Journal of Environmental Management 261 (2020) 110203 Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: http://www.elsevier.com/locate/jenvman Research article Predicting the impact of sea-level rise on intertidal rocky shores with remote sensing Nina Schaefer a,*, Mariana Mayer-Pinto a,b, Kingsley J. Griffin a, Emma L. Johnston a, William Glamore c, Katherine A. Dafforn a,b,d a Centre for Marine Science & Innovation and Evolution & Ecology Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW, 2052, Australia b Sydney Institute of Marine Science, Mosman, NSW, 2088, Australia c Water Research Laboratory, School of Civil and Environmental Engineering, UNSW, Sydney, NSW, Australia d Department of Environmental Sciences, Macquarie University, North Ryde, NSW, 2109, Australia ARTICLE INFO ABSTRACT Keywords: Sea-level rise is an inevitable consequence of climate change and threatens coastal ecosystems, particularly Sea level rise intertidal habitats that are constrained by landward development. Intertidal habitats support significant biodi­ Climate change versity, but also provide natural buffers from climate-threats such as increased storm events. Predicting the LiDAR effects of climate scenarios on coastal ecosystems is important for understanding both the degree of habitat loss IUCN red list of ecosystems for associated ecological communities and the risk of the loss of coastal buffer zones. We take a novel approach Conservation management by combining remote sensing with the IUCN Red List of Ecosystem criteria to assess this impact. We quantified the extent of horizontal intertidal rocky shores along ~200 km of coastline in Eastern Australia using GIS and remote-sensing (LiDAR) and used this information to predict changes in extent under four different climate change driven sea-level rise scenarios. We then applied the IUCN Red List of Ecosystems Criterion C2 (habitat degradation over the next 50 years based on change in an abiotic variable) to estimate the status of this ecosystem using the Hawkesbury Shelf Marine Bioregion as a test coastline. We also used four individual rocky shores as case studies to investigate the role of local topography in determining the severity of sea-level rise impacts. We found that, if the habitat loss within the study area is representative of the entire bioregion, the IUCN status of this ecosystem is ‘near threatened’, assuming that an assessment of the other criteria would return lower categories of risk. There was, however, high spatial variability in this effect. Rocky shores with gentle slopes had the highest projected losses of area whereas rocky shores expanding above the current intertidal range were less affected. Among the sites surveyed in detail, the ecosystem status ranged from ‘least concern’ to ‘vulnerable’, but reached ‘endangered’ under upper estimates of the most severe scenario. Our results have important implications for conservation management, highlighting a new link between remote sensing and the IUCN Red List of Ecosystem criteria that can be applied worldwide to assess ecosystem risk to sea-level rise. 1. Introduction predictions for the level of this rise vary depending on the amount of anthropogenic contributions (in the form of emissions and land-use Climate change threatens marine ecosystems at a global scale change) to radiative forcing. Radiative forcing is a measure of change through changes in temperature, ocean acidification and sea-level rise in the balance between incoming solar radiation and outgoing infrared (Brierley and Kingsford, 2009; Doney et al., 2012; Hoegh-Guldberg and radiation due to a forcing agent (IPCC, 2013). Four global scenarios Bruno, 2010). Sea-level rise is a consequence of thermal expansion of the developed by the International Panel for Climate Change (IPCC) are ocean and the melting of water stored in glaciers and ice-caps (Church used to represent the effect of radiative forcing in 2100, relative to et al., 2011; IPCC, 2013). Under climate change, sea-level rise has been preindustrial levels: RCP2.6, RCP4.5, RCP6.0, RCP8.5 (IPCC, 2013). projected to exceed previously observed rates (IPCC, 2013), but Under these scenarios, global sea-level rise is expected to increase at a * Corresponding author. E-mail address: [email protected] (N. Schaefer). https://doi.org/10.1016/j.jenvman.2020.110203 Received 31 January 2019; Received in revised form 16 January 2020; Accepted 25 January 2020 Available online 2 March 2020 0301-4797/© 2020 Elsevier Ltd. All rights reserved. N. Schaefer et al. Journal of Environmental Management 261 (2020) 110203 rate of 4.4, 6.1, 7.4 and 11.2 mm/year (values represent median values), rocky shorelines (a triangular irregular network of contour