PADI Distinctive Specialty
Reef Demographer
Count the life. Watch it change. 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.
Why count reef life?
It stops being a blur.
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.
What you'll make
One census, provenance and all
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.
The report
Turn confirmed counts into an index
Client-side calculators take your human-confirmed counts and compute the census metrics — no login, no app, works offline once loaded.
Relative Density
The mean relative-density index across your confirmed counts for a site and season.
Noise Floor
The threshold below which a difference between surveys can't be told from method noise.
Shannon & Simpson
Two classic diversity indices computed from your species proportions.
Pielou & Hill
Evenness, plus the unified Hill diversity profile at q = 0, 1, 2.
Turnover
Bray–Curtis and Jaccard between two surveys — how much of the community changed.
Open the report →
One tabbed app. Confirmed counts in, census metrics out.
Before the course
Prerequisites & recommendations
Reef Demographer is an independent distinctive specialty — not a PADI-owned course. A clean census depends on holding position and staying off the reef while the camera does the work.
Required: PADI Advanced Open Water Diver, PADI Enriched Air (Nitrox) Diver, PADI Peak Performance Buoyancy Specialty, and Reef Cartographer Distinctive Specialty.
Counts as one of the five specialties toward PADI Master Scuba Diver.
The series
From reading a coral to leaving the record
Reef Demographer is the third of five independent specialties that build on one another — each worthwhile alone, and together a recreational citizen-science pathway: from knowing what a coral is and reading its condition, to mapping a reef, to reading its life, to measuring the water all of it sits in, to leaving a record of all four.
CoralWatch Coral Health Chart
What a coral is, how it bleaches, and how to record its color colony by colony into a global database — CoralWatch's course, taught under their permission.
Reef Cartographer
Turn a reef's shape into a record — acoustic and optical mapping of the structure that life lives on.
Reef Demographer
A repeatable, relative-index census of who actually lives there — and how that changes, season over season.
Reef Hydrocaster
The water all of it is sitting in — its heat, its light, its clarity, each with a measured uncertainty.
Reef Chronicler
What the reef looks like, added to the other three and filed as one dated entry a stranger can re-occupy.
Interested? Get in touch.
Send me your questions and I'll get back to you with dates, locations, and guidance — wherever you're based.