Saudi Red Sea - Cement Reef (Thuwal)
Part of the regional summaries: Saudi Arabia - Jeddah / KAUST (Thuwal) / Rabigh, Saudi Arabia, and Red Sea
2024-01-12
2024-02-23
2024-11-29
More info
Al Madinah and Makkah (NOAA CRW virtual station)Cement Reef, named for a nearby shipwreck, is a high-relief spur-and-groove structure honeycombed with swim-throughs, with dense pocilloporid thickets and cobalt digitate Acropora on the upper slope, thinning to sparse rubble and sand lower down. The published 22% cover and 20% bleaching figures come from 469 photographs scored across four dives between September 2023 and February 2024; bleached colonies appear in many of the September 2023 frames, among them a large massive colony uniformly white beside normally pigmented neighbors, and Anderson noted a bleached acroporid in February 2024.
شعاب الإسمنت، المسماة باسم حطام سفينة قريب، بنية مرتفعة التضاريس من الأخاديد والنتوءات تتخللها ممرات سباحة، مع أجمات كثيفة من البوسيلوبوريات وAcropora أصبعية كوبالتية على المنحدر العلوي، تتناقص إلى أنقاض ورمل متفرقين في الأسفل. ويأتي رقما التغطية المنشورة 22% والابيضاض 20% من 469 صورة جرى تقييمها عبر أربع غطسات بين سبتمبر 2023 وفبراير 2024؛ وتظهر مستعمرات مبيضّة في كثير من إطارات سبتمبر 2023، ومنها مستعمرة كتلية كبيرة بيضاء بالكامل إلى جانب جيران مصطبغين طبيعيًا، ودوّن أندرسون مرجانًا أكروبوريًا مبيضًّا في فبراير 2024.
ترجمة هذا الملخص بالذكاء الاصطناعي؛ النص الإنجليزي هو المعتمد.
One independent survey station shown with the program’s logo — click one to see how far it is from this site.
Two other CRD dive sites with their own pages within 5 km shown in orange — click a marker to open its page.
8 of the 20 photographs on this page are shown beside the text that discusses them under "Site description" below.
Site description
Setting
A Thuwal outer-reef site named for the cement carrier that went down nearby, dived five times between September 2023 and November 2024 with Coastline (KAUST). On the last dive, on 29 November 2024 (to 33.2 m), Anderson logged extensive bleaching mortality, with only one or two live acroporids, and less mortality below 25 m. The reef is a high-relief spur-and-groove limestone structure honeycombed with swim-throughs; Anderson photographed one from inside, looking up through a coral tunnel at a diver silhouetted in the blue (e.g., Image 21).
General benthic features
The upper slope carries dense pocilloporid thickets in lavender, dusty pink, and cream, striking cobalt-blue digitate Acropora, tabulate and corymbose Acropora, encrusting plates, and cream-to-tan massive boulder colonies, with black damselfish and butterflyfish working the crest (e.g., Image 1, Image 2, Image 3, Image 5, Image 6, Image 9, Image 10).
Below and away from the spurs the structure changes completely: a low pavement-and-rubble ridge crusted in coralline algae and turf with only scattered coral, then a wide white sand plain studded with isolated coral bommies of pocilloporids and small Acropora. A large free-living mushroom coral (Fungia, Anderson's identification), elongate with a long central furrow, was seen lying free on the sand, olive-green and apparently healthy.
Coral cover
- Reference: Mayfield (2025)
- Data file: (Mayfield, 2025-appendix A)
- CoralNet submission package (accession #5546)
- 22% across 469 photographs scored from four dives between September 2023 and February 2024 (± 17% per-photo standard deviation), with 20% of coral tissue bleached.
- Per dive, the published values are 23% cover with 25% of coral tissue bleached on 2 September 2023 (202 photographs); 23% cover with 6.7% bleached (47 photographs) and 21% cover with 15% bleached (97 photographs) on the two 12 January 2024 dives; and 22% cover with 20% bleached on 23 February 2024 (123 photographs).
Stressors
Debris: one of Anderson's frames from the second 12 January 2024 dive (a frame outside this page's gallery) shows an old line across the reef, colonized by a small branching coral.
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, one independent station, Furby et al. (2013) at Offshore reef 1, 1.66 km away, read a mean of 31% in 2010.
Survey summary
Cement Reef: surveyed 3 times, Sep 2023–Feb 2024 (CoralNet point counts; Mayfield 2025, Environments 12:248). Surveyed in partnership with Coastline (KAUST).
CV model comparison
More info
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, DINOv3 ran on the site's benchmark frames (the photographs the author annotated point by point), 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) | 22.4 | |
| In-house DINOv3 | 26.4 | n = 95 |
| CoralSCOP edited | 29.4 | n = 471 |
| Claude (edited photos) | 24.3 | n = 478 · SE 0.8 |
The three computer-vision methods agree within 5.1 pp (24.3–29.4%) and read within 7.0 pp of the published point count (22.4%).
See a more detailed, stand-alone version of this table.
Dive history
| Date | Time in | Max depth (m) | Bottom time (min) |
|---|---|---|---|
| 2023-09-02 | 12:44 | 12.5 | 54 |
| 2024-01-12 | 10:45 | 15.0 | 45 |
| 2024-01-12 | 12:45 | 24.0 | 45 |
| 2024-02-23 | 12:41 | 20.4 | 61 |
| 2024-11-29 | 10:30 | 33.2 | 49 |
Independent surveys nearby
Coral Reef Diagnostics surveyWithin 5 km, 1 independent survey station recorded hard coral cover in 2010. The most recent nearby survey is from 2010, so these values predate recent heat stress. This site's own pooled estimate (22%) sits 9 points below the one nearby survey station (31%); 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 |
|---|---|---|---|---|---|
| Furby et al. (2013) | Offshore reef 1 | 2010 | 31% (3 records) | 1.66 km | doi:10.1007/s00338-012-0998-5 |
Data & links
- CoralNet image repository for this region ↗
- Photo portfolio ↗
- Photo portfolio ↗
- Photo portfolio ↗
- Coral Reef Diagnostics country page ↗
All images from Coral Reef Diagnostics. Data are from Coral Reef Diagnostics and the organizations named in the data sources above.
© Coral Reef Diagnostics.