data) found respectively (IPCC, 2013). that a rise in sea-level between 0.3 and 1.9 m will, in some areas, result Sea-level rise will have the greatest ecological impact along low lying in a loss of 10%–50% of rocky shore extent (Jackson and McIlvenny, coastlines through increasing inundation of the intertidal zone, which 2011). Furthermore, under a 1.9 m sea-level rise scenario, slopes are supports important ecological assemblages such as mangroves, sea­ predicted to steepen in these areas, with at least 50% of rocky shores � grasses, saltmarshes and rocky shores (FitzGerald et al., 2008; Nicholls becoming vertical (�45 ) (Jackson and McIlvenny, 2011). The transi­ and Cazenave, 2010; Nicholls et al., 1999). Apart from providing habitat tion to a steeper relief from a flatrocky shore may force organisms into for intertidal biodiversity, these habitats provide a buffer from greater densities and increase pressure from competition, particularly in destructive ocean forces, reducing the impact of storm events and areas where static vertical barriers such as seawalls prevent a landward mitigating erosion (Gedan et al., 2011; Shepard et al., 2011; Spalding migration (Pontee, 2013). Yet little is known about the effect of sea-level et al., 2014). It is therefore important to quantify the risks to important rise on intertidal rocky shores in other areas of the world or in the coastal habitats from sea-level rise. In this study we used the Hawkes­ context of multiple climate change scenarios. Sea-level rise is an inevi­ bury Shelf Marine Bioregion as a test region and applied remote sensing table consequence of climate change, and understanding the possible to investigate the threat of sea-level rise to intertidal rocky shores negative consequences is essential to inform conservation and mitigate (Fig. 1). impacts. We take a novel approach to understand this change and its Intertidal rocky shores are the most common coastal habitat world­ potential impacts by combining remote sensing data (LiDAR) and the wide and are ecologically valuable (Thompson et al., 2002). They sup­ IUCN Red List of Ecosystems criteria. Remote sensing provides solutions port a diverse array of species, which is attributed to the high structural to rapidly collect geospatial data over large spatial scales, whereas the complexity of rocky shores (Blanchard and Bourget, 1999; Chapman, IUCN Red List of Ecosystem criteria provide a consistent framework for 2003; Sebens, 1991). Intertidal rocky shores and the communities living ecosystem risk assessments that can be applied worldwide. on them provide numerous ecosystem functions and services. Here, by following the framework of the IUCN Red List of Ecosystems Filter-feeders such as oysters improve water quality and further promote criteria (Keith et al., 2013), we assessed the current status of ~200 km of biodiversity by creating additional habitat for other intertidal organisms coastline within the Hawkesbury Shelf Marine Bioregion in order to (Coen et al., 2007; Grabowski et al., 2012). Intertidal rocky shore also estimate the status of intertidal rocky shores of the entire bioregion and act as important nursery and feeding ground for fish during high tide discuss potential effects of sea-level rise on associated biota. Under the and shorebirds during low tide (Burrows et al., 1999; Cantin et al., 1974; IUCN system, the status of an ecosystem is assessed against fivecriteria, Rangeley and Kramer, 1995). Yet rocky shores are also amongst the most with the final ecosystem status determined based on the highest risk vulnerable marine systems, facing a variety of anthropogenically returned for any one category. We focus on criterion C2, which involves induced threats (Halpern et al., 2007; Thompson et al., 2002). an assessment of the extent and relative severity of habitat degradation Since alternating periods of emersion and submersion is the key in the next 50 years. We used a high-resolution LiDAR (light detection physical driver on intertidal rocky shores (Menge and Branch, 2001), and ranging) survey of coastal elevation to estimate the net loss/gain of rapid changes in sea-level can have particularly severe consequences for intertidal rocky shores under sea-level rise scenarios. the availability of habitat. In Scotland, a study used existing maps of Fig. 1. Map of the coastline (~210 km) that has been assessed for rocky shores (highlighted in blue) on the coast of NSW, Australia (projection: GCS_GDA_1994). Approximate extent of the Hawkesbury Shelf Marine Bioregion is indicated. Rocky shores that were additionally assessed are highlighted in green (BH: Bradleys Head, CB: Cape Banks, D: Delwood, F: Freshwater). (For interpretation of the references