Regional summary of 9 dive sites. Figures are averages across the sites that report them (n = sites with a value); each site's own page has its individual values. Part of the Chagos Archipelago overview.
⬇ Download this region as a report card
Egmont atoll's reefs, two Danger Island stations, and outlying Cauvin Bank were dived in March 2015, while bleaching was still building. One Egmont dive captured the whole sequence on tabular corals, from healthy tissue through bleaching to freshly dead, algae-covered skeleton.
Heat stress
Long-term record: 3 years since 1985 reached 8 or more °C-weeks at NOAA’s Chagos station. Download the annual DHW data (CSV).
9 sites in this region — click a marker to open that site.
Regional setting
Egmont is one of the five true atolls of the Chagos Archipelago (Spalding et al. 2001). The atlas map places it just southwest of the Great Chagos Bank, with Danger Island on the bank's western rim and Cauvin Bank at its southeastern edge. The Great Chagos Bank itself is a mostly submerged atoll and, at about 13,000 km², the world's largest atoll structure, and Danger Island was declared a Strict Nature Reserve in 1998. The archipelago formed over the volcanic trace of the Réunion hotspot and is the newest, southernmost section of the Chagos–Laccadive Ridge. It is also remote, some 500 km from the Maldives and more than 1,500 km from Sri Lanka. With about 220 scleractinian species, its reefs rank among the most diverse in the Indian Ocean. They include Ctenella chagius, the only living member of the family Meandrinidae in the Indo-Pacific, which may be restricted to the Chagos. Spalding et al. (2001) report coral cover of typically 50–80% on seaward and lagoon slopes before 1998, and an estimated average loss of 80–85% on seaward reefs during that year's bleaching. They estimate about 3,770 km² of reef across the whole archipelago, and Souter et al. (2021) give 2,731 km² for the Chagos ecoregion.
The earliest monitoring data in the South Asia analysis of Souter et al. (2021) come from the Chagos in 1978, and the subregion's record shows coral cover recovering from the 1998 losses until about 2015, then falling after the 2016 bleaching. Across South Asia, that event killed more than 42% of living hard coral, and localized bleaching from 2017 to 2019 extended the decline. The authors warn that repeated bleaching may leave reefs too little time to recover between events, although atoll reefs along the ridge have rebounded better than mainland ones. With restricted access and the region's largest marine protected area (MPA), the Chagos face little local human pressure, and bleaching is the main threat. Earlier, Wilkinson (2006), summarizing the 2004 status report, had noted encouraging recovery in the Chagos after 1998.
Overview
This unit covers Egmont atoll, two Danger Island stations and the outlying Cauvin Bank, surveyed between 9 and 14 March 2015 on the earliest leg of the expedition. Logged maximum depths ran from 11.0 m at BIEG07 to 30.5 m at BIEG04. The six Egmont sites carry 29.2% (BIEG04) to 47.5% (BIEG07) coral cover. Where coral is alive at BIEG04 it is almost entirely Acropora. BIEG05 (46.7%) is built largely of tabular Acropora. BIEG07 holds a richly mixed small-scale community, including a huge, fully pigmented brain-coral boulder.
The two Danger Island stations differ sharply. BIDI11, a forereef outside the lagoon at 23 m, had only four coral genera on its single short transect, with Porites making up three-quarters of its 40% coral and algae at just 21.0%. BIDI16.5 is the bleaching site of the Danger Island set, with strongly mottled Pocillopora colonies (19.7% bleached). Cauvin Bank is a separate, outlying bank about 114 km from the other sites in the unit, not part of Egmont's reef system. Its single site, BICA01, has the second-lowest coral cover of all 112 Chagos stations (4.6%), above only BIDI12 on the Great Chagos Bank. Its corals are a thin but unusually diverse and evenly mixed veneer on open ground, with a third of the bottom bare and no bleaching recorded.
The Egmont dives came before the 2015 bleaching had fully developed. Across a temperature span of 28.9 to 30.0°C, published values rose from 0.5% at BIEG04, a clean pre-event baseline, to 18.3% at BIEG07, the warmest site. Branching Acropora and Pocillopora whitened first while massive corals stayed pigmented. A single dive at BIEG05 recorded the full sequence on tabular Acropora, from healthy tissue through partial and full bleaching to freshly dead, algae-overgrown skeleton. At BIEG06 new coral recruits were settling on dead framework. A crown-of-thorns starfish was photographed beside a collection tool at BIEG02, along with two Culcita cushion stars. Silvertip and gray reef sharks were seen at several Egmont sites, and BIEG04 held a bait ball of thousands of small silver fish.
