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Ecosystem resilience and threshold response in the Galápagos Coastal Zone

By Alistair W.R. Seddon, Cynthia A. Froyd, Melanie J. Leng, Glenn A. Milne and Katherine J. Willis

Abstract

Background: The Intergovernmental Panel on Climate Change (IPCC) provides a conservative estimate on rates of sea-level\ud rise of 3.8 mm yr21 at the end of the 21st century, which may have a detrimental effect on ecologically important mangrove\ud ecosystems. Understanding factors influencing the long-term resilience of these communities is critical but poorly\ud understood. We investigate ecological resilience in a coastal mangrove community from the Gala´pagos Islands over the last\ud 2700 years using three research questions: What are the ‘fast and slow’ processes operating in the coastal zone? Is there\ud evidence for a threshold response? How can the past inform us about the resilience of the modern system?\ud Methodology/Principal Findings: Palaeoecological methods (AMS radiocarbon dating, stable carbon isotopes (d13C)) were\ud used to reconstruct sedimentation rates and ecological change over the past 2,700 years at Diablas lagoon, Isabela,\ud Gala´pagos. Bulk geochemical analysis was also used to determine local environmental changes, and salinity was\ud reconstructed using a diatom transfer function. Changes in relative sea level (RSL) were estimated using a glacio-isostatic\ud adjustment model. Non-linear behaviour was observed in the Diablas mangrove ecosystem as it responded to increased\ud salinities following exposure to tidal inundations. A negative feedback was observed which enabled the mangrove canopy\ud to accrete vertically, but disturbances may have opened up the canopy and contributed to an erosion of resilience over\ud time. A combination of drier climatic conditions and a slight fall in RSL then resulted in a threshold response, from a\ud mangrove community to a microbial mat.\ud Conclusions/Significance: Palaeoecological records can provide important information on the nature of non-linear\ud behaviour by identifying thresholds within ecological systems, and in outlining responses to ‘fast’ and ‘slow’ environmental\ud change between alternative stable states. This study highlights the need to incorporate a long-term ecological perspective\ud when designing strategies for maximizing coastal resilience

Publisher: Public Library of Science
Year: 2011
DOI identifier: 10.1371/journal.pone.0022376
OAI identifier: oai:nora.nerc.ac.uk:15187

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