### BINI80 — Nelson Island / Great Chagos Bank North
**CRD page:** [Blenheim, Nelson Island & Victory Bank Coral Surveys (Apr 2015)](https://coralreefdiagnostics.com/new-page-4)

**21 Apr 2015** (two dives, same day — see Photo review)
**GPS:** 5.71253°S, 72.04568°E
**Setting:** protected submerged bank reef, forereef outside the lagoon; **site depth cell is blank** in the published table
**Coral cover:** 42.8% (3 depth transects, D2–D4; **algal cover 39.5%**) · **published image bleaching: the cell is BLANK** — one of 11 of 109 Chagos sites with no `Mean(%bleaching)` value. No substitute computed.
**Live hard coral cover across methods:** formal transects 42.8% · **no CoralNet or Coralscapes product exists for this site** (BINI80 has no row in `chagos_multimethod_cover_by_site.csv`). These products have different sampling footprints and denominators and should not be averaged — including any CV figure generated for this site later.
**Temperature:** 29.8 °C · **Salinity:** 34.2
**Photo review:** **all 24 of 24 stills examined across two folders and two dives on the same day** — `BiGc80a-COTS-finished` (16 frames, morning, 09:24:54–09:57:21) and `BiGc80b-finished` (8 frames, midday, 11:50:52–12:16:44), both **21 Apr 2015**, Olympus TG-2, verified from `DateTimeOriginal` EXIF and consistent with the `P4210NNN` stamps. Sharing a date, they are reported together with the dive noted per observation.
**Representative photos:** P4210883.jpg, P4210905.jpg, P4210918.jpg, P4210899.jpg, P4210911.jpg

BINI80 is a protected submerged bank reef on the north of the Great Chagos Bank, filed to the Nelson Island region, and it carries **42.8% coral cover against 39.5% algae — 41st of 109 Chagos sites for coral cover and 57th of 109 for algal cover.** The algal budget is turf, not coralline: fleshy turf (PTTS) is **19.4% of total benthos, 7th-highest of the 109 sites**, while crustose coralline algae (PCCATS) is 8.4%, ranking 92nd of 109 — low. Erect algae adds 7.1%, turf-plus-sediment 2.8% and macroalgae 1.8%. Bare substrate is **16.4%** and non-coral invertebrates only 1.3%. Coral, algae, bare substrate and invertebrates sum to exactly 100.0% of benthos. **A reef with top-decile turf, bottom-quartile CCA and 16% bare substrate is one with a lot of recently vacated hard surface**, and the two dives on 21 April show a mechanism actively at work there — see the predation paragraph, which is the finding at this site.

Coral cover is spread across **20 nonzero genera, 78th of 109 for genus richness**, and the 20 genus percentages sum to 42.7917% of the benthos, an exact match to the published cover figure. All values below are percent of total benthos, not percent of coral. **The assemblage is overwhelmingly monogeneric: *Acropora* alone is 32.21% of the benthos — 75% of every scleractinian on the site.** *Porites* is a distant second at 5.58% (13%), then *Pocillopora* 1.58% (4%) and *Goniastrea* 0.88% (2%); those four hold 94% of the coral. The remaining 16 genera are all trace — *Stylophora* 0.42%, *Favia* 0.33%, *Symphyllia* 0.33%, *Astreopora* 0.25%, *Platygyra* 0.17%, *Psammocora* 0.17%, *Echinopora* 0.13%, *Montipora* 0.13%, *Pavona* 0.13%, *Stylocoeniella* 0.13%, *Cyphastrea* 0.08%, *Fungia* 0.08%, *Leptoseris* 0.08%, and *Favites*, *Gardineroseris* and *Isopora* at 0.04% each. **Three-quarters of the coral at this site belonging to a single genus is the context for everything that follows**, *Acropora* being the preferred prey of the predator documented in the photographs; the transect and the photographic observations are independent records and this shard does not claim a tested causal link.

