### BIDI16 — Danger Island
**Date:** 2015-03-14
**GPS:** 6.34088°S, 71.25667°E
**Frames reviewed:** 13 of 13 (100% of the site folder, `BiDi16-finished`)
**Coral cover:** 30.4% (formal transect surveys) · **% bleached:** 0.0% (CoralNet analysis of informal survey images; Mayfield & Dempsey 2026, Oceans) — **but see the flag below: two small white branching colonies are visible in P3140315.**
**Live hard coral cover across methods** (n=13 photos): transect 30.4% · CoralNet points 23.6% · Coralscapes 24.2%. Deviation vs transect -6.8 to -6.2 pp. **Mean of 3: 26.1% ± 3.8** — the two photo methods agree with each other to within 0.6 pp, the closest human-model agreement of any Danger Island site.
**Coral genera identified:** 8 scleractinian + 1 hydrocoral — *Platygyra*/*Leptoria* (exceptional specimens), *Porites* (massive, lobed/columnar, and broad plating), *Acropora* (corymbose, branching and tabular), *Pocillopora*, *Montipora* (encrusting/plating), *Favites*/*Goniastrea*, *Astreopora*, *Stylophora*; hydrocoral *Millepora*. Growth-form calls from photographs, given as "compatible with".
**Representative photos:** P3140297.jpg, P3140314.jpg, P3140315.jpg, P3140313.jpg, P3140296.jpg

BIDI16 is a **protected back-reef** — the only back-reef habitat among the Danger Island sites — and it looks the part: a broad, gently sloping pavement of consolidated white carbonate and coralline rubble across which coral grows as **hundreds of small, discrete, well-spaced colonies** rather than as continuous framework. P3140295, P3140312, P3140313, P3140315, P3140318 and P3140319 all show the same architecture: corymbose and branching *Acropora*, brown *Pocillopora*, olive plating *Montipora* or *Porites*, domal *Porites*, cup corals and encrusting sheets, each colony separated from the next by bare white pavement. **P3140315 is the best single illustration** — a downward view resolving perhaps forty distinct colonies of a dozen growth forms in one frame. P3140296 adds large lobed and columnar *Porites*, and P3140317 is a close study of a broad olive-green encrusting sheet with polyp detail and a small dead patch at its centre.

**The site's outstanding subjects are its brain corals.** P3140297 and P3140298 are near-spherical meandroid colonies compatible with *Platygyra* or *Leptoria*, dark chocolate-brown with tightly and evenly sinuous valleys, sitting isolated on clean white sand. Photographed from directly above with the pale substrate as a natural backdrop, they are the cleanest specimen images in the collection — and with the BIDI15 macros they make Danger Island the archipelago's brain-coral locality.

**On bleaching, the recorded figure and the imagery disagree slightly, and it should be stated rather than smoothed over.** The site is logged at **0.0% bleached**, yet **P3140315 contains two small, bright bone-white branching colonies** in the lower centre of the frame, unmistakable against the surrounding pigmented colonies and pale-but-textured pavement. **P3140311** additionally shows a branching *Acropora* with distinctly pale to white branch tips. Neither observation overturns a 0.0% figure derived from point annotation — two small colonies among the many hundreds visible at this site is entirely consistent with a bleached fraction that rounds to zero, and the point set may simply not have landed on them. But **"0.0%" should not be read as "no bleaching present at BIDI16"**, and if that value feeds a site-level bleaching analysis it is worth confirming the frames behind it.

Faunally the site is quiet, consistent with a sheltered back-reef: **two divers cross the blue in P3140314**, snappers or rudderfish compatible with *Macolor* or *Kyphosus* hang in mid-water in the hazy P3140316 alongside an angelfish, damselfishes and *Chromis* work the colonies, and a spotted holothurian compatible with *Bohadschia* lies on the pavement in P3140312. There are no large aggregations of the kind that dominate BIDI08–BIDI10.

<b>Assemblage composition.</b> The cover line carries the numbers. BIDI16 is a further confirmation of the pattern established across this atoll: **CoralNet 23.6% and Coralscapes 24.2% agree to within 0.6 pp** — the closest human-model agreement at Danger Island — while both sit ~6.5 pp below the transect. That is a small, consistent, *shared* offset of exactly the kind expected where coral is low-relief and discrete, and it contrasts sharply with BIDI08's tabular −25 pp. Notably, this site's architecture — many small colonies on open pavement — is close to ideal for both photographic methods, which is why they converge here.

**Flags:** (1) **BLEACHING DISCREPANCY — the site is recorded 0.0% bleached, but P3140315 shows two small bone-white branching colonies and P3140311 shows an *Acropora* with white branch tips.** Not necessarily an error (two colonies among hundreds rounds to zero, and the points may not have landed on them), but **0.0% must not be reported as "no bleaching present"**. Verify the frames behind the figure before using it in any site-level bleaching analysis. (2) **P3140297/P3140298 are the cleanest coral specimen images in the collection** — isolated brain corals shot from directly above against white sand. Flagged for illustrative use alongside BIDI15's polyp macros. (3) **P3140315 is an excellent colony-density/diversity frame** — ~40 discrete colonies of a dozen growth forms in one image; useful for any recruitment or colony-size analysis. (4) Two divers in P3140314. (5) The small white cup-shaped objects recurring on the pavement (P3140296, P3140315, P3140317) are unresolved — cup corals, ascidians or foraminifera; do not score as scleractinian cover without closer inspection. (6) This is **the only back-reef site** in the Danger Island set, which likely explains both its architecture and its quiet fish community. (7) No per-frame depth data.

**Benthic data:** [Download BIDI16 benthic survey data (CSV)](../benthic_data/BIDI16_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).