### BIVB99 — Victory Bank
**CRD page:** [Nelson Island, Victory Bank & Blenheim Reef Surveys](https://coralreefdiagnostics.com/new-page-4)

**27 Apr 2015**
**GPS:** 5.53102°S, 72.24508°E
**Setting:** protected submerged lagoonal patch reef, 30.1 m (leeward in the master workbook — see Flag 3)
**Coral cover:** 55.6% (2 formal transects, D3–D4; **algal cover 36.4%**) · **published image bleaching:** 6.8%
**Live hard coral cover across methods:** formal transects 55.6% · CoralNet points 16.1% · Coralscapes masks 35.4% (11 frames). These products have different sampling footprints and denominators and should not be averaged.
**Temperature:** 29.9 °C · **Salinity:** 34.2
**Photo review:** all 11 frames examined
**Representative photos:** P4270889.jpg, P4270897.jpg, P4270864.jpg, P4270905.jpg, P4270848.jpg

**BIVB99 is a blue-coral reef, and the strongest one in the archipelago.** ***Heliopora* holds 44.14% of the benthos — 79% of all coral recorded** — well above the 31.33% at BITB58, the only other site where the genus dominates. Coral cover is 55.6%, 16th of the 109 Chagos sites, against 36.4% algae. Every other genus is marginal: *Stylophora* 4.34%, *Acropora* 3.13%, *Pocillopora* 1.29%, then *Montipora* and *Hydnophora* at 0.38%, *Favia* 0.33% and *Echinopora* 0.30%, with a further tail below that across 17 non-zero codes. Coralline algae hold 13.1% of the benthos, erect algae 9.8%, turf 9.9%, bare substrate 6.7%, macroalgae 3.4% and non-coral invertebrates only 1.4%.

**Both transects are *Heliopora* stands and the shallower one is nearly a monoculture.** D3 carries 64.5% coral with ***Heliopora* at 54.38% — 84% of the coral on that transect** — across 12 genera. D4 falls to 46.6% with *Heliopora* at 33.90% (73% of coral) across 14 genera, and *Acropora* rising to second place at 4.65%. Algal cover is high and steady in both bands (34.4% and 38.4%).

**This site supplies the photographic evidence that BITB58 lacked.** The BITB58 shard flags that its 93%-cover blue-coral transect was never captured on camera — the photographer shot the tabular *Acropora* zone instead. Here the thicket is the subject. P4270864 and P4270886 show extensive vertical relief where upright folded sheets occupy most of the available hard surface; P4270897 shows repeated ridges and folded blades standing at multiple heights; P4270904 through P4270906 retain that dense structure, interrupted by compact branching colonies and bright red-purple encrusting material. The sequence begins at a sandier margin in P4270848, with open sand and scattered low colonies beside a table in the foreground, then moves quickly into the thicket. **The upright, folded, blade-like growth form in these frames is exactly what a *Heliopora coerulea* stand looks like**, and it is the best imagery of the genus in the Chagos set.

The habitat is structurally intricate, its complexity generated by upright sheets rather than broad tables, with narrow channels and cavities between closely packed vertical blades. Red, pink and purple encrusting surfaces are abundant beneath the sheets; some are compatible with crustose coralline algae — which the transects put at 13.1% — while others could be sponges or other encrusting organisms, and the stills do not support a single taxonomic label for every patch. Small reef fishes use the narrow spaces between folds and branches throughout.

Bleaching is conspicuous but confined to the minority growth form. P4270889 shows several compact branching colonies nearly white across intact branches, immediately adjacent to purple-pigmented compact colonies and dark upright sheets; smaller white colonies recur in P4270905. **The dominant *Heliopora* sheets are not the affected component** — they commonly carry pale rims, but those narrow margins may be normal growth, edge lighting or species coloration and are not classified as bleaching. That the pale colonies occupy only part of a densely pigmented scene is consistent with the low published site value of **6.8%, 55th of 98**, and the close-up deliberately centres the most striking colonies, so no proportion should be inferred from it.

<b>Assemblage composition.</b> Formal surveys give 55.6% coral, 36.4% algae and 1.4% non-coral invertebrates, the coral 79% *Heliopora*. The photographs document the blue-coral thicket itself — upright folded blades at multiple heights — plus heavy red-purple encrustation, a sandier outer margin, and localised bleaching restricted to compact branching colonies rather than the dominant sheets.

**Flags:** (1) **The `HELI` code means *Heliopora*, not *Heliofungia*.** The LOF codebook maps HELI to *Heliofungia*, but the field data are *Heliopora* (A. Mayfield, 2026-08-25): a solitary free-living mushroom coral cannot form 44% cover, `HEFU` is used only 3 times across all 3,067 GRE transects, and the photographs here show unambiguous upright blue-coral growth form. Cross-reference [BITB58](desc_BITB58.md), which carries the same correction. (2) **The three cover methods disagree by up to 39 percentage points** (55.6% / 16.1% / 35.4%). CoralNet in particular reads this site very low — plausibly because a vertical blade thicket presents little horizontal area to a downward point grid — but this is untested. (3) **Exposure differs between sources.** `BIOT-1-MASTER-WkBk.xlsx` records *leeward*; the published `exposure-revised` column records *protected*. The Setting line uses the revised value for corpus consistency; the master value is preserved rather than silently converted. (4) The `Mean(%bleaching)` source column carries at least one known bad value (BITB58 at 22.22% where the corrected figure is 0.77%), so the rank is approximate. (5) No crown-of-thorns starfish, focal fresh feeding scar, diagnostic disease band or tissue sloughing was visible in any retained frame; a few broken or darkened colony margins occur but lack the spatial pattern needed to infer disease from stills. (6) **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 **6.75%, rank 63 of 110** (1st training: 6.75%, rank 62 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 BIVB99 benthic survey data (CSV)](../benthic_data/BIVB99_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).