Response of Posidonia oceanica growth to dredging effects of different magnitude

The response of the seagrass Posidonia oceanica in an area physically disturbed by 2 dredging events was evaluated to understand the recovery time of this species and compared to 2 reference locations. An asymmetrical 'beyond BACI' (Before/After, Control/Impact) sampling design was applied in combination with reconstructive techniques to compare vertical rhizome elongation and leaf production in P. oceanica during 4 yr before and 4 yr after each dredging event in 1 disturbed and 2 reference locations. On average, vertical rhizome elongation increased from before to after each dredging event, with higher growth being recorded in the disturbed location compared to the reference locations. This effect appeared to be driven by a combination of the application of different dredging techniques and exposure to prolonged stress, as rhizomes had not completely recovered from the first impact by the time the second, lower magnitude disturbance occurred. No difference in leaf production was found. This work highlights the importance of disturbance history and dredging method in determining the response of P. oceanica to multiple disturbances, and provides insights into the recovery time of the seagrass when repetitive effects to the same meadow occur. This becomes particularly relevant as infrastructure development continues to expand along the world's coastline and seagrasses are challenged with the exponential increase of physical disturbance.