Coastal tectonics and habitat squeeze: Response of a tidal lagoon to co-seismic sea-level change

Abstract

We investigated the response of a tidal lagoon system to a unique situation of relative sea-level change induced by powerful earthquakes (up to Mw 7.1) on the east coast of New Zealand in 2010–2011. Spatiotemporal impacts were quantified using airborne light detection and ranging (LiDAR) datasets complemented by hydrodynamic modelling and evaluation of anthropogenic influences. Ground-level changes included examples of uplift and extensive subsidence (ca. 0.5 m) associated with intertidal area reductions, particularly in supratidal zones. ‘Coastal squeeze’ effects occurred where incompatible infrastructure prevented upland ecosystem movement with relative sea-level rise. Despite large-scale managed retreat, legacy effects of land-filling have reduced the reversibility of human modifications, impairing system resiliency through poor land-use design. Elsewhere, available space in the intertidal range shows that natural environment movement could be readily assisted by simple engineering techniques though is challenged by competing land-use demands. Quantification of gains and losses showed that lagoon expansion into previously defended areas is indeed required to sustain critical habitats, highlighting the importance of a whole-system view. Identifiable coastal planning principles include the need to assess trade-offs between natural and built environments in the design of hazard management plans, requiring greater attention to the natural movement of ecosystems and areas involved. Treating these observations as a scenario illustrates the mechanisms by which coastal squeeze effects may develop under global sea-level rise, but our purpose is to help avoid them by identifying appropriate human responses. We highlight the need for an improved focus on whole-system resilience, and the importance of disaster recovery processes for adaptation to climate change.