Indonesia - Halmahera: Reene's Rock (Pulau Gewang)

General benthic features

What the photographs show is a field of very large rounded boulders, several of them meters across, standing on coralline-pink rubble pavement and clean sand channels, with a dense encrusting community over their tops and flanks (e.g., Image 7, Image 9, Image 36).

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The boulder-top community (roughly 24 frames) is the site's defining habitat and it is more filter feeder than stony coral: crimson and pink branching and encrusting sponges, orange, yellow, and dark-red sponge sheets, cobalt-blue colonial ascidians scattered like beads across every rock face, pink and mauve Dendronephthya-type soft corals, whip corals consistent with Junceella and Cirrhipathes standing up in the current in two frames, gorgonian fans, green algal turf, and pink crustose coralline algae (e.g., Image 1, Image 8, Image 14, Image 15, Image 16, Image 17, Image 22, Image 26, Image 30, Image 31, Image 44).

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Set into it is a real but scattered stony-coral assemblage: gray-white table and corymbose Acropora perched on the boulder crests, tan meandroid brains consistent with Platygyra and Favites, extensive concentrically ridged gray plates consistent with Pachyseris covering most of one boulder, cream foliose and laminar discs, and pale yellow-green lobed massive colonies consistent with Porites in one frame (e.g., Image 3, Image 4, Image 6, Image 18, Image 19, Image 24, Image 29, Image 38).

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The rubble-and-sand pavement between the boulders (about 6 frames) is genuinely sparse — coralline-encrusted rubble with isolated colonies on it, the finest of which is a large, perfectly concentric spiral scroll coral consistent with Turbinaria, sitting alone on pavement (e.g., Image 2, Image 37, Image 42).

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The shallow crest at the end of the dive is the one place where the site behaves like a reef: two frames cross a continuous olive-cream thicket of fine-branched Acropora running to the limit of visibility with no bare substrate in it at all, under a wall of damselfish (e.g., Image 39, Image 43).

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The brown boulder beside the massives in that frame carries a fine sediment and turf skin, which at this site is bare rock rather than dead coral (e.g., Image 18).

Coral cover

• Reference: Claude CV point count (this site's photos)
• Coral cover: 13% — a blind Claude computer-vision point count of 39 of Anderson's unedited photographs (20 points per photo; water, fish, and obstructions excluded). Other computer-vision methods are listed in the method table.
• One close, brightly lit boulder face is mostly crimson encrusting sponge, blue ascidians, and a sediment-covered lobed mass, with live stony coral perhaps a quarter of it (e.g., Image 12). Another frame is two-thirds open blue water with divers, with an orange-brown encrusting community on the boulder wall filling the left third (e.g., Image 11). The shallow thicket appears in two consecutive frames of the same continuous Acropora thicket (e.g., Image 39, Image 43).
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• A crop of the second frame at full sensor resolution settles that these are branching stony corals with fine radial corallites, not octocorals.

Stressors

Condition was good and unremarkable. No bleaching, no disease, no crown-of-thorns, and no predation scars were seen in any of the 39 frames. Two pale subjects were checked and resolved: the pale yellow-green lobed massives have normal lobing, texture, and clear green pigment and are a natural Porites color morph rather than bleached tissue, and the blue-white Acropora in two frames is ambient-blue-light white balance at depth on intact, normally textured branches. One small white bushy colony could not be resolved as living or dead; cause unclear (e.g., Image 5).

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Fish and other fauna

Fauna was the strong point, as the field note says: dense clouds of anthias and blue-green chromis over every boulder crest, damselfish walls in the shallow thicket, butterflyfish, a yellow-tail fusilier school, bicolor chromis, blue-green damsels alongside neon damsels over the pavement, black crinoids, and cobalt ascidians on every rock (e.g., Image 10, Image 21, Image 23, Image 28, Image 34, Image 35, Image 40).

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Comparisons with other data

We found no other surveys at this site as of 2026. In 2024, WCS Indonesia surveyed nine stations in the Guraici islands (Guraici MPA 2024; data via MERMAID), recording 18–59% hard coral cover. Because this pin's position is approximate (an island-area anchor, not a dive-site fix), no station is compared with this site by distance; station names are not dive-site names.

Dive record

Reene's Rock, off Pulau Gewang, was dived once on 15 August 2026, the first dive of the day on the August 2026 Halmahera crossing aboard the liveaboard Ambai (Wallacea Dive Cruises), to a maximum of 26.8 m in 24-25°C water.

Other notes

Anderson's own field note is the most accurate one-line description of the place and the imagery confirms it in every frame: very strong current for most of the dive, the fish life was good, and the site is not a reef but a coral community growing on boulders (e.g., Image 5, Image 20).

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All 39 frames were reviewed.