Kenya - Diani Beach (Diani) snorkel

Setting

Water quality is not uniform across the set. Roughly two-thirds of the frames are clear blue-green with 10 m-plus visibility and open blue water above a sloping reef; a minority are distinctly green and turbid. This is not a low-relief flat: two frames look down a genuine reef slope falling into blue water, and the reef carries meter-scale coral structure of its own.

General benthic features

The substrate between colonies is turfed hardground, rubble, and dark red-brown fleshy macroalgae, with pink coralline pavement in the shallows. The backbone of Diani is foliose plate coral. Tiered, shingled plate mounds a meter and more across recur throughout — three frames center on stacked plate colonies tall enough to be the dominant feature of their frames, and five more show plate beds running away across the reef (e.g., Image 1).

1

Several of the largest mounds carry a small gray-white massive colony perched on their upper surface (e.g., Image 3).

3

Two further groups are abundant here. First, branching and corymbose Acropora: dense thickets run through four frames, and scattered corymbose colonies appear in eight others. Second, massives and meandroid brains: pale Platygyra-type brains in five frames, and mauve to gray-brown massive Porites and faviid boulders in four others. Gold-green Turbinaria plates and a large rust-red encrusting-foliose colony round out the assemblage.

Coral cover

• Reference: Mayfield (2025)
• Data file: (Mayfield, 2025-Supplemental File S1)
• CoralNet submission package (accession #4963)
• Coral cover 35% — and 75% of hard coral tissue bleached (March-April 2024).
• Measured from 50 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.
• Across the 20 Kenyan sites the mean was 30% coral cover and 77% of tissue bleached.

Stressors

Three-quarters of the hard coral tissue here was bleached, and the set shows it as a mosaic rather than a wipeout, with almost every frame containing colonies in more than one state. Fully white colonies: the field of stark-white tabular and plating Acropora in one frame, with a single rust-red pigmented plate on the right edge for contrast; white corymbose Acropora scattered across four frames; a bleached plate stack; white foliose colonies against an orange-brown Acropora thicket; and a close-up of a plating acroporid gone cream-white with blue-white margins and a healthy brown colony immediately above it (e.g., Image 2).

2

Intermediate colonies: one frame shows the two-meter tiered table, washed tan-gold across the plate with pale blue-white growing margins and one small chocolate-brown corymbose colony riding on top that has not bleached at all, a white plate beside it — three conditions in one frame (e.g., Image 4).

4

Colonies in three frames are pale mauve-pink, stressed but still pigmented. Some plate mounds did hold pigment — the gold-tan tiered colonies of four frames, and the olive plate beds of two more — but as many are cream to gray-white (four frames, and the white foliose colonies of another). The groups that most consistently kept full brown-gold pigment at Diani were the dense branching Acropora thickets and the rust-red encrusting colony — while the meandroid brains beside that same red colony are pale gray-white. Massive Porites went both ways: pigmented mauve and gray-brown domes in two frames, pale ones in two others. No crown-of-thorns appear anywhere in the set. One mauve massive colony carries pale patches and dark, turf-filled grooves; no disease lesion is identifiable. 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 32.0°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

Fauna is sparse in the frames: a wrasse in one, small damsels and anthias over the Acropora in two others, and a scattering of fish in another.

Comparisons with other data

McClanahan & Mutere (1994) surveyed this site (Diani). Within 5 km, ten independent stations (WCS Kenya via MERMAID and submitted to MERMAID by Kosgei J, Musembi P.*) recorded station-year means of 9.2–32% hard coral cover between 2009 and 2024, all with MERMAID bleaching-protocol quadrats; the nearest, WCS Kenya via MERMAID (quadrats) at Nzidzani, 0.57 km away, read 16% in 2014.

Dive record

Snorkeled 16 Mar 2024 off Diani Beach during the 2024 Western Indian Ocean mass bleaching event, on the whale-shark trip that covered reefs 4 and 5. Surveys were run with Whale Shark Adventures.