### BITB48 — Three Brothers
**CRD page:** [Three Brothers/Central Chagos Coral Surveys BITB38-BITB49 (Mar 2015)](https://coralreefdiagnostics.com/three-brotherscentral-chagos-20150321-to-0324)

**24 Mar 2015**
**GPS:** 6.06785°S, 71.67516°E
**Setting:** intermediate-exposure submerged lagoonal patch reef, inside the lagoon — **the published depth cell is blank**, so the site is placed only by strata D3–D4 with no metre value
**Coral cover:** 32.4% (14 formal transects, D3–D4; **algal cover 37.0%**) · **published image bleaching:** the `Mean(%bleaching)` cell is blank for this site — no value exists, and none may be inferred
**Live hard coral cover across methods:** formal transects 32.4% · CoralNet points — none · Coralscapes masks — none. **No imagery exists for BITB48, so neither computer-vision product was ever generated and no multi-method comparison is possible here.** Where those products do exist elsewhere in Chagos they carry different sampling footprints and denominators from the transects and should not be averaged with them; at this site the transect figure stands alone.
**Temperature:** published cell blank · **Salinity:** published cell blank
**Photo review:** **none — no photographs exist for this site anywhere.** No folder under `edited site photos for website` resolves to site number 48 under any prefix or casing, and the site returns zero photo directories and zero frames. The site was dived and formally surveyed by the Living Oceans Foundation team, but no habitat photographs were taken or retained. This is a field-record gap, not a mislaid folder. **Everything below therefore rests on transect point counts alone, and reef condition at BITB48 cannot be assessed** — bleaching, tissue loss, disease, predation scarring, COTS, fish and macrofauna are all simply *unavailable*, and must never be read as zero or inferred from neighbouring sites.

BITB48 is a patchy, algae-dominated lagoonal patch reef on the inner side of Three Brothers. Fourteen formal transects across two depth strata give **32.4% live coral against 37.0% algae — 71st of 109 Chagos sites for coral cover and 63rd of 109 for algal cover**, both squarely mid-pack and both below the archipelago's coral mean of 37.9%. Within Three Brothers it is sixth of ten sites, just under the island mean of 35.3%. Bare substrate is 19.0% and non-coral invertebrates 11.6%, so coral, algae, bare rock and invertebrates together account for essentially the whole benthos. The raw transect mean is 33.61% ± 14.06 SD over a **12–62% range**, so the tidy site figure conceals a fivefold swing between individual transects; on this reef, "32%" is an average of very unequal ground rather than a description of any one patch.

Coral is spread across **22 nonzero genera — 70th of 109 sites for genus count**, mid-to-low for the archipelago. All values below are **percent of total benthos, not percent of coral**, and the 22 genus columns sum to 32.45%, an exact match to the published cover figure. *Porites* leads at **11.97% of the benthos (36.9% of the live coral present)**, followed by *Acropora* **9.27% (28.6%)** — together those two genera supply about 65% of all coral recorded. Behind them: *Pocillopora* 1.98%, *Montipora* 1.89%, *Platygyra* 1.29%, *Favites* 1.25% and *Leptastrea* 1.03%. A fifteen-genus tail below 1% of the benthos — *Favia*, *Hydnophora*, *Echinopora*, *Acanthastrea*, *Cantharellus*, *Montastrea*, *Millepora*, *Pavona*, *Stylophora*, *Ctenella*, *Goniastrea*, *Astreopora*, *Coscinaraea*, *Oxypora* and *Cyphastrea* — adds the diversity without adding much cover. Diversity indices computed from these columns are H′ = 1.94, evenness J′ = 0.63, effective diversity 6.99: a two-genus reef with a long, thin tail.

**The depth contrast at BITB48 is compositional rather than quantitative, and it is a clean shallow-branching to deep-massive handover.** Total cover barely moves — D3 averages 34.49% coral against 39.15% algae (11 transects), D4 averages 30.40% against 34.87% (3 transects) — a four-point difference that is trivial beside the 12–62% spread *within* D3 alone. What changes is who holds the space. At D3, *Acropora* leads at 11.67% of the benthos with *Porites* second at 8.20%, *Pocillopora* third at 3.96%, then *Montipora* 2.25%, *Leptastrea* 2.05% and *Favites* 1.89%, across 21 genera. At D4 that order inverts: ***Porites* nearly doubles to 15.73% while *Acropora* falls to 6.87%**, *Platygyra* climbs from 0.11% to 2.47%, *Hydnophora* from 0.20% to 1.13% — and ***Pocillopora* and *Leptastrea* both drop out entirely**, from 3.96% and 2.05% to exactly zero, on 15 genera. The substrate tells the same story: bare substrate rises steeply from 10.98% at D3 to **26.93% at D4**, while non-coral invertebrates halve (15.38% → 7.80%) and sediment-laden turf falls from 17.05% to 9.27%. Crustose coralline algae is nearly flat (14.29% → 15.13%) and plain turf barely moves (5.02% → 6.07%). **Read together, the shallower stratum is a branching *Acropora*/*Pocillopora* patch reef over sediment-bound turf; the deeper one is a sparser, massive-*Porites* and faviid ground over a quarter bare rock.** The site-level figures of 11.97% *Porites* and 9.27% *Acropora* describe neither stratum accurately.

