### BIPB68 — Peros Banhos
**CRD page:** [Peros Banhos Coral Surveys (16–17 Apr 2015)](https://coralreefdiagnostics.com/peros-banhos-20150416-to-0417)

**16 Apr 2015**
**GPS:** 5.2563°S, 71.76861°E
**Setting:** protected emergent fringing reef, 23 m
**Coral cover:** 55.1% (4 formal transects, D1–D4; **algal cover 35.0%**) · **published image bleaching:** 0.87%
**Live hard coral cover across methods:** formal transects 55.1% · CoralNet points 33.6% · Coralscapes masks 33.9% (43 frames). These products have different sampling footprints and denominators and should not be averaged.
**Temperature:** 30.9 °C · **Salinity:** 34.5
**Photo review:** all 43 frames examined (all 43 sit one level down in the `BiPb68-CoralNet` subfolder; the parent folder holds no stills of its own)
**Representative photos:** P4160728.jpg, P4160742.jpg, P4160746.jpg, P4160749.jpg, P4160762.jpg

BIPB68 sits at the coral-abundant end of the Chagos distribution: **55.1% transect coral cover against 35.0% algae**, with bare substrate reduced to just 4.6% of the benthos and non-coral invertebrates only 5.3%. Between coral, algae and crustose coralline algae (9.4% of the substrate categories), almost the entire reef surface is biologically occupied. Twenty-seven coral genera were recorded — one of the more genus-rich transect sets in the Chagos dataset (compare BIPB62's sixteen) — yet the assemblage is still carried by one genus: ***Acropora* holds 27.76% of the benthos, roughly 50% of all coral recorded**, with *Echinopora* a distant second at 8.35% (15% of coral) and *Porites* third at 4.60% (8% of coral). *Lobophyllia* (2.78%), *Goniastrea* (2.29%), *Halomitra* (1.20%), *Turbinaria* (1.18%) and *Galaxea* (1.08%) form the next tier, and a long tail of nineteen further genera — *Pocillopora*, *Fungia*, *Favia*, *Platygyra*, *Stylophora*, *Symphyllia*, *Favites*, *Leptoseris*, *Alveopora*, *Ctenactis*, *Montipora*, *Physogyra*, *Herpolitha*, *Pachyseris*, *Leptastrea*, *Pavona*, *Hydnophora*, *Acanthastrea* and *Cyphastrea* — each contribute under 0.5% of the benthos. Turf algae (13.6% plus 2.6% turf-with-sediment) and erect algae (8.3%) account for most of the 35.0% algal cover; macroalgae proper is negligible at 0.9%.

**The four transects trace a clear decline in coral cover with depth, and a genus handover along the way.** D1 carries 58.3% coral of which *Acropora* alone is 42.70% — 73% of the coral on that transect — with *Porites* a distant second (10.30%, 18% of the coral present); this is close to a two-genus reef. D2 holds the site's highest cover at 64.4%, still led by *Acropora* (40.69%, 63% of coral) but with *Echinopora* now clearly second (11.89%, 18% of coral) and *Lobophyllia* appearing (2.63%). D3 holds 63% coral on the profile's lowest algal cover (25.7%): *Acropora* has fallen to 27.67% (44% of coral), *Echinopora* holds near-steady at 11.00% (17%), and *Lobophyllia* has grown to 7.00% (11%) alongside *Halomitra* (4.67%) and *Pocillopora* (3.00%) — the widest genus spread of the four transects, with a larger unlisted tail than any other depth. D4 is the outlier: coral cover collapses to 34.5% — roughly half the D2 figure — while algal cover peaks at 47%, the highest of the profile. *Acropora* drops out of the leading six genera entirely; the transect is instead led by *Echinopora* (10.50%, 30% of its coral) and *Goniastrea* (9.00%, 26%), with *Porites* (4.50%) and *Galaxea* (4.00%) filling out the tier. **The site-level figure of 27.76% *Acropora* describes no single transect**: it is the average of a near-monoculture shallow zone and a low-cover, algae-heavy, *Acropora*-depleted deep zone (D-code order is used here as the standard shallow-to-deep convention for this dataset; per-transect depths in meters are not published for BIPB68 — Flag 4).

