Saltmarshes are dynamic ecosystems that play crucial roles in supporting biodiversity, protecting coasts from flooding, and storing carbon. Understanding how these ecosystems adapt to environmental changes is vital for their conservation, especially under increasing pressures from climate change.
We investigated how saltmarshes respond to the shifting positions of tidal channels over several decades, examining aerial images from three estuaries in Wales spanning 67 years. Tidal channels naturally migrate across estuaries, reshaping the landscape by eroding marshes in some places while creating new areas suitable for marsh growth elsewhere.
We found clear evidence of a phenomenon we term “geomorphic compensation”: when tidal channels shift – causing marsh erosion on one side of an estuary – there is often simultaneous marsh expansion elsewhere, effectively balancing out habitat losses. Remarkably, we observed expansion rates reaching as high as 6 meters per year, ensuring that the overall marsh area across each estuary remained relatively stable despite considerable local changes.
This geomorphic compensation occurred in three distinct ways. First, marsh erosion on one bank of an estuary was often balanced by marsh expansion directly opposite, highlighting a cyclical pattern tied to channel migration. Second, when marshes eroded, new marshes could form further along the same bank. Third, erosion and expansion frequently occurred simultaneously within the same marsh, showing local adjustments within a single habitat.
This resilience mechanism is essential for sustaining marsh ecosystems over the long term, as it allows marshes to adapt to natural environmental fluctuations. Understanding this pattern is particularly important in the context of climate change and sea-level rise, where marshes may need to respond quickly to changing conditions.
Our findings highlight the importance of considering landscape-scale processes when managing and conserving saltmarsh ecosystems. Conservation efforts should not only focus on preventing erosion at specific locations but also support the natural processes of marsh regeneration and expansion elsewhere in estuaries.
Ultimately, by acknowledging and supporting these natural adaptive processes, we can better ensure the long-term health and resilience of our vital coastal marshes, securing their valuable ecosystem services well into the future.