### BIEG04 — Egmont
**Date:** 2015-03-10
**GPS:** 6.64751°S, 71.36836°E · **In-situ temperature:** 29.3°C
**Frames reviewed:** 25 of 25 (100% of the site folder, `BiEg04-finished`)
**Coral cover:** 29.2% (formal transect surveys) · **0.5%** of coral bleached (CoralNet analysis of informal survey images; Mayfield & Dempsey 2026, Oceans)
**Live hard coral cover across methods** (n=25 photos): transect 29.1% · CoralNet points 22.1% · Coralscapes 15.4%. Deviation vs transect -13.7 to -7.0 pp. **Mean of 3: 22.2% ± 6.9.** (SD here reflects systematic method bias, not precision — photo methods read low at high cover; see CHAGOS_MULTIMETHOD_README.md.)  
**Coral genera identified:** 7 scleractinian + 2 octocoral — *Acropora* (tabular, corymbose, digitate and staghorn), *Pocillopora*, *Porites* (massive domes and encrusting plates), *Montipora*, *Favites*/*Dipsastraea*, *Astreopora*, *Lobophyllia*; octocorals *Sinularia* and *Lobophytum*. Growth-form calls from photographs, given as "compatible with"; the *Lobophyllia* call (a single lobed colony in P3100419) is the least secure.
**Representative photos:** P3100415.jpg, P3100401.jpg, P3100409.jpg, P3100407.jpg, P3100418.jpg

BIEG04 is an exposed Egmont forereef whose 25 frames divide almost evenly between two states, and the division matters more than the site mean. Roughly half the set — P3100402, P3100418, P3100420, P3100401, P3100405 — shows genuinely dense *Acropora* development: overlapping lilac and fawn corymbose tables packed edge to edge, with orange anthias compatible with *Pseudanthias* and purple-and-yellow fairy basslets clouding above them. The other half — P3100403, P3100412, P3100413, P3100414, P3100419 — crosses broad pale carbonate pavement where turf-dusted hardground carries only isolated colonies and coral cover by eye is well under 10%. The two single most striking benthic frames are both isolated structures standing on that pavement rather than parts of a continuous framework: **P3100415**, a large, perfectly formed tabular *Acropora* (*A. cytherea*/*hyacinthus*-type) with a clean white growth margin, and **P3100404**, a broad yellow-green table on the upper slope. Massive domes compatible with *Porites* recur throughout as isolated bommies, joined by polygonal-corallite faviids compatible with *Favites* or *Dipsastraea*, fine-pored domes compatible with *Astreopora*, a lobed fleshy colony compatible with *Lobophyllia* in P3100419, and a large yellow encrusting-to-plating sheet in P3100414. Two macro frames (P3100388, P3100389) add the octocorals — brown finger-lobed colonies with white polyps compatible with *Sinularia* and *Lobophytum*, growing beside grey digitate and orange tube sponges on rubble crusted with red coralline algae.

Bleaching is effectively absent, and the 0.5% site figure is well supported: across all 25 frames not one colony is bleached white. The only pallor worth noting is in **P3100406**, a club-branched *Pocillopora* whose branch tips are cream-white — but the pattern is confined to the apical few millimetres of each branch with fully pigmented tissue immediately behind, which reads as normal actively growing tips rather than thermal stress, and it is recorded here as such. This is a 10 March dive, the earliest leg of the expedition and well ahead of the 2015 event's development at Egmont; the value of BIEG04 in the bleaching record is as a **clean pre-event baseline** for this atoll rather than as an impact site.

