A climate adaptation strategy for Mai Po Inner Deep Bay Ramsar site: Steppingstone to climate proofing the East Asian-Australasian Flyway

Ramsar site will be less impacted. Most fishponds are privately owned and could be devel- oped in the future, including into high rise apartments; thus, securing them for conservation should be an important climate change adaptation strategy for Mai Po, since they provide essential habitats for birds under future climate change scenarios. But Mai Po is only one steppingstone along the EAAF, and hundreds of other wetlands are also threatened by encroaching infrastructure and climate change. Thus, similar analyses for the other wet- lands are recommended to develop a flyway-wide climate-adaptation conservation strategy before available options become lost to wetland conversion. Introduction Millions of birds undertake annual long-distance seasonal migrations along the East Asian- Australasian Flyway (EAAF), which stretches for over 13,000 km from the Arctic Circle to Australia and New Zealand [1]. The ecological functionality of this migration corridor depends on a network of coastal wetlands that represent steppingstones used by the birds as staging areas and over-wintering sites [2, 3]. Over the past several decades many of the wet- lands along the EAAF have been converted for development, from agriculture and aquaculture to coastal infrastructure [4–7]. Over 65% of the intertidal mudflats in the Yellow Sea, one of the more important staging areas along the flyway, have been lost in recent decades [8–10]. Continued loss of strategically located wetlands could drastically impact connectivity, prevent-

ing birds from completing their migrations, resulting in eventual species population declines, extirpation and eventual collapse of this important ecological and evolutionary phenomenon that has evolved over millennia [2, 3, 11]. But like many coastal wetlands across the world the EAAF wetlands are also under addi- tional threat from global climate change and its consequences, notably sea level rise (SLR) and extreme storms that are accompanied by stronger wave and tidal surges [5, 12]. The impacts of SLR and natural disasters are further compounded by subsidence and decreasing coastal sedi- mentation that is necessary to counter SLR [13–16]. Iwamura et al. [17] estimate that between 23 to 40% of the intertidal habitat will be lost and unavailable for migratory birds along the EAAF because of sea level rise, with some regions losing more than others. Coastal develop- ment, which has resulted in loss of wetlands, can now also place the remaining wetlands in a situation where they will be subjected to coastal squeeze; unable to migrate further inland in the event of SLR because of the adjacent hard infrastructure [18–20]. Thus, important wetlands along the flyway should be assessed for the impacts of climate change and associated drivers of ecological and environmental change to plan and implement proactive climate adaptation strategies. These analyses should be conducted at site scales to identify site-scale conservation strategies based on habitat availability, current and planned landuse, and restoration opportu-

nities. Because wetland conversion and coastal development is still continuing apace these analyses are urgently needed before options for conservation and restoration disappear. In Hong Kong, projections suggest rising sea levels and warmer, wetter weather that can spawn a higher number of severe typhoons [21, 22]. But, while the sea is rising, the deltas and mudflats in the Pearl River Delta could be shrinking. A model of sediment deposition and coastal nourishment of the Pearl River Delta projected that the fluvial sediment supply that fed the Pearl River Delta has decreased by 71% from the previous ‘natural state’, and any potential compensation from increased river flows attributed to climate change will only be about 1% of this deficit by the end of the 21st century, assuming impacts from human activities are PLOS ONE Climate adaptation strategy for Mai Po Inner Deep Bay Ramsar site PLOS ONE | https://doi.org/10.1371/journal.pone.0239945 October 21, 2020 2 / 16 opendata.arcgis.com/datasets/mai-po-wetland- habitats with a Creative Commons Attribution 4.0 International License, and copyright is duly referenced in the manuscript. The underlying SLAMM datalayers have been uploaded to Zenodo, and are available here: https://doi.org/10.5281/ zenodo.3935747. Funding: The analysis was supported by the general Mai Po Nature Reserve management fund, which is capitalized from multiple sources and managed by WWF Hong Kong. The salaries of EW, CO, XW, FC are supported by WWF Hong Kong (but not from the Mai Po Nature Reserve management fun). Authors FC and AS were

provided with a consultancy by WWF HK, through Here+There Mapping Solutions to conduct the analysis. The funder (WWF Hong Kong) provided support in the form of salaries for authors [EW, CO, XW, FC], but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section. FC and AS received a consultancy from WWF Hong Kong through Here+There Mapping Solutions, to run the SLAMM model. Competing interests: FC and AS received a consultancy from WWF Hong Kong through Here +There Mapping Solutions, to run the SLAMM model. This does not alter our adherence to PLOS ONE policies on sharing data and materials.