**Unlike the other sites in this batch, the depth profile shows no genus handover at all — *Acropora* dominates every station — but coral cover halves at the deepest one.** D2 carries 53.0% coral against 44.75% algae, with ***Acropora* at 42.00% of the benthos, 79% of all the coral on that transect**, ahead of *Porites* 6.75%, *Pocillopora* 1.75%, *Stylophora* 1.25%, *Fungia* 0.25% and *Favia* 0.25%. D3 is almost a repeat: 51.4% coral against 45.75% algae, ***Acropora* 39.62% (77% of the transect's coral)**, then *Porites* 4.50%, *Pocillopora* 2.00%, *Goniastrea* 1.12%, *Astreopora* 0.75% and *Favia* 0.75%. Then D4, the deepest station, **falls to 24.0% coral against 28.0% algae — less than half the shallow cover — and *Acropora* still leads at 15.00%, 62% of that transect's coral**, with *Porites* 5.50%, *Goniastrea* 1.50%, *Pocillopora* 1.00% and *Symphyllia* 1.00%. *Acropora*'s share of the coral falls only from 79% to 62% across the profile while absolute cover collapses, so the site-level 32.21% describes the shallow and mid reef fairly and overstates the deep one. At D4, coral and algae together account for only 52% of the benthos, leaving **roughly 48% unaccounted for by this depth-level summary** (against 2% at D2 and 3% at D3) — presumably bare pavement and sand not itemized by depth, and flagged below.

The photographs across both dives document a broad, gently sloping bank-top plain built almost entirely of acroporid tables and staghorn thickets over a maroon-red encrusted dead framework. **Morning dive (16 frames).** **P4210863**, **P4210865** and **P4210868** are wide views over dense staghorn and corymbose *Acropora* thickets separated by bright white sand channels, with deep maroon-brown plates in between; **P4210866**, **P4210867** and **P4210884** show large golden-yellow tabular *Acropora* plates standing over that maroon framework; **P4210878** and **P4210876** are the coral-abundant end of the plain, near-continuous cream, lavender and maroon corymbose colonies. **P4210882** is the counter-view: a field of large, flat, dead tabular plates coated in maroon-pink algal film with only two living yellow-green tables left in it. A **whitetip reef shark** cruises the plain in **P4210874** and **P4210875**, and a **second shark or the same animal resting** appears in **P4210897** on the midday dive. **Midday dive (8 frames).** **P4210918** is the site's best structural portrait — a stacked field of large golden-yellow *Acropora* tables in clear water; **P4210897** and **P4210917** show the same tables with white patches on them; **P4210899** is a survey frame with a measuring pole and marked line laid across the plain. Growth-form calls from photographs are given as "consistent with"; the genus percentages above are transect identifications.

**CROWN-OF-THORNS STARFISH ARE PRESENT AT THIS SITE IN NUMBERS, ON ACTIVE FEEDING FRONTS, ON BOTH DIVES. This is the finding at BINI80 and it is unambiguous.** The morning folder is named `-COTS-` and the imagery fully justifies the name:

- **P4210883** (morning) — **an aggregation of at least six crown-of-thorns starfish clustered together**, ranging from purple-brown to dark blue-grey, sitting on a continuous sheet of stark white, freshly-exposed coral skeleton, immediately adjacent to cream-yellow living staghorn *Acropora*. A seventh animal is partly in frame at the lower margin. The single most emphatic COTS image in this batch.
- **P4210879** (morning) — a **single COTS** on pavement between a cream staghorn *Acropora* below and a pigmented maroon pocilloporid above.
- **P4210905** (midday) — a **COTS sitting exactly on the boundary** between olive-green living *Acropora* plate tissue and a large stark-white area of freshly-killed skeleton: the animal in place on its own feeding front, the clearest single demonstration of the mechanism at the site.
- **P4210911** (midday) — a **COTS on a sheet of freshly-killed white skeleton**, with cream-yellow staghorn *Acropora* above it and maroon-red dead framework around.
- **P4210919** (midday) — an overhead view in which **at least two COTS sit at the margin of a large table**, on the boundary between the table's remaining pale tissue and a bright white advancing bare zone.

**That is a minimum of eleven COTS sightings across five frames on one day.** Frames within a dive may re-photograph the same individuals, so eleven is a count of sightings and a floor on abundance, **not an independent census** — but the P4210883 aggregation alone puts six or more animals in a single field of view, which is not an incidental encounter. Extensive fresh white feeding scars appear in further frames without a visible animal (**P4210881**, **P4210917**, **P4210898**, **P4210919**), and the white in these frames has the clean, corallite-detailed appearance of recently exposed skeleton rather than of bleached living tissue.

