Chronic light reduction reduces overall resilience to additional shading stress in the seagrass Halophila ovalis

[Display omitted] •We subjected two populations of H. ovalis seagrass to two levels of shading stress.•One population (from a low-light site) died while the other showed sub-lethal effects.•Chronic low-light affects the ability of seagrass to cope with additional shading.•Acclimation to low-light conditions alters a species’ minimum light requirement (MLR).•Results show that MLR is dependent on the prevailing light environment. Seagrasses have substantial capacity to survive long periods of light reduction, but how acclimation to chronic low light environments may influence their ability to cope with additional stress is poorly understood. This study examines the effect of temporal light reduction by adding two levels of shading to Halophila ovalis plants in two meadows with different light histories, one characterized by a low light (turbid) environment and the other by a relatively high light (clear) environment. Additional shading resulted in complete mortality for both shading treatments at the turbid site while the clear site showed a pattern of decreased shoot density and increased photochemical efficiency (Fv/Fm) with increased shading. These contrasting results for the same species in two different locations indicate that acclimation to chronic low light regimes can affect seagrass resilience and highlights the importance of light history in determining the outcome of exposure to further (short-term) stress.