Research article
Predicting the impact of sea-level rise on intertidal rocky shores with remote sensing

https://doi.org/10.1016/j.jenvman.2020.110203Get rights and content

Highlights

  • Future sea-level rise (SLR) threatens intertidal ecosystems worldwide.

  • We combined remote sensing and the IUCN Red List for a novel impact assessment.

  • 50 km of Australian rocky shores were identified to test this methodology.

  • Rocky shore status is ‘vulnerable’ to upper predictions of severe SLR scenario.

  • Our methodology provides a global tool to assess ecosystem impacts of future SLR.

Abstract

Sea-level rise is an inevitable consequence of climate change and threatens coastal ecosystems, particularly intertidal habitats that are constrained by landward development. Intertidal habitats support significant biodiversity, but also provide natural buffers from climate-threats such as increased storm events. Predicting the effects of climate scenarios on coastal ecosystems is important for understanding both the degree of habitat loss for associated ecological communities and the risk of the loss of coastal buffer zones. We take a novel approach 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.

Introduction

Climate change threatens marine ecosystems at a global scale through changes in temperature, ocean acidification and sea-level rise (Brierley and Kingsford, 2009; Doney et al., 2012; Hoegh-Guldberg and Bruno, 2010). Sea-level rise is a consequence of thermal expansion of the ocean and the melting of water stored in glaciers and ice-caps (Church et al., 2011; IPCC, 2013). Under climate change, sea-level rise has been projected to exceed previously observed rates (IPCC, 2013), but predictions for the level of this rise vary depending on the amount of anthropogenic contributions (in the form of emissions and land-use change) to radiative forcing. Radiative forcing is a measure of change in the balance between incoming solar radiation and outgoing infrared radiation due to a forcing agent (IPCC, 2013). Four global scenarios developed by the International Panel for Climate Change (IPCC) are used to represent the effect of radiative forcing in 2100, relative to preindustrial levels: RCP2.6, RCP4.5, RCP6.0, RCP8.5 (IPCC, 2013). Under these scenarios, global sea-level rise is expected to increase at a rate of 4.4, 6.1, 7.4 and 11.2 mm/year (values represent median values), respectively (IPCC, 2013).

Sea-level rise will have the greatest ecological impact along low lying coastlines through increasing inundation of the intertidal zone, which supports important ecological assemblages such as mangroves, seagrasses, saltmarshes and rocky shores (FitzGerald et al., 2008; Nicholls and Cazenave, 2010; Nicholls et al., 1999). Apart from providing habitat for intertidal biodiversity, these habitats provide a buffer from destructive ocean forces, reducing the impact of storm events and mitigating erosion (Gedan et al., 2011; Shepard et al., 2011; Spalding et al., 2014). It is therefore important to quantify the risks to important coastal habitats from sea-level rise. In this study we used the Hawkesbury Shelf Marine Bioregion as a test region and applied remote sensing to investigate the threat of sea-level rise to intertidal rocky shores (Fig. 1).

Intertidal rocky shores are the most common coastal habitat worldwide and are ecologically valuable (Thompson et al., 2002). They support a diverse array of species, which is attributed to the high structural complexity of rocky shores (Blanchard and Bourget, 1999; Chapman, 2003; Sebens, 1991). Intertidal rocky shores and the communities living on them provide numerous ecosystem functions and services. Filter-feeders such as oysters improve water quality and further promote biodiversity by creating additional habitat for other intertidal organisms (Coen et al., 2007; Grabowski et al., 2012). Intertidal rocky shore also act as important nursery and feeding ground for fish during high tide and shorebirds during low tide (Burrows et al., 1999; Cantin et al., 1974; Rangeley and Kramer, 1995). Yet rocky shores are also amongst the most vulnerable marine systems, facing a variety of anthropogenically induced threats (Halpern et al., 2007; Thompson et al., 2002).

