Short-term effect of filamentous macroalgae Chaetomorpha linum on Cymodocea nodosa: Does clonal integration alleviate macroalgae impacts?

Seagrasses are clonal plants that can form meadows in shallow coastal water. Under natural conditions, drift macroalgae can be found associated with seagrass but when facilitated by high nutrient input, opportunistic macroalgae can grow excessively and form mats that impose stressful and highly competitive conditions for seagrasses. In this study, we experimentally investigate the ecological significance of clonal integration in the ability of Cymodocea nodosa to tolerate biotic stress triggered by interactions with the drift macroalgae Chaeotomorpha linum. Our findings provide little support for the hypothesis that clonal integration can influence C. nodosa response to stress, as disconnected plants did not show significant differences in structural and morphological characteristics compared to intact plants. However, the physiological analysis suggests that C. nodosa may still benefit from shared resources with neighbouring plants to mitigate stress caused by C. linum. Moreover, the results indicate that C. nodosa adapts to the presence of the filamentous drift macroalgae C. linum by increasing leaf photosynthetic content, reducing growth rate, and modulating its morphology, regardless of its integration status.