### BIBL82 — Blenheim (Blenheim)
**Date:** 2015-04-22
**GPS:** 5.25432°S, 72.45724°E
**Frames reviewed:** 22 of 22 (100% of the site folder, `BiBl82-great site-finished`)
**Coral cover:** 37.9% · **% bleached:** 7.8%
**Live hard coral cover across methods** (n=19 photos): transect 37.9% · CoralNet points 24.2% · Coralscapes 21.2%. Deviation vs transect -16.7 to -13.7 pp. **Mean of 3: 27.8% ± 8.9.** (SD here reflects systematic method bias, not precision — photo methods read low at high cover; see CHAGOS_MULTIMETHOD_README.md.)  
**Coral genera identified:** 12 scleractinian + 2 octocoral — *Acropora* (tabular, corymbose, digitate and staghorn growth forms all present), *Pocillopora*, *Porites*, *Montipora*, *Millepora*, *Platygyra*, *Dipsastraea*/*Goniastrea*, *Astreopora*, *Galaxea*, *Fungia*, *Turbinaria*, *Diploastrea*; octocorals *Sarcophyton* and *Sinularia*. All calls are growth-form-based from photographs and are given as "compatible with" — no specimen was examined.
**Representative photos:** P4220837.jpg, P4220845.jpg, P4220851.jpg, P4220905.jpg, P4220910.jpg

BIBL82 earns its "great site" folder tag: across all 22 frames the reef reads as one of the most completely coral-covered surfaces in the Chagos set, and the photographs comfortably support — arguably exceed — the 37.9% formal transect figure. The site is a shallow-to-mid forereef pavement and gentle slope that shoals into a coral-capped ridge and drops away to open sand at its margin. The single most characteristic view is the near-vertical downward shot P4220837, in which small corymbose and digitate colonies compatible with *Pocillopora*, purple-pink and packed shoulder to shoulder, leave almost no bare substrate; tan encrusting-to-laminar plates compatible with *Montipora*, low meandroid domes compatible with *Platygyra*, and mottled faviid boulders compatible with *Dipsastraea* or *Goniastrea* fill the remaining gaps. That packing density holds across the sequence P4220875, P4220876, P4220900–P4220906, where digitate and corymbose *Acropora* — including *A. humilis*-type stout-branched colonies in orange, gold and lilac — share the pavement with pocilloporids and with domal *Porites*. Deeper and along the slope the community shifts: P4220838 and P4220839 show upper-slope fields of tabular and staghorn *Acropora* pale against the blue, while the steeper wall frames (P4220859, P4220839) are dominated instead by branched yellow-tan colonies compatible with *Millepora*, growing among red and magenta encrusting sponge and crustose coralline algae with black-coral wire whips compatible with *Cirrhipathes* trailing off the substrate. A distinct third habitat appears in P4220845: a broad stand of tiered olive-green foliose plates compatible with *Montipora* or *Echinopora*, stacked in overlapping storeys around massive domes compatible with *Porites* and *Diploastrea*. Two macro frames add most of the remaining generic diversity — P4220852 resolves brain colonies compatible with *Platygyra*, a dark plate with yellow polyps compatible with *Turbinaria*, and a free-living disc compatible with *Fungia* against extensive pink CCA; P4220860 adds a pale tubular-polyped colony compatible with *Galaxea* and a domal *Astreopora*. Octocorals are a minor but real component: a large folded leather compatible with *Sarcophyton* occupies the right of P4220861, and lobed leathers compatible with *Sinularia* recur in P4220900 and P4220901.

