doi.org/10.1007/s10811-008-9364-y

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  • DOI: https://doi.org/10.1007/s10811-008-9364-y

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