**Bleaching and predation cannot be cleanly separated in this set, and the published record cannot arbitrate because the bleaching cell is blank.** Two observations are recorded as bleaching with reasonable confidence: **P4210899** (midday) shows **several stark-white massive colonies consistent with *Porites*** in the foreground of a survey frame, a growth form COTS take late and a whole-colony pallor pattern typical of bleaching; and **P4210864** (morning) shows pale grey-white staghorn thickets amid pigmented ones. Against that, **P4210898** — a large table photographed from directly above, pale grey-cream across the plate with a bright white advancing rim and grazed notches — and **P4210917** — a large area of stark bone-white corymbose and tabular *Acropora* — are **recorded as ambiguous**: on a dive with eleven COTS sightings and multiple animals photographed on active feeding fronts, a white *Acropora* table is at least as likely to be freshly grazed as bleached, and a single still cannot separate bleached living tissue from clean recent skeleton. **P4210877** shows a pale plating colony with a blotchy white patch, also recorded rather than interpreted. **No substitute bleaching percentage has been computed and the blank published cell has not been filled.** No *Drupella* aggregation and no diagnostic disease lesion was identified in either folder.

Fauna beyond the starfish: whitetip reef sharks on both dives (**P4210874**, **P4210875**; a resting animal in **P4210897**), surgeonfish, unicornfish and a purple tang in **P4210882**, parrotfish in **P4210876**, and a brown ruffled foliose colony consistent with *Turbinaria* in **P4210884**.

<b>Assemblage composition.</b> Formal transects give 42.8% coral against 39.5% algae — the algal side turf-dominated, with PTTS at 19.4% of benthos (7th-highest of 109 sites) against only 8.4% CCA (92nd of 109) and 16.4% bare substrate — across 20 nonzero genera, of which ***Acropora* alone accounts for 32.2% of benthos, 75% of all the coral present**. The depth profile is unusual in showing no genus handover: *Acropora* leads at every station (79%, 77%, 62% of transect coral at D2, D3, D4) while absolute cover halves from 53.0% at D2 to 24.0% at D4. The photographs from the two 21 April dives document that same acroporid plain — staghorn thickets, golden tabular plates, maroon dead framework, whitetip reef sharks — and, decisively, **at least eleven crown-of-thorns starfish sightings across five frames, including an aggregation of six or more and two animals photographed on active feeding fronts, with extensive fresh white feeding scars in further frames.**

