Patterns in marine hydrozoan richness and biogeography around southern Africa: implications of life cycle strategy

Authors

  • Mark J. Gibbons,

    Corresponding author
    1. Department of Biodiversity and Conservation Biology, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa
      Mark J. Gibbons, Department of Biodiversity and Conservation Biology, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa.
      E-mail: mgibbons@uwc.ac.za
    Search for more papers by this author
  • Emmanuel Buecher,

    1. Department of Biodiversity and Conservation Biology, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa
    Search for more papers by this author
  • Delphine Thibault-Botha,

    1. Department of Biodiversity and Conservation Biology, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa
    2. Aix-Marseille Université, CNRS, LOPB-UMR 6535, Laboratoire d’Océanographie Physique et Biogéochimique, OSU/Centre d’Océanologie de Marseille, Campus de Luminy, Case 901, Marseilles 13288, France
    Search for more papers by this author
  • Rebecca R. Helm

    1. Department of Biodiversity and Conservation Biology, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa
    2. Marine and Coastal Management, Department of Environmental Affairs and Tourism, Private Bag X2, Roggebaii 8012, South Africa
    3. 80 Waterman Street, Box G-W, Brown University, Providence, RI 02912, USA
    Search for more papers by this author

Mark J. Gibbons, Department of Biodiversity and Conservation Biology, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa.
E-mail: mgibbons@uwc.ac.za

Abstract

Aim  To examine patterns of marine hydrozoan richness around southern Africa and to test the hypothesis that patterns of biogeography become weaker with increasing dispersal ability.

Location  The coastline of southern Africa from 21° S, 14° E to 28° S, 33° E, extending from the intertidal zone seawards a distance of 200 nautical miles.

Methods  Published and unpublished information on the distribution of marine Hydrozoa was entered as presence/absence data onto a gridded coastline of the region. A similarity matrix between the species composition of grid squares was constructed using the Bray–Curtis index and visualized using non-metric multidimensional scaling ordinations. Separate analyses were conducted, and compared, on the three major life cycle groupings: holoplanktic, meroplanktic and benthic.

Results  Over 450 species of marine Hydrozoa have been reported from the region, and species richness increases eastwards, in a manner at odds with the distribution of sampling effort. There was a significant correlation between the geographic structures of the resemblance matrices generated for the three life cycle groupings. In other words, all three groups showed similar patterns of biogeography around the region, and these were broadly similar to those reported by others. However, there were differences between them that reflect the resolution at which the data were examined. At a level of 40% similarity, there was no biogeographic structure to the holoplanktic fauna, the meroplanktic taxa were simply sub-divided into cool- and warm-temperate/subtropical elements, and in the case of benthic taxa, the cool-water fauna was further split into a southern Namaqua and a depauperate northern Namib component. Even at a resolution of 70% similarity, the holopelagic taxa could be separated only into cool-temperate and warm-temperate/subtropical faunas.

Main conclusions  Holoplanktic taxa show comparatively less biogeographic structure than meroplanktic taxa, which in turn show less clearly defined biogeographic structure than benthic taxa. It is suggested that this is related to the interaction between oceanography and dispersive-stage duration. The role that the Agulhas Current plays in influencing the Benguela Current fauna is highlighted. This study has implications for conservation planning exercises based on protecting representative biotopes in different biogeographic regions.

Ancillary