Highlights
- BIEG05 recorded the full bleaching sequence on tabular Acropora in a single dive
- Egmont's 28.9-30.0°C span lined up with bleaching from 0.5% (BIEG04) to 18.3% (BIEG07)
- New coral recruits settling on dead branching framework beside pale Acropora plains (BIEG06)
- BIDI11: only four coral genera, with Porites making up three-quarters of its 40% coral
- Cauvin Bank (BICA01), an outlying bank about 114 km away, has the second-lowest cover of all 112 Chagos stations (4.6%)
- Silvertip and gray reef sharks at Egmont, and a bait ball of thousands of fish at BIEG04
Notable observations
- Chagos Archipelago - Egmont (BIEG02): Crown-of-thorns starfish unambiguously present, photographed alongside a stainless steel bone-rongeur laid beside it; two Culcita cushion stars. Bleaching 3.6% as a tight cluster of fully white Acropora; one large dead, algae-covered Porites read as recent mortality.
- Chagos Archipelago - Egmont (BIEG03): Four to five fully bleached branching Acropora colonies in one frame (site figure 4.0%).
- Chagos Archipelago - Egmont (BIEG05): Bleaching 6.5%: a completely bleached Pocillopora, and tabular Acropora showing healthy, partially bleached, wholly bleached, freshly dead, and CCA-overgrown stages on one dive.
- Chagos Archipelago - Egmont (BIEG06): Bleaching 10.4%: widespread pale, washed-out Acropora plains, colonies with bone-white branch tips, and standing dead branching framework colonized by algae; new recruits on dead substrate.
- Chagos Archipelago - Egmont (BIEG07): Bleaching 18.3%; bleaching or paling on branching Acropora and Pocillopora in three of eight frames.
- Chagos Archipelago - Danger Island (BIDI16.5): Bleaching 19.7%: several Pocillopora colonies strongly mottled with bone-white branch clusters; pale patches on massive Porites more likely partial mortality or older die-off.
Coral cover over time (pooled)
the year includes his Global Reef Expedition dives with the Khaled bin Sultan Living Oceans Foundation (CRD+LOF data).Sites in this region
- Chagos Archipelago - Cauvin Banks (BICA01) — 4.6% coral cover
- Chagos Archipelago - Danger Island (BIDI11) — 40% coral cover
- Chagos Archipelago - Danger Island (BIDI16.5) — 46% coral cover
- Chagos Archipelago - Egmont (BIEG02) — 32% coral cover
- Chagos Archipelago - Egmont (BIEG03) — 37% coral cover
- Chagos Archipelago - Egmont (BIEG04) — 29% coral cover
- Chagos Archipelago - Egmont (BIEG05) — 47% coral cover
- Chagos Archipelago - Egmont (BIEG06) — 44% coral cover
- Chagos Archipelago - Egmont (BIEG07) — 48% coral cover
% coral cover by method
Pooled across 104 dive sites
| Method | Mean % coral cover | Std. dev. between dive sites | n dive sites | Note |
|---|---|---|---|---|
| Manual point count (author) | 34.0% | ±13 | 28 | frame-weighted 40.1% over 613 frames |
| CoralNet automated point classifier | 32.8% | ±11 | 89 | frame-weighted 34.0% over 1,895 frames |
| CoralSCOP (SAM-based mask-sum), edited photos | 32.2% | ±8.3 | 104 | frame-weighted 33.9% over 2,498 frames |
| Claude (Anthropic), blind point count | 26.5% | ±11 | 104 | frame-weighted 29.0% over 2,495 frames |
| In-house DINOv3 point classifier | 30.5% | ±11 | 104 | frame-weighted 31.2% over 2,500 frames |
| In-water diver transect (line/point intercept) | 37.7% | ±16 | 101 | — |
The mean is an UNWEIGHTED mean of the dive site values — each dive site counts once, whatever its photo count — which is the convention of the published tables and of every other figure on this page. The frame-weighted alternative is given per method in the Note column; where the two differ, the difference is a photo-count imbalance, not a coral-cover finding.
