Kenya - North Canyon (Watamu)

Setting

Despite the name, the photographs do not show a canyon. There is no frame in the whole set of a vertical wall, a swim-through, or a steep undercut face. What the set shows is an extensive hardground reef top of low to moderate relief — coralline-encrusted pavement, boulder and rubble aprons, sand pockets, and low bommie mounds — with the outer edge sloping away into open blue in the wider frames (e.g., Image 4).

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General benthic features

The reef is also not densely packed with coral. Across most of the set, colonies sit as discrete, well-separated individuals on algal pavement, and several frames hold only two or three corals in the whole field of view. Foliose and laminar plates are the commonest growth form — Turbinaria-, Echinopora-, and Montipora-type laminae and agariciid plates, some a meter or more across, stacked and overlapping on the low mounds. Massive and meandroid colonies are the second element: Platygyra brains, Lobophyllia and Symphyllia with thick banded ridges, cerioid Favites and Goniastrea, and nodular Astreopora and Porites boulders. Branching coral is present but subordinate and always in small isolated stands. Free-living fungiid discs sit on the rubble in two frames. Soft corals and leathers are scattered rather than dominant, and orange, red, and gray sponges and pink crustose coralline fill the interstitial rock. Deep red fleshy and coralline algae are conspicuous across the pavement in roughly half the set, with bright green filamentous and Halimeda-type turf increasing through the later frames.

Coral cover

• Reference: Mayfield (2025)
• Data file: (Mayfield, 2025-Supplemental File S1)
• CoralNet submission package (accession #4963)
• The coral here is scattered, not continuous: the published 22% sits well below the 30% Kenyan mean.
• Coral cover 22% — and 95% of hard coral tissue bleached (March-April 2024).
• Measured from 83 white-balanced photographs taken at this site during the 2024 Western Indian Ocean mass bleaching event and point-annotated in CoralNet, published in Mayfield, A.B. (2025) A Citizen Science Approach for Documenting Mass Coral Bleaching in the Western Indian Ocean. Environments 12(8):276. doi:10.3390/environments12080276, Supplemental File S1.
• This is a published diver-photograph point-annotation value, not a computer vision estimate, and it is not recomputed here.

Stressors

The full set is emphatic, and it confirms rather than softens the published 95%. In frame after frame every scleractinian colony in view is bone-white, cream, pale mint, pale blue, or pastel lilac (e.g., Image 1).

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The most complete examples are massive and laminar: a large sheeting meandroid colony gone uniformly chalk-white in one frame; big white plates in ten frames; a fully white knobby dome in another; a white Platygyra in another (e.g., Image 3).

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Branching coral fared no better — every branching colony in the set is bone-white, with the corymbose and digitate Acropora in five frames white right down to the branch bases. The striking thing at North Canyon is the color the surviving colonies turned. A large number of massive and meandroid corals are not brown and not white but pastel: violet and mauve cerioid Favites, lilac and pink-gray lobate colonies, salmon-pink and cream banded Lobophyllia, a pale pink Platygyra abutting a stark white lobate colony in one frame, a mauve-pink brain dome, and lilac free-living fungiids (e.g., Image 2).

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One frame is the clearest single example: a large gray-blue encrusting colony carrying a distinct patch of retained salmon-pink. This is the fluorescent-pigment stress response of a colony that has lost its symbionts but not yet its tissue, and it is the visual signature of this site. A small minority of colonies held normal brown or olive pigment, and they are worth naming because they are the exception and because they act as the internal control on the color-adjusted frames: a dark brown Platygyra dome (e.g., Image 21), a tan tabular Acropora with a clean white growing margin (e.g., Image 12), a dark olive-green encrusting colony among red algae (e.g., Image 22), tan-brown tabulate plates (e.g., Image 23), and a brown-gray brain hard against a bright white lobate colony in one frame (e.g., Image 24).

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That last frame, and the frame with the pale pink Platygyra abutting a white lobate colony, are the two clearest within-frame contrasts in the set: pigmented and bleached skeletons side by side under one exposure. Several white colonies carry dark mottled patches that could be turf settling on newly dead skeleton, but the photographs do not resolve whether these are early tissue loss or sediment and shadow, and no unambiguous disease lesion is visible anywhere in the set. No crown-of-thorns seastars appear in any of the 82 frames. What does recur is bleached anemones: large host anemones with fully expanded but stark white or cream tentacles in four frames, and paler ones in two others — a non-scleractinian bleaching signal on top of the coral figure. Typical recent thermal stress: mean annual maximum of 4.9 degree heating weeks (2021-2025, NOAA CRW; Kenya virtual station). Seawater here was an estimated 32.3°C during the survey (read from the TG7 underwater camera and not validated, per Mayfield 2025, Environments 12:276, Table 1; the Kenya survey-wide mean of 32.0°C matched the 1998 event), and NOAA recorded a peak of 13.5 degree-heating weeks on 18 April 2024, the highest for Kenya since records began in 1985. For the 2024 Kenya survey as a whole, Mayfield (2025, Environments 12:276) estimated that in situ temperatures ran about 1.3°C above NOAA's, so that "nearly 22 DHWs may actually have transpired"; those in situ readings came from the TG7 underwater camera and have not been validated.

Fish and other fauna

Large mixed schools of yellow-and-blue fusiliers stream over the reef through the first third of the dive and are the dominant fish signal. Dark damselfish and chromis hang over the plates, an angelfish passes, and a red squirrelfish- or soldierfish-type fish sits in a crevice. Fish life reads as normal and abundant over an almost entirely bleached benthos.

Comparisons with other data

WCS Tanzania and WCS Kenya (via MERMAID) surveyed a nearby station (Watamu), 0.50 km from the pin; we could not confirm that it is the same reef. Within 5 km, seven independent stations (WCS Kenya / WCS Tanzania via MERMAID and WCS Kenya via MERMAID) recorded hard coral cover between 2008 and 2024: one by benthic survey, 28%, and seven by MERMAID bleaching-protocol quadrats, station-year means of 8.8–25% (one station appears in both); the nearest, WCS Kenya / WCS Tanzania via MERMAID at Watamu, 0.50 km away, read a mean of 28% in 2024.

Dive record

Dived 29 Mar 2024 off Watamu, at the height of the 2024 Western Indian Ocean mass bleaching event. Surveys were run with Extra Divers.