### BINI77 — Nelson Island
**CRD page:** [Blenheim, Nelson Island & Victory Bank Coral Surveys (Apr 2015)](https://coralreefdiagnostics.com/new-page-4)

**20 Apr 2015**
**GPS:** 5.70590°S, 72.32407°E
**Setting:** protected (leeward) submerged lagoonal patch reef, inside the lagoon, 21.8 m
**Coral cover:** 43.0% (3 depth transects, D2–D4; **algal cover 36.0%**) · **published image bleaching:** 16.1%
**Live hard coral cover across methods:** formal transects 43.0% · CoralNet points 17.6% · Coralscapes masks 18.0% (11 frames). These products have different sampling footprints and denominators and should not be averaged.
**Temperature:** 29.5 °C · **Salinity:** 34.2
**Photo review:** all 11 of 11 frames examined (folder `BiNi77-meter site-finished`)
**Representative photos:** P4200854.jpg, P4200872.jpg, P4200855.jpg, P4200870.jpg, P4200863.jpg

BINI77 is a submerged lagoonal patch reef inside Nelson Island's lagoon, on the protected side, surveyed at 21.8 m — the coolest site in this batch at 29.5 °C. **Coral cover is above average at 43.0%, ranking 40th of 109 Chagos sites, against 36.0% algae, which is mid-pack at 67th of 109.** Unlike the other lagoonal sites in this batch, the algal budget here is dominated by hard, encrusting growth rather than sediment: **crustose coralline algae accounts for 18.2% of total benthos (34th of 109 — comfortably in the upper third), fleshy turf 11.8% (41st of 109), macroalgae 2.9%, erect algae 2.2%, and sediment-laden turf almost nothing at 0.9%.** Bare substrate is 11.7% and non-coral invertebrates 9.4%. The five algal categories sum exactly to the published 35.96%. A patch reef this deep inside a lagoon carrying this much coralline pavement and almost no sediment-trapping turf reads as a well-flushed, hard-bottomed site, and the imagery — full of pink and mauve coralline crusts on massive dead framework — bears that out.

**The assemblage is *Porites*-led at the site level, with an unusually even second tier.** Twenty-two nonzero genera are recorded (74th of 109 for genus richness), and the twenty-two genus percentages sum to 42.9583% of the benthos, an exact match to the published cover figure. All values below are percent of total benthos, not percent of coral. *Porites* leads at 16.54% of the benthos — 39% of all the coral at the site — followed by *Acropora* 8.46% (20%) and *Pocillopora* 5.08% (12%); **those three hold 70% of the coral present.** Then an unusually flat second tier: *Platygyra* and *Stylophora* at 2.67% each and *Favia* at 2.58%, followed by *Gardineroseris* 1.42% and *Favites* 0.96%. The tail runs *Pachyseris* 0.50%, *Turbinaria* 0.42%, *Montipora* and *Pavona* 0.25% each, *Heliopora* 0.21%, *Hydnophora*, *Psammocora* and *Symphyllia* 0.17% each, *Acanthastrea* and *Montastrea* 0.13% each, ***Ctenella* 0.08%** — a rare genus in these tables and worth confirming (see Flags) — and *Cyphastrea*, *Echinopora* and *Galaxea* at 0.04% each.

**The depth transects show cover climbing gently with depth while the leading genus changes completely at each station — the clearest finding at this site.** D2 carries 40.88% coral against 40.88% algae (the two are identical to four decimal places in the source), and it is the one *Acropora*-led station: ***Acropora* 16.88% of the benthos, 41% of that transect's coral**, ahead of *Porites* 8.62%, *Stylophora* 5.00% (its profile peak), *Favia* 2.25%, *Pocillopora* 2.25% and *Turbinaria* 1.25%. At D3 cover is 42.50% against 39.00% algae and **no genus dominates**: *Porites* 10.00% (24% of that transect's coral), *Pocillopora* 9.50% (22% — its profile peak), *Platygyra* 7.00% (16% — also its peak), *Acropora* down to 4.50%, *Stylophora* 3.00% and *Favites* 2.50%. At D4 cover reaches its maximum of 45.50% while algae falls to 28.00%, and ***Porites* takes over completely at 31.00% of the benthos — 68% of all the coral on that transect** — with *Acropora* just 4.00%, *Favia* 3.50%, *Pocillopora* 3.50%, *Gardineroseris* 2.50% and *Platygyra* 1.00% behind. **The site-level figures of 16.54% *Porites* and 8.46% *Acropora* describe no single transect**: *Porites* runs 8.62 → 10.00 → 31.00 across the profile while *Acropora* runs 16.88 → 4.50 → 4.00, and the two cross over between D2 and D3. Coral and algae together leave 18.3 pp of the benthos unaccounted for at D2, 18.5 pp at D3 and 26.5 pp at D4, consistent with the site-level bare-substrate and non-coral-invertebrate readings, which are not itemised by depth.