Closest to the reference
Over the dive sites where an independent reference exists, Manual point count (author) sits closest to it — a mean absolute deviation of 9.5 pp across 27 dive sites, then CoralNet automated point classifier 10.5 pp (n=86), Claude (Anthropic), blind point count 13.2 pp (n=101). A mean absolute deviation is not an accuracy score: a model with a consistent offset is correctable, while one with the same deviation scattered in both directions is not.
By dive site
| Dive site | Manual point count | CoralNet | CoralSCOP (edited) | Claude | DINOv3 | Diver transect | coralscapes_v1 | coralscapes |
|---|---|---|---|---|---|---|---|---|
| BIBL82 | 17.5% n=4 | 27.6% n=18 | 35.8% n=22 | 28.3% n=22 | 26.1% n=22 | 37.9% | 42.0% n=22 | 50.2% n=22 |
| BIBL83 | 20.8% n=9 | 25.6% n=6 | 40.7% n=15 | 23.8% n=15 | 24.7% n=15 | 33.1% | 42.2% n=15 | 45.2% n=15 |
| BIBL86 | — | 31.9% n=27 | 25.1% n=27 | 34.4% n=27 | 36.0% n=27 | 47.2% | 50.5% n=27 | 49.4% n=27 |
| BIBL87 | — | 27.9% n=35 | 29.5% n=35 | 30.3% n=35 | 34.0% n=35 | 40.6% | 41.5% n=35 | 48.0% n=35 |
| BICC35 | — | 17.0% n=15 | 20.5% n=15 | 6.7% n=15 | 13.1% n=15 | 13.8% | 21.0% n=15 | 23.9% n=15 |
| BICC36 | — | 19.4% n=15 | 24.7% n=15 | 6.4% n=15 | 18.2% n=15 | 5.8% | 21.0% n=15 | 26.5% n=15 |
| BICC50 | — | 29.4% n=11 | 28.8% n=11 | 15.7% n=11 | 30.0% n=11 | 12.1% | 36.9% n=11 | 48.0% n=11 |
| BICC51 | — | 21.9% n=17 | 27.5% n=17 | 20.7% n=17 | 24.1% n=17 | 15.4% | 26.9% n=17 | 28.4% n=17 |
| BIDI08 | — | 36.4% n=35 | 38.9% n=35 | 35.2% n=35 | 29.1% n=35 | 59.0% | 50.2% n=35 | 53.1% n=35 |
| BIDI09 | — | 38.0% n=30 | 32.2% n=30 | 33.6% n=30 | 23.6% n=30 | 37.7% | 56.2% n=30 | 61.0% n=30 |
| BIDI10 | — | 27.1% n=13 | 32.9% n=13 | 22.5% n=13 | 16.2% n=13 | 23.0% | 44.2% n=13 | 49.4% n=13 |
| BIDI12 | — | 10.4% n=14 | 17.9% n=14 | 2.9% n=14 | 11.0% n=14 | 4.2% | 8.2% n=14 | 10.0% n=14 |
| BIDI13 | — | 20.5% n=11 | 24.9% n=11 | 17.8% n=11 | 18.2% n=11 | 7.8% | 22.0% n=11 | 23.5% n=11 |
| BIDI14 | — | 23.5% n=9 | 30.3% n=9 | 19.2% n=9 | 21.9% n=9 | 15.2% | 26.7% n=9 | 26.2% n=9 |
| BIDI15 | — | 24.6% n=9 | 20.6% n=9 | 36.4% n=9 | 37.0% n=9 | 20.1% | 45.3% n=9 | 48.3% n=9 |
| BIDI16 | — | 25.6% n=13 | 30.9% n=13 | 24.4% n=13 | 22.3% n=13 | 30.4% | 32.2% n=13 | 35.6% n=13 |
