Saudi Red Sea - Mr. Umluj (Yanbu)
Part of the regional summaries: Saudi Arabia - Yanbu, Saudi Arabia, and Red Sea
2024-04-19
2024-08-09
2024-11-08
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Al Madinah and Makkah (NOAA CRW virtual station)Mr. Umluj has two very different faces — a steep, densely built slope of branching, table, and knobby massive corals, and a broad, gently sloping reef top of soft corals and small hard colonies with patches of pale pavement and rubble, with a fish-filled channel between two reef walls. Bleaching barely moved between a cool April 2024 visit (28% of coral tissue, zero heat stress) and an August 2024 visit taken inside the marine heatwave (27%, 14.2 DHW).
لشعاب مستر أملج وجهان مختلفان جدًا - منحدر شديد الانحدار كثيف البناء من مرجانيات متفرعة وطاولية وكتلية عُقدية، وقمة شعاب واسعة قليلة الانحدار من المرجان اللين ومستعمرات صلبة صغيرة مع رقع من الرصيف الشاحب والأنقاض، مع قناة ملأى بالأسماك بين جدارين شعابيين. وبالكاد تغيّر الابيضاض بين زيارة باردة في أبريل 2024 (28% من نسيج المرجان، إجهاد حراري صفري) وزيارة في أغسطس 2024 جرت داخل موجة الحر البحرية (27%، 14.2 DHW).
ترجمة هذا الملخص بالذكاء الاصطناعي؛ النص الإنجليزي هو المعتمد.
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Note: NOAA's regional station series averages 2.6°C warmer than the satellite pixel nearest this site (3.8 km away), which is used here instead.Two independent survey stations shown with the program’s logo — click one to see how far it is from this site.
8 of the 20 photographs on this page are shown beside the text that discusses them under "Site description" below.
Site description
Setting
An offshore reef in the Umluj area worked with Umluj Dive Center, logged four times and photographed twice, and one of the sites carrying a per-visit series in the site record.
General benthic features
The reef has two faces. One face is a steep, densely built slope: lavender and purple pocilloporids, corymbose and table colonies, knobby massives, small domed corals, and encrusting growth packed close, with red anthias in clouds over it and black wire corals springing off the edge into blue water (e.g., Image 1, Image 3, Image 4, Image 5, Image 6, Image 7, Image 8, Image 9).
The other is a broad, gently sloping reef top covered in soft corals and small hard colonies, with patches of pale, algal-turfed pavement and rubble, and a deeper channel running between two densely built reef walls, wire corals along both sides, fish stacked in the gap.
Coral cover
- Reference: Mayfield (2025)
- Data file: (Mayfield, 2025-appendix A)
- CoralNet submission package (accession #5546)
- 17% ± 14% SD across 326 photographs.
- The site record carries the two photographed visits separately: 17% cover with 28% of coral tissue bleached in April 2024 at zero DHW and 26.5°C, and 16% cover with 27% bleached in August 2024 at 14.2°C-weeks and 33.5°C.
Stressors
Remarkably little moved between a cool spring dive and one taken inside the 2024 marine heatwave. White colonies sit among pigmented neighbors in both photographed visits: white lobed massives and white-topped knobby mounds on the wall in April, and a stark-white branching colony and a large white plating colony at the base of a wall in August (photos not shown).
Comparisons with other data
Apart from our own published survey shown here, we found no other surveys at this site as of 2026. Within 5 km, two Aeby et al. (2021) stations recorded station-year means of 42–50% hard coral cover in 2015; the nearest, Aeby et al. (2021) at Yanbu 2, 3.78 km away, read 42% in 2015.
Survey summary
Mr. Umluj: surveyed 2 times in the published dataset, Apr 2024–Aug 2024 (dives on 7 Oct 2023 and 8 Nov 2024 are in the dive record but were not among the analyzed surveys) (CoralNet point counts; Mayfield 2025, Environments 12:248). Surveyed in partnership with Umluj Dive Center.
CV model comparison
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The reference is this dive site's own published CoralNet point count by the author (Mayfield 2025, Environments 12:248, Appendix A; most frames annotated by CoralNet's AI, trained and checked by the author). The computer-vision rows are this site's own values: Claude is a blind point count of all of the site's edited photographs, and CoralSCOP is the site's finished survey of its edited photographs. They are on different frame sets from the published count, a row under 30 frames is indicative only, and no computer-vision method yet estimates coral cover accurately on new images.| Method | Hard coral cover (%) | Photos (n) ± SE |
|---|---|---|
| Published point count (CoralNet-assisted) | 16.6 | |
| CoralSCOP edited | 22.2 | n = 326 · SE 0.6 |
| Claude (edited photos) | 17.0 | n = 326 · SE 0.8 |
The two computer-vision methods agree within 5.2 pp (17.0–22.2%) and read within 5.6 pp of the published point count (16.6%).
See a more detailed, stand-alone version of this table.
Dive history
Coral bleached: computer-vision (CoralNet) estimate from the survey images, per dive, as published in Mayfield (2025, Environments 12:248), Supplementary File S1.
| Date | Time in | Max depth (m) | Bottom time (min) | Coral bleached (%) |
|---|---|---|---|---|
| 2023-10-07 | 08:54 | 33.7 | 51 | — |
| 2024-04-19 | — | — | — | 27.7 |
| 2024-08-09 | — | — | — | 26.6 |
| 2024-11-08 | 10:54 | 32.3 | 63 | — |
Independent surveys nearby
Coral Reef Diagnostics surveyWithin 5 km, 2 independent survey stations recorded hard coral cover in 2015. The most recent nearby survey is from 2015, so these values predate recent heat stress. This site's own pooled estimate (17%) is not compared with these surveys: none lies within 2 km.
Collected by other programs using different methods, so these are context for the figures above, not a like-for-like comparison. Where a station was surveyed more than once, the cell shows either the range of its values or, as a single value, the mean of surveys made in one year. Station names are not dive-site names.
| Agency | Site / location | Date | Hard coral cover (%) | Distance | Link |
|---|---|---|---|---|---|
| Aeby et al. (2021) | Yanbu 2 | 2015 | 42% | 3.78 km | doi:10.1371/journal.pone.0246854 |
| Aeby et al. (2021) | Yanbu 3 | 2015 | 50% | 4.22 km | doi:10.1371/journal.pone.0246854 |
Data & links
All images from Coral Reef Diagnostics. Data are from Coral Reef Diagnostics and the organizations named in the data sources above.
© Coral Reef Diagnostics.
References
- Mayfield AB (2025). Using Tourist Diver Photos to Assess the Effects of Marine Heatwaves on Central Red Sea Coral Reefs. Environments 12:248. PDF
- Aeby GS, Shore A, Jensen T, Ziegler M, Work T, Voolstra CR (2021). A comparative baseline of coral disease in three regions along the Saudi Arabian coast of the central Red Sea. PLOS ONE 16:e0246854. PDF