Raja Ampat - Pulau Koon dive 3

Setting

Pulau Koon, the third of the trip's dives on this island, off the eastern tip of Seram in the Banda Sea — not Raja Ampat. Anderson's log records a medium-strength current and poor visibility, worse than on the two earlier dives; the deeper frames carry a plankton haze, and the schooling planktivores and trevally fit the current; the deepest frames darken to a low-light blue, although the logged maximum was 15.7 m.

General benthic features

This reef is the opposite of the trip's Triton Bay sites: it is hard coral dominated, high-relief, and structurally spectacular. The dominant architecture is Acropora in every form the genus takes. Tabulate colonies are everywhere and many are very large — flat discs well over a meter across with clean white or lilac growing rims, stacked two and three deep down the slope (e.g., Image 1).

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Their colors are unusually vivid: several are deep magenta-purple with pale blue-white rims, one is a rich burgundy, others gray-blue, gold, or plain brown. Corymbose and staghorn Acropora thickets fill the gaps, with crisp white axial tips indicating active growth. Alongside them, and just as abundant, are extensive shingled fields of foliose and plating coral — whorled, tiered plates forming continuous rosette terraces over the deeper slope, each plate rimmed in pale living margin. Massive corals supply the reef's backbone: multi-lobed Porites domes over a meter high, several standing free of the reef like boulders; tightly meandering brain corals; a striking brain colony with bright green valley walls against brown ridges; and knobby Pocillopora and Goniopora-type colonies scattered through (e.g., Image 2, Image 5).

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Soft corals are present in quantity but as a second layer rather than the main story: broad frilly Sarcophyton mushroom leathers, digitate and finger-form Sinularia in salmon, pink, and tan (one stand of long flaccid tan fingers is a set piece of its own), lilac and cream pulsing-polyp carpets running over dead pavement, and tree-like soft corals in orange and red on shaded faces (e.g., Image 4).

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Bushy brown pinnate growths recur in a large fraction of frames — feather-shaped fronds most consistent with feather hydroids of the Aglaophenia type or brown-tissued black-coral bushes; the imagery does not separate the two (e.g., Image 3).

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Other conspicuous invertebrates: orange cup corals in dense sheets on overhangs and vertical faces, large red-brown barrel sponges consistent with Xestospongia, brown and purple tube sponges, green colonial ascidians, several yellow-and-purple sea squirts unmistakably Polycarpa aurata, and free-living crinoids.

Coral cover

• Reference: Claude CV point count (this site's photos)
• Coral cover: 30% — a blind Claude computer-vision point count of 98 of Anderson's edited photographs (20 points per photo; water, fish, and obstructions excluded). Other computer-vision methods are listed in the method table.

Stressors

Condition is mixed. Most of the reef looks vigorous, but the photographs show a clear, repeated signal of partial mortality on large colonies: at least three large table Acropora carry conspicuous patches of bare or algal-filmed skeleton on their upper surfaces; one large massive dome has roughly half its visible surface bleached, pale gray-white with its polyps still present, plus a few small bare patches (e.g., Image 71); a second massive colony shows scattered small white lesions and purple-pink pigmentation-response margins; and two large brain corals show eroded holes and pale scars.

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Against that, no whole-colony bleaching front, no crown-of-thorns, and no anchor or blast damage were seen. There is also a broad, greenish, algal-filmed plate colony whose upper surface reads as recently dead, and old dead pavement colonized by turf and vermetid tubes at the base of one encrusting colony. These are partial-mortality and lesion observations from photographs, not a disease diagnosis.

Fish and other fauna

The fish assemblage is what marks this out as a current-swept, well-fed site. Two frames show a school of large, blunt-headed parrotfish moving in open blue water (e.g., Image 76, Image 77).

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One frame shows a passing school of bigeye trevally, another a wall of small planktivores (chromis and fusiliers) filling the whole water column (e.g., Image 46, Image 14).

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On the reef itself: dense green and black chromis over the plate fields, yellow-and-blue fusiliers, several squirrelfish and soldierfish resting under plate margins, a red-toothed triggerfish, moorish idols, raccoon and pyramid butterflyfish, a blue tang, humbug damsels in the staghorn, a large carpet anemone holding at least three orange-and-white anemonefish, and cleaner wrasse working two batfish.

Comparisons with other data

Ceccarelli et al. (2022) surveyed this site (Koon MPA) in 2016, 2018, and 2020. Within 5 km, eleven independent stations recorded station-year means of 18–47% hard coral cover between 2016 and 2023; the nearest, Institut Pertanian Bogor (IPB) at KOE02, 0.17 km away, read a mean of 26% in 2023.

Regional context, not a survey of this site: Razak et al. (2026) found no significant trend in hard coral cover at Koon, the marine protected area off eastern Seram (a rise of 0.2% per year at 17 sites, surveyed by point-intercept transect at about 8–10 m in 2016, 2018, and 2020 by Yayasan WWF Indonesia); this is a trend for that location, not this site’s cover. Koon warmed by 0.25°C per decade over 1985–2023, and the only NOAA bleaching alerts the study lists there ran from December 2022 to February 2023 (73 days at Bleaching Alert Level 1).

Dive record

Dive log: 17 October 2018, entry 13:38, maximum depth 15.7 m, bottom time 70 min, a single dive-computer water temperature reading of 25.0°C, the third of the day's three dives at Pulau Koon.