| BIEA18 | — | 22.3% n=35 | 28.1% n=35 | 17.7% n=35 | 14.6% n=35 | 20.7% | 32.9% n=35 | 32.4% n=34 |
| BIEA19 | — | 27.2% n=14 | 39.2% n=14 | 30.8% n=14 | 25.5% n=14 | 27.5% | 41.9% n=14 | 44.8% n=14 |
| BIEA20 | — | 24.6% n=19 | 27.1% n=19 | 22.2% n=19 | 16.0% n=19 | 10.8% | 30.8% n=19 | 35.4% n=19 |
| BIEA22 | — | 49.2% n=23 | 50.0% n=23 | 30.8% n=23 | 44.8% n=23 | 21.6% | 44.0% n=23 | 46.1% n=23 |
| BIEA23 | — | 35.7% n=24 | 39.5% n=24 | 28.5% n=24 | 28.8% n=24 | 24.6% | 43.8% n=24 | 49.2% n=24 |
| BIEA24 | — | 40.6% n=11 | 39.2% n=11 | 37.4% n=11 | 41.2% n=11 | 12.7% | 48.5% n=11 | 49.3% n=11 |
| BIEA25 | — | 29.5% n=19 | 29.8% n=19 | 16.4% n=19 | 25.6% n=19 | 15.7% | 31.1% n=19 | 32.8% n=19 |
| BIEA26 | — | 21.0% n=30 | 27.2% n=30 | 14.5% n=30 | 14.1% n=30 | 21.0% | 23.3% n=30 | 28.4% n=30 |
| BIEA52 | — | 38.1% n=22 | 39.1% n=22 | 34.5% n=22 | 21.8% n=22 | 34.1% | 49.6% n=22 | 50.0% n=22 |
| BIEG02 | 25.5% n=21 | — | 23.7% n=21 | 18.2% n=21 | 23.7% n=21 | 31.8% | 31.1% n=21 | 34.5% n=21 |
| BIEG03 | 23.9% n=36 | — | 25.7% n=36 | 16.6% n=36 | 18.4% n=36 | 37.3% | 31.5% n=36 | 34.0% n=36 |
| BIEG04 | 33.9% n=19 | — | 28.2% n=19 | 25.9% n=19 | 35.1% n=19 | 29.2% | 36.4% n=19 | 38.7% n=19 |
| BIEG05 | 40.7% n=35 | 57.8% n=24 | 41.4% n=59 | 39.1% n=59 | 40.2% n=59 | 46.7% | 61.2% n=59 | 63.6% n=59 |
| BIEG06 | — | 44.2% n=30 | 22.6% n=30 | 31.6% n=30 | 34.0% n=30 | 43.5% | 46.0% n=30 | 46.5% n=30 |
| BIEG07 | 40.6% n=8 | — | 26.8% n=8 | 28.5% n=8 | 56.7% n=8 | 47.5% | 30.9% n=8 | 33.5% n=8 |
| BINI77 | — | 29.8% n=11 | 33.5% n=11 | 25.7% n=11 | 26.1% n=11 | 43.0% | 38.2% n=11 | 41.1% n=11 |
| BINI78 | — | 24.4% n=16 | 28.4% n=16 | 24.8% n=16 | 29.0% n=16 | 19.1% | 26.9% n=16 | 28.6% n=16 |
| BINI79 | — | 19.4% n=15 | 21.2% n=15 | 17.9% n=15 | 21.6% n=15 | 31.5% | 27.2% n=15 | 25.0% n=15 |
| BINI80 | 37.6% n=10 | 26.8% n=14 | 34.9% n=24 | 29.4% n=24 | 36.9% n=24 | 42.8% | 42.4% n=24 | 45.9% n=24 |
| BIPB110 | — | 36.6% n=45 | 36.7% n=44 | 29.5% n=45 | 36.6% n=45 | 39.3% | 44.3% n=43 | 49.6% n=43 |
| BIPB112 | 43.6% n=14 | — | 37.7% n=14 | 28.7% n=14 | 44.3% n=14 | 45.0% | 50.6% n=14 | 55.0% n=14 |
| BIPB114 | 29.0% n=22 | 34.4% n=7 | 35.2% n=29 | 20.0% n=29 | 31.7% n=29 | 39.6% | 37.0% n=29 | 38.5% n=29 |