The dive's fauna is dominated by sharks, and the record needs correcting on their identity. Sharks appear in **six frames** (P3100382, P3100383, P3100384, P3100385, P3100386, P3100409). Most are grey reef sharks compatible with *Carcharhinus amblyrhynchos* — P3100409 is an unambiguous close pass over the reef, showing the broadly black-margined caudal fin. But **the animals in P3100384 and P3100385 carry conspicuous white tips on the first dorsal, pectorals and caudal lobe, which is the signature of the silvertip shark, *Carcharhinus albimarginatus*** — not the "whitetip/blacktip-type" recorded previously. Whitetip reef shark (*Triaenodon obesus*) is a slender, blunt-headed, bottom-resting animal and is not what these frames show. Beyond the sharks, **P3100311 is the dive's most spectacular frame**: a bait ball of many thousands of small silver fish, compatible with cardinalfishes or sweepers, packed into a reef hollow and filling the entire field of view. A single jack compatible with *Caranx* or *Seriola* patrols the blue in P3100417, and butterflyfishes, damselfishes and dense *Chromis* clouds populate the reef frames throughout.

**Two frames document the survey methodology directly, and are worth keeping for that reason alone.** P3100401 shows a **white PVC photoquadrat frame resting on a dense *Acropora* stand with the transect line running through it and a diver working in the upper right** — this is the point-count method that produced the site's cover figures, photographed in the act. **P3100407 shows a stainless steel bone-rongeur laid across a digitate *Acropora* colony**, plainly a fragment-collection or measurement shot; the identical tool appears at BIEG02 beside the crown-of-thorns. These frames tie the photographic record to the physical sample and transect archive, and should not be dismissed as incidental gear shots.

<b>Assemblage composition.</b> Across 25 analysed frames the Coralscapes masks put live hard coral at 15.4% of image area, of which <i>Acropora</i> (non-tabular) is the largest component at 49.1%; the rest breaks down as tabular <i>Acropora</i> 15%, other hard coral 13.8%, massive and meandroid 13.1%, <i>Pocillopora</i> 6.5% of live cover. The independent 30-point human annotation of the same frames (750 points) gives live hard coral as 22.1% of all points and apportions it <i>Acropora</i> 71.1%, <i>Porites</i> 11.4%, <i>Pocillopora</i> 9.6%, other hard coral 7.8% of live coral. Non-coral cover is dominated by crustose coralline algae 2.9%, turf 18.1% of all points. Structural loss registers as dead coral 1.9% of image area and rubble 8.2%. Bleaching stands at 0.9% of annotated points, concentrated in <i>Acropora</i> 0.8%, other hard coral 0.1% of points. Conspicuous fauna and sessile invertebrates appear as sponges in 6 frames, sea cucumbers in 4 frames, urchins in 1 frame, anemones in 1 frame. The dominance of <i>Acropora</i> in both methods (49.1% of masked live cover, 71.1% of live points) matches the visual impression exactly — where this reef is alive, it is almost entirely acroporid.

**Flags:** (1) **Shark ID corrected** — the white-tipped animals in P3100384 and P3100385 are silvertips (*Carcharhinus albimarginatus*-type), **not** whitetip or blacktip reef sharks as previously recorded; the rest are grey reef sharks. Six shark frames, not "at least seven". (2) The previous entry's claim that P3100409 and P3100412 both show close shark passes is half right — P3100409 does; P3100412 is a benthic frame with no shark. (3) The white branch tips in P3100406 are read as **active growth tips, not bleaching**, and are deliberately excluded from the bleaching log. (4) P3100401 (photoquadrat + transect + diver) and P3100407 (rongeur on an *Acropora*) are methodology documentation, linking this site's photos to its transect and sample records. (5) The bait ball in P3100311 is left at family level — cardinalfish vs sweeper cannot be separated at this distance. (6) The jack in P3100417 could be *Caranx* or *Seriola*; the yellow lateral stripe is suggestive but not diagnostic here. (7) No per-frame depth data; the two-zone structure is inferred from framing and light.

**Benthic data:** [Download BIEG04 benthic survey data (CSV)](../benthic_data/BIEG04_benthic.csv) — scleractinian cover by genus with full names, plus substrate and algal categories (bare substrate, CCA, turf, macroalgae, invertebrates), from the LOF BIOT-1 survey (Mayfield & Dempsey 2026, *Oceans*, supplemental file S1).