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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-329
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-329
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 26 Sep 2019

Submitted as: research article | 26 Sep 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Multi-decadal changes in structural complexity following mass coral mortality on a Caribbean reef

George Roff1, Jennifer Joseph2, and Peter J. Mumby1 George Roff et al.
  • 1Marine Spatial Ecology Lab, School of Biological Sciences, University of Queensland, QLD 4072 Australia
  • 2College of Earth, Ocean & Environment, University of Delaware, Newark, DE, USA

Abstract. In recent decades, extensive mortality of reef-building corals throughout the Caribbean region has led to erosion of reef frameworks and declines in biodiversity. Using field observations, structural models and high-precision U-th dating methods, we quantify changes in structural complexity in the major framework building coral Orbicella annularis over a 20-year period at Long Cay (Belize). Despite extensive mortality following the mass coral bleaching event of 1998, structural complexity of frameworks remained largely unchanged between 1998 (rugosity index = 2.35 ± 0.1) and 2018 (2.29 ± 0.1). Reef-scale structural complexity was maintained through rapid growth of surviving ramets (0.69 ± 0.1 cm yr−1) offsetting slower bioerosion of dead ramets (−0.11 ± 0.16 cm yr−1). Despite apparent stability of structural complexity at reef-scales, bioerosion of individual dead ramets over two decades led to declines in microhabitat complexity, with an overall reduction of the depth of microhabitats within frameworks. Altered microhabitat complexity appears to have negative effects for cryptic fauna, with the grazing urchin Echinometra viridis declining from 1.5 ± 0.4 per m2 in 1998 to 0.02 ± 0.02 per m2 in 2018. Changes in microhabitat complexity have the potential to alter ecological interactions that can impact recovery dynamics on coral reefs in ways that are undetectable using reef-scale metrics of structural complexity.

George Roff et al.
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George Roff et al.
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Short summary
In recent decades, extensive mortality of reef-building corals throughout the Caribbean region has led to erosion of reef frameworks and declines in biodiversity. Using field observations, models and high-precision U-th dating, we quantified changes in structural complexity in the coral reef frameworks over the past two decades. Structural complexity was stable at reef-scales, yet bioerosion led to declines in small-scale microhabitat complexity with cascading effects on cryptic fauna.
In recent decades, extensive mortality of reef-building corals throughout the Caribbean region...
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