Figure 1.
The Western Indian Ocean, defined by the East African coast and the Saya de Malha, Nazareth and Cargados Carajos banks of the Mascarene Plateau.
The principal currents that define the region are coded by the circled letters A–E (see Table 1). Bathymetric contours were selected to illustrate the main plateau and bank features, at 60, 200 and 1000 m depth.
Table 1.
Principle currents of the Western Indian Ocean, their relevance and consequences for the biogeography of the reef building coral fauna.
Figure 2.
Ecoregions and provinces of the Western Indo-Pacific Realm, excluding the Andaman Seas in the East.
a) Marine Ecoregions of the World (MEOW) [36] provinces and ecoregions (abbreviations and numbers in circles), and sample locations (numbers, see Table 2). MEOW province and ecoregion codes (see Table 2 and fig. 4): Province - Red Sea/Gulf of Aden (RSGA): ecoregions - North Central Red Sea (87), Southern Red Sea (88), Gulf of Aden (89, GA); Province - Somali-Arabian Seas (SAS): ecoregions - Persian (90), Oman (91), West Arabian Sea (92), Central Somali (93); Province - Western Indian Ocean (WIO): ecoregions - North Monsoon Current (94, Mons), East African Coral Coast (95, EAC), Seychelles (96, Sey), Cargados/Tromelin (97, Car), Mascarene Islands (98, Mas), Southeast Madagascar (99), West & North Madagascar (100, W&NM), Sofala (101), Delagoa (102); Province - West & South India (WSI): ecoregions - West India (103), South India/Sri Lanka (104); Province - Central Indian Ocean (CIO): ecoregions - Maldives (105), Chagos (106). The star shows the position of Tromelin Island (France). b) adjustments to the MEOW ecoregions and provinces suggested by this study (see Table 4) and discussion. A possible east-west split in the southern Mozambique Channel is shown by a dotted line.
Figure 3.
Cluster analysis of coral species from the IUCN Red List of Threatened species by MEOW provinces and ecoregions.
a) All provinces in the tropical Indo-Pacific coded by Realm, and b) ecoregions within the West Indo-Pacific Realm, excluding the Andaman Seas, coded by province (see caption to fig. 2 for full province names). Significant groupings shown as thin red lines: a) ANOSIM, R = 0.609, p<0.001; b) ANOSIM R = 0.917, p<0.01; Primer v 6.0.
Table 2.
Survey locations in the Western Indian Ocean.
Figure 4.
Cluster analysis of coral species presence/absence for study locations in the Western Indian Ocean.
Study locations are listed in Table 2 and coded by MEOW ecoregion. Significant clusters are joined by thin red lines (ANOSIM R = 0.837, p<0.001).
Figure 5.
Multi-dimensional scaling (MDS) bi-plot of locations in the Western Indian Ocean excluding the outliers from Djibouti to Reunion island (from fig. 4).
The outliers were excluded to more clearly represent relationships among the more highly related locations. Significant groups of locations (ANOSIM R = 0.837, p<0.001) coded as Northern Mozambique Channel (NMC), Northern Mozambique Channel group b (NMCb), islands in the northern Mozambique Channel and western Seychelles (Isl) and Northern Monsoon current (Mons). Similarity contours are shown at 75, 80 and 85% similarity.
Figure 6.
Estimated maximum species richness of reef-building corals at survey locations in the Western Indian Ocean, ordered by decreasing diversity.
The graph shows Smax, derived from the Michaelis-Menten regression equation on presence/absence from a pool of 369 coral species across all locations, and the number of species sampled. Symbols against the x axis correspond to the significant cluster symbols from fig. 5.
Table 3.
Reported and sampled distributions of coral species restricted to the Indian Ocean.
Figure 7.
Comparison of coral species richness for areas in the Western Indian Ocean, between this study and Sheppard [18].
Reported species richness is from [18] and estimated asymptotic number of species (Smax) is from this study. Maximum Smax is shown where there were multiple locations from this study corresponding to areas in [18].
Table 4.
Proposed changes to province, ecoregion and Large Marine Ecosystem classifications in the Indo-West Pacific Realm, based on reef-building corals.
Table 5.
Maximum diversity (species richness) estimators applied to the NE Madagascar surveys, based on random samples of 6, 7, 8, 10, 12, 15, 20, 25, 30 and 36 samples*.