Table 1. Principle currents of the Western Indian Ocean, their relevance and consequences for the biogeography of the reef building coral fauna.

Main current	Biogeographic relevance	Consequence	Evidence
A) South Equatorial Current (SEC)	Immigration of species/gene flow from the Central Indo-Pacific Realm, similarity of Chagos/northern Mozambique Channel fauna, species accumulation in the WIO.	High diversity in WIO	[18], [19] this study
	Isolation and low diversity of islands north (Seychelles) and south (Mascarene islands) of the SEC.	Low diversity and endemism in the islands	[41], [42] this study
B) Eddies and the Comoros Gyre in the Mozambique Channel	High connectivity within the northern Mozambique Channel (NMC); high retention of larvae and genetic diversity within the channel.	High species richness in the northern Mozambique Channel	[22], [96] this study
	High connectivity within the southern Mozambique Channel, higher productivity due to eddy-shelf interactions, mixing with the East Madagascar Current and upwelling from the South Madagascar Plateau	Transition to colder/higher nutrient fauna and habitats. Lower coral diversity	[44], [45]
C) East Africa Coastal Current (EACC)	Linear transport from NMC to 2°S (north Kenya) then monsoon current reversals and influence of Somali upwelling system.	Declining diversity with distance, transition to different coral fauna	[1], [46] this study
D) Somali Current, monsoon reversals &upwelling	Monsoon current reversals, Somali upwelling system, exchange with the northern Indian Ocean (Red Sea, Gulfs of Aden/Oman/Arabia)	Different coral fauna, colder/higher nutrient conditions and extreme environments.	[11], [14], [15], [97]
E) Agulhas Current	Merging of Mozambique Channel waters and East Madagascar Current to form the Agulhas Current.	Colder/marginal conditions, declining coral diversity	[97], [98]

Sources of evidence for the biogeographic patterns are listed in the table, and discussed in the text. See main text for references relevant to oceanographic features. Letter codes for each current correspond to letters in fig. 2a.