About the Corals of Chagos
By Charles Sheppard, Douglas Fenner, Anne Sheppard
The location of the Chagos Archipelago in the centre of the Indian Ocean makes its ecological role particularly important – it serves as a stepping stone between East and West and it is a refuge and reservoir for species. The region has been termed the ‘Chagos Stricture’ by Veron (1995) in connection with coral distributions and biogeography.
This huge area covers about 60,000 square km of shallow limestone platform on which the atolls and reefs are based. The corals are pre-eminent in building the reefs, and although earlier lists of the corals living there have been published (Sheppard 1981, 1987) an updated account of the corals there is overdue, as is an illustrated guide to what they are.
Corals of Chagos documents the approximately 300 corals and reef building relatives that we and others have found in the Chagos Archipelago. Coral taxonomy can be fairly straightforward but sometimes it is also contested, and nothing today is challenging coral identification more than the relatively new use of genetics to determine classification of species.
The names used here sometimes use this ‘new’ taxonomy, but sometimes we use judgement or ‘history’ instead when we think radically new classifications to be premature. At the moment we must recognise that this is a time of flux in naming many groups of organisms, not only corals.
For example: We use the two generic names Astrea and Phymastrea for the group that used to be called Montastrea, the latter now being considered to be a Caribbean genus only. On the other hand, some genetic-based argument suggests that the very large genera of Favia and Favites in the Indo-Pacific should likewise be renamed, but we have not gone that far here (yet!).
There is a good argument in taxonomic rules to retain a strictly ‘incorrect’ name in cases where overwhelming and common usage requires it and where changing the name would cause more, not less, confusion.
We have sometimes but not always gone along with names as noted by WoRMS (the World Register of Marine Species), but again, we have not always done so, such as with the genus Fungia, where the several different groups within the genus that were once formally termed subgenera are elevated to full genera in WoRMS.
The species names in such cases do not change in any case, and whether or not the old subgeneric names are correct is not (yet) universally agreed. Also, finding a correct name is something that genetics cannot solve by itself - studies following the Code of Zoological Nomenclature are needed for that, and at this point genetics by itself cannot be the sole evidence for new species of animals.
At the present time, we have elected to use names as used by Veron in the Corals of the World website (Veron 2016) which, apart from its undoubted authority, imparts a consistency to the present Guide. All interpretations are of course ours.
The corals of Chagos are strongly connected biogeographically to those of the Western Indian Ocean/East African region. However, more corals than previously thought are from the Asian area. This might add strength to the idea that the Chagos Archipelago acts as a stepping stone between East and West – the ‘Chagos Stricture’ noted above is more of a ‘Chagos Link’.
Also, there are a few species that we think look clearly separate, which have not yet been described or named formally, and if we have the opportunity to work on these then these will be described as new species.
Other than these, there seem to be no species at all which are endemic to Chagos (even Ctenella has been photographed by Dr David Obura nearly 2000 km away to the southwest at St Brandon).
Customarily, endemic species have been a measure of the importance of a site, and this is readily understood – for example, Madagascar has a higher proportion of endemic mammals so its protection from loss is paramount – rightly so.
But most places have some endemics, and having no endemics at all is very unusual. It indicates that, far from the importance of the place being diminished, it is increased: Chagos lies on the main thoroughfare between east and west, and it is a stepping stone of paramount importance, not only for corals in fact but for many marine groups. It is a reservoir and refuge of species – it is the ‘Chagos Link’. It is the species illustrated here that build the reefs and, by definition, the archipelago itself.
In this guide, photos are almost all from the Chagos reefs unless noted. Where a museum specimen is illustrated, those photos are placed after the live coral photos. For some species where a museum specimen from Chagos exists but no photos of live specimens, then the museum specimen photos come first and photos of live examples from other locations follow the Chagos specimen.
: Underwater photos are by two of the authors (AS and DF) except in one or two cases where the photographer is acknowledged. For help in identifying one early batch of coral photos we are grateful to Dr Emre Turak. The Natural History Museum contains many hundreds of coral specimens from Chagos collected in the 1970s, and these were searched through also, and many photographed, which revealed a few species for which we had no underwater photos. Helen Pitman, Director, Chagos Conservation Trust,
assisted with museum photos. Some species of the huge genus Acropora are included where there are confirmed specimens in the Museum of Tropical Queensland (Wallace et al 2012) but which we did not find, in which case the species is illustrated with photos from other areas.
Sheppard, C.R.C. 1981. The reef and soft substrate coral fauna of Chagos, Indian Ocean. Journal of Natural History 15:607-621
Sheppard, C.R.C. 1987. Coral species of the Indian Ocean and adjacent seas: a synonymised compilation and some regional distribution patterns. Atoll Research Bulletin 307:1-32.
Veron J.E.N., Stafford-Smith M.G., Turak E. and DeVantier L.M. (2017). Corals of the World. Accessed 04/01/2017, version 0.01 (Beta). http://www.coralsoftheworld.org.
Veron, J.E.N. 1995. Corals in Space and Time. The biogeography and evolution of the Scleractinia. University of New South Wales Press, Sydney.
Wallace, C.C., Done, B.J. & Muir, P.R. 2012 06 30. Revision and catalogue of worldwide staghorn corals Acropora and Isopora (Scleractinia: Acroporidae) in the Museum of Tropical Queensland. Memoirs of the Queensland Museum — Nature 57: 1–255. Brisbane. ISSN 0079-8835.