Kenya - Brain Coral (Mombasa)

Setting

Water and habitat. Mombasa's reputation is earned here: a large share of the wide frames are green, hazy, and backscattered, with the far reef dissolving within a few meters. A minority of frames — mostly those shot upward into open water over the deeper bommies — are genuinely blue and clear. The reef itself is a low- to moderate-relief mosaic: rounded bommies and long runs of encrusting-to-plating pavement, sand and rubble lanes between them, and turf, crustose coralline, and fine sediment on everything not held by living tissue.

General benthic features

There are no branching thickets of any size; this is a massive-and-plate reef. The site name is borne out by the full set of photographs. Meandroid colonies are one of the defining elements: a meter-scale domed brain coral of Platygyra type, cleanly ridged; a broad, deeply folded Lobophyllia/Symphyllia type colony in violet; a second large meandroid dome with pale, worn ridges; a compact green meandroid colony sitting in rubble; and smaller Platygyra-type heads recurring across the reef. Alongside them sit the other two structural pillars: very large helmet-shaped massive Porites mounds — one single dome among them with its crown paled and its flanks still pigmented — and cerioid Favites/Goniastrea colonies whose deep maroon-brown reticulate corallites are among the most strongly pigmented corals in the entire set. Laminar and foliose plates are everywhere: Turbinaria-type cups and folded vases, thin Montipora/Echinopora-type sheets with clean white growing margins, ridged Pachyseris-type colonies, and one striking dark plate speckled with white polyps (e.g., Image 3).

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Galaxea was seen with green tentacle tips fully extended and looking untouched. Acropora is present but subordinate — a few tables, some corymbose colonies with pale tips, and stands of fine yellow-brown branching colonies — and Pocillopora/Stylophora-type verrucose colonies fill gaps between the massives (e.g., Image 4).

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Soft corals are abundant and, in places, dominant: brown Sarcophyton leathers by the dozen, Sinularia, purple and lilac soft-coral fields spread over rubble, and orange-red Dendronephthya-type colonies off the rock (e.g., Image 2).

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Coral cover

• Reference: Mayfield (2025)
• Data file: (Mayfield, 2025-Supplemental File S1)
• CoralNet submission package (accession #4963)
• Coral cover 27% — and 47% of hard coral tissue bleached (March-April 2024).
• Measured from 136 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.
• This is a published diver-photograph point-annotation value, not a computer vision estimate.

Stressors

One frame of a free-living Fungia disc shows bare skeleton with the septa still sharp — possible recent mortality (one frame), not old rubble. One frame shows a fouled fishing line or net draped over a branching colony; the branches beneath it are dead and algae-covered, while the rest of the colony is alive. Bleaching, read from structure. Roughly one frame in six carries at least one colony that is unambiguously bleached on structural grounds: bone-white foliose and laminar plates standing out against pigmented neighbors; a stark white bulbous colony; a white encrusting sheet with a sharp margin against brown tissue; several chalk-white plates in an otherwise brown plate field; and a large pale plating colony whose surface texture is intact but whose tissue is white throughout. Against that, a great many colonies are plainly still pigmented — the maroon Favites, the olive-green plates, the brown leathers, most of the massive domes. The impression from the full set is a reef about half-affected, with the massives and the meandroid brains holding pigment better than the thin plates: consistent with the published figure of 47% of hard coral tissue bleached, which is far below the 77% Kenyan mean. Note again that the frames are color-adjusted, so the widespread lilac and mauve casts are not counted as bleaching here. 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 32.5°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. No crown-of-thorns starfish (COTS) or other corallivores were evident.

Fish and other fauna

Fish and macro life. Bluestripe snapper (Lutjanus kasmira) are the signature: dense schools recur in eight separate frames, some hundreds strong, streaming over the bommies with yellow-and-blue-striped sweetlips, emperors, and fusiliers mixed in — Anderson noted the reef as an effective marine protected area (e.g., Image 1).

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Also recorded: longfin batfish (Platax), a grouper wedged under a plate, parrotfish and wrasse working the rubble, clouds of anthias and cardinalfish over a coral head, damselfish and chromis throughout, two scorpionfish sitting cryptic on coral, a large spotted-black-and-white sweetlips in midwater, a sea cucumber, a blue Linckia sea star and an orange star, and a ray whose tail is visible under a ledge. Flatworms are well documented on this dive (Anderson's field notes call them nudibranchs, but the frames show thin, flat animals with ruffled margins and folded front tips): a pale blue one with a black-edged white stripe and an orange front seen five times, a dark blue one with yellow spots and a turquoise margin seen four times, and a pale blue one with black stripes and an orange midline seen twice.

Comparisons with other data

WCS Kenya (via MERMAID) surveyed a nearby station (Mombasa Braincoral) in 2009, 1.32 km from the pin. Within 5 km, twenty independent stations recorded hard coral cover between 2003 and 2023: one by benthic survey, 22%, and nineteen by MERMAID bleaching-protocol quadrats, station-year means of 8.0–54%; the nearest, WCS Kenya via MERMAID (quadrats) at Mombasa Green turtle, 0.36 km away, read 54% in 2017.

Dive record

Surveyed 11 Mar 2024 with Mombasa Marine Park, during the 2024 Western Indian Ocean mass bleaching event.