GARY C. WILLIAMS
California Academy of Sciences, Department of Invertebrate Zoology and Geology,
Golden Gate Park, San Francisco, California 94118, U.S.A.
Abstract
The geographical and bathymetric distribution of southern African octocorals is analyzed. Of the over 200 estimated species of regional octocorals, 81 confirmed and adequately described species are studied using a radial sector method. Two primary faunal components are recognized - endemic (53.3% of the fauna by numbers of species) and Indo-Pacific (39.4%). An Atlantic component contributes only minimally (about 1.7%), while the remaining fauna is made up of cosmopolites (2.8%), and scattered species (2.8%). A subantarctic component is not evident for the present-day, although evidence for previous contact is presented. A sister-group analysis using genera as a guide to sister species, shows the biogeographic affinities for the present-day fauna as a whole to be 45% Indo-Pacific, 31% cosmopolitan, 10% endemic, 10% Atlantic, and 4% southern oceans (subantarctic). Applying the same method to only those genera with endemic species shows the affinities of the present-day endemic fauna to be 27.5% Indo-Pacific, 27.5% endemic, 24% cosmopolitan, 14% Atlantic and 7% subantarctic. Clearly defined boundaries for west, south, and east coast faunas (as recognized by previous authors in describing various intertidal faunas) are found not to be present with regard to the octocoral fauna (largely due to its overwhelmingly subtidal nature). Instead two primary zoogeographic provinces are recognized - the Cape Endemic Province (extending from Lüderitz to Inhaca Island) and the south-western fringe of the Indo-Pacific Province from East London north-eastwards. An overlap zone between these two is recognized between East London and Inhaca Island, with the region in the Vicinity of Richards Bay having an essentially evenly mixed fauna (roughly 50% Cape Endemic Province and 50% Indo-Pacific). Of the 84 octocoral genera recorded for the region, seven (or 8.3%) are endemic, and of these, five are monotypic while two are ditypic. The fauna is shown to be predominantly sublittoral (about 95% by numbers of species), the shallow sublittoral (<100 m in depth) being the region with highest species richness. Pennatulaceans are eurybathic (intertidal to 4756 m) and clearly show a high proportion of cosmopolites (20% of presently identified species). Soft corals are stenobathic and restricted to the intertidal , continental shelf and uppermost portion of the continental slope (<500 m), while gorgonians are intermediate in depth distribution (intertidal to 1200 m). No cosmopolitan alcyonaceans are presently recorded. The centre of the Cape Endemic Province is the Agulhas Bank - an extensive region of shallow continental shelf (<200 m in depth) between Cape Town and East London. Two regions of octocoral radiation for southern Africa are postulated - the Agulhas Bank and the western Indian Ocean.
Table of Contents
Introduction
Methods
Sources of data
Procedures of definitions
Results and discussion
Importance of the regional fauna
Composition of the fauna and faunal boundaries
Affinities of the fauna, sister-group relationships and vicariance
Bathymetric distribution
Distributional patterns
Factors affecting distribution
Variability, endemism and radiation
Varying levels of endemism
Conclusion
Acknowledgements
References
Appendices
The entire article is contained in the following citation:
Biological Journal of the Linnean Society 46(4): 351-401[August 1992]