Saudi Red Sea - Long Reef (Thuwal)

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Part of the regional summaries: Saudi Arabia - Jeddah / KAUST (Thuwal) / Rabigh, Saudi Arabia, and Red Sea

Photo: Anderson Mayfield/Coral Reef Diagnostics

Country

Saudi Arabia

Survey date(s)

2023-11-17

Coordinates

22.3497, 38.8572

Coral cover

14%

Manual point count (90 photos) · other methods below

Observations

bleaching

Heat stress

Today’s heat load

33.4°C 3.6°C-weeks

16 Sep 2026 · Bleaching Warning

5-year thermal stress load

5-year mean max. degree heating weeks (DHW)

14.3°C-weeksⁱ

2021–2025

NOAA Coral Reef Watch — Makkah-Madine Saudi Arabia virtual station

i 5-year mean max. DHW is the mean of the annual maximum DHWs over the five complete years named above, not conditions today.

More info

Makkah-Madine Saudi Arabia (NOAA CRW virtual station) · Northern and Central Red Sea ecoregion mean=12.2°C-heating weeks

Photographs

Site summary

Read this summary in:

Long Reef is a steep-sided ridge with two very different faces - a densely mixed reef top (Porites, Astreopora, Goniastrea, 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 a cluster of pale blue-white colonies on the wall plus a few frankly white branching corals on the reef top.

Max. depth dived

20.0 m

Three independent survey stations shown with the program’s logo — click one to see how far it is from this site.

One other CRD dive site within 5 km shown in orange — click a marker to open its page.

4 of these 50 photographs are shown beside the text that discusses them under "Site description" below.

Photo credit & attribution

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 Astreopora and Goniastrea domes, table and corymbose Acropora, encrusting Montipora-type 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).

A pale cream Millepora-type fire coral plate and several table Acropora cantilever off the lip.

Coral cover

Coral cover is 13.9% ± 12.4 across 90 photographs, quoted verbatim from Mayfield, A.B. (2025) Environments 12:248 — Red Sea 2023-24 bleaching; CoralNet point annotation, Appendix A — a manual, diver-annotated CoralNet point count from Anderson's own published work, not a computer vision output and not recomputed here. The site record's prose gives the 17 November visit as 14% cover with 19.6% of coral tissue bleached at roughly 16.5°C-weeks DHW; the site-level fields carry 13.9% and 19.8%.

Fish and other fauna

Fauna is reef-typical for Thuwal in November: dense anthias, coral grouper, surgeonfish, and unicornfish drifting over the crest.

Comparisons with other data

No independent survey was made at this exact site; the nearest ones are listed in the table below.

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

Computer vision on this site's own photographs gives ⚠ In-house DINOv3 point classifier 48% — reported alongside rather than merged, because as of September 2026 no computer-vision method estimates coral cover accurately on new images.

Headline is the reference value; every other row is listed beside it for comparison and none is averaged in.

More info

The reference row is this dive site's own published value (Mayfield 2025, Appendix A, 90 photos); the other rows are AREA-level (Thuwal) comparisons, not run on this site's frames. ⚠ The comparison rows are REGIONS, not dive sites: the paper's main tables report cover by region, and this site's own value comes from its Appendix A. ⚠ The manual column and the CV columns are on DIFFERENT FRAME SETS. The published cover spans the region's full photo set (173–2,567 frames, most of them CoralNet robot-labeled); the CV arms ran only on the hand-scored reference subset, which is 6 frames at Thuwal, 274 at Jeddah and 173 at Rabigh. Read Thuwal's model columns as indicative only. CoralNet is n/a by design: the reference set IS the hand-scored set, so those frames carry no independent robot label to compare against. DINOv3 is restricted to frames it never saw, and reads roughly double the published cover at every Red Sea region. ⚠ 'unassigned region' is not a place: 135 frames carry no region label in the CoralNet metadata and map to no published row. It has no manual value and is excluded from the pooled reference. CoralNet automated point classifier: n/a — the reference set IS the hand-scored set; these frames carry no independent CoralNet robot label to compare against CoralSCOP (SAM-based mask-sum), unedited photos: pending — CoralSCOP run: 370/747 images scored at build time CoralSCOP (SAM-based mask-sum), edited photos: pending — CoralSCOP run: 370/747 images scored at build time

Method	Hard-coral cover (%)
Manual (published)	13.9
In-house DINOv3	47.5
Claude	23.9

Independent surveys nearby

Data availability near this site
Agency / program	Year(s)	Stations / distance	Link
Aeby et al. (2021)	2015	1 station, 1.31 km	Records ↓
Furby et al. (2013)	2010	1 station, 4.67 km	Records ↓
Monroe et al. (2018)	2015	1 station, 1.31 km	Records ↓

Within 5 km, 3 independent survey stations recorded hard coral cover in 5 surveys between 2010 and 2015. The most recent nearby survey is from 2015, so these values predate recent heat stress. This site's own estimate (14%) sits 13.9 points below the range of these surveys (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 range is shown. Station names are not dive-site names.

Independent survey data near this site
Agency	Site / location	Date	Hard coral cover (%)	Distance	Link
Furby et al. (2013)	Offshore reef 1	2010	31% (3 surveys)	4.67 km	HeatCRD database
Monroe et al. (2018)	Offshore reef 1	2015	28%	1.31 km	HeatCRD database
Aeby et al. (2021)	Shi'b Nazar	2015	39%	1.31 km	HeatCRD database

Data & links

All images from Coral Reef Diagnostics. Data are from Coral Reef Diagnostics and the organizations named in the data-sources table above.

References

Furby KA, Bouwmeester J, Berumen ML (2013). Susceptibility of central Red Sea corals during a major bleaching event. Coral Reefs 32:505-513. 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
Mayfield AB (2025). Using Tourist Diver Photos to Assess the Effects of Marine Heatwaves on Central Red Sea Coral Reefs. Environments 12:248. PDF