Regional summary of 4 dive sites. Figures are averages across the sites that report them (n = sites with a value); each site's own page has its individual values.
Heat-stress figures: NOAA Coral Reef Watch — Bahrain 5-km virtual station. Each pill links its source record and carries the values behind it.
Heat stress
sea surface temperature (SST) (left axis)DHW under 2DHW 2–3DHW 3–5DHW 5–8DHW 8–10DHW over 10 (🔥 above 12)
Daily SST (line) and weekly maximum Degree Heating Weeks (bars), Jan 2023–Oct 2026, NOAA Coral Reef Watch 5-km Bahrain virtual station. Dashed line: bleaching threshold (maximum monthly mean 33.4°C + 1°C). DHW ≥ 4: bleaching likely; ≥ 8: severe bleaching and mortality likely. A bar is drawn only where DHW exceeds zero, so a stretch with no bar is accumulated heat stress of zero, not missing data — the SST line runs the full period.
4 sites in this region — click a marker to open that site.
Overview
Bahrain's 4 sites come from two days in the Arabian Gulf. On 23 September 2023 Anderson dived Dilmunia Rock, a shallow rocky ledge less than 2 km off the coast, and a nearby artificial reef of dome-shaped units on sand in turbid water. On 23 August 2024 Anderson went offshore with Sea Addicts from Amwaj Marina, first to the Al-Boom wreck and then to Hayr Bul Thamah (Bul Thamah), an offshore reef about 80 km northeast of the main island inside a marine protected national park.
Coral cover is low everywhere. Blind Claude computer-vision point counts of Anderson's photographs give 0.5% at Dilmunia Rock and 0.9% at the artificial reef, where turf and sediment rather than coral cover the structures, and 9.9% at Hayr Bul Thamah, where red algal turf covers most of the rock between scattered brain and meandroid colonies, sea fans, and fields of whip corals. Hayr Bul Thamah also holds a single healthy-looking golden branching colony, notable because a 2017–2018 survey found no branching corals there. Some brain colonies there show patches of tissue loss now overgrown by algae, and a few colonies are pale or white. The Al-Boom wreck, an upright, heavily fouled hull wrapped in schools of yellow snappers, gave 0.0%; as a wreck it is counted in the regional mean like every other site.
Other programs' older surveys mostly put Bul Thamah above today's photo-based value: Reef Check recorded 24–46% hard coral in 1998–1999 but about 12% in 2000, published surveys found about 15–16% in the 2010s, and the 2010 bleaching event is estimated to have cost the reef about two-thirds of its coral. The 2024 dives were in late August, when Gulf water is at its warmest (34°C on Anderson's dive computer).
Highlights
Hayr Bul Thamah: 9.9% coral cover, with a golden branching colonyphoto: Hayr Bul Thamah (Bahrain)
Reef Check recorded 24–46% hard coral at Bul Thamah in 1998–1999 and about 12% in 2000
Al-Boom Wreck: an upright, fouled wreck full of yellow snappers (wreck habitat; counted in the regional mean)photo: Al-Boom Wreck (Bahrain)
Wire fish traps photographed on both Hayr Bul Thamah and the Al-Boom wreckphoto: Hayr Bul Thamah (Bahrain)
Notable observations
Hayr Bul Thamah (Bahrain): A healthy-looking golden branching colony, at a reef where no branching corals were found in 2017 or 2018
Hayr Bul Thamah (Bahrain): Brain colonies with patches of tissue loss now overgrown by algae, and a few pale or white colonies, including a small disc-shaped colony that appears to be a mushroom coral
One point per year: the mean of every hard coral cover value available for this region that year — Anderson’s own dives and every independent survey station within 5 km of them. The vertical bar is the full range behind that mean. Different programs use different methods at different stations, so this is a regional summary, not a single comparable series. Years resting on fewer than three values are drawn as smaller points (1998, 1999, 2000, 2023, 2024). Non-CRD points are from Reef Check Foundation. Marker shape: Anderson’s own dives, other organizations’ surveys.
photo: Hayr Bul Thamah (Bahrain)
photo: Al-Boom Wreck (Bahrain)
photo: Hayr Bul Thamah (Bahrain)
