Ecosystem Engineering by Plants on Wave-Exposed Intertidal Flats Is Governed by Relationships between Effect and Response Traits

Abstract

In hydrodynamically stressful environments, some species—known as ecosystem engineers—are able to modify the environment for their own benefit. Little is known however, about the interaction between functional plant traits and ecosystem engineering. We studied the responses of Scirpus tabernaemontani and Scirpus maritimus to wave impact in full-scale flume experiments. Stem density and biomass were used to predict the ecosystem engineering effect of wave attenuation. Also the drag force on plants, their bending angle after wave impact and the stem biomechanical properties were quantified as both responses of stress experienced and effects on ecosystem engineering. We analyzed lignin, cellulose, and silica contents as traits likely effecting stress resistance (avoidance, tolerance). Stem density and biomass were strong predictors for wave attenuation, S. maritimus showing a higher effect than S. tabernaemontani. The drag force and drag force per wet frontal area both differed significantly between the species at shallow water depths (20 cm). At greater depths (35 cm), drag forces and bending angles were significantly higher for S. maritimus than for S. tabernaemontani. However, they do not differ in drag force per wet frontal area due to the larger plant surface of S. maritimus. Stem resistance to breaking and stem flexibility were significantly higher in S. tabernaemontani, having a higher cellulose concentration and a larger cross-section in its basal stem parts. S. maritimus had clearly more lignin and silica contents in the basal stem parts than S. tabernaemontani. We concluded that the effect of biomass seems more relevant for the engineering effect of emergent macrophytes with leaves than species morphology: S. tabernaemontani has avoiding traits with minor effects on wave attenuation; S. maritimus has tolerating traits with larger effects. This implies that ecosystem engineering effects are directly linked with traits affecting species stress resistance and responding to stress experienced.

Coping with waves: Plasticity in tidal marsh plants as self‐adapting coastal ecosystem engineers

“…Biomechanical properties of intertidal plants have already been assessed in a number of studies (e.g., Carus et al for S. maritimus sampled from the field; Coops and Van der Velde for Phragmitis australis and Scirpus lacustris sampled from the field; Heuner et al for S. maritimus and S. tabernaemontani grown under controlled and sheltered conditions; Möller et al for Puccinellia maritima and Elymus athericus sampled from the field; Rupprecht et al for Spartina anglica , Puccinellia maritima , and E. athericus sampled from the field; Silinski et al for S. maritimus grown under controlled and sheltered conditions). The results presented here are, overall, in the same range as the ones reported by these studies.…”

Habitatmapping Sea Scheldt supralittoral: Partim pioneer club-rush species

“…B. maritimus, in contrast, develops a slightly lower ratio on rip rap than on soft sediments. Heuner et al (2015) and Gevers et al (2012) conclude that changes in morphological response of S. tabernaemontani and B. maritimus are in fact indications of environmental stress. To fully understand increase in stress on plant performance due to the aquatic environment, growth characteristics could be modelled in function of position towards the river channel or studied by means of controlled experiments.…”

Development of an Outdoor Wave Basin to Conduct Long-Term Model Tests with Real Vegetation for Green Coastal Infrastructures

“…Numerous field studies show that the development of coastal ecosystem and its services are affected by wave load [24][25][26][27][28][29]. Firstly, the rough environmental conditions in the wave impact zone result in a decreasing ecological niche leading to a limitation of the species richness in the coastal ecosystems [24].…”