Extreme temperatures, foundation species, and abrupt ecosystem change: an example from an iconic seagrass ecosystem

Our plain-English summary of Extreme temperatures, foundation species, and abrupt ecosystem change: an example from an iconic seagrass ecosystem, by J.A. Thomson, D.A. Burkholder, M.R. Heithaus, et al (Global Change Biology, 2015).

The study

• Authors: J.A. Thomson, D.A. Burkholder, M.R. Heithaus, J.W. Fourqurean, M.W. Fraser, J. Statton, G.A. Kendrick
• Journal: Global Change Biology
• Published: 2015;21(4):1463-74
• Cited by: 102 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Extreme climatic events can trigger abrupt and often lasting change in ecosystems via the reduction or elimination of foundation (i.e., habitat-forming) species. However, while the frequency/intensity of extreme events is predicted to increase under climate change, the impact of these events on many foundation species and the ecosystems they support remains poorly understood. Here, we use the iconic seagrass meadows of Shark Bay, Western Australia--a relatively pristine subtropical embayment whose dominant, canopy-forming seagrass, Amphibolis antarctica, is a temperate species growing near its low-latitude range limit--as a model system to investigate the impacts of extreme temperatures on ecosystems supported by thermally sensitive foundation species in a changing climate. Following an unprecedented marine heat wave in late summer 2010/11, A. antarctica experienced catastrophic (>90%) dieback in several regions of Shark Bay. Animal-borne video footage taken from the perspective of resident, seagrass-associated megafauna (sea turtles) revealed severe habitat degradation after the event compared with a decade earlier. This reduction in habitat quality corresponded with a decline in the health status of largely herbivorous green turtles (Chelonia mydas) in the 2 years following the heat wave, providing evidence of long-term, community-level impacts of the event. Based on these findings, and similar examples from diverse ecosystems, we argue that a generalized framework for assessing the vulnerability of ecosystems to abrupt change associated with the loss of foundation species is needed to accurately predict ecosystem trajectories in a changing climate. This includes seagrass meadows, which have received relatively little attention in this context. Novel research and monitoring methods, such as the analysis of habitat and environmental data from animal-borne video and data-logging systems, can make an important contribution to this framework.

© 2014 John Wiley & Sons Ltd.

In plain English

This article does not concern asbestos. It is an ecology field study of seagrass and green turtles in Shark Bay, Western Australia, after a 2010/11 marine heat wave. The authors resurveyed 113 seagrass sites in 2012 that had been surveyed in 2007 to 2009. They took biomass cores at five Wooramel Bank sites. They compared turtle-borne video from 1999 to 2003 and 2011 to 2012, and rated the health of green turtles captured from 2000 to 2013. Where the seagrass Amphibolis antarctica was present during at least one visit, median cover fell from 87.4% in 2007 to 2009 to 3.7% in 2012. In the Wooramel Bank cores, its below-ground biomass decreased sixfold in the 2 years after the heat wave. In the videos, turtles spent 97% of their time over lush, dense seagrass before the heat wave and 4% after. Green turtle health status declined from 2011 to 2013. The authors concluded that temperature extremes have the potential to abruptly restructure ecosystems. They noted that a flood may have affected the Wooramel biomass results and that unsampled areas need study.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Field study comparing seagrass surveys, plant biomass cores, turtle-borne video footage and green turtle health assessments from before and after a marine heat wave
• Who was studied: Seagrass sites in Shark Bay, Western Australia: 113 sites revisited in 2012 (42 on the Monkey Mia Banks and 71 in three other regions). Five biomass coring sites on the Wooramel Bank. Turtle-borne video from green and loggerhead turtles. Health assessments of 424 individual green turtles (447 captures) from 2000 to 2013.
• Exposure: A marine heat wave in late summer 2010/11 (not asbestos)
• Main results:
  • Across the 113 sites, A. antarctica was observed at 71 sites in 2012, with median percent cover of 1.7%. Before the heat wave it had been observed at 93 sites, with median cover of 83.4%.
  • At sites where A. antarctica was present during at least one visit, median cover declined from 87.4% in 2007 to 2009 to 3.7% in 2012, which the authors described as a 96% dieback.
  • On the Wooramel Bank, below-ground biomass of A. antarctica (rhizomes and roots) decreased sixfold in the 2 years after the heat wave.
  • In the two known reproductive populations of the seagrass Posidonia australis, 100% of fruit aborted seed production during the heat wave.
  • In turtle-borne video, turtles spent 97% of their time over the most lush, dense seagrass in 1999 to 2003. In 2011 to 2012 the figure was 4%, and no A. antarctica in the highest condition category was encountered.
  • Green turtle health status declined consistently from 2011 to 2013. In 2012, 6% of turtles were in the highest health category, compared with an average of 35% in 2000 to 2006. In 2013, no turtles were in that category.
• The authors' conclusion: The authors concluded that temperature extremes such as the 2010/11 heat wave have the potential to abruptly restructure ecosystems by reducing or eliminating thermally sensitive foundation species.
• Limitations the authors state:
  • A flood of the Wooramel River in January 2011 may have contributed to the biomass trends at the Wooramel Bank coring sites.
  • The extent of the dieback in unsampled regions of Shark Bay is unknown.
  • Only a small number of samples was taken at each site, so that enough sites could be covered.

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