N. GBR - Pink (AUHI165)

Setting

This near-vertical wall dive at Hilder Reef, run in a fairly strong 1-knot current, with chain-tangling problems that limited the survey to four transects, told two different stories depending on depth. The two depth bands Anderson's notes distinguish are both visible.

General benthic features

The photographs cover both bands: the wall frames look along the face itself, sponge-textured and thinly covered, dropping away into deep blue with butterflyfish and sergeant majors working the face, while the shallower frames show a crowded, colorful crest of small pink, mauve, and mustard colonies over rubble. Numerous sponge species added texture to the mid-depths. What the line crosses in Image 1 and Image 2 is instructive: crusted, algal-dark framework carrying scattered small branching and digitate colonies, a black long-spined urchin, and a good deal of bare and turfed rock between colonies.

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The wall frames (e.g., Image 14), Image 17, Image 21, and Image 22 look along a steep, sponge- and turf-textured face dropping into deep blue with only thin, patchy live cover, and Image 22 shows a deep vertical chute or crevice cutting into the reef; these are the low-relief, rubble-dominated stretches.

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Against that, the shallower frames are strikingly dense. Image 12, Image 16, Image 18, Image 19, and Image 20 show a broad, near-horizontal reef platform where small colonies are packed almost edge to edge over the framework in mustard, olive, tan, salmon, rose, mauve, and pale blue — mostly corymbose, digitate, and knobby branching colonies and small encrusting and submassive colonies, with almost no clean rock showing. Image 16 is the single most striking frame: a large brown colony well over a meter across with thick, fleshy meandering ridges sprawls across the foreground beneath that packed platform, with a striped damselfish beside it; the growth form is unmistakable but the genus cannot be settled from the photograph and is not asserted. Image 12 adds a big tan knobby-lobed mound at the right edge and a parrotfish working the rock.

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Sponges, coralline crusts, and dark turf are conspicuous throughout, and pink and magenta coralline patches show clearly in Image 9.

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Coral cover

• Reference: Khaled bin Sultan Living Oceans Foundation, Global Reef Expedition (in situ transect)
• Higher up, on a genuinely vertical 10 m section, cover rebounded to around 30% with Pocillopora verrucosa, P. meandrina, Stylophora pistillata, and both sickly and healthy Seriatopora hystrix.
• Overall site cover measured 29% by point-count.
• One transect was scored at this station (29%; n = 1, so no SE; Living Oceans Foundation per-transect benthic data); it is the expedition's station value printed above.

Stressors

Down at 21 m, Anderson described the reef as showing "signs of a severe disturbance," abundant coral rubble but almost no living coral, cover of just 1-2%, with the cause left unspecified in his notes. Several frames show conspicuously white colonies among pigmented neighbors; they are recorded here without a call on their cause. The five or six small white knobby-lobed colonies photographed close in Image 5 are soft corals by their form, and every colony of that form in the frame is equally white, so no bleaching is claimed for them (the lilac, mauve, and brown colonies beside them are branching hard corals); Image 12 and Image 20 each contain one or two conspicuously white corymbose colonies in otherwise well-pigmented assemblages.

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His notes mention only sickly Seriatopora hystrix at 10 m; whether the white corymbose colonies in Image 12 and Image 20 are paled hard corals cannot be settled at this image scale, and no bleaching extent is estimated. Elsewhere across the 22 frames no disease lesions or crown-of-thorns feeding scars are discernible.

Comparisons with other data

No other surveys have been conducted at this site to date. Within 5 km, one independent station, AIMS manta tow at HILDER REEF, 1.94 km away, read 5.5–40% between 1994 and 2023.

Other notes

The survey itself is in the set. Image 1 and Image 2 look straight down on the reef with the yellow transect line lying across it, (Image 11) shows a diver up in the blue with the line running down the face below, and Image 15 has two divers working the wall.

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