Extreme climate events lower resilience of foundation seagrass at edge of biogeographical range

• Published in: Journal of Ecology
• Main Authors: Fraser, Matthew W., Kendrick, Gary A., Statton, John, Hovey, Renae K., Zavala‐Perez, Andrea, Walker, Diana I.
• Other Authors: Lee, John, Caring for our Country
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2014
• Subjects: Antarc*; Antarctica
• Online Access: http://dx.doi.org/10.1111/1365-2745.12300; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2F1365-2745.12300; https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/1365-2745.12300

Summary Extreme climatic events will dictate the response of ecosystems to climate change, yet are understudied in marine ecosystems. The interaction of stressors from such events has the potential to amplify negative impacts and drive ecosystems into alternate states. Here, we show a drastic response of a temperate seagrass species ( Amphibolis antarctica ) in Shark Bay – a World Heritage Site in Western Australia at a temperate–tropical transition zone – to two stressors driven by concurrent extreme climatic events: a marine heatwave (Ningaloo Niña) and the Gascoyne floods that impacted the west coast of Australia in the austral summer of 2010–2011. Widespread defoliation (leaf loss) of A. antarctica was observed in the months following the extreme events and was highest at sites affected by flooding (Wooramel River floods). We propose that the negative impact was magnified by the synergistic interactions both stressors had on the carbon balance of the plant. The elevated temperatures increased plant demand for carbon, which could not be met through photosynthesis due to turbid floodwaters reducing light availability, resulting in the plant having a negative carbon balance. Two years following the extreme events, recovery of leaf biomass was evident, though still 7–20% of historical averages. In contrast, below‐ground biomass decreased by an order of magnitude in the two years following the events. As below‐ground reserves underpin the tolerance of large seagrass species like A. antarctica to disturbances, the declining trajectory of below‐ground biomass will likely manifest as a loss of resilience in A. antarctica to future disturbances. Synthesis . Given the ecological importance of Amphibolis antarctica in Shark Bay as a foundation species – accounting for 85% (˜3700 km 2 ) of the cover of seagrasses in Shark Bay – predicted increases in the frequency and magnitude of similar climatic events could have catastrophic implications for the future of this World Heritage embayment. Where extreme climatic events ...