Saudi Red Sea - Long Reef (Thuwal)
Part of the regional summaries: Saudi Arabia - Jeddah / KAUST (Thuwal) / Rabigh, Saudi Arabia, and Red Sea
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Al Madinah and Makkah (NOAA CRW virtual station)Long Reef is a steep-sided ridge with two very different faces — a densely mixed reef top (knobby Porites, massive domes, and table and corymbose Acropora, bound together by heavy pink coralline algae) and a sparser, more sculptural wall dropping into blue water. A single November 2023 visit measured 14% cover with about 20% of coral tissue bleached, and the photographs show several pale table Acropora off the lip (probable bleaching or strong paling, not confirmed).
الشعاب الطويلة حافة شديدة الانحدار لها وجهان مختلفان جدًا — قمة شعاب مختلطة كثيفة (Porites عُقدية وقباب كتلية وAcropora طاولية وعنقودية، تربطها طحالب مرجانية وردية كثيفة) وجدار أقل كثافة وأكثر نحتًا ينحدر إلى المياه الزرقاء. وقاست زيارة واحدة في نوفمبر 2023 تغطية 14% مع ابيضاض نحو 20% من نسيج المرجان، وتُظهر الصور عدة مستعمرات شاحبة من Acropora الطاولية عند الحافة (ابيضاض محتمل أو شحوب شديد، غير مؤكد).
ترجمة هذا الملخص بالذكاء الاصطناعي؛ النص الإنجليزي هو المعتمد.
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Anderson's dive computer's 21.1°C is an import placeholder and is not used. Note: NOAA's regional station series averages 1.7°C warmer than the satellite pixel nearest this site (2.9 km away), which is used here instead.Three independent survey stations shown with the program’s logo — click one to see how far it is from this site.
Three other CRD dive sites with their own pages within 5 km shown in orange — click a marker to open its page.
13 of the 50 photographs on this page are shown beside the text that discusses them under "Site description" below.
Site description
Setting
The reef is a long, steep-sided ridge — a near-vertical face on one side dropping into open blue, a broad rounded reef top on the other. The two sides look like different reefs.
General benthic features
On top, the frames show a genuinely dense mixed community: pale cream and olive knobby Porites, gray-green massive domes, table and corymbose Acropora, encrusting plates, small pocilloporids, xeniid soft corals with polyps extended, and a lot of pink and magenta crustose coralline algae binding the spaces (e.g., Image 1, Image 2, Image 3).
The wall face is sparser and more sculptural — encrusting growth, sponges, coralline, small colonies clinging to a near-vertical surface with anthias hanging off it in red streams (e.g., Image 4).
Several pale table Acropora cantilever off the lip (e.g., Image 7).
Coral cover
- Reference: Mayfield (2025)
- Data file: (Mayfield, 2025-appendix A)
- CoralNet submission package (accession #5546)
- 14% ± 12% SD across 90 photographs.
- The 17 November visit recorded about 14% cover with 20% of coral tissue bleached at roughly 16.5°C-weeks DHW on the survey date (17 November 2023; NOAA Coral Reef Watch, Madinah-Makkah (Saudi Arabia) virtual station).
Fish and other fauna
Fauna is reef-typical for Thuwal in November: dense anthias, coral grouper, surgeonfish, and unicornfish drifting over the crest. A sea turtle forages over the reef, with divers close by in several frames (e.g., Image 12, Image 27, Image 31, Image 35, Image 36, Image 38), and a large triggerfish works the reef (e.g., Image 40, Image 47).
Comparisons with other data
We found no other surveys confirmed at this site as of 2026. Within 5 km, three independent stations recorded station-year means of 21–39% hard coral cover between 2013 and 2015; the nearest, Monroe et al. (2018) at Offshore reef 1, 0.57 km away, read 28% in 2015.
Dive record
A single afternoon dive to 20 m on 17 November 2023, the second dive of a day that began at Rose Reef, worked with Coastline (KAUST).
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) | 13.9 | |
| CoralSCOP edited | 24.3 | n = 91 |
| Claude (edited photos) | 11.5 | n = 88 · SE 1.2 |
The two computer-vision methods disagree by 12.8 pp (11.5–24.3%) and read on both sides of the published point count (13.9%); the headline is the published point count because it is the site's published value (CoralNet-assisted: most frames were annotated by CoralNet's AI, trained and checked by the author).
See a more detailed, stand-alone version of this table.
Independent surveys nearby
| Agency / program | Year(s) | Stations / distance | Link |
|---|---|---|---|
| Aeby et al. (2021) | 2015 | 1 station, 0.57 km | Records ↓ |
| Khalil et al. (2017) | 2013 | 1 station, 4.46 km | Records ↓ |
| Monroe et al. (2018) | 2015 | 1 station, 0.57 km | Records ↓ |
Coral Reef DiagnosticsYear-average (illustrative only, programs differ)Within 5 km, 3 independent survey stations recorded hard coral cover in 4 records between 2013 and 2015. The most recent nearby survey is from 2015, so these values predate recent heat stress. This site's own estimate (14%) sits 14 points below the range of these station-year means up to 2 km away (28–39%); the methods differ, so the comparison is context, not a like-for-like test.
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 |
|---|---|---|---|---|---|
| Khalil et al. (2017) | — | 2013 | 21% (2 records) | 4.46 km | doi:10.7717/peerj.3410 |
| Monroe et al. (2018) | Offshore reef 1 | 2015 | 28% | 0.57 km | doi:10.1371/journal.pone.0195814 |
| Aeby et al. (2021) | Shi'b Nazar | 2015 | 39% | 0.57 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
- Khalil MT, Bouwmeester J, Berumen ML (2017). Spatial variation in coral reef fish and benthic communities in the central Saudi Arabian Red Sea. PeerJ 5:e3410. DOI
- Monroe AA, Ziegler M, Roik A, Röthig T, Hardenstine RS, Emms MA, et al. (2018). In situ observations of coral bleaching in the central Saudi Arabian Red Sea during the 2015/2016 global coral bleaching event. PLOS ONE 13:e0195814. 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