| BIPB60 | 38.8% n=38 | — | 41.9% n=38 | 29.5% n=38 | 33.4% n=38 | 42.2% | 55.5% n=38 | 57.2% n=38 |
| BIPB61 | 17.9% n=14 | — | 32.5% n=14 | 17.0% n=14 | 22.1% n=14 | 20.0% | 41.0% n=14 | 43.0% n=14 |
| BIPB62 | 48.0% n=19 | — | 31.6% n=19 | 33.6% n=19 | 35.3% n=19 | 59.6% | 57.6% n=18 | 57.5% n=18 |
| BIPB63 | 46.9% n=29 | — | 38.4% n=29 | 35.0% n=29 | 33.3% n=29 | 56.0% | 66.2% n=29 | 66.7% n=29 |
| BIPB64 | 22.7% n=21 | — | 33.3% n=21 | 22.8% n=21 | 26.2% n=21 | 31.2% | 34.3% n=21 | 41.4% n=21 |
| BIPB65 | 32.9% n=19 | — | 27.5% n=19 | 30.3% n=19 | 32.3% n=19 | 41.4% | 52.3% n=19 | 54.9% n=19 |
| BIPB66 | 12.5% n=6 | — | 28.8% n=6 | 2.3% n=6 | 26.1% n=6 | 7.0% | 41.9% n=6 | 40.9% n=6 |
| BIPB67 | 36.4% n=41 | — | 29.5% n=41 | 26.1% n=41 | 33.8% n=41 | 41.9% | 49.3% n=41 | 52.2% n=41 |
| BIPB68 | 44.9% n=43 | — | 39.2% n=43 | 36.8% n=43 | 38.5% n=43 | 55.0% | 71.9% n=43 | 73.8% n=43 |
| BIPB69 | 54.2% n=110 | 56.1% n=6 | 42.6% n=116 | 39.1% n=116 | 47.4% n=116 | 64.7% | 74.4% n=116 | 75.4% n=116 |
| BIPB70 | 45.4% n=28 | 45.1% n=27 | 35.7% n=55 | 34.9% n=55 | 40.2% n=55 | 60.3% | 56.6% n=55 | 59.5% n=55 |
| BIPB72 | 50.5% n=41 | 56.1% n=34 | 39.9% n=75 | 44.3% n=75 | 49.2% n=75 | 72.4% | 64.4% n=75 | 69.0% n=75 |
| BIPB73 | — | 45.2% n=45 | 46.9% n=45 | 37.6% n=45 | 45.3% n=45 | 50.1% | 48.0% n=45 | 50.6% n=45 |
| BIPB74 | 39.3% n=8 | 56.0% n=13 | 47.1% n=21 | 51.1% n=21 | 48.9% n=21 | 62.4% | 64.5% n=21 | 65.9% n=21 |
| BIPB75 | — | 39.2% n=9 | 43.7% n=9 | 32.4% n=9 | 42.2% n=9 | 43.9% | 51.0% n=9 | 56.5% n=9 |
| BIPB76 | — | 29.9% n=20 | 29.0% n=20 | 20.9% n=20 | 31.5% n=20 | 35.9% | 34.7% n=20 | 39.8% n=20 |
| BISA102 | — | 31.1% n=27 | 34.4% n=27 | 21.5% n=27 | 30.1% n=27 | 30.9% | 33.2% n=27 | 34.7% n=27 |
| BISA103 | — | 28.4% n=19 | 36.1% n=19 | 30.1% n=19 | 37.2% n=19 | 32.5% | 40.5% n=19 | 44.5% n=19 |
| BISA104 | — | 44.2% n=16 | 41.0% n=16 | 35.7% n=16 | 45.6% n=16 | 36.2% | 46.0% n=16 | 50.6% n=16 |
| BISA105 | — | 23.8% n=19 | 23.4% n=19 | 27.8% n=19 | 36.0% n=19 | 50.3% | 41.8% n=19 | 47.0% n=19 |
| BISA107 | — | 18.0% n=12 | 21.7% n=12 | 18.5% n=12 | 20.6% n=12 | 24.6% | 32.1% n=12 | 41.2% n=12 |
| BISA84 | 25.8% n=2 | 16.7% n=5 | 40.1% n=7 | 17.5% n=7 | 28.6% n=7 | 48.8% | 35.3% n=7 | 34.3% n=7 |
