Original Articles

Composition, species richness and similarity of ichthyofaunas in eelgrass Zostera capensis beds of southern Africa


Abstract

This study collates published and unpublished data on the ichthyofaunas associated with beds of eelgrass Zostera capensis in eight estuaries and one lagoon in southern Africa. These macrophyte beds are utilized predominantly by small teleosts, both species which breed in the estuary and juvenile marine fish. By far the most abundant of the 97 species of fish recorded in these beds were Atherina breviceps, Gilchristella aestuaria, Liza dumerilii, Liza richardsonii and Rhabdosargus holubi. Classification grouped the ichthyofaunas of the six warm-temperate estuaries in the South-Eastern and Southern Cape at a similarity level >50 per cent. Ordination produced a similar clustering and also demonstrated that the subtropical Richards Bay and warm-temperate Mngazana estuary, together with the cold-temperate Langebaan Lagoon, were outliers. Classification and ordination showed that, within an estuary, the ichthyofaunas of dense and sparse Zostera areas were more similar than either was with those of non-vegetated areas. The species richness (R) of fish within eelgrass habitats along the southern African coast tended to decrease from north-east to south-west, a trend attributable to an attenuation in the number of tropical/subtropical Indo-Pacific species. The numerically dominant fish families in eelgrass beds in South Africa showed a greater degree of overlap with those of south-eastern Australia than with those of either southern Japan or eastern North America.

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