On the fate of dead coral colonies

Abstract

1. Carbonate budgets dynamically balance production and loss of calcium carbonate (CaCO 3 ) on coral reefs. To sustain or expand the coral reef framework, CaCO 3 production by calcifying organisms must be higher than erosion. However, global climate change has been negatively impacting carbonate production, with bleaching events causing widespread coral mortality. Although bleaching and coral mortality are well documented, the fate of coral colonies after their death, including their erosion rates, are still poorly known.2. We followed the fate of 143 recently dead individual coral colonies with complex growth forms (arborescent, caespitose, corymbose, digitate and tabular), whose mortality was triggered by two consecutive bleaching events. These colonies, spread over 16 km 2 of the Lizard Island reef complex, were tracked for up to 5 years, allowing detailed examination of erosion rates and post-mortality structural persistence. We also tested how variables that are commonly used in coral reef erosion studies relate to spatial and temporal variability in the erosion rates of dead coral colonies.3. We revealed rapid erosion of dead coral colonies, with an average of 79.7% of dead colonies completely disintegrating within 60 months. The predicted halflife of a dead coral colony was 40 months, with limited variation among wave exposure levels. Remarkably, we found no effect of estimated parrotfish bioerosion, wave exposure, nor coral growth form, on observed erosion rates. 4. Our results suggest that our understanding of the erosion of dead corals may be more limited than previously thought. The rapid loss of coral colonies on our study sites calls for a re-evaluation of the role of corals with complex growth forms in reef growth and of parrotfishes in reef erosion.

Stony coral tissue loss disease indirectly alters reef communities

“…4). This is consistent with other observations of erosion following coral mortality (60)(61)(62)(63). Because predictions were based on existing relationships between live coral and rugosity in the Caribbean, these modeled reductions in rugosity following SCTLD are likely underestimates, as bioerosion will continue to lower rugosity, even without additional coral death.…”

The global biogeography of reef morphology

“…Similarly, in St. Croix, US Virgin Islands, Hubbard et al (1990) described the local reef framework as a ‘garbage pile’ of carbonate reef detritus rather than an array of in situ coral framework assemblages. Montaggioni (2005) likewise identified coral and skeletal rubble facies as the most prominent features of reef cores in the Indo‐Pacific, occupying up to 60% of the total core volume, while Morais et al (2022) showed that dead coral skeletons may have a negligible contribution to local, in situ, reef accretion.…”

“…reef growth). Indeed, the accumulation of stressors on coral reefs in the Anthropocene may cause further decoupling of the processes that support reef accretion from the more visible ecological coral-based processes that appear to drive carbonate production on the reef surface (Morais et al, 2022).…”

3D photogrammetry and deep‐learning deliver accurate estimates of epibenthic biomass

“…To date, SfM has been used from tropical reefs (e.g. Fukunaga et al, 2019), to temperate (Spyksma et al, 2022), polar (Piazza et al, 2019) and deep-water environments (De Oliveira et al, 2021) and has been used to assess habitat complexity (Aston et al, 2022;Bayley et al, 2019;Price et al, 2019), growth rates (Olinger et al, 2019;Prado et al, 2021), bioerosion (Morais et al, 2022), habitat provision (Urbina-Barreto et al, 2021) and benthic cover (Raoult et al, 2016). Furthermore, Palma et al (2018) used SfM-derived surface area measurements to estimate biomass of Mediterranean sea fans and Ríos et al (2020) estimated biomass of the deep-sea sponges from SfM-derived sponge perimeter.…”