### BIVB108 — Victory Bank
**CRD page:** [Nelson Island, Victory Bank & Blenheim Reef Surveys](https://coralreefdiagnostics.com/new-page-4)

**30 Apr 2015**
**GPS:** 5.52648°S, 72.22646°E
**Setting:** protected submerged lagoon-side reef, 26.5 m — **the reef-type cell is blank in the published table** (see Flags)
**Coral cover:** 45.7% (15 formal transects across 3 depth strata, D2–D4; **algal cover 43.8%**) · **published image bleaching:** 10.7%
**Live hard coral cover across methods:** formal transects 45.7% · CoralNet points 18.9% · Coralscapes masks 19.1% (3 frames). These products have different sampling footprints and denominators and should not be averaged.
**Temperature:** 30.2 °C · **Salinity:** 34.2
**Photo review:** all 15 of 15 frames examined (single dive, 30 Apr 2015, 14:20–14:56 UTC by file `DateTimeOriginal`)
**Representative photos:** P4300902.jpg, P4300901.jpg, P4300884.jpg, P4300922.jpg, P4300883.jpg

BIVB108 sits inside the lagoon at Victory Bank, on submerged reef at 26.5 m under protected exposure, and it carries **above-average coral cover for the archipelago: 45.7% coral against 43.8% algae, ranking 34th of 109 Chagos sites for coral cover and 39th of 109 for algal cover.** Unlike most of the high-cover Chagos sites, the algal budget here is genuinely turf-led rather than coralline: fleshy turf (PTTS) is 13.9% of total benthos, **24th-highest of 109 sites**, against crustose coralline algae (PCCATS) at 11.9%, which is only **68th of 109** — a reversal of the ranking pattern seen at hard, well-grazed forereef sites. Turf-plus-sediment (PTSTS) adds 6.5%, macroalgae (PMTS) 6.4% and erect algae (PETS) 5.1%. Bare substrate (PB) is 7.2% and non-coral invertebrates (PITS) an unusually low 3.4%. Coral, algae, invertebrates and bare rock sum to exactly 100.0% at the site level.

Coral cover is spread over a broad taxon list: **28 nonzero genera, 36th of 109 for genus richness.** All values below are percent of total benthos, not percent of coral. *Acropora* leads decisively at 18.56% of the benthos — **41% of all the coral at the site** — followed by *Porites* 7.54% (17%), *Favia* 3.21% (7%), *Pocillopora* 2.98% (7%) and *Stylophora* 2.26% (5%); those five hold 76% of the coral recorded. Then *Millepora* 1.34%, *Montipora* 1.28%, *Platygyra* 1.15%, *Gardineroseris* 1.06% and *Isopora* 0.94%, and a tail of 18 further genera — *Leptastrea*, *Favites*, *Goniastrea*, *Pavona*, *Montastrea*, *Astreopora*, *Fungia*, *Echinopora*, *Heliopora*, *Symphyllia*, *Cyphastrea*, *Acanthastrea*, *Oxypora*, *Psammocora*, *Ctenella*, *Galaxea*, *Hydnophora* and *Leptoseris* — each under 0.85% of the benthos. Two entries in that tail are worth naming: *Heliopora* (0.24%), the blue octocoral, and *Ctenella* (0.05%), a monotypic genus whose only species, *C. chagius*, is named for this archipelago. **The 28 genus percentages sum to 45.6643% against a published site cover of 45.6810% — a shortfall of 0.017 percentage points**, which is a rounding artefact rather than a missing taxon, but it is reported here rather than reconciled silently.

