Modeling the Responses of Macrobenthic Species and Estuarine Morphology to Sea Level Rise
Abstract
Estuaries are one of the most valuable marine environments; however, their functioning is threatened by predicted sea level rise. Macrobenthic organisms occupy muddy estuarine sediments, where they forage for food and can destabilize local mud. Through this bioturbation activity, they can cause erosion and modify local and system-scale morphology. While mud flats in general reduce bar dynamics and bank erosion, sea level rise may increase bed shear stresses and macrobenthic species may respond to those, resulting in modified bioturbation strength. We still lack understanding of how sea level rise will alter the feedbacks between morphology, species growth and bioturbation in estuaries, how estuarine morphology will evolve and if bioturbators will decline or adapt to the changing environment. To investigate these feedbacks, we couple a two-dimensional hydro-morphodynamic model of an idealized estuary with rules for species-specific growth and biomass-dependent bioturbation of two bioturbators, a moderate sand-prone bioturbator (lugworm) and an efficient mud-prone bioturbator (mud shrimp). Local mud erodibility is based on species pattern predicted through hydrodynamics, soil mud content and competition. The model allows us to test 1) the response of estuarine morphology to the combined effects of different rates of sea level rise and bioturbation, and 2) the response of the two bioturbators to changes in their habitat. With increasing sea levels and bioturbation, the modelled estuary experiences erosion, resulting in decreasing mean bed levels and a wider intertidal area. Especially the efficient mud shrimp induces estuary widening and increases accommodation space. However, bioturbation effects reduce with increasing sea level rise rates as the habitat of the mud shrimp degrades. In contrast, the sand-prone lugworm is able to adapt to sea level rise by cause of their habitat preferences and moderate bioturbation activity. When both species are present, these species-specific feedbacks cause a shift in dominating species in favour of the lugworm. Our results demonstrate that bioturbation can induce relevant geomorphic changes under sea level rise resulting in new emerging species distributions and provide important insights in how tidal landscapes will develop under rising sea levels.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFMEP45A1509B