Since alternating periods of emersion and submersion is the key physical driver on intertidal rocky shores (Menge and Branch, 2001), rapid changes in sea-level can have particularly severe consequences for the availability of habitat. In Scotland, a study used existing maps of rocky shorelines (a triangular irregular network of contour data) found that a rise in sea-level between 0.3 and 1.9 m will, in some areas, result in a loss of 10%–50% of rocky shore extent (Jackson and McIlvenny, 2011). Furthermore, under a 1.9 m sea-level rise scenario, slopes are predicted to steepen in these areas, with at least 50% of rocky shores becoming vertical (≥45°) (Jackson and McIlvenny, 2011). The transition to a steeper relief from a flat rocky shore may force organisms into greater densities and increase pressure from competition, particularly in areas where static vertical barriers such as seawalls prevent a landward migration (Pontee, 2013). Yet little is known about the effect of sea-level rise on intertidal rocky shores in other areas of the world or in the context of multiple climate change scenarios. Sea-level rise is an inevitable consequence of climate change, and understanding the possible negative consequences is essential to inform conservation and mitigate impacts. We take a novel approach to understand this change and its potential impacts by combining remote sensing data (LiDAR) and the IUCN Red List of Ecosystems criteria. Remote sensing provides solutions to rapidly collect geospatial data over large spatial scales, whereas the IUCN Red List of Ecosystem criteria provide a consistent framework for ecosystem risk assessments that can be applied worldwide.

Here, by following the framework of the IUCN Red List of Ecosystems criteria (Keith et al., 2013), we assessed the current status of ~200 km of coastline within the Hawkesbury Shelf Marine Bioregion in order to estimate the status of intertidal rocky shores of the entire bioregion and discuss potential effects of sea-level rise on associated biota. Under the IUCN system, the status of an ecosystem is assessed against five criteria, with the final ecosystem status determined based on the highest risk returned for any one category. We focus on criterion C2, which involves an assessment of the extent and relative severity of habitat degradation in the next 50 years. We used a high-resolution LiDAR (light detection and ranging) survey of coastal elevation to estimate the net loss/gain of intertidal rocky shores under sea-level rise scenarios.

Section snippets

IUCN red list of ecosystems

The IUCN Red List of Ecosystems was established to fill the demand for biodiversity assessments that address levels of biodiversity above those of single species, such as those of ecosystems (Rodríguez et al., 2011). It assesses the risk of an ecosystem collapse, which occurs when an ecosystem loses its defining biotic or abiotic features, and the characteristic native biota and ecosystem processes are lost (Keith et al., 2013). The framework of the IUCN Red List of Ecosystems to assess the

Net loss of intertidal rocky shore extent

The current area of intertidal rocky shores is estimated at 374,689 m2 along approximately 50 km of rocky shore within the assessed 210 km of the NSW coastline. However, the area is likely to be underestimated due to the lack of reliable elevation data available in the low and mid-intertidal zones (see Methods: Spatial analysis).

Model predictions based on median sea-level rise rates suggest that the available habitat for intertidal organisms will be reduced over the next 50 years at an overall

Discussion

Coastal ecosystems are changing worldwide as a result of climate change, including sea-level rise. Here we quantified the sea-level rise threat to rocky intertidal communities along ~200 km of coastline in SE Australia using the criteria applied in the IUCN Red List of Ecosystems. Under the IUCN Criterion C2, which considers the degradation of an abiotic variable over the next 50 years, we found that intertidal rocky shores in this bioregion should be classified as ‘near threatened’ due to the

Conclusion

This study highlighted the high degree of risk to intertidal rocky shore environments from sea-level rise. We found that the IUCN threshold for ‘vulnerable’ classification is not exceeded for median estimates of sea-level rise in the next 50 years, but it is certain that rising sea-levels will increase the inundation of rocky shores into the future. The overall status of ‘near threatened’ highlights the need for ongoing assessment of this habitat such that proactive management and conservation

CRediT authorship contribution statement

Nina Schaefer: Conceptualization, Methodology, Formal analysis, Writing - original draft. Mariana Mayer-Pinto: Conceptualization, Writing - review & editing, Supervision. Kingsley J. Griffin: Methodology, Formal analysis, Visualization, Writing - review & editing. Emma L. Johnston: Conceptualization, Writing - review & editing, Supervision, Funding acquisition. William Glamore: Methodology, Resources, Writing - review & editing. Katherine A. Dafforn: Conceptualization, Writing - review &

Acknowledgements

We thank Valentin Heimhuber for his assistance and advice on GIS processing. The authors further thank three anonymous reviewers and the editor for their comments, which significantly improved the manuscript. The authors declare no conflicts of interest. This research was funded by an Australian Research Council Linkage Grant LP140100753 awarded to Katherine A. Dafforn and Emma L. Johnston.

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