| BISA88 | — | 45.8% n=13 | 43.4% n=13 | 42.7% n=13 | 54.1% n=13 | 56.7% | 55.3% n=13 | 59.9% n=13 |
| BISA91 | — | 46.7% n=13 | 44.0% n=13 | 40.3% n=13 | 55.6% n=13 | 52.4% | 58.0% n=13 | 64.8% n=13 |
| BISA92 | — | 29.4% n=39 | 29.0% n=39 | 18.8% n=39 | 25.6% n=39 | 24.5% | 33.1% n=39 | 34.3% n=39 |
| BISA93 | — | 38.7% n=27 | 26.4% n=28 | 33.0% n=27 | 26.4% n=28 | 39.1% | 58.3% n=26 | 61.0% n=27 |
| BISA94 | — | 47.4% n=2 | 21.4% n=2 | 23.1% n=2 | 56.7% n=2 | 40.3% | 43.5% n=2 | 63.2% n=2 |
| BISA97 | — | 51.1% n=12 | 29.4% n=12 | 51.1% n=12 | 49.7% n=12 | 54.4% | 67.8% n=12 | 69.3% n=12 |
| BISP100 | — | 21.7% n=7 | 27.0% n=7 | 31.9% n=7 | 34.8% n=7 | 53.9% | 42.2% n=7 | 43.2% n=7 |
| BISP101 | — | 39.1% n=13 | 32.6% n=13 | 23.0% n=13 | 32.1% n=13 | 50.0% | 42.2% n=13 | 43.5% n=13 |
| BISP89 | — | 17.2% n=13 | 27.6% n=13 | 19.9% n=13 | 21.5% n=13 | 33.2% | 28.6% n=13 | 29.9% n=13 |
| BISP90 | — | 27.6% n=8 | 37.9% n=8 | 24.7% n=8 | 30.8% n=8 | 39.8% | 41.6% n=8 | 43.2% n=8 |
| BISP95 | — | 21.9% n=26 | 23.1% n=25 | 17.8% n=26 | 20.4% n=26 | 56.9% | 28.0% n=26 | 27.6% n=26 |
| BISP96 | — | 55.6% n=18 | 48.2% n=18 | 51.5% n=18 | 49.3% n=18 | 86.0% | 69.0% n=18 | 72.7% n=18 |
| BITB27 | — | 34.5% n=16 | 37.5% n=16 | 23.8% n=16 | 24.4% n=16 | 36.6% | 45.9% n=16 | 47.8% n=16 |
| BITB28 | — | 26.9% n=43 | 29.0% n=43 | 18.5% n=43 | 20.2% n=43 | 28.5% | 33.5% n=43 | 37.5% n=43 |
| BITB29 | — | 29.6% n=49 | 25.9% n=49 | 18.5% n=49 | 23.7% n=49 | 30.2% | 39.5% n=49 | 42.1% n=49 |
| BITB30 | — | 29.9% n=12 | 30.3% n=12 | 14.0% n=12 | 18.3% n=12 | 42.5% | 33.9% n=12 | 38.2% n=12 |
| BITB32 | — | 16.7% n=19 | 19.9% n=19 | 11.7% n=19 | 11.8% n=19 | 30.3% | 17.9% n=19 | 19.8% n=19 |
| BITB33 | — | 20.3% n=27 | 22.3% n=27 | 7.9% n=27 | 11.5% n=27 | 18.5% | 18.4% n=26 | 17.5% n=26 |
| BITB34 | — | 41.4% n=11 | 46.6% n=11 | 37.0% n=11 | 34.5% n=11 | 61.1% | 56.5% n=11 | 66.7% n=10 |
| BITB37 | — | 37.3% n=56 | 42.4% n=57 | 29.0% n=56 | 29.6% n=57 | 38.8% | 51.2% n=55 | 54.5% n=55 |
| BITB38 | — | 33.7% n=44 | 31.5% n=44 | 26.3% n=44 | 28.1% n=44 | 56.0% | 54.1% n=44 | 56.3% n=44 |
| BITB39 | — | 40.1% n=60 | 44.4% n=61 | 36.7% n=60 | 31.7% n=61 | 50.3% | 53.3% n=59 | 57.5% n=59 |
| BITB40 | — | 28.5% n=5 | 30.8% n=5 | 23.6% n=5 | 22.7% n=5 | 44.9% | 39.7% n=5 | 45.7% n=5 |
