Saudi Red Sea - Cement Wreck (Thuwal)
Part of the regional summaries: Saudi Arabia - Jeddah / KAUST (Thuwal) / Rabigh, Saudi Arabia, and Red Sea
2024-04-27
2024-07-26
2024-11-09
More info
Al Madinah and Makkah (NOAA CRW virtual station)Cement Wreck pairs a low-cover steel shipwreck — its hull colonized only patchily by coralline algae, sponges, and scattered small corals — with a steeper natural reef slope beside it carrying massive boulder colonies, a large Diploastrea heliopora colony, and tabulate Acropora. Across three visits (Sept 2023, April 2024, July 2024) cover ran 10-17% and 19-32% of coral tissue was bleached, but bleaching did not track heat stress: 25% was bleached in April 2024 with no accumulated heat stress, and 19% during the July 2024 heatwave; a blue-spotted stingray sheltering under the hull was a fauna highlight.
يجمع حطام الإسمنت بين حطام سفينة فولاذية منخفض التغطية — استعمرت هيكلها الطحالب المرجانية والإسفنج ومرجانيات صغيرة متفرقة على نحو متقطع فقط — ومنحدر شعابي طبيعي أشد انحدارًا بجانبه يحمل مستعمرات جلمودية كتلية ومستعمرة كبيرة من Diploastrea heliopora وAcropora طاولية. وعبر ثلاث زيارات (سبتمبر 2023 وأبريل 2024 ويوليو 2024) تراوحت التغطية بين 10-17% وكان 19-32% من نسيج المرجان مبيضًّا، لكن الابيضاض لم يتبع الإجهاد الحراري: إذ ابيضّ 25% في أبريل 2024 دون أي إجهاد حراري متراكم، و19% خلال موجة الحر في يوليو 2024؛ وكانت لخمة ذات بقع زرقاء تحتمي تحت الهيكل من أبرز الحيوانات.
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.
Three 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 steel shipwreck lying on sand alongside the Thuwal reef line, dived four times between September 2023 and November 2024 with Coastline (KAUST), with a per-visit cover series attached to it. On the fourth dive, on 9 November 2024, Anderson logged that most of the corals on the wreck had died from bleaching.
General benthic features
The wreck itself dominates the dive: a substantial iron hull broken along its length, deck beams and bulkheads standing proud of a pale sand bottom, plating rusted to deep red-brown and colonized in patches rather than uniformly — encrusting coralline algae, small sponges, turf, barnacle scars, and scattered small hard corals rather than the dense soft-coral cladding that older Red Sea wrecks often carry (e.g., Image 1, Image 3, Image 4).
It is a low-cover artificial substrate. The natural reef beside it is a steeper mixed slope: cream and tan massive boulder colonies, a very large Diploastrea heliopora colony (Anderson's identification), tabulate Acropora, encrusting plates, lavender pocilloporids, cream-white soft corals, and encrusting sponges, over pavement, and rubble that carry considerably more coralline algae than live coral (e.g., Image 2, Image 6, Image 7, Image 8, Image 9).
Coral cover
- Reference: Mayfield (2025)
- Data file: (Mayfield, 2025-appendix A)
- CoralNet submission package (accession #5546)
- 13% across 383 photographs (± 13% per-photo standard deviation).
- The site record carries the three visits separately: 12% cover / 32% bleaching in September 2023 during the late-summer thermal-stress event, 10% / 25% in April 2024 with thermal stress absent, and 17% / 19% in July 2024 during the 2024 marine heatwave.
Fish and other fauna
Fauna is wreck-typical: a blue-spotted stingray tucked under a hull plate on the sand, a black-and-white polyclad flatworm on a massive coral nodule; anthias and small reef fish swim over the reef edge.
Comparisons with other data
Apart from our own published survey shown here, we found no other surveys confirmed at this site as of 2026. Within 5 km, one independent station, Furby et al. (2013) at Offshore reef 1, 1.88 km away, read a mean of 31% in 2010.
Survey summary
Cement Wreck: surveyed 3 times, Sep 2023–Jul 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) | 12.8 | |
| In-house DINOv3 | 33.7* | n = 11 |
| CoralSCOP edited | 21.1 | n = 391 |
| Claude (edited photos) | 12.4 | n = 387 · SE 0.7 |
The three computer-vision methods disagree by 21.3 pp (12.4–33.7%) and read on both sides of the published point count (12.8%); 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).
*Based on only 11 reef-habitat photos; this estimate is less certain.
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 (%) |
|---|---|---|---|---|
| 2023-09-08 | 10:55 | 14.0 | 50 | 32.0 |
| 2024-04-27 | — | — | — | 25.3 |
| 2024-07-26 | — | — | — | 18.7 |
| 2024-11-09 | 10:00 | 18.0 | 60 | — |
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 (13%) sits 18 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) | 1.88 km | doi:10.1007/s00338-012-0998-5 |
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.