Metrics

Shannon Diversity Index

A statistical measure of species diversity accounting for richness and evenness.

A statistical measure of species diversity that accounts for both richness (number of species) and evenness (their relative abundance). Higher values indicate a more diverse, resilient population.

Formula:

$H' = -\sum_{i=1}^{S} p_i \ln(p_i)$

Where:

$H'$ = Shannon diversity index
$S$ = number of species
$p_i$ = proportion of individuals belonging to species $i$

Two variants are computed:

Variant	Scope
`shannon_diversity_spp`	Taxonomic diversity — is the species mix representative of the reference site?
`shannon_diversity_mc`	Genetic diversity — are fragments drawn from enough distinct mother colonies?

Why it matters: A genetically or taxonomically homogeneous restoration is vulnerable to disease and bleaching events. Tracking both variants ensures we are building resilient ecosystems, not monocultures.

Methodology note: The 2025 Methodology Manual prescribes maximum species and morphological diversity from the reference site but does not name Shannon as the metric. Shannon H' is computed downstream in the ReefOS Data API (shannon() in query_firestore.py) and stored as part of the donor stats payload.

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Survival Rate

The proportion of living fragments — a key success metric for restoration.

EVI (Ecological Volume Index)

A proxy for coral biomass — volume in cm³ computed from L × W × H field measurements.