Systematics and zoogeography of Asteroidea (Echinodermata) from Inhaca Island, Mozambique

Sixteen out of the seventeen species of shallow-water starfishes reported with certainty from Inhaca Island and Maputo Bay were collected by the author. The seventeenth, Archaster angulatus, was recorded from there by Jangoux (1973). An identification key to these species, both in English and in Portuguese is presented. Four species have not been mentioned previously from Inhaca waters, viz. Astropecten monacanthus (because of earlier incorrect identifications), Monachaster sanderi, not known to occur further south than Zanzibar, Fromia milleporella and Ophidiaster hemprichii, which were not previously known to occur south of Madagascar. Stellaster equestris was found washed ashore on a sandy beach a little north of Maputo. The earlier recorded presence in Inhaca waters of some species, viz. Astropecten granulatus, A. acanthifer, A. antares, Leiaster leachii, Asterina coronata, Patiriella dyscrita and Linckia guildingii is doubtful. Patiriella exigua, which is widely distributed in subtropical-temperate waters of the southern hemisphere, possibly including South America, is the only species occuring on the exposed rocks of Cabo da Inhaca (figs. 2 and 33); it is absent in the warmer, sheltered waters of Inhaca Island and Maputo Bay, where the sixteen other species were found. The last-named species are all tropical and widely distributed in the western Indian Ocean, the Indo-West Pacific and sometimes even reaching the East Pacific Barrier. For ten of them, Inhaca Island and Maputo Bay form the southern-most limit of distribution. A juvenile specimen of the usually reef dwelling Linckia laevigata was found on exposed tidal rocks at Ponta de Ouro, on the border with South Africa. Four species are recorded as far south as Natal (29° S). On the eastern side of its distribution area, Stellaster equestris has been reported from northern New South Wales, Australia; in the western Indian Ocean, Maputo Bay is the southern-most locality (fig. 16). The results thus agree well with those of A.M. Clark & Courtman-Stock (1976). The fact that Mozambique lies in the lee of Madagascar and has reduced wave action compared to northern Natal (Hartnoll, 1976), combined with the sheltering effect of the eastern ridge of Inhaca Island itself, may be the reason why, as far as asteroids are concerned, the East African Tropical Province extends into Maputo Bay. The taxonomy of some starfishes, notably the "Scoparius- group" of Astropecten and the asterinids, needs further clarification. The investigation of the coral communities off northern Natal could also render interesting data.