INDIAN OCEAN ECHINODERMS 



29 



DISCUSSION 



The crinoids of the tropical Indo-west Pacific region (Africa, 

 Indonesia, Philippines, tropical Australia and the South Pacific) 

 are relatively well-documented (Clark & Rowe, 1971). The region 

 between the Red Sea and Indonesia has to date produced a rela- 

 tively depauperate crinoid record, but the reasons for this are not 

 clear. Unfortunately, the Sindbad collection does not resolve the 

 problem. The low number of crinoids in this collection from the 

 Laccadives and from Sri Lanka is probably due to a combination 

 of two factors: lower abundance and diversity of this group in the 

 localities collected, and limited sampling time available in those 

 regions. This situation is unfortunate, as the areas of the northern 

 Indian Ocean, except for the western fringe of Indonesia, are not 

 well-represented in any collections of echinoderms, so that spe- 

 cies and even generic distributions within the region are not 

 well-known. In fact, the majority of specimens collected during 

 the Sindbad Voyage are from around the small island of Pula We, 

 at the western tip of Sumatra, Indonesia. SE Asia is the region of 

 the Indo-West Pacific associated with greatest echinoderm species 

 richness (Clark & Rowe, 1971), and Indonesia in particular is 

 commonly regarded as the centre of distribution for coral reefs, 

 other invertebrate groups and marine tropical diversity in general 

 (Veron, 1995; Gray, 1997). 



Crinoid records from this voyage's collection are divided into the 

 different regions sampled in Table 1, which also shows the equiva- 

 lent zoogeographic subdivisions adopted by Clark & Rowe (1971). 

 The observed distribution is highly skewed, with all but two of the 30 

 species collected in Sumatra, eight in Sri Lanka and only three in the 

 Laccadives. Regional comparison based on more comprehensive 

 records, including Indian Ocean data of Clark and Rowe ( 1 97 1 ) and 

 the results of James (1989) for the Laccadives (13 additional spe- 

 cies) and Sri Lanka (14 additional species), shows species 

 distributions to be less uneven. Nevertheless, the resulting pattern 

 reveals a progressive increase in species richness from the Maldive 

 area to Sri Lanka to East Indies/Indonesia, as suggested in the 

 Sindbad data (Table 1). However, the Laccadives, in particular, 

 probably remain undersampled. These islands are a prohibited area 

 under the control of India, and access will probably continue to be 

 restricted. 



Range extensions, to the western fringe of Indonesia (Pula We) 

 and into the Indian Ocean, are recorded for at least six of the 30 

 crinoid species collected during the Sindbad Voyage, as follows: 

 Clarkcomanthus albinotus (Indonesia/East Indies); Comanthus 

 briareus (Sri Lanka area); Comanthus gisleni (Sri Lanka area & 

 Indonesia/East Indies); Comanthus suavia (Sri Lanka area & In- 

 donesia/East Indies); Comanthus wahlbergii (Maldive area, Sri 

 Lanka area & Indonesia/East Indies); Oxycomanthus bennetti (In- 

 donesia/East Indies); and possibly also Comaster parvicirrus (Sri 

 Lanka area - depending on validity of an earlier record) and 

 Comaster multifidus (Maldive area?- specimens poorly pre- 

 served). 



Of the crinoids represented, Capillaster multiradiatus and 

 Oxycommanthus bennetti were the most common, each occurring in 

 19% of the samples, followed by Comanthus parvicirrus which 

 occurred in 9% of the samples. The first two species also occupied a 

 relatively wide range of depths (2-30 m) and habitats compared to 

 most other species collected. A more comprehensive ecological and 

 biogeographic assessment of echinoderms of Pula We, Sumatra is 

 currently in progress. 



Acknowledgements. We are grateful to Dr R. Dalley, P. Hunnam, P. 

 Dobbs and D. Tattle for their considerable assistance during field work. One 

 of us (A.R.G.P.) would also like to thank T. Severin, leader of the Sindbad 

 Voyage, for the kind invitation to participate in the expedition which was 

 made possible by generous support from the Ministry of Natural Heritage and 

 Culture, Sultanate of Oman. Financial assistance to A.R.G.P. from the 

 Leverhulme Trust is gratefully acknowledged. Thanks are also due to Dr 

 Anne Hoggett (Lizard Island Research Station, GBR, Australia) for assist- 

 ance with identification of specimens in doubt; and to Dr Frank Rowe for 

 confirming several identifications. 



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