Struggle & Emergence: On critical geometry and dynamics in tidal ecosystems

Abstract

Many ecosystems are characterized by sharp transitions between two states. So are many tidal ecosystems. Consider, for example, the sharp transitions and the patchy zones with (ir)regular abrupt transitions between salt-marsh vegetation or reef-building organisms and the bare mudflats. These sharp transitions often arise as a result of interactions between strong feedbacks and stochastic processes. Near and at this interface, establishing and sustaining organisms is a struggle due to the harsh fluctuating environmental conditions. To increase the chance of sustained establishment, organisms often modify the environment, which leads to strong feedbacks. However, those feedbacks interacting with stochasticity makes it very difficult to estimate: i) how these ecosystems respond and how resilient they are under natural and anthropogenic changes, ii) whether the settlement opportunities are sufficiently favourable and how likely these transitions are, and iii) how the patchiness of habitat-modifying organisms affect their local and extended functioning. Within this thesis, we looked at which (statistical) regularities can occur in those tidal systems and at these critical transitions in order to better assess their response resilience, chance of sustained settlement and influence on the environment. For this, different methods are used and developed from conceptual and statistical modeling, analysis of spatiotemporal dataset to measurements and experiments in the field and laboratory. Tidal ecosystems near their critical transitions are shown to exhibit generic features which provide fundamental insights for their sustainable and effective use as nature-based solutions for issues related to climate adaptation and coastal safety.