| BITB41 | — | 31.8% n=13 | 39.5% n=13 | 24.9% n=13 | 31.8% n=13 | 41.9% | 40.3% n=13 | 42.0% n=13 |
| BITB42 | — | 31.1% n=49 | 35.4% n=51 | 22.6% n=49 | 24.4% n=51 | 36.2% | 39.5% n=50 | 42.8% n=51 |
| BITB43 | — | 35.9% n=12 | 36.6% n=12 | 22.3% n=12 | 14.7% n=12 | 28.7% | 46.7% n=12 | 50.3% n=12 |
| BITB44 | — | 33.2% n=36 | 38.7% n=36 | 26.9% n=36 | 29.4% n=36 | 40.5% | 44.2% n=36 | 47.0% n=36 |
| BITB45 | — | 44.5% n=13 | 36.1% n=13 | 33.3% n=13 | 39.2% n=13 | 45.6% | 50.5% n=13 | 51.9% n=13 |
| BITB46 | — | 27.5% n=11 | 31.3% n=11 | 18.4% n=11 | 15.2% n=11 | 25.8% | 34.5% n=10 | 37.7% n=10 |
| BITB47 | — | 43.0% n=2 | 33.2% n=2 | 25.5% n=2 | 35.0% n=2 | 53.7% | 46.0% n=2 | 45.2% n=2 |
| BITB53 | — | 35.2% n=22 | 27.4% n=22 | 23.4% n=22 | 30.8% n=22 | 36.7% | 40.7% n=22 | 42.0% n=22 |
| BITB54 | — | 34.3% n=99 | 30.9% n=99 | 29.8% n=99 | 20.8% n=99 | 49.5% | 50.0% n=97 | 53.9% n=97 |
| BITB55 | — | 43.3% n=14 | 38.3% n=14 | 33.2% n=14 | 33.8% n=14 | 47.6% | 47.1% n=14 | 51.0% n=14 |
| BITB56 | — | 19.9% n=13 | 18.0% n=13 | 19.4% n=13 | 20.3% n=13 | 21.3% | 25.0% n=13 | 26.2% n=13 |
| BITB57 | — | 44.0% n=111 | 36.4% n=111 | 43.4% n=111 | 33.2% n=111 | 40.1% | 65.6% n=111 | 67.8% n=111 |
| BITB58 | — | 31.0% n=1 | 29.9% n=1 | 31.0% n=1 | 40.0% n=1 | 67.0% | 28.1% n=1 | 32.6% n=1 |
| BIVB108 | 40.0% n=1 | 25.1% n=10 | 28.2% n=11 | 11.7% n=11 | 23.9% n=11 | 45.7% | 23.2% n=10 | 18.1% n=11 |
| BIVB109 | 36.7% n=1 | 35.0% n=32 | 24.9% n=33 | 35.0% n=33 | 39.0% n=33 | 34.7% | 67.3% n=33 | 66.1% n=33 |
| BIVB81 | — | 37.8% n=5 | 49.2% n=5 | 56.7% n=5 | 44.7% n=5 | 51.7% | 60.9% n=5 | 63.4% n=5 |
| BIVB99 | — | 20.8% n=11 | 18.5% n=11 | 35.4% n=11 | 24.5% n=11 | 55.6% | 64.2% n=11 | 62.9% n=11 |
| BICA01 | 0.0% n=1 | — | 0.3% n=1 | 0.0% n=1 | 3.3% n=1 | 4.6% | 1.3% n=1 | 0.4% n=1 |
| BIDI16.5 | 45.6% n=13 | 38.7% n=11 | 29.7% n=11 | 26.3% n=11 | 41.8% n=11 | — | 37.2% n=11 | 39.4% n=11 |
| BIEA24.5 | — | 19.6% n=5 | 21.2% n=5 | 15.2% n=5 | 20.7% n=5 | — | 20.3% n=5 | 22.0% n=5 |
| BITB34.5 | — | 47.2% n=3 | 33.4% n=3 | 21.9% n=3 | 53.3% n=3 | — | 29.2% n=3 | 28.6% n=3 |
n under each value is the number of photographs that method scored at that dive site. ⚠ marks a cell that is not an independent check.
