Shifting Seas - a gene landscape approach to understanding saltmarsh vulnerability and resilience to sea-level rise

Saltmarsh is a vital component of so-called Nature based Solutions (NbS) to coastal defence, a role central to developing UK Government policy, that aims to better manage, protect and restore this habitat over the next 25 years. In order to deliver this policy, and the wider ecosystem and societal benefits that accrue, we must understand the risks and opportunities to coastal habitats from sea level rise (SLR) and associated coastal flooding and erosion. 'Shifting Seas' takes a gene to landscape scale approach to elucidate saltmarsh response to SLR, incorporating state of the art, interdisciplinary approaches including tidal hydrodynamics, geomorphology and sedimentology, plant genetics, saltmarsh ecology, field experiments and ecological modelling. We explore the following four objectives
Objective 1 - Saltmarsh zonation is generated by the different, but overlapping, ranges of individual species, reflecting their ability to tolerate factors associated with tidal submergence. Because elevation and inundation frequency exerts primary controls on a species 'fundamental' and 'realised' niche, changes to tidal range through SLR could have consequences for saltmarsh community structure and function. Saltmarshes will be surveyed to determine the range of component species, but with a particular focus on typical high- , mid-, and low- marsh species, and how key physical variables vary in tandem. This provides a baseline from which the elevation niche of each species can be set against present day position in the tidal frame (i.e. inundation frequencies, inundation duration, emergence duration) determined through a combination of UAV survey, water level measurements and tidal modelling. These data will build a niche model to predict the extent to which saltmarsh plants may occur or invade an area and the processes controlling population and community structure under different ACC and management scenarios.
Objective 2 - Marsh elevation can influence the genetic diversity of component species and with it resilience to continued SLR and associated environmental factors. Moreover, genotypic variation in plant response to simulated seawater inundation signpost flooding as a potential selective filter that could eliminate key species and reduce functional sustainability, ecosystem resilience to SLR, and contribution to coastal defence. From Objective 1, we select two sites to represent typical 'high resilience' (sediment accretion matches SLR) and 'high vulnerability' (sediment accretion lags SLR) scenarios. We will use a genotype by sequencing approach for SNP discovery in polyploids to determine the population structure, genetic diversity and differentiation of selected species across the marsh elevation at the selected 'high resilience' and 'high vulnerability' sites.
Objective 3 - Elucidation of the hydrodynamic properties operating at 'high resilience/vulnerability' sites, coupled with an understanding of the local distribution of key component plant species, their genetic diversity, and response to seawater immersion and sediment deposition, may reveal much about saltmarsh adaptation to SLR. 'Using the 'marsh organ' technique, we will plant different genotypes of the target plant species across an elevational gradient, the results informing a model forecasting how species- and genetic-variably influences marsh resilience / vulnerability to SLR.
Objective 4 - We will deliver a spatially explicit 'opportunity mapping tool' informing management interventions necessary to support adaptation pathways for the conservation, restoration and protection of saltmarsh ecosystems. By elucidating the some of the (genetic, hydrodynamic, ecological) barriers to SLR adaptation, we provide crucial evidence needed to predict changes and risks to saltmarsh ecosystems and species, and in turn target solutions resilient to long-term sea-level change.