**The three depth strata show coral cover nearly doubling from the shallowest station downward, with *Acropora* driving essentially all of the increase and the turf-and-sediment ground disappearing as it does so.** D2 (4 transects, the shallowest stratum sampled) carries just 29.5% coral against the profile's highest algal cover, 59.0% — and that algal budget is the turf-heavy one, PTTS 18.3%, PTSTS 15.5%, PCCATS 14.3%, PMTS 8.8%, PETS 2.3%. The coral there is comparatively even: *Acropora* 7.50% of the benthos (only 25% of that transect's coral), with *Pocillopora* 4.75% and *Porites* 4.75% level behind it, then *Montipora* 2.25%, *Favia* 1.75% and *Stylophora* 1.50%. At D3 (7 transects) cover jumps to 54.1% and algae falls to 38.5%, and **the assemblage tips hard toward *Acropora*, which triples to 22.83% of the benthos — 42% of that transect's coral** — ahead of *Favia* 5.09%, *Stylophora* 4.54%, *Porites* 4.43%, *Gardineroseris* 2.29% and *Millepora* 2.26%. At D4 (4 transects) cover stays high at 53.4% while algae drops further to 33.8%, and **turf-plus-sediment all but vanishes, from 15.5% at D2 to 0.45% here**; *Acropora* peaks at 25.35% (47% of that transect's coral) with *Porites* second at 13.45% (25%), then *Pocillopora* 2.85%, *Favia* 2.80%, *Leptastrea* 1.85% and *Pavona* 1.05%. **The site-level figure of 18.56% *Acropora* therefore describes no single stratum**: it averages a shallow station at well under half that value, where *Acropora*, *Pocillopora* and *Porites* are nearly co-dominant over turf-and-sediment ground, against two deeper stations where *Acropora* holds two to three times as much benthos on progressively cleaner substrate. Coral and algae together account for 88.5%, 92.7% and 87.2% of the benthos at D2, D3 and D4 respectively, so 7–13% at each stratum is bare substrate or non-coral invertebrate cover that this depth-level summary does not itemise.

The photographs — all 15 frames — document a spectacular, near-continuous coral field that visually reads even higher than 45.7%, and they are unusually consistent with one another. P4300884, P4300919 and P4300920 are wide shots of an essentially unbroken carpet of small corymbose and digitate colonies running to the limit of visibility, with almost no open sand and only narrow pavement gaps; P4300921 shows the same ground from closer in, where dense maroon and deep-purple *Pocillopora*-type and *Stylophora*-type clumps sit between pale corymbose *Acropora*-type colonies — the deep purple-red pigmentation recurring through the set is characteristic of chromoprotein-pigmented colonies rather than of algal overgrowth. Large tabular *Acropora* plates a metre or more across are the structural signature of the deeper frames: P4300901, P4300902, P4300903 and P4300905 each carry several, some tan and healthy, others stark white. P4300883 shows a broad healthy tan table in the foreground against a mixed field behind. P4300900 and P4300922 are close-range frames showing the substrate between colonies: maroon-purple crustose coralline crust, small encrusting sponges, and turf-coated dead framework. Reef fish are present but sparse and undistinguished in the set — scattered damsels, butterflyfish and small anthias — and no large-animal encounter, COTS individual, *Drupella* aggregation, disease lesion or predation scar was identified in any frame.

**Condition is the finding that the photographs press hardest on, and they suggest the published figure understates it.** The published image-based bleaching value is **10.7%, ranking 25th of 98 Chagos sites carrying a value — inside the top quartile for bleaching severity** — and the frames corroborate a real, unambiguous, colony-scale bleaching signal rather than a marginal one. **P4300902 is the clearest single record: a large tabular colony rendered brilliant chalk-white across its entire surface, surrounded by several more white tables and white branching colonies, with fully pigmented tan and maroon colonies in the same frame providing within-frame contrast that exposure or strobe artefact cannot explain.** P4300901 shows a second fully white table beside a healthy tan one. P4300903 places a large healthy tan table directly beside white branching colonies on both flanks. P4300884 is a wide shot in which dozens of colonies across the field are stark white. P4300922 contains a completely white plate/foliose colony in the foreground alongside pale lavender branching colonies. Because a single still cannot separate a freshly bleached colony from a very recently dead one — both read chalk-white before turf colonises the skeleton — these are recorded as **frame-level bleaching-or-recent-mortality observations, not as a recalculated site percentage**. The important point for downstream use is directional: the visual severity in this 15-frame set is at least as high as the published 10.7%, and an independent point recount in `chagos_pct_bleached_recomputed.csv` also runs higher (12.8%). See Flags.