The photographs — all eleven frames in the folder — document a reef of two parts, and the split matters for how the cover figures are read. P4200837 looks across a broad white sand plain at the reef margin, scattered with small dark conical structures (consistent with garden eels or small sponges, not resolved here) and two vivid violet-blue reef fish, with consolidated reef only along the right-hand edge — a low-cover frame. The remaining ten frames sit on the reef proper. **P4200854, P4200855 and P4200862 are dominated by extensive, stacked fields of large tabular plate colonies** — dozens of overlapping tables tiling the slope — and this is where the imagery and the transects appear to diverge: **many of those tables carry a uniform pale grey-green tone with no visible live-tissue texture, consistent with standing dead framework veneered in turf and coralline algae rather than living tabular *Acropora***, which would reconcile a photograph full of tables with a transect in which *Porites* is the leading live genus and *Acropora* only a fifth of the coral. That reading is offered as a hypothesis, not a measurement; the transects, not the images, define cover. P4200853, P4200863, P4200871 and P4200891 show the live assemblage well: massive and lobate mounds consistent with *Porites*, brain-patterned colonies consistent with *Platygyra*, abundant knobby and corymbose branching colonies, foliose plates, and heavy pink-mauve coralline crusting on the older framework. Fish are conspicuous and varied — a school of fusiliers streaming over the reef in P4200863, dark schooling rudderfish and a parrotfish in P4200856, three moorish idols across P4200862, P4200871 and P4200872, powder-blue surgeonfish, an anthias and a bicolor chromis — and a diver is visible in the background of P4200856. The set is not standardised for fish abundance.

**Condition is the second major finding, and the imagery supports the published figure strongly.** The published image bleaching value is **16.1%, ranking 11th of the 98 Chagos sites carrying a value — just outside the top decile of bleaching severity.** Bleaching is unmistakable rather than marginal in these frames. **P4200872 shows a single large, stark-white tabular colony in the centre of the frame, entirely white against a fully pigmented surround.** **P4200854 carries several bright-white plate and encrusting colonies clustered together in the mid-ground.** **P4200870 is a close mixed frame in which multiple cream-to-white knobby branching colonies (growth form consistent with *Pocillopora* or *Stylophora*) sit beside normally pigmented neighbours**, and **P4200863 shows a stark-white corymbose colony and a white flat plate in the same frame as healthy yellow-green and olive colonies.** P4200856 and P4200891 add further pale-cream corymbose and branching colonies. The within-frame contrast in each of these cases rules out exposure or white-balance artefact. These are recorded as frame-level bleaching observations supporting the published value; **no new site percentage is calculated from them.** No disease lesion margins or tissue-loss bands were identified, so the white colonies are logged as bleaching rather than disease; no *Drupella* aggregations, no parrotfish scarring, and no crown-of-thorns starfish or COTS feeding scars were seen in any of the eleven frames.

<b>Assemblage composition.</b> Formal transects give 43.0% coral against 36.0% algae — the algae being mostly crustose coralline pavement (18.2% of benthos) and clean turf (11.8%), with sediment-laden turf all but absent — across 22 nonzero genera led by *Porites* (16.5%), *Acropora* (8.5%) and *Pocillopora* (5.1%). The depth profile runs 40.88% cover at D2, where *Acropora* is 41% of the coral, through a genus-balanced D3 at 42.50%, to 45.50% at D4 where *Porites* alone accounts for 68% of the coral present. The eleven photographs show a sand-margined patch reef whose slope is tiled with large tabular framework — much of it apparently dead and coralline-encrusted — over a live assemblage of *Porites*-type mounds, brain colonies and abundant branching corals, and they document multiple unambiguously bleached colonies consistent with this site's high published bleaching figure.

