Future-proofing conservation priorities for sea level rise in coastal urban ecosystems

Highlights

• Priority areas for coastal conservation change with future SLR projections.

• Planning for the future has fiscal advantages across the land-sea interface.

• Multiple scenarios and sensitivity tests identify high agreement priority areas.

• Current protected areas may not adequately protect critical areas for future SLR.

Abstract

Decision makers are calling for actionable science to protect coastal ecosystems from adverse impacts. Future sea level rise (SLR) is expected to alter the spatial configuration of coastal habitats and their services. Ensuring conservation efforts are in optimal areas can be achieved using systematic conservation planning, yet plans rarely address multiple goals and uncertainties. We developed and applied a novel multi-ecosystem approach for planning the conservation of coastal ecosystems under future SLR scenarios. Decision support tool Marxan was used to determine priority areas that incorporate habitat connectivity, SLR modelling scenarios and feasibility for conservation in urbanised Moreton Bay in Queensland, Australia, as a case-study. We found that planning based on present conditions will not adequately capture conservation priorities for the future, and has associated financial consequences. Priority conservation areas of Moreton Bay are not well aligned with current protected areas (<35%), with further misalignment for future scenarios. This study highlights the importance of a multi-ecosystem approach for protecting coastal habitats as well as leveraging the current management system. Our approach helps inform policy and guides conservation actions in urbanised coastal regions facing SLR.

Introduction

Coastal ecosystems are highly threatened due to cumulative human impacts, with a resulting habitat loss of ~30–50% globally (Alongi, 2002; Waycott et al., 2009). To stem further declines, The United Nations has called for urgent action to protect and strengthen the resilience of coastal ecosystems from adverse impacts (Sustainable Development Goal 14; UN, 2015). However, determining where to apply conservation efforts becomes a challenge when spatial configurations of coastal habitats are expected to shift. Climate change impacts are predicted to cause the global mean sea level to rise with predictions between 0.28 and 1.32 m (IPCC, 2019; Horton et al., 2020) by the year 2100. Sea level rise (SLR) may cause coastal habitats to decline in size, or expand, depending on their capacity to migrate landward (Schuerch et al., 2018). Hence, conservation efforts should take into account locations where future habitats will exist (Lawler et al., 2020).

Protecting coastal ecosystems is of great socioeconomic importance (Schinko et al., 2020). Approximately 40% of the world's population lives within coastal urban environments (within 100 km from the coast; Agardy and Alder (2005)), with high vulnerability to coastal flooding from SLR (Woodruff et al., 2013). Coastal habitats such as tidal flats, reefs, seagrass, beaches, saltmarshes and mangroves can effectively reduce the amount of wave energy reaching coastlines and the impacts of SLR on coastal flooding and erosion (Guannel et al., 2016). Not only are coastal habitats a natural defence to SLR, they are also considered cost-effective, adaptive and resilient in comparison to alternative built (“grey”) infrastructure (Sutton-Grier et al., 2015). Furthermore, they provide important ecosystem services such as habitats for a diversity of marine species (Waycott et al., 2009), nurseries for commercial fish stocks (Laegdsgaard and Johnson, 1995), and sequestration of carbon (Lovelock and Duarte, 2019).

Decision makers tackling SLR impacts are emphasising the need for actionable science (Beier et al., 2017); whereby information is aggregated and synthesised to support the design of adaptation strategies that incorporate uncertainties (Hall et al., 2019). Model-based scenarios of future climate projections often inform planning decisions, but such models have tended to focus on single taxon groups or habitats (e.g. birds; Vale et al., 2018, seagrass; Telesca et al., 2015). Yet, linked ecosystems are critical for biodiversity and fisheries productivity because of the range of habitats used through complex life histories (Olds et al., 2012), and maintaining linkages among coastal habitats is essential to help them respond to SLR (Saunders et al., 2014). Systematic conservation plans that incorporate climate change are an emerging tool, with the goal of prioritising future habitat protection by incorporating forecasts from species distribution models (Jones et al., 2016). Such plans, however, have rarely addressed multiple goals and require more integrative approaches to incorporate multiple climate change impacts and uncertainties (Jones et al., 2016). Here we aim to provide a multi-ecosystem systematic plan which accounts for impacts of predicted SLR, and considers goals of habitat connectivity and cost efficiency (reaching conservation targets for the least cost) while minimising uncertainty.

Our study identifies conservation priorities for coastal habitats under projected SLR scenarios. To illustrate the application of our approach to urbanised coastlines we use the diverse coastal seascape adjacent to the metropolis of Brisbane, Australia as a case study. Firstly, we synthesise and model available habitat data to represent current (2020) and future distributions (years 2050 and 2100). The resulting distributions are then used to inform a systematic conservation plan identifying priority conservation areas. Specifically, we compare planning scenarios (present day, 2050 and 2100), examining how priority conservation areas change, and their alignment with existing protected areas.