Understanding seagrass resilience in temperate systems: the importance of timing of the disturbance

Temperate seagrass meadows form valuable ecosystems in coastal environments and present a distinctseasonal growth. They are threatened by an increasing amount of stressors, potentially affecting theircapacity to recover from disturbances. We hypothesized that their resilience to disturbances is affectedby seasonal dynamics. Hence, we investigated the effect of the timing of the disturbance on seagrassLeaf Area Index (as a proxy for presence, or ‘visible’ status), recovery from disturbance (as a proxy formeadow resilience), and rhizome carbohydrates (as a proxy for longer term resilience) by a series offour disturbance-recovery field experiments spread over the growing season at two sites in ShandongProvince, China. During the course of the growing season, we found the highest recovery at the start of thegrowing season, lowest recovery when Leaf Area Index peaked around mid-growing season, and interme-diate recovery when Leaf Area Index decreased at the end of the growing season. Rhizome carbohydrateswere not affected by disturbances during any of the four experimental periods and could not explain thelow recovery during mid-growing season. The two sites differed in exposure and in the occurrence ofincidents like a green tide and storms, which affected recovery. However, general patterns were similar;timing strongly influenced the indicator of meadow resilience and its correlation with presence duringthe two main seagrass growth phases. Our results emphasize the importance of carefully consideringtiming in the evaluation of seagrass resilience in temperate systems. Furthermore, our study impliesthat, to effectively protect seagrass beds, conservation management should aim at avoiding disturbancesparticularly during the peak of the growing season, when resilience is lowest