seagrass meadows of the Great Barrier Reef at low tide. We measured effective quantum yield (/PSII),
growth, senescence and mortality in four tropical seagrasses to experimental short-duration (2.5 h)
spikes in water temperature to 35 C, 40 C and 43 C, for 6 days followed by one day at ambient temperature.
Increasing temperature to 35 C had positive effects on /PSII (the magnitude varied between days
and was highly correlated with PPFD), with no effects on growth or mortality. 40 C represented a critical
threshold as there were strong species differences and there was a large impact on growth and mortality.
At 43 C there was complete mortality after 2–3 days. These findings indicate that increasing duration
(more days in a row) of thermal events above 40 C is likely to affect the ecological function of tropical
seagrass meadows.