Testing for thresholds of ecosystem collapse in seagrass meadows |
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| Authors: | Sean D Connell Milena Fernandes Owen W Burnell Zoë A Doubleday Kingsley J Griffin Andrew D Irving Jonathan YS Leung Samuel Owen Bayden D Russell Laura J Falkenberg |
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| Affiliation: | 1. Southern Seas Ecology Laboratories, School of Biological Sciences and The Environment Institute, North Terrace, The University of Adelaide, South Australia, Australia;2. Australian Water Quality Centre, South Australian Water Corporation, Adelaide, South Australia, Australia;3. South Australian Research and Development Institute ‐ Aquatic Sciences, South Australia, Australia;4. Evolution and Ecology Research Centre, 5. School of Biological, Earth and Environmental Science, University of New South Wales, Kensington, Australia;6. School of Medical and Applied Sciences, CQ University, Rockhampton, Queensland, Australia;7. The Swire Institute of Marine Science, School of Biological Sciences, The University of Hong Kong, Hong Kong, SAR, China;8. Norwegian Institute for Water Research, Bergen, Norway |
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| Abstract: | Although the public desire for healthy environments is clear‐cut, the science and management of ecosystem health has not been as simple. Ecological systems can be dynamic and can shift abruptly from one ecosystem state to another. Such unpredictable shifts result when ecological thresholds are crossed; that is, small cumulative increases in an environmental stressor drive a much greater change than could be predicted from linear effects, suggesting an unforeseen tipping point is crossed. In coastal waters, broad‐scale seagrass loss often occurs as a sudden event associated with human‐driven nutrient enrichment (eutrophication). We tested whether the response of seagrass ecosystems to coastal nutrient enrichment is subject to a threshold effect. We exposed seagrass plots to different levels of nutrient enrichment (dissolved inorganic nitrogen) for 10 months and measured net production. Seagrass response exhibited a threshold pattern when nutrient enrichment exceeded moderate levels: there was an abrupt and large shift from positive to negative net leaf production (from approximately 0.04 leaf production to 0.02 leaf loss per day). Epiphyte load also increased as nutrient enrichment increased, which may have driven the shift in leaf production. Inadvertently crossing such thresholds, as can occur through ineffective management of land‐derived inputs such as wastewater and stormwater runoff along urbanized coasts, may account for the widely observed sudden loss of seagrass meadows. Identification of tipping points may improve not only adaptive‐management monitoring that seeks to avoid threshold effects, but also restoration approaches in systems that have crossed them. |
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| Keywords: | eutrophication habitat loss nutrients phase shift tipping point cambio de fase eutrofizació n momento crí tico nutrientes pé rdida de há bitat |
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