Preprints
https://doi.org/10.5194/bg-2021-61
https://doi.org/10.5194/bg-2021-61

  24 Mar 2021

24 Mar 2021

Review status: this preprint is currently under review for the journal BG.

Will community calcification reflect reef accretion on future, degraded coral reefs?

Coulson A. Lantz1,2, William Leggat2, Jessica L. Bergman1, Alexander Fordyce2, Charlotte Page1, Thomas Mesaglio1, and Tracy D. Ainsworth1 Coulson A. Lantz et al.
  • 1University of New South Wales, School of Biological, Earth and Environmental Sciences, Kensington, 2033 NSW Australia
  • 2University of Newcastle, School of Environmental and Life Sciences, Callaghan 2309 NSW Australia

Abstract. Coral bleaching events continue to drive the degradation of coral reefs worldwide, causing a shift in the benthic community from coral to algae dominated ecosystems. Critically, this shift may decrease the capacity of degraded coral reef communities to maintain net positive accretion during warming-driven stress events (e.g., reef-wide coral bleaching). Here we measured rates of net ecosystem calcification (NEC) and net ecosystem production (NEP) on a degraded coral reef lagoon community (coral cover < 10 % and algae cover > 20 %) during a reef-wide bleaching event in February of 2020 at Heron Island on the Great Barrier Reef. We found that during this bleaching event, rates of community NEP and NEC across replicate transects remained positive and did not change in response to bleaching. Repeated benthic surveys over a period of 20 d indicated an increase in the percent area of bleached coral tissue, corroborated by relatively low Symbiodiniaceae densities (~0.6 × 106 cm−2) and dark-adapted photosynthetic yields in photosystem II of corals (~0.5) sampled along each transect over this period. Given that a clear decline in coral health was not reflected in the overall community NEC estimates, it is possible that elevated temperatures in the water column that compromise coral health enhanced the thermodynamic favourability for calcification in other, ahermatypic benthic calcifiers. These data suggest that positive NEC on degraded reefs may not equate to the net positive accretion of reef structure in a future, warmer ocean. Critically, our study highlights that if coral cover continues to decline as predicted, NEC may no longer be an appropriate proxy for reef growth as the proportion of the community NEC signal owed to ahermatypic calcification increases and coral dominance on the reef decreases.

Coulson A. Lantz et al.

Status: open (until 05 May 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-61', Thomas DeCarlo, 17 Apr 2021 reply

Coulson A. Lantz et al.

Coulson A. Lantz et al.

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Short summary
Coral bleaching events continue to drive the degradation of coral reefs worldwide. In this study we measured rates of coral reef community calcification and photosynthesis during a reef-wide bleaching event. Despite a measured decline in coral health across several taxa, there was no change in overall community calcification and photosynthesis. These findings highlight potential limitations of these community-level metrics to reflect actual changes in coral health.
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