Zoogeography of the shallow-water holothuroids of the western Indian Ocean
Samyn, Y.; Tallon, I. (2003). Zoogeography of the shallow-water holothuroids of the western Indian Ocean, in: Samyn, Y. Towards an understanding of the shallow-water holothuroid fauna (Echinodermata: Holothuroidea) of the western Indian Ocean. pp. 340-356
In: Samyn, Y. (2003). Towards an understanding of the shallow-water holothuroid fauna (Echinodermata: Holothuroidea) of the western Indian Ocean. PhD Thesis. Vrije Universiteit Brussel: Brussel. III, 384 + 1 cd-rom pp., more
Aim: Determination of the zoogeography of the shallow-water holothuroids of the western Indian Ocean. To what extent do differences in species' ability to disperse across potential barriers shape that pattern?Location: Shallow-waters (50 m isobaths) of the western Indian Ocean, the area ranging from Suez to Cape Town and from the coastline of East Africa up to 65° East.Methods: Cluster analysis on several f3-diversity coefficients; parsimony analyses of endemicity.Results: The shallow-water holothuroid fauna of the western Indian Ocean is highly diverse and part of the larger Indo-Pacific and the South African biogeography provinces. The western Indian Ocean is however best split into several biogeograpbic units. To the north, we found some evidence that the northern Red Sea holothuroid fauna differs from the southern Red Sea fauna, the latter bears closest affinity with South-East Arabia and the Persian Gulf and thus the biogeographic barrier of Bab-el-Mandab nowadays seems to be of minor significance. The important cold upwelling at the east coast of Somalia forms an effective barrier for holothuroids and especially those with lecitotrophic (short-lived) larvae. The circumtropical biogeographical pattern was not well-resolved, but important taxonomic turn overs suggest that it is composed of several distinct subprovinces. The biogeography of the western Indian Gcean is best explained with (i) species' dispersion ability, (ii) the prevalent current patterns and (iii) recent geological history. As a by-product of this research we demonstrate that Rapport’s rule does not hold for the shallow-water holothuroid fauna in the here studied latitudinal gradient.Main conclusions: The shallow-water biota of the western Indian Ocean (WIG) were generally believed to belong to the tropical Indo-West Pacific and in the far South (Cape area) to the South African biogeographic Province. This study analysed this simple biogeographic model and concluded that the western Indian Ocean best be split in (at least) three biogeographic realms. Conspicuous differences in dispersion abilities of the three dominant orders are identified as the shaping factors. As a serendipitous find, we found that Rapport’s rule does not hold in the western Indian Ocean.
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