Data from: A meta-analysis reveals a positive correlation between genetic diversity metrics and environmental status in the long-lived seagrass Posidonia oceanica

The seagrass Posidonia oceanica is a key engineering species structuring
coastal marine systems throughout much of the Mediterranean basin. Its
decline is of concern, leading to the search for short- and long-term
indicators of seagrass health. Using ArcGIS maps from a recent,
high-resolution (1–4 km) modelling study of 18 disturbance factors
affecting coastal marine systems across the Mediterranean (Micheli et al.
2013, http://globalmarine.nceas.ucsb.edu/mediterranean/), we tested for
correlations with genetic diversity metrics (allelic diversity,
genotypic/clonal diversity and heterozygosity) in a meta-analysis of 56
meadows. Contrary to initial predictions, weak but significantly positive
correlations were found for commercial shipping, organic pollution
(pesticides) and cumulative impact. This counterintuitive finding suggests
greater resistance and resilience of individuals with higher genetic and
genotypic diversity under disturbance (at least for a time) and/or
increased sexual reproduction under an intermediate disturbance model. We
interpret the absence of low and medium levels of genetic variation at
impacted locations as probable local extinctions of individuals that
already exceeded their resistance capacity. Alternatively, high diversity
at high-impact sites is likely a temporal artefact, reflecting the
mismatch with pre-environmental impact conditions, especially because
flowering and sexual recruitment are seldom observed. While genetic
diversity metrics are a valuable tool for restoration and mitigation,
caution must be exercised in the interpretation of correlative patterns as
found in this study, because the exceptional longevity of individuals
creates a temporal mismatch that may falsely suggest good meadow health
status, while gradual deterioration of allelic diversity might go
unnoticed.