Bleaching at BIBL82 is real but genuinely limited, and the frame-by-frame pattern tracks the 7.8% site figure closely rather than exceeding it. The overwhelming impression across the 22 frames is of normally pigmented purple, gold, olive and tan tissue; white appears as scattered individual colonies rather than as any site-wide whitening. The clearest cases are all branching: a small bleached cluster tucked among healthy faviids in the macro frame P4220851, a stark bone-white corymbose *Acropora* in the middle of an otherwise pigmented flat in P4220901, and — the most severe frame at the site — P4220905, where a fully bleached staghorn-type *Acropora* and an adjacent white *Pocillopora* sit side by side while brown-orange digitate *Acropora* and healthy *Porites* immediately around them retain full colour. Partial-colony pallor (blanched branch tips, whitened plate margins) shows up more diffusely in P4220838, P4220845, P4220903 and P4220906. The growth-form partitioning is the notable signal: branching and corymbose acroporids and pocilloporids carry essentially all the visible bleaching here, while massive, meandroid and encrusting colonies are unaffected in every frame — the same form-dependent response seen at the 2015 event's other Chagos sites, caught here early and mildly.

The dive's fauna is modest but consistent with a healthy, fished-free reef. Moorish idols compatible with *Zanclus cornutus* and several butterflyfishes move through the coral in P4220837 and P4220860; bannerfish compatible with *Heniochus* appear over the foliose stand in P4220845; a loose school of fusiliers compatible with *Caesio* or *Pterocaesio* streams across the upper slope in P4220838, with damselfishes compatible with *Chromis* dense over the wall in P4220839 and P4220859; surgeonfishes compatible with *Acanthurus* or *Ctenochaetus* graze the flat in P4220901. The one conspicuous invertebrate is the black, white-tubercled sea star in P4220905 — a chocolate-chip star compatible with *Protoreaster nodosus*, sitting immediately beside the bleached branching colonies. **This is not a crown-of-thorns and must not be counted as one**, nor as benthic cover. The photo sequence closes as it would on a real swim: the reef thins to rubble-and-pavement with smaller colonies (P4220907), rises over a shallow surge-lit bommie (P4220908), gives way entirely to rippled open sand (P4220909), and ends with a diver working the reef edge back toward the drop (P4220910).

<b>Assemblage composition.</b> Across 19 analysed frames the Coralscapes masks put live hard coral at 21.2% of image area, of which massive and meandroid is the largest component at 30.9%; the rest breaks down as other hard coral 25.2%, <i>Stylophora</i> 13.9%, <i>Acropora</i> (non-tabular) 9.5%, <i>Millepora</i> 7.8% of live cover. The independent 30-point human annotation of the same frames (570 points) gives live hard coral as 24.2% of all points and apportions it other hard coral 39.1%, <i>Acropora</i> 30.4%, <i>Porites</i> 29%, <i>Pocillopora</i> 1.4% of live coral. Non-coral cover is dominated by crustose coralline algae 12.8%, turf 16.5% of all points. Structural loss registers as dead coral 3.6% of image area and rubble 0.9%. Bleaching stands at 1.9% of annotated points, concentrated in other hard coral 1.2%, <i>Acropora</i> 0.3%, <i>Pocillopora</i> 0.3% of points. Conspicuous fauna and sessile invertebrates appear as sponges in 13 frames, giant clams in 1 frame, urchins in 1 frame.

**Flags:** (1) The "great site" folder tag is well supported — coral packing in P4220837/P4220875/P4220876 is near-continuous, and the photo-derived cover figures (21–24%) almost certainly understate this site, consistent with the archipelago-wide photo-vs-transect bias at high cover. (2) The sea star in P4220905 is a chocolate-chip star (*Protoreaster*-type), **not** COTS — logged so it is not mistaken for predation. (3) The *Stylophora* component reported by the Coralscapes model (13.9% of live cover) was not corroborated visually in any of the 22 frames; the small purple-pink digitate colonies it most likely keyed on read as *Pocillopora* to the eye — treat that model class with caution here. (4) The mottled brown masses in P4220900 are read as soft-coral leathers (*Sinularia*-type) but an octopus cannot be entirely excluded from that frame's resolution. (5) Depth is not recorded for any frame; the three habitats described (shallow flat, slope, wall) are inferred from framing, light and blue-water backdrop, not from instrument data.

**Benthic data:** [Download BIBL82 benthic survey data (CSV)](../benthic_data/BIBL82_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).