**Flags:** (1) **BLEACHING OBSERVATION — this site should be carried into the running COTS/bleaching/disease log.** Frame-level evidence: a single large fully white tabular colony in **P4200872**; a cluster of white plate/encrusting colonies in **P4200854**; multiple cream-to-white branching colonies beside pigmented neighbours in **P4200870**; a white corymbose colony and white plate in **P4200863**; further pale colonies in P4200856 and P4200891. Published image bleaching 16.1%, 11th of 98 sites. (2) **The published bleaching figure is a COMPUTER-VISION product, not an in-situ observation.** It comes from CoralNet annotation of the informal survey images (Mayfield & Dempsey 2026, *Oceans*). Per-image human-vs-model agreement is substantially weaker for bleaching than for cover: r = 0.40 for bleached against r = 0.72 for live hard coral (`CHAGOS_MULTIMETHOD_README.md`). Never read it as a diver's field estimate. (3) **Any rank taken off the `Mean(%bleaching)` column is approximate** — that column carries at least one known bad value (BITB58 listed at 22.22% against a corrected 0.77%), so the 11th-of-98 placement has not been independently audited, though the photographs independently support a high value here. (4) **Multi-method deviation is large at this site:** CoralNet points 17.6% and Coralscapes masks 18.0% sit 25.4 and 25.0 pp below the formal transect figure of 43.0% — one of the wider gaps in this batch, and consistent with the documented tendency of the photo methods to under-read by roughly 23 pp at 40%+ transect cover (`CHAGOS_MULTIMETHOD_README.md`). Do not average the three; the transect is treated as ground truth for cover. (5) **The CV/photo figures rest on an 11-frame scored subset**, which happens to equal the folder count here — a coincidence that does not make the denominators comparable — and **one of those frames (P4200837) is largely open sand**, which will depress any image-derived cover estimate. (6) **`coralnet_points_pct` is documented as a human 30-point read, not a model prediction** (`CHAGOS_MULTIMETHOD_README.md`), but only roughly a quarter of Chagos image annotations corpus-wide are Anderson-confirmed; do not present 17.6% as verified ground truth. (7) **APPARENT IMAGE-VS-TRANSECT MISMATCH — worth a targeted re-look.** Three frames (P4200854, P4200855, P4200862) are dominated by extensive tabular plate fields, while the transects give *Acropora* only 8.5% of benthos (20% of coral) against *Porites* at 39%. The most likely reconciliation is that much of the tabular framework is standing dead and coralline-veneered, which this dataset does not separate from bare substrate; that is a hypothesis from imagery, not a measurement, and no cover figure is revised on it. (8) ***Ctenella* is recorded at trace level (0.08% of benthos)** — a rare genus in these tables and one whose identification is worth confirming against the raw transect sheets before it is quoted anywhere downstream. (9) **Formal replication is thin: `N Rows` = 3**, and **there is no D1 transect** — the shallowest reef zone is unsampled and the profile starts at D2. (10) **The depth codes D2–D4 carry no metre boundaries** in `Chagos benthic data by site-depth (n=336 rows).csv`; they are ordered shallow-to-deep stations, and the 21.8 m in the header is the site-level survey depth, not the depth of any one transect. (11) **At D2 the coral and algal cover values are identical (40.875% each)** in the source file. This is recorded as published; it is almost certainly a coincidence of the point counts, but flagged in case it indicates a transcription error in that row. (12) **18.3–26.5 pp of the benthos is unaccounted for by the coral and algae columns at each depth** — the depth-level summary does not itemise bare substrate or non-coral invertebrates. (13) **The photo folder is named `BiNi77-meter site-finished`, implying an instrument (logger/PAR meter) deployment at this site, but no instrument is visible in any of the eleven frames.** If a logger was deployed here, its data are not linked from this folder and should be tracked down. (14) **The identity of the small dark conical structures on the sand plain in P4200837 is unresolved** (garden eels versus small sponges); no call is made. (15) **No COTS, disease or predation scarring was observed** across the full 11-frame review — an explicit absence-of-evidence finding, though eleven frames cannot support a strong site-level absence claim. (16) **HOUSEKEEPING — the CRD page URL is the `new-page-4` placeholder** shared with the other Blenheim / Nelson Island / Victory Bank sites, and needs repointing once that page is renamed. (17) **NON-CANONICAL BLEACHING RANK — added 2026-08-26.** Any "of 98" bleaching rank above was computed off the site table's `Mean(%bleaching)` column, which equals the **1st** CoralNet training run. Anderson's decision of 2026-08-26 (HOW_TO rule 4e) makes **`% bleaching (2nd training)` canonical**, The file carries TWO pools for it, and they are not interchangeable: a **110-row pool** ranking every dive (revisit dives included, so BIPB70B/72B/69C compete) and a **99-site pool** ranking one value per site. The rank quoted below is on the 110-row dive pool. For this site the canonical value is **16.09%, rank 20 of 110** (1st training: 16.09%, rank 15 of 110). The two runs agree to <0.05 pp on 100 of 110 rows and diverge only on the bleaching-onset dives, so for most sites the distinction changes the rank but not the number.

**Benthic data:** [Download BINI77 benthic survey data (CSV)](../benthic_data/BINI77_benthic.csv) — scleractinian cover by genus with full names, plus substrate and algal categories, from the LOF BIOT-1 survey (Mayfield & Dempsey 2026, *Oceans*, supplemental file S1).