Part of the regional summaries: Chagos Archipelago - Great Chagos Bank West / Brothers / Eagle and Chagos Archipelago
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Chagos (NOAA CRW virtual station)A coral-rich forereef off South Brother (48% cover) where tabular and corymbose Acropora in the shallows give way to a near-monoculture of massive Porites at depth. The reef looks well pigmented, though a small crown-of-thorns starfish was spotted, along with a resident octopus. Surveyed on the Living Oceans Foundation's Global Reef Expedition.
Three independent survey stations shown with the program’s logo — click one to see how far it is from this site.
Thirteen other CRD dive sites within 5 km shown in orange — click a marker to open its page.
🗺 Detailed map of the Global Reef Expedition dive sites, Three Brothers, Chagos (Khaled bin Sultan Living Oceans Foundation; opens in a new window)
17 of these 30 photographs are shown beside the text that discusses them under "Site description" below.
Site description
Setting
BITB55 is a coral-abundant fringing forereef off South Brother in the Three Brothers group, surveyed at intermediate exposure to about 30 m depth.
General benthic features
The reef is a mix of Porites and Acropora, with Porites edging out overall, though shallower ground is dominated by tabular and corymbose Acropora while deeper ground shifts toward a near-monoculture of massive Porites (e.g., Image 3, Image 4, Image 15, Image 17, Image 24, Image 33).
Photographs show a structurally rich, well-pigmented reef with no visible bleaching, plus a resident octopus and a small crown-of-thorns sea star observed during the survey (e.g., Image 1, Image 5, Image 8, Image 10, Image 11, Image 12, Image 13, Image 21, Image 29, Image 30, Image 32).
Coral cover
Published transects record 48% coral cover against 24.4% algae, with only 8.1% of surveyed coral showing signs of bleaching. The bleaching percentage is a computer vision figure — CoralNet annotation of the informal survey images, not a diver's field estimate — and human-vs-model agreement is weaker for bleaching (r = 0.40) than for coral cover (r = 0.72). Image-based methods read this reef 12–18 points lower than the transects (CoralNet 35.6%, Coralscapes 29.9%); the three are not interchangeable and should not be averaged (see the full report).
Comparisons with other data
No independent survey was made at this exact site; the nearest ones are listed in the table below.
CV model comparison
More info
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. The transect is THE coral-cover value for this site and stands alone. The rows below it are a methods comparison only: no computer-vision value is averaged with it, feeds the headline, or carries over to the site's cover figure (Anderson, 2026-09-22).| Method | Hard-coral cover (%) |
|---|---|
| Transect (published) | 47.6 |
| CoralNet | 43.3 |
| In-house DINOv3 | 33.8 |
| CoralSCOP edited | 38.3 |
| Claude | 33.2 |
Independent surveys nearby
| Agency / program | Year(s) | Stations / distance | Link |
|---|---|---|---|
| Sheppard et al. (2008) | 2006 | 1 station, 3.70 km | Records ↓ |
| Spalding et al. 2025 (Chagos 2024 bleaching report) | 2024 | 1 station, 2.98 km | Records ↓ |
| XL Catlin Seaview Survey | 2015 | 1 station, 3.08 km | Records ↓ |
Dr. Coral (CRD)Year-average (no detectable trend)Within 5 km, 3 independent survey stations recorded hard coral cover in 7 records between 2006 and 2024. One survey since 2021 recorded 50%. This site's own estimate (48%) is indistinguishable from the recent value (50%): the 2.4-point gap is inside the ±7 percentage-point noise between methods; the methods differ, so the comparison is context, not a like-for-like test.
Collected by other programs using different methods (the XL Catlin Seaview Survey uses photo-transects with automated image annotation), so these are context for the figures above, not a like-for-like comparison. Where a station was surveyed more than once the range is shown. Station names are not dive-site names.
| Agency | Site / location | Date | Hard coral cover (%) | Distance | Link |
|---|---|---|---|---|---|
| Sheppard et al. (2008) | Great Chagos Bank | 2006 | 41% (5 surveys) | 3.70 km | HeatCRD database |
| XL Catlin Seaview Survey | transect 36004 | 2015 | 21% | 3.08 km | — |
| Spalding et al. 2025 (Chagos 2024 bleaching report) | Great Chagos Bank - Middle Brother, lagoon (E aspect, 1-3 m) | 2024 | 50% | 2.98 km | — |
Data & links
- Read the full site report ↗
- Download benthic survey data (CSV) ↗
- Download all LOF-GRE data (933 sites) ↗
- CoralNet image repository for this region ↗
- HeatCRD database ↗
- (reference) ↗
- Photo portfolio ↗
- Coral Reef Diagnostics page for this area ↗
All images from Coral Reef Diagnostics. Data are from Coral Reef Diagnostics and the organizations named in the data-sources table above.
© Coral Reef Diagnostics.
References
- 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