Sediment burial negatively impacts the growth of seagrass Posidonia sinuosa

Burial disturbances affect foundation plant species in marine ecosystems. Deposition of dredge spoil can bury seagrass meadows yet we have limited threshold information to predict the trajectory of impact from burial or possible recovery. To investigate the response to burial by dredge spoil, established seagrass ramets of Posidonia sinuosa were collected from a population in Western Australia and exposed to cutter suction dredge spoil sediment. Plant responses were measured during a burial phase after 2, 4 and 8 weeks to assess the influence of duration to burial depths (0, 1, 4, 8 and 16 cm). Sediments were then removed, and recovery was monitored after 5 and 8 weeks. P. sinuosa was unaffected by burial of 1 and 4 cm whereas greater depths of burial led to negative impacts on ramet photophysiology and growth. In the 8 and 16 cm treatments, declines in seagrass growth were significant and sediment redox damaged seagrass health, reflecting conditions consistent with impaired plant physiology and anoxic sediment in the root zone. After burial was removed, seagrass growth rates in 8 and 16 cm treatments showed no recovery after 8 weeks. Although shoots were not lost, reduced growth and no shoot recovery in the short-term, 8 cm or more of dredge-deposition sediment could be used as a threshold for dredging management. Plant response under 16 cm of sediment suggests that the greater the seagrass burial depth the greater the adverse effect on the seagrass community including an impeded ability to recover and reduced population resilience.