A recreational specialty that teaches certified divers to make a repeatable, relative-index census of reef life — from 360-degree video capture, an AI-assisted first-pass count you confirm by hand, and species IDs settled in iNaturalist.
Ask two divers how a reef is doing and you get two impressions. A census replaces impression with a number you can compare — this reef, this method, this count, repeated next season. Decline in reef life is slow and easy to miss, because each visit gets measured against memory instead of a record. Counting the same way twice turns "it felt emptier" into something specific.
The output is a relative index, not an absolute population — but made honestly and the same way each time, it's enough to show change. And once you've counted a reef, you stop seeing an undifferentiated shimmer of life and start seeing who is actually there.
You capture the reef in 360-degree video, let an AI make a first-pass count of what it sees, then confirm every number by eye. Species are identified through iNaturalist. The pipeline produces a mean relative-density index with a stated noise floor, plus community diversity measures — a documented record you can re-run next season to reveal what changed.
Every count carries its provenance: which model and version produced the first pass, the raw machine number, and your human-confirmed count. The raw AI number is logged but is never the count of record — the number you stand behind is the one you verified.
Client-side calculators take your human-confirmed counts and compute the census metrics — no login, no app, works offline once loaded.
The mean relative-density index across your confirmed counts for a site and season.
The threshold below which a difference between surveys can't be told from method noise.
Two classic diversity indices computed from your species proportions.
Evenness, plus the unified Hill diversity profile at q = 0, 1, 2.
Bray–Curtis and Jaccard between two surveys — how much of the community changed.
One tabbed app. Confirmed counts in, census metrics out.
Reef Demographer is an independent distinctive specialty — not a PADI-owned course. It builds on comfortable buoyancy and navigation at roughly the Advanced Open Water level, since a clean census depends on holding position and staying off the reef while the camera does the work.
The exact required and recommended certifications are set in the course guide. Ask us for the current list and whether it counts toward Master Scuba Diver.
Send your questions and we'll get back to you with dates, locations, and guidance — wherever you're based.