Effects of wind waves versus ship waves on tidal marsh plants: a flume study on different life stages of Scirpus maritimus

• Published in: PloS one Vol. 10; no. 3; p. e0118687
• Main Authors: Silinski, Alexandra, Heuner, Maike, Schoelynck, Jonas, Puijalon, Sara, Schröder, Uwe, Fuchs, Elmar, Troch, Peter, Bouma, Tjeerd J, Meire, Patrick, Temmerman, Stijn
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 23-03-2015; Public Library of Science (PLoS)
• Subjects: Adults; Aquatic plants; Biodiversity and Ecology; Biology; Biomechanics; Coastal ecosystems; Colonization; Constraining; Cyperaceae - physiology; Developmental stages; Drag; Ecosystem biology; Ecosystems; Environmental factors; Environmental Sciences; Estuaries; Geomorphology; Hydrology; Marine ecosystems; Marshes; Mean sea level; Mud flats; Ocean currents; Plant resistance; Plant Shoots - physiology; Plant tissues; Sea level; Sedimentation & deposition; Sediments; Sediments (Geology); Seedlings; Seeds - physiology; Ships; Shoots; Soil erosion; Stems; Stiffness; Survival; Tidal marshes; Tidal Waves; Water levels; Water waves; Wave period; Wetlands; Wind; Wind effects; Wind waves; Belgium; Netherlands; Germany
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0118687

Recent research indicates that many ecosystems, including intertidal marshes, follow the alternative stable states theory. This theory implies that thresholds of environmental factors can mark a limit between two opposing stable ecosystem states, e.g. vegetated marshes and bare mudflats. While elevation relative to mean sea level is considered as the overall threshold condition for colonization of mudflats by vegetation, little is known about the individual driving mechanisms, in particular the impact of waves, and more specifically of wave period. We studied the impact of different wave regimes on plants in a full scale flume experiment. Seedlings and adult shoots of the pioneer Scirpus maritimus were subjected to two wave periods at two water levels. Drag forces acting on, and sediment scouring occurring around the plants were quantified, as these are the two main mechanisms determining plant establishment and survival. Depending on life stage, two distinct survival strategies emerge: seedlings present a stress avoidance strategy by being extremely flexible, thus limiting the drag forces and thereby the risk of breaking. Adult shoots present a stress tolerance strategy by having stiffer stems, which gives them a higher resistance to breaking. These strategies work well under natural, short period wind wave conditions. For long period waves, however, caused e.g. by ships, these survival strategies have a high chance to fail as the flexibility of seedlings and stiffness of adults lead to plant tissue failure and extreme drag forces respectively. This results in both cases in strongly bent plant stems, potentially limiting their survival.