The photographs are dominated by exactly the structure D1–D3 predict: wide, tabular and corymbose *Acropora* fields tiling the reef slope into blue water. P4160728, P4160747, P4160760, P4160765, P4160766 and P4160770 all show broad plating and table colonies — golden-tan, olive and grey — stacked across the frame with corymbose and staghorn thickets filling the gaps, a visual match for D1/D2's 63–73%-*Acropora* composition. Massive and lobate growth forms consistent with *Porites*, *Goniastrea* or massive-form *Echinopora* appear as large cream-to-olive domes and boulders in P4160746, P4160751, P4160762, P4160764, P4160768 and P4160769, often anchoring the foreground while tabular *Acropora* recedes into the background — the visual counterpart of the D4 transect. P4160742 and P4160763 are close-in, high-diversity frames packed with purple, cream, yellow-green and blue-tipped branching and digitate colonies (forms consistent with *Stylophora*, *Pocillopora* and *Acropora* growth sub-types) growing shoulder to shoulder with encrusting purple coralline algae — the photographic counterpart of the 9.4% CCA and the site's 27-genus richness. Open sand patches and bare pavement appear in several of the wider frames (P4160743, P4160748, P4160768), consistent with the algae-and-bare-substrate increase recorded at D4.

**Condition is consistent between the transects and the imagery, and both point to a healthy reef.** The published image-based bleaching figure of just **0.87%** is among the lowest recorded in the Chagos dataset, and nothing in the 43 frames contradicts it: colony pigmentation throughout is typical tan, olive, cream, purple and gold, with none of the stark white, tissue-intact colonies flagged at other Peros Banhos sites such as BIPB62. Two frames (P4160767, P4160769) do show large pale cream-white massive dome colonies in the mid-background; unlike genuine bleaching, neither shows adjacent pigmented tissue of the same colony for contrast, and the pattern is most consistent with a naturally pale *Porites*-type colony rather than an active bleaching event — flagged for the record but not read as bleaching (Flag 3).

Reef fish are a minor but repeated presence in the imagery: butterflyfish consistent with *Chaetodon* (both a black-and-white banded morph and an orange-and-white banded morph) forage over the branching *Acropora* in P4160749 and P4160761, and a dark, torpedo-shaped silhouette crosses the outer slope in the background of P4160762 — too distant and backlit to identify with confidence, possibly a shark or large jack (Flag 2). A diver is visible for scale in P4160730 and P4160743, confirming these are wide-angle reef-slope shots rather than close macro work.

<b>Assemblage composition.</b> Formal surveys give 55.1% coral, 35.0% algae and only 4.6% bare substrate across four transects, the coral roughly 50% *Acropora* on average but ranging from a 73%-*Acropora* shallow transect to an *Acropora*-depleted, *Echinopora*/*Goniastrea*-led deep transect where cover halves and algae peaks. The photographs document both ends of that gradient — tabular and corymbose *Acropora* fields in the shallower-looking imagery, massive lobate domes and a high-diversity branching/digitate assemblage with abundant coralline algae in the rest — and show no photographic evidence contradicting the near-zero published bleaching figure.

**Flags:** (1) **Transect-vs-photo cover mismatch of roughly 21 percentage points.** Formal transects average 55.1% coral, while both CoralNet points (33.6%) and Coralscapes masks (33.9%) — scored on all 43 available frames, so this is not a frame-count shortfall — sit close to the D4 transect value (34.5%) rather than the site mean. This may reflect the 43 photographed frames disproportionately sampling the deeper, lower-cover, algae-dominated part of the reef profile rather than the shallow near-monoculture *Acropora* zone that pulls the transect average up, but this has not been confirmed and the three products should not be averaged. (2) **Unidentified dark silhouette in P4160762.jpg**, mid-water over the outer slope — possibly a shark or large jack, too distant and backlit for confident identification. (3) **Pale massive dome colonies in P4160767.jpg and P4160769.jpg** could be misread as bleaching on a quick pass; neither shows the adjacent-pigmented-tissue contrast seen in genuine partial bleaching elsewhere in the Chagos set, and the published site bleaching figure is only 0.87%, so a naturally pale *Porites*-type colony is the more likely explanation. Flagged for the record, not asserted as bleaching. (4) **Per-transect depths in meters are not published for BIPB68** — only D-codes (D1–D4). The depth-zonation paragraph above follows the shallow-to-deep D-code convention used elsewhere in this dataset, but that ordering has not been independently confirmed for this site. (5) All 43 BIPB68 frames sit in the `BiPb68-CoralNet` subfolder; the parent `BiPb68-finished` folder holds no stills of its own.

**Benthic data:** [Download BIPB68 benthic survey data (CSV)](../benthic_data/BIPB68_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).