Self-organisation in striped seagrass meadows affects the distributional pattern of the sessile bivalve Pinna nobilis

Optimal wave reflection as a mechanism for seagrass self-organization

Ecosystems threatened by climate change can boost their resilience by developing spatial patterns. Spatially regular patterns in wave-exposed seagrass meadows are attributed to self-organization, yet underlying mechanisms are not well understood. Here, we show that these patterns could emerge from feedbacks between wave reflection and seagrass-induced bedform growth. We derive a theoretical model for surface waves propagating over a growing seagrass bed. Wave-induced bed shear stress shapes bedforms which, in turn, trigger wave reflection. Numerical simulations show seagrass pattern development once wave forcing exceeds a critical amplitude. In line with Mediterranean Sea field observations, these patterns have half the wavelength of the forcing waves. Our results raise the hypothesis that pattern formation optimizes the potential of seagrass meadows to reflect wave energy, and a clear direction for future field campaigns. If wave-reflecting pattern formation increases ecosystem resilience under globally intensifying wave climates, these ecosystems may inspire nature-based coastal protection measures.

A Digital Twin modelling framework for the assessment of seagrass Nature Based Solutions against storm surges

In this paper we demonstrate a novel framework for assessing nature-based solutions (NBSs) in coastal zones using a new suite of numerical models that provide a virtual "replica" of the natural environment. We design experiments that use a Digital Twin strategy to establish the wave, sea level and current attenuation due to seagrass NBSs. This Digital Twin modelling framework allows us to answer "what if" scenario questions such as: (i) are indigenous seagrass meadows able to reduce the energy of storm surges, and if so how? (ii) what are the best seagrass types and their landscaping for optimal wave and current attenuation? An important result of the study is to show that the landscaping of seagrasses is an important design choice and that seagrass does not directly attenuate the sea level but the current amplitudes. This framework reveals the link between seagrass NBS and the components of the disruptive potential of storm surges (waves and sea level) and opens up new avenues for future studies.

Restoration of Seagrass Meadows in the Mediterranean Sea: A Critical Review of Effectiveness and Ethical Issues

Some species of seagrasses (e.g., Zostera marina and Posidonia oceanica) have declined in the Mediterranean, at least locally. Others are progressing, helped by sea warming, such as Cymodocea nodosa and the non-native Halophila stipulacea. The decline of one seagrass can favor another seagrass. All in all, the decline of seagrasses could be less extensive and less general than claimed by some authors. Natural recolonization (cuttings and seedlings) has been more rapid and more widespread than was thought in the 20th century; however, it is sometimes insufficient, which justifies transplanting operations. Many techniques have been proposed to restore Mediterranean seagrass meadows. However, setting aside the short-term failure or half-success of experimental operations, long-term monitoring has usually been lacking, suggesting that possible failures were considered not worthy of a scientific paper. Many transplanting operations (e.g., P. oceanica) have been carried out at sites where the species had never previously been present. Replacing the natural ecosystem (e.g., sandy bottoms, sublittoral reefs) with P. oceanica is obviously inappropriate in most cases. This presupposes ignorance of the fact that the diversity of ecosystems is one of the bases of the biodiversity concept. In order to prevent the possibility of seagrass transplanting from being misused as a pretext for further destruction, a guide for the proper conduct of transplanting is proposed.

Theory of scale-dependent feedback: An experimental validation and its significance for coastal saltmarsh restoration

Theory of self-organization, i.e., scale-dependent feedback (SDF), has been widely used to explain mechanisms of spatial patterns in different ecosystems. Studies have demonstrated that self-organization is one of the mechanisms through which ecosystem resilience is maintained. However, the application of SDF in real ecological restoration practices is a challenge due to the lack of a controlled experimental validation. In the present study, multiple scales of vegetation patches were constructed along an elevation gradient in the saltmarsh ecosystem on Nanhui coasts and were investigated to verify if there was an effect of SDF. Results of the density-variation curves analyses revealed that most constructed self-organized patches could survive and an optimal curve was found of which the density-dependent feedback was proven through fitting with the asymptotic regression model. The large vegetation patches exhibited considerable increases in density when compared to the small vegetation patches, which occurred in challenging environments, i.e., on the verges of elevation thresholds, and with a tendency to shrink. Analyses using one-way ANOVA revealed that there was an optimal patch scale and elevation in the study area, i.e., 1 m × 1 m scale and 3.2 m, respectively. Optimal scale and elevation provide a comprehensively explanations of SDF, although with the positive effects gradually decreased along the distance away from the optimal condition. The present study provides novel insights on applying the theory of SDF in facilitating the restoration process of coastal saltmarshes.