Kenya - Shimoni night dive (Shimoni-Wasini)

Setting

This site is a low-relief, sediment-influenced back-reef rather than a coral-dominated slope.

General benthic features

Pale carbonate sand and rubble pavement, veneered with silt, carries scattered thickets of branching Acropora rather than a continuous coral framework. The widest frames are mostly bare silty rubble with pink coralline crusts, small orange encrusting sponges, and loose Acropora fragments lying free on the sediment. Branching Acropora is the dominant hard coral and appears in more than twenty frames, from single hand-sized colonies to thickets a meter or more across (e.g., Image 1).

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Almost all of them carry bright white branch tips against tan or gold-brown branches — these are growing tips, not bleaching, and they are the single most likely thing at this site to be misread. A pale-blue to turquoise encrusting patch recurs at the base of several Acropora colonies, and a small blue-purple branching colony sits beside the Acropora in one frame (e.g., Image 1). Fungiid mushroom corals appear four times, twice seen off the bottom against black water (e.g., Image 9) (one photo not shown) and twice close up at the margin (e.g., Image 10) (one noted by Anderson as a bleaching Fungia Image 11), all showing cream-white septal ridges with green-tipped marginal tentacles.

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A small recruit-scale colony, which Anderson identified as a young pocilloporid, is growing among turf with a white tunicate beside it, and another is a bushy pocilloporid-form colony with polyps fully expanded. A pavement of small encrusting polyps with acid-green and yellow oral discs on maroon tissue runs across three frames and covers substantial areas of rock (e.g., Image 2).

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Because it is a night dive, almost every cnidarian in the set is caught with polyps out, and soft corals and fleshy polyp colonies are disproportionately represented: pale pink and cream colonies with feather-tipped, turquoise-green polyps in fifteen frames, a fat lobed white soft coral, and dense fields of long cream tentacles in three more.

Coral cover

• Night-dive frames are unsuitable for a cover estimate — they are macro and critter shots under artificial light, not benthic quadrat views — and no transect or diver survey exists for this site.
• No number should be read into the site record, and none was derived from these photographs.

Stressors

Sedimentation shows on the corals themselves: a small, partially buried Acropora colony is half-drowned in sand, and sand sits in the interstices of several thickets. Anderson recorded bleaching on this dive: the field captions name four frames "bleached coral" (e.g., Image 12), "bleached polyps" (e.g., Image 13), "bleached polyps Kenya" (e.g., Image 14), and "bleaching Fungia" (e.g., Image 11).

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The three polyp frames show broad fields of fully expanded white tentacles, the bleached polyps recorded. In the fungiid frames the disc is uniformly pale cream-white with the septal ridges standing out sharply, while the marginal tentacles in the same frame still hold green pigment. The dive was made at the peak of the 2024 Western Indian Ocean mass bleaching event, with 6 degree heating weeks on the day, and the REEFolution nursery reef a few hundred meters away in the same channel, surveyed the same day, has a published figure of 73% of hard coral tissue bleached. No crown-of-thorns starfish, no Drupella aggregations, and no disease lesions appear in any of the 98 frames reviewed. The Shimoni-Wasini regional dive-computer mean was 32.0°C (no reading exists for this night dive itself), and NOAA recorded 6 degree-heating weeks on the day of the dive (Mayfield 2025, Environments 12:276, Table 1).

Fish and other fauna

Tube-dwelling cerianthid anemones are the most-photographed single subject on the dive — at least eight frames, each a white-and-lavender crown of long tentacles spread flat over open sand (e.g., Image 3).

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The invertebrate list is the best part of the set. Nudibranchs appear repeatedly: a Spanish dancer, Hexabranchus sanguineus, in scarlet with white mottling and its gill plume erect; a pink-orange dorid with fine red reticulation and white-tipped rhinophores, seen twice; a small slug with purple and orange appendages crawling over an orange sponge; and a dark, ruffle-margined animal seen twice on rubble. A tiger cowrie turns up three times, once as a bare polished shell and once with the animal out and the foot extended; a second large gastropod sits out on the reef with its aperture and orange mantle exposed. There is a big pale-yellow animal on sand, compatible with a sea cucumber, photographed twice (e.g., Image 5), plus a translucent red-banded shrimp on sand, small crustaceans sheltering inside Acropora branches (e.g., Image 1), a long-antennaed, white-spotted red hermit crab in an algae-furred shell on Acropora (e.g., Image 6), and a hermit crab with green-ringed eyes on banded stalks in a spotted shell carrying a small anemone (e.g., Image 7).

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Fish are all night fish. Two moray eels are out of their holes with the jaws open; a blue-gray, white-barred eel is seen hunting across open sand in three frames; a dwarf lionfish or scorpionfish with banded fan pectorals is seen twice; a longhorn cowfish hangs in black water and a second boxfish-type head appears in another frame; a porcupinefish rests on sand with its spines part-raised; a parrotfish sleeps wedged into an Acropora thicket; and a pink, yellow-eyed fish rests on the sand twice. Anderson identified a seahorse in three frames.

Comparisons with other data

WCS Kenya (via MERMAID) surveyed a nearby station (Mji wa Kale 1 (Mkwiro)), 0.29 km from the pin; we could not confirm that it is the same reef. Within 5 km, seventeen independent stations (REEFolution Foundation, WCS Kenya via MERMAID, and submitted to MERMAID by Kosgei J, Musembi P.*) recorded hard coral cover between 2011 and 2024: six by benthic survey, station-year means of 0.0–66%, and eleven by MERMAID bleaching-protocol quadrats, station-year means of 18–55%; the nearest, WCS Kenya via MERMAID (quadrats) at Mji wa Kale 1 (Mkwiro), 0.29 km away, read 33% in 2019.

Dive record

Dived on the night of 20 March 2024 off Shimoni on Kenya's far south coast, in the Shimoni-Wasini channel, as the second dive of Anderson's Shimoni leg — after the REEFolution nursery that morning and before the Kisite-Mpunguti park sites.

Other notes

This description draws on 98 of the 110 frames on file. It is a night dive, so most frames are close-focus subjects lit by strobe, but roughly a dozen pull back to colony and thicket scale, and those are enough to settle what the habitat is.