Preprints
https://doi.org/10.5194/bg-2021-90
https://doi.org/10.5194/bg-2021-90

  03 May 2021

03 May 2021

Review status: a revised version of this preprint is currently under review for the journal BG.

The Bouraké semi-enclosed lagoon (New Caledonia). A natural laboratory to study the life-long adaptation of a coral reef ecosystem to climate change-like conditions

Federica Maggioni1, Mireille Pujo-Pay2, Jérome Aucan1, Carlo Cerrano3, Barbara Calcinai3, Claude Payri1, Francesca Benzoni4, Yves Letourneur1, and Riccardo Rodolfo-Metalpa1 Federica Maggioni et al.
  • 1UMR ENTROPIE (UR-IRD-IFREMER-CNRS-UNC), Centre IRD, BP A5, 98848 Nouméa cedex, New Caledonia
  • 2LOMIC, Laboratoire d’Océanographie Microbienne, Laboratoire Arago Banyuls sur Mer, France
  • 3Department of Life and Environmental Sciences (DiSVA), Polytechnic University of Marche, Ancona, Italy
  • 4Red Sea Research Center, Division of Biological and Environmental Science and Engineering, King Abdullah University of Science and Technology, 23955-6900 Thuwal, Saudi Arabia

Abstract. According to current experimental evidence, coral reefs could disappear within the century if CO2 emissions remain unabated. However, recent discoveries of diverse and high cover reefs that already thrive under extreme conditions seem to contradict these projections. Volcanic CO2 vents, semi-enclosed lagoons and mangrove estuaries are unique study sites where one or more ecologically relevant parameters for life in the oceans are close or even worse than currently projected for the year 2100. These natural analogues of future conditions hold new hope for the future of coral reefs and provide unique natural laboratories to explore how reef species could keep pace with climate change. To achieve this, it is essential to characterize their environment as a whole, and accurately consider all possible environmental factors that may differ from what is expected in the future and that may possibly alter the ecosystem response.

In this study, we focus on the semi-enclosed lagoon of Bouraké (New Caledonia, SW Pacific Ocean) where a healthy reef ecosystem thrives in warm, acidified and deoxygenated water. We used a multi-scale approach to characterize the main physical-chemical parameters and mapped the benthic community composition (i.e., corals, sponges, and macroalgae). The data revealed that most physical and chemical parameters are regulated by the tide, strongly fluctuate 3 to 4 times a day, and are entirely predictable. The seawater pH and dissolved oxygen decrease during falling tide and reach extreme low values at low tide (7.2 pHT and 1.9 mg O2 L−1 at Bouraké, vs 7.9 pHT and 5.5 mg O2 L−1 at reference reefs). Dissolved oxygen, temperature, and pH fluctuates according to the tide of up to 4.91 mg O2 L−1, 6.50 °C, and 0.69 pHT units on a single day. Furthermore, the concentration of most of the chemical parameters was one- to 5-times higher at the Bouraké lagoon, particularly for organic and inorganic carbon and nitrogen, but also for some nutrients, notably silicates. Surprisingly, despite extreme environmental conditions and altered seawater chemical composition, our results reveal a diverse and high cover community of macroalgae, sponges and corals accounting for 28, 11 and 66 species, respectively. Both environmental variability and nutrient imbalance might contribute to their survival under such extreme environmental conditions. We describe the natural dynamics of the Bouraké ecosystem and its relevance as a natural laboratory to investigate the benthic organism’s adaptive responses to multiple stressors like future climate change conditions.

Federica Maggioni et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on bg-2021-90', Alexia Dubuc, 19 May 2021
    • AC1: 'Reply on CC1', Federica Maggioni, 27 May 2021
  • RC1: 'Comment on bg-2021-90', Anonymous Referee #1, 25 May 2021
    • AC2: 'Reply on RC1', Federica Maggioni, 30 May 2021
  • RC2: 'Comment on bg-2021-90', Anonymous Referee #2, 08 Jun 2021
    • AC3: 'Reply on RC2', Federica Maggioni, 15 Jun 2021

Federica Maggioni et al.

Federica Maggioni et al.

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Short summary
Based on current experimental evidence, climate change will affect up to 90 % of coral reefs worldwide. The originality of this study arises from our recent discovery of an exceptional study site, where environmental conditions (temperature, pH and oxygen) are even worse than those forecasted for the future. While these conditions are generally recognized as unfavorable for marine life, we found a rich and abundant coral reef thriving well under such extreme environmental conditions.
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