Abstract :
[en] The distribution of Thaliacea collected by several oceanographic cruises throughout the occidental sector of the Indian Ocean has been examined. Between the South of the Mozambique Strait on one hand and the Persian Gulf and the Gulf of Aqaba on the other hand, some 25 species have been identified and the behavior of the most numerous ones, analysed.
Most of the species have been found at Nosy-Bé, during a year of regular collections. The sharing of the species between the pelagic zone and the neritic one was observed and the annual cycle of some, defined.
Doliolum denticulatum – like D. mülleri – is a mainly pelagic species while D. gegenbauri seems more neritic with a secondary and temporary widespreading towards the outer zone. D nationalis, especially in neritic areas, e.g. the Persian Gulf, has been found under the phorozooid stage and therefore undergoes a short cycle of development like their relatives I, the Mediterranean Sea.
A few colonies of both Pyrosoma ambulata and P. fixata have been collected between Mozambique and the Gulf of Aden. In the southern area, their presence is recorded for the first time.
Among Salps, some were not found, e.g.: Cyclosalpa affinis and C. floridana, Traustedtia multitentaculata and Thetys vagina, although previously caught by the earlier investigators of the Ocean. A few species were rare, e.g.: Ritteriella amboinensis and R. picteti, Salpa maxima, Pegea confoederata, with not many specimens in the catches as a whole. Iasis zonaria and Metcalfina hexagona were found above the great depths and Brooksia rostrata, Thalia democratica and Salpa cylindrica gathered as well in the neritic areas as in the pelagic areas, while Cyclosalpia pinnata is neritic at Nosy-Bé and pelagic but rare in the Arabian Sea. Salpa fusiformis has been caught at Nosy-Bé during austral winter and spring; in the open sea, both Salpa fusiformis and Salpa fusiformis aspera are living together.
The thaliacean fauna of the Persian Gulf and the Gulf of Oman was considered for the first time and proved to be less diversified than that in the Gulfs of Suez and Aqaba. Three species of Salpae (Thalia democratica, Salpa cylindrica and Iasis zonaria), four species of Doliolids (D. mülleri, D. denticulatum, D. nationalis and D. gegenbauri) were found in the catches from the Gulf of Oman; Pyrosomes are lacking. Iasis zonaria does not enter the Persian Gulf, Thalia democratica and Doliolum denticulatum are limited to the eastern part while Salpa cylindrica and Doliolum nationalis are observed at the innermost stations.
The Gulf of Aden is richer and most of its species have been also observed in the Red Sea; exception to this rule seems, as far as our present knowledge, to be Iasis zonaria, Metcalfina hexagona, the Cyclosalps and Pyrosomes.
The need for more systematic investigations in areas mentioned above must be stressed.
