Estuaries are considered valuable regions, both socio-economically and ecologically. The gradients in physical characteristics like salinity present result in a high biodiversity, while the provision of many ecosystem services have attracted human settlement and activity. Human activities and estuarine biodiversity are often at odds with each others, leading to socio-ecological trade-offs in decision- and policy-making in which the ecological perspective is generally underrepresented. In this study, we implemented a hydrodynamic model to explore the socio-ecological implications of reopening the closed-off Haringvliet estuary in the Netherlands. Our socio-ecological evaluation considers the trade-off between freshwater availability and ecological diversity. In the case of the Haringvliet, we have shown that partially opening the gates enhances diversity in the system against no — or limited — loss of freshwater availability. All in all, the use of representative (non-monetary) performance indicators for the considered stakeholders allowed us to demonstrate the trade-offs in a clear fashion: the Pareto-front resulting from these performance indicators is an intuitive visualization for decision- and policy-makers as well as the communication to the public.

The restoration and creation of tidal freshwater wetlands is increasingly becoming important, yet the success of these efforts is limited by salt intrusion, a growing concern due to climate change and human activities. Key topographical features, such as (re)constructed channel network, might help mitigate salt intrusion in these areas. Using a hydrodynamic model and idealized topographies based on real-world data from natural marshes and various constructed wetlands, we analysed how topographies respond to saltwater intrusion events. Our findings reveal that, although wetland topographies based on natural marshes experience faster salinity increases at the onset of an event, they also achieve quicker salinity reductions at its conclusion, resulting in shorter overall periods of salinization compared to artificial wetland designs (e.g. up to 8.10 % in the drought simulations and 48.72 % in the storm surge simulations). The rapid reduction in salinity is driven by the distinct topography of natural marshes, particularly the creek system, which amplifies salt fluxes. Compared to the reference topography, the natural marsh topography exhibited 6.50 % higher salt fluxes in drought (S + W) simulations and up to 41.02 % higher in storm surge (S + W) simulations. These findings emphasize the importance of incorporating natural marsh characteristics, such as slope and channel network design, into tidal freshwater wetland restoration and creation projects to improve resilience against salt intrusion and ensure their long-term sustainability in the face of climate change.

KEY POINTS (I) A biophysical model framework (BMF) for corals is developed in which four environmental factors are included: (1) light; (2) hydrodynamics; (3) temperature; and (4) acidity. (II) The full feedback loop between corals and their environment forms the core of this model framework, where the morphological development is new and closes the feedback loop. (III) The developed BMF predicts the coral response to environmental input via (mainly) process-based relations within the accuracy of climate projections. (IV)- The BMF supports both the deep reef refugia hypothesis and the turbid reef refugia hypothesis. (V) The BMF contributes to the development of protection and recovery programs and is not site-specific. (VI) The BMF is developed for long-term predictions - in the order of decades to centuries - but runs on daily averages and is therefore applicable for assessing the response of corals on shorter time-scales; such as months to years. SUMMARY The increasing pressure on Earth’s ecosystems due to climate change becomes more and more evident. These pressures are especially visible at coral reefs. Therefore, a good understanding of the biophysical mechanisms controlling these ecosystems is needed, so that accurate predictions of their survival can be made. Such an understanding is also needed to develop efficient recovery and protection programs vital to the maintenance of these ecosystems. Because the research on marine ecosystems is relatively young and the phenomenon of coral bleaching is yet to be fully understood, there is no comprehensive framework in which the complex interactions between corals and their environment are combined. In this study, a biophysical model is developed in which four environmental factors are included in a feedback loop with the coral’s biology: (1) light; (2) hydrodynamics; (3) temperature; and (4) acidity. Literature from multiple disciplines is combined to find the interdependencies between the corals and their environment. These relations include coral growth, coral bleaching, storm damage, and recruitment/recolonization of corals. For the connection with the hydrodynamics, a coupling is made between the biological model developed here and Delft3D-FM. The composed biophysical model is a big leap forward in understanding the world of coral reefs, as it is the first construction of a model framework including four environmental factors in which the hydrodynamics are included in the feedback loop. Furthermore, it creates the ability to assess recovery and protection programs based on the four aforementioned environmental factors; e.g. the susceptibility of coral bleaching can be reduced by increasing the attenuation of light through the water column. Because more environmental factors have a role to play in the coral dynamics, the framework is constructed such that these can be added relatively easily.