**Flags:** (1) **ACTIVE CROWN-OF-THORNS PREDATION, CONFIRMED, ON AN *ACROPORA*-DOMINATED REEF. THIS IS THE FLAG TO ACT ON.** At least **eleven COTS sightings across five frames on 21 Apr 2015** — P4210883 (aggregation of ≥6, morning), P4210879 (1, morning), P4210905 (1 on an active feeding front, midday), P4210911 (1 on fresh skeleton, midday), P4210919 (≥2 on a table margin, midday) — plus fresh feeding scars without a visible animal in P4210881, P4210917, P4210898 and P4210919. Frames within a dive may re-photograph the same individuals, so this is a **minimum sighting count, not a census**. The site's coral is **75% *Acropora***, the preferred prey. **These records belong in `chagos_cots_bleaching_log.csv` as human-confirmed observations** — that log's existing COTS rows are Coralscapes-mask detections at `confidence=probable`, whereas these are direct visual confirmations. Not written here; shard files only. (2) **THE PUBLISHED BLEACHING CELL IS BLANK.** `Mean(%bleaching)` is empty for BINI80 — one of 11 of 109 Chagos sites with no value — so this site contributes nothing to any archipelago bleaching statistic or map layer. **No substitute was computed and none should be back-filled here**, and note that at this site a back-fill would be actively unsafe: see flag 3. (3) **BLEACHING AND COTS SCARRING ARE CONFOUNDED IN THIS IMAGERY AND MUST NOT BE SCORED APART BY A COLOUR-BASED METHOD.** P4210898 (large table, pale plate with a bright white advancing rim and grazed notches) and P4210917 (large area of bone-white corymbose/tabular *Acropora*) are recorded as **ambiguous**: white *Acropora* on a reef with confirmed active COTS feeding is at least as likely to be freshly exposed skeleton as bleached tissue, and a single wide-angle still cannot separate the two. **Any CoralNet or Coralscapes bleaching product later generated for this site will over-call bleaching for exactly this reason**, and the corpus-wide human-vs-model bleaching agreement of r = 0.40 is already the weak end of that comparison. Only P4210899 (white massive *Porites*-type colonies) and P4210864 (pale staghorn thickets) are recorded as bleaching with reasonable confidence. (4) **NO MULTI-METHOD ROW EXISTS FOR THIS SITE.** BINI80 is absent from `chagos_multimethod_cover_by_site.csv` — no CoralNet points, no Coralscapes mask, no `n_photos` subset. The 42.8% transect figure stands alone; do not pair it with the folder frame-count (24) as a CV sample size. The missing CV product is also the likely reason flag 2 exists, the published bleaching column being itself a CoralNet product. (5) **THE SITE DEPTH CELL IS BLANK** in `Chagos benthic data by site (n=109).csv` — no site-level survey depth is published for BINI80, so the header above carries none. The depth codes D2–D4 exist and are ordered shallow-to-deep stations, but they **carry no metre boundaries** in `Chagos benthic data by site-depth (n=336 rows).csv`, which means **this site has no depth information at all in absolute terms**. Anything requiring a depth value for BINI80 will need it sourced elsewhere. (6) **FOUR-WAY NAMING MISMATCH.** The site is `BINI80` in the benthic tables; its `island` field reads **GCB-North** while its `region` field reads **Nelson Island**; the photo folders are `BiGc80a-COTS-finished` and `BiGc80b-finished` (prefix **BiGc**, not BiNi); and `chagos_site_to_page.json` keys the CRD page under **`BIGC80`** — there is no `BINI80` key in that file. Folders and page keys resolve by **number**, not prefix. A lookup on the literal site code returns null and will silently drop the page link. Same trap as BICC51/BiTb51 in this batch. (7) **TWO DIVES, ONE DATE.** Both folders are **21 Apr 2015** — morning 09:24:54–09:57:21 (16 frames) and midday 11:50:52–12:16:44 (8 frames), verified from `DateTimeOriginal` EXIF on every file. **This is the exception to the usual a/b-suffix rule**, under which sub-dive suffixes normally denote different dates; here they denote two dives on the same day, so the folders are reported together with the dive noted per observation. Any pipeline that assumes an `a`/`b` suffix implies distinct dates will assign this site a spurious second survey date. (8) **No D1 transect exists** — the profile starts at D2, so the shallowest reef zone is unsampled (`N Rows` = 3). (9) **D4 HAS ROUGHLY 48% OF ITS BENTHOS UNACCOUNTED FOR** by coral (24.0%) plus algae (28.0%) in the site-depth summary, against 2–3% unaccounted at D2 and D3. Presumably bare pavement and sand not itemized by depth, but the residual is large enough that D4's algal figure should not be used on its own. (10) ***Acropora* IS 75% OF ALL CORAL AT THIS SITE (32.21% of benthos of a 42.79% total).** Any site-level statistic here is effectively an *Acropora* statistic, and the site is unusually exposed to a single-genus disturbance — which flag 1 shows is not hypothetical. This is a within-site share computed from the site row, not an archipelago ranking. (11) **7th-highest fleshy turf of 109 sites (19.4% of benthos) against low CCA (8.4%, 92nd of 109) and 16.4% bare substrate.** Consistent with the extensive maroon-filmed dead tabular framework and fresh bare skeleton visible throughout both folders, though this shard does not test whether the COTS predation caused it. (12) **GENUS-CODE BUG IN `sitefacts.py` — code `SCOE` IS MIS-RESOLVED AND AFFECTS OTHER SHARDS.** `sitefacts.py` line 8 maps **both** `SCOE` and `SCOL` to *Scolymia*, but `benthic_data/BINI80_benthic.csv` — built from the published supplement — resolves `SCOE` to ***Stylocoeniella***. *Stylocoeniella* is correct: *Scolymia* is an Atlantic/Caribbean genus and does not occur in the Indo-Pacific. This shard uses *Stylocoeniella* (0.13% of benthos). **`SCOE` appears in 8 of the per-site benthic CSVs, and `desc_BIBL87.md` and `desc_BIPB61.md` already carry the incorrect *Scolymia* name** — both need correcting, along with the `GEN` dictionary in `sitefacts.py`. Not fixed here; this shard writes only itself. (13) **A survey pole and marked line are visible in P4210899** — standard field documentation, not a data issue. (14) **Where the published bleaching figure does exist elsewhere in Chagos it is a COMPUTER-VISION product, not an in-situ observation** — 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`). That column also carries at least one known bad value (BITB58 listed at 22.22% against a corrected 0.77%), so any rank taken off it is approximate. Never read those percentages as a diver's field estimate.

**Benthic data:** [Download BINI80 benthic survey data (CSV)](../benthic_data/BINI80_benthic.csv) — scleractinian cover by genus with full names, plus substrate and algal categories (bare substrate, CCA, turf, turf+sediment, macroalgae, erect algae, invertebrates, cyanobacteria), from the LOF BIOT-1 survey (Mayfield & Dempsey 2026, *Oceans*, supplemental file S1).