The algal budget is unusual for its turf composition rather than its size. Of 37.0% total algae, **crustose coralline algae is 14.71% (51st of 109 sites) and sediment-laden turf is 13.16% — nearly as large a share**, with plain turf 5.54% (90th of 109, in the low quartile), macroalgae 2.47%, erect algae 1.12% and cyanobacteria exactly zero. That the sediment-turf category rivals CCA is the notable feature: this is a lagoonal patch reef with a real sediment signal, concentrated in the shallower D3 stratum, and it sits alongside a mid-pack CCA reading rather than replacing it. Across the fourteen transects, dead coral averages 0.96% (range 0–5%) and **recently dead coral reads exactly 0.00% on every transect** — whatever mortality this reef has experienced is not recent, though with no imagery there is no independent check on that.

<b>Assemblage composition.</b> Fourteen transects at two strata give 32.4% coral against 37.0% algae across 22 nonzero genera, led by *Porites* (11.97% of benthos, 36.9% of coral) and *Acropora* (9.27%, 28.6%), which between them hold about two-thirds of the coral. The depth profile hands the reef over from a shallow *Acropora*/*Pocillopora* assemblage on sediment-laden turf at D3 to a *Porites*/*Platygyra*/*Hydnophora* assemblage over 27% bare substrate at D4, with *Pocillopora* and *Leptastrea* disappearing completely between the two. **There is no photographic record whatsoever, so none of this can be corroborated visually and no statement about the reef's condition — bleaching, mortality, disease, predation or fauna — is possible at BITB48.**

**Flags:** (1) **NO PHOTOGRAPHS EXIST FOR THIS SITE.** Zero photo directories resolve to site number 48 under any prefix or casing. There are consequently no CoralNet points, no Coralscapes masks, no multi-method comparison, and **no basis for any condition assessment**. Bleaching, disease, predation, COTS and fauna are unavailable — not zero — and must not be inferred from formal cover or from neighbouring Three Brothers sites. (2) **THE PUBLISHED `Mean(%bleaching)` CELL IS BLANK** for BITB48; the site carries no bleaching value in either CoralNet training run and appears in the `formal vs. informal comparison` sheet only as a placeholder. Corpus-wide the published bleaching figure is a **computer-vision product**, not an in-situ observation, and per-image human-vs-model agreement is r = 0.40 for bleached against r = 0.72 for live hard coral (`CHAGOS_MULTIMETHOD_README.md`) — but at this site there is no figure at all to caveat. (3) **THE PUBLISHED DEPTH, TEMPERATURE AND SALINITY CELLS ARE ALL BLANK.** BITB48 is the only site in this photo-less group missing all three environmental readings; depth exists only as strata D3–D4, with no metre value anywhere. Recommend backfilling from the raw LOF datasheet if it can be found. (4) **THE SITE FIGURE IS THE UNWEIGHTED MEAN OF TWO STRATUM MEANS, NOT THE MEAN OF FOURTEEN TRANSECTS** — (34.49 + 30.40) / 2 = 32.45, whereas the raw fourteen-transect mean is 33.61%. **D4 rests on only three transects yet carries a full 50% of the headline number**, against eleven transects at D3. That is a thin stratum by the archipelago's own standard and should be flagged wherever the 32.4% figure is quoted. (5) **THE SITE MEAN HIDES A FIVEFOLD TRANSECT RANGE** (12–62%, SD 14.06 ≈ 42% of the mean), and D3 alone spans that entire range: this reef is heterogeneous at transect scale, and 32.4% is not a uniform condition. (6) **POINT-COUNTS ARE MIXED AND UNWEIGHTED** — nine 100-point and five 500-point transects, 3,400 points total, pooled without effort weighting. This affects how the SD reads and slightly changes what a "mean transect" means. (7) **Integrity checks pass:** the 22 genus columns sum to 32.45% against a published 32.4455%; the six algal categories sum to 37.01% against a published 37.0061%. Both reconcile within rounding, with no unexplained shortfall. (8) **Genus count of 22 sits 70th of 109**, mid-to-low, and the site is in the lower half of the effort distribution at 3,400 points — corpus-wide, recorded richness scales with survey effort, so the count is a floor rather than a ceiling. (9) **Recently dead coral reads 0.00% on all fourteen transects** — an explicit zero from the point counts, but with no imagery it cannot be cross-checked, and it says nothing about bleaching, which is not measured here at all.

**Benthic data:** [Download BITB48 benthic survey data (CSV)](../benthic_data/BITB48_benthic.csv) — scleractinian cover by genus with full names, plus substrate and algal categories (bare substrate, CCA, turf, sediment-laden turf, macroalgae, erect algae, non-coral invertebrates), from the LOF BIOT-1 survey (Mayfield & Dempsey 2026, *Oceans*, supplemental file S1).