Reference: IN-WATER DIVER TRANSECT, independent of the imagery (Mayfield & Dempsey 2026, Oceans 7:1). Denominator: line/point intercept along the transect; not a photo-point denominator. Source: published (Mayfield & Dempsey 2026, Oceans 7:1, suppl. S1); formal 38.7% cover / 30.5% bleaching, tourist-diver 35.1% / 31.8% ⚠ The reference here is NOT the same instrument as at Mauritius, Oman, Kenya or the Red Sea. Those are point counts on the photographs; this is a diver swimming a transect. The models and the reference never saw the same thing. ⚠ SITE-LEVEL ONLY. The 2,500 frames were not associated with any transect taken within 200 m of them, so transect-vs-image comparisons are site means, never frames. The transect value is already in the pin `cover` field (109 of 112 pins, sourced to the paper's suppl. S1) and is read from there, never re-imported.
Nearby external survey stations
11 independent survey records within 5 km of a site in this region (deduplicated across sites).
- Sheppard et al. (2008) — Egmont (2006): 19% hard coral cover, 1.01 km from Chagos Archipelago - Egmont (BIEG05)
- Spalding et al. 2025 (Chagos 2024 bleaching report) — Egmont Manta Alley (ocean, NE aspect, 2-5 m) (2024): 5.0% hard coral cover, 0.34 km from Chagos Archipelago - Egmont (BIEG04)
- Spalding et al. 2025 (Chagos 2024 bleaching report) — Egmont Manta Alley (ocean, NE aspect, 5-8 m) (2024): 80% hard coral cover, 0.34 km from Chagos Archipelago - Egmont (BIEG04)
- Spalding et al. 2025 (Chagos 2024 bleaching report) — Egmont Manta Alley (ocean, NE aspect, 8-10 m) (2024): 80% hard coral cover, 0.34 km from Chagos Archipelago - Egmont (BIEG04)
- Spalding et al. 2025 (Chagos 2024 bleaching report) — Egmont Outer reef North (ocean, N aspect, 5-8 m) (2024): 80% hard coral cover, 1.46 km from Chagos Archipelago - Egmont (BIEG06)
- Spalding et al. 2025 (Chagos 2024 bleaching report) — Egmont Outer reef North (ocean, N aspect, 8-10 m) (2024): 80% hard coral cover, 1.46 km from Chagos Archipelago - Egmont (BIEG06)
- Spalding et al. 2025 (Chagos 2024 bleaching report) — Egmont West (ocean, W aspect, 12-15 m) (2024): 20% hard coral cover, 0.66 km from Chagos Archipelago - Egmont (BIEG05)
- Spalding et al. 2025 (Chagos 2024 bleaching report) — Egmont West (ocean, W aspect, 7-10 m) (2024): 30% hard coral cover, 0.66 km from Chagos Archipelago - Egmont (BIEG05)
- Spalding et al. 2025 (Chagos 2024 bleaching report) — Egmont, NW Lagoon (lagoon, S aspect, 2-3 m) (2024): 70% hard coral cover, 1.16 km from Chagos Archipelago - Egmont (BIEG06)
- XL Catlin Seaview Survey — transect 36028 (2015): 11% hard coral cover, 2.17 km from Chagos Archipelago - Egmont (BIEG03)
- XL Catlin Seaview Survey — transect 36029 (2015): 29% hard coral cover, 1.94 km from Chagos Archipelago - Egmont (BIEG07)
All images from Coral Reef Diagnostics. Data are from Coral Reef Diagnostics and XL Catlin Seaview Survey (University of Queensland).
© Coral Reef Diagnostics.
References
- Souter D, et al. (eds) (2021) Status of Coral Reefs of the World: 2020. International Coral Reef Initiative / Global Coral Reef Monitoring Network. [PDF]
- Spalding MD, et al. (2001) World Atlas of Coral Reefs. University of California Press, Berkeley. [PDF]
- Wilkinson C (2006) Status of coral reefs of the world: summary of threats and remedial action. In: Côté IM, Reynolds JD (eds) Coral Reef Conservation. Cambridge University Press, Cambridge. [PDF]
- Mayfield AB, Dempsey AC (2026). Using tourist diver images to estimate coral cover and bleaching prevalence in a remote Indian Ocean coral reef system. Oceans 7(1):1. PDF
- Sheppard C, Harris A, Sheppard A (2008). Archipelago-wide coral recovery patterns since 1998 in the Chagos Archipelago, central Indian Ocean. Marine Ecology Progress Series 362:109-117. PDF
- Spalding M, Bourasseau M, et al. (2025). Coral bleaching and mortality in the Chagos Archipelago, 2024. British Indian Ocean Territory Administration report (gray literature). PDF