Metrics

Health Score

A 1–6 Likert scale where 1 = healthiest.

A 1–6 Likert scale where 1 = healthiest, 6 = poorest health.

Raw value	Meaning
1	Healthiest
3	Moderate
6	Dead

Alive / dead threshold: A health score of 6 = dead. A fragment is considered alive when health < 6. This threshold is how the methodology's health assessment maps to survival calculations.

Note on direction: Health and bleach scores share the same 1–6 scale and are read in the same direction — lower is better in both cases.

Provenance

The 1–6 health scale is adapted from the CoralWatch Coral Health Chart (Siebeck et al. 2006), which uses a 1–6 colour brightness scale to assess bleaching state. CoralWatch maps 1 = lightest (most bleached) to 6 = darkest (healthiest). Coral Gardeners inverts this direction so that 1 = healthiest — keeping both health and bleach scales consistent, where lower numbers always mean better condition.

Siebeck, U.E., Marshall, N.J., Klüter, A. & Hoegh-Guldberg, O. (2006). Monitoring coral bleaching using a colour reference card. Coral Reefs, 25, 453–460. doi:10.1007/s00338-006-0123-8

Methodology note: The 2025 Methodology Manual references "health condition" monitoring (ReefApp, 20% of nursery corals) but does not define the 1–6 scale or its provenance. The scale definition is operational practice. The scale is planned to move from 1–6 to 1–5.