Data from: Sensitivity and legacy effects in phytoplankton growth and traits under sequential environmental change

When environments change sequentially, past conditions can leave legacies
that modify population growth and trait expression under subsequent
stress. Under global change, sequences such as marine heatwaves followed
by pollution runoff increase the likelihood and consequence of such
legacies for population and community dynamics. We tested for
sequence-dependent legacy effects in six globally distributed strains of
the marine phytoplankton Synechococcus sp. using a full‑factorial
microcosm experiment with warming, herbicide pollution, and control
treatments as both chronic (constant) and sequential (changing) exposures.
We quantified chronic and acute sensitivities as changes in population
density, per‑capita growth rate, cell size, and chlorophyll content
following respective exposures. Significant chronic sensitivity occurred
in 58.3% of strain-exposure combinations and significant acute sensitivity
in 48%; acute responses often showed decoupling between growth and traits.
Comparisons of chronic and acute sensitivities demonstrate that past
environments systematically alter subsequent responses, producing strain‑
and exposure‑specific overcompensation or undercompensation. Consequently,
incorporating sequence-based legacies into predictions of biodiversity
dynamics and ecosystem function under global change is essential.