<b>Assemblage composition.</b> Formal transects give 45.7% coral against 43.8% algae across 28 nonzero genera, led by *Acropora* (18.6% of benthos, 41% of all coral), *Porites* (7.5%), *Favia* (3.2%), *Pocillopora* (3.0%) and *Stylophora* (2.3%), with the western Indian Ocean endemic *Ctenella* and the blue octocoral *Heliopora* in the tail. The depth profile runs 29.5% cover at D2 — turf-and-sediment ground, *Acropora* only a quarter of the coral — to 54.1% at D3 and 53.4% at D4, where *Acropora* takes 42–47% of the coral and turf-plus-sediment falls to under half a percent. The photographs match: a near-continuous field of corymbose and digitate colonies punctuated by metre-scale tabular *Acropora*, with deep purple-red pigmented *Pocillopora*/*Stylophora* clumps between them — and with clear, colony-scale bleaching in at least five of the 15 frames, consistent with this site's top-quartile published bleaching figure.

**Flags:** (1) **THE CV FIGURES REST ON A 3-FRAME SUBSET.** `chagos_multimethod_cover_by_site.csv` records `n_photos = 3` for BIVB108, against **15 frames in the photo folder** and **11 images** used in `chagos_pct_bleached_recomputed.csv`. Three source files therefore disagree on how many images were scored at this site (3 / 11 / 15). The CoralNet (18.9%) and Coralscapes (19.1%) figures above should be read as resting on three frames only and are correspondingly fragile. **Someone should establish which image subset each product actually used.** (2) **Multi-method deviation is large.** CoralNet points (18.9%) and Coralscapes masks (19.1%) sit ~27 percentage points below the formal-transect figure (45.7%; deviation range −26.8 to −26.6 pp). Do not average the three figures; the transect value is treated as ground truth for cover. (3) **The CoralNet points figure is a CV product, not verified ground truth**; point-annotation data corpus-wide is roughly 76% unconfirmed machine output. (4) **BLEACHING SOURCE MISMATCH — flagged for action.** `chagos_pct_bleached_recomputed.csv` recomputes 12.82% for this site (10 bleached of 78 coral points, 330 points, 11 images) against the published 10.70%, a **+2.12 pp delta explicitly marked `MISMATCH`** in that file. The published `Mean(%bleaching)` column is authoritative here and the header quotes it verbatim; the recomputed figure is recorded only because the mismatch is logged and unresolved. Bleaching is never recomputed from point counts for publication. (5) **The photographs suggest the published bleaching figure is conservative.** At least five of 15 frames (P4300884, P4300901, P4300902, P4300903, P4300922) contain colony-scale, fully white colonies with pigmented colonies in the same frame. No site percentage is derived from this; it is logged as a direction-of-error note. (6) **White colonies cannot be separated from recently dead ones in a single still.** These records are "bleached or recently dead", not confirmed active bleaching; no lesion margin or tissue-loss band consistent with disease was visible in any frame. (7) **THE REEF-TYPE CELLS ARE BLANK.** `reef type`, `reef type-simplied` and `exposure-original` are all empty for BIVB108 in `Chagos benthic data by site (n=109).csv`. Only `exposure-revised` = protected, `reef location` = lagoon, `lagoon` = inside and `reef emergence` = submerged are populated. The header above states what is recorded and invents no class. (8) **Genus percentages sum to 45.6643% against a published cover of 45.6810%** — a 0.017 pp shortfall, reported rather than reconciled. (9) **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 strata, and the 26.5 m in the header is the site-level survey depth, not the depth of any one transect. **No D1 stratum exists for this site**, so the shallowest reef zone is unsampled. (10) **Replication is uneven across strata** — D2 n=4, D3 n=7, D4 n=4 transects — so the D3 values carry more weight than the D2 and D4 values in the site-level mean. (11) **Coral and algae leave 7–13% of the benthos unaccounted for at each depth stratum**, likely bare pavement and non-coral invertebrate cover not itemised by depth in this dataset. (12) **No COTS, disease, *Drupella* or predation scarring was observed** across the full 15-frame review — an explicit absence-of-evidence finding. (13) **CRD page URL is the `new-page-4` placeholder** shared by all Nelson Island / Victory Bank / Blenheim sites, and needs repointing with the rest of that group once the page is renamed. (14) **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`). Treat the site bleaching percentage as the weaker of the two published numbers, and never read it as a diver's field estimate. (15) **Ranks off the `Mean(%bleaching)` column are approximate** — that column carries at least one known bad value (BITB58 listed at 22.22% against a corrected 0.77%), so the 25th-of-98 placement has not been independently audited. (16) **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 **10.70%, rank 35 of 110** (1st training: 10.70%, rank 31 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 BIVB108 benthic survey data (CSV)](../benthic_data/BIVB108_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).