Projections of coral cover and habitat change on turbid reefs under future sea-level rise

Morgan, Kyle M.; Perry, Chris T.; Arthur, Rangel; Williams, Hywel T. P.; Smithers, Scott G.

doi:10.1098/rspb.2020.0541

Cited by 19 publications

(17 citation statements)

References 40 publications

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“…Our data suggests that vertical reef compression is being driven from the bottom-up, as the photic zone contracts and fine silts accumulate at depth (Figure 8), reducing both habitat availability and coral diversity (e.g., Morgan et al, 2020). Sediment deposited on reef slope corals had distinct size distributions, which replicated those exhibited by gross and net sedimentation trapping methods (Figure 6).…”

Section: Discussionsupporting

confidence: 58%

“…The maximum depth limit of coral growth is primarily dependent on the euphotic depth [i.e., the depth where photosynthetic available radiation (PAR) is 1% of its surface value], below which net photosynthesis occurs. Even minor local increases in suspended sediment load (e.g., 1-10 mg l −1 ), which may have limited direct physiological impacts on the corals themselves, can disproportionately influence coral distribution by attenuating more light and further shallowing the photic floor on these already light-limited reefs (Jones et al, 2015;Storlazzi et al, 2015;Morgan et al, 2020). While a conceptual understanding of vertical reef compression currently exists, the physical environments of turbid reef settings are not well quantified, and greater knowledge of the cause-effect pathways that limit the depth range of coral reef development is needed.…”

Section: Introductionmentioning

confidence: 99%

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Light Limitation and Depth-Variable Sedimentation Drives Vertical Reef Compression on Turbid Coral Reefs

et al. 2020

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Turbid coral reefs experience high suspended sediment loads and low-light conditions that vertically compress the maximum depth of reef growth. Although vertical reef compression is hypothesized to further decrease available coral habitat as environmental conditions on reefs change, its causative processes have not been fully quantified. Here, we present a high-resolution time series of environmental parameters known to influence coral depth distribution (light, turbidity, sedimentation, currents) within reef crest (2–3 m) and reef slope (7 m) habitats on two turbid reefs in Singapore. Light levels on reef crests were low [mean daily light integral (DLI): 13.9 ± 5.6 and 6.4 ± 3.0 mol photons m–2 day–1 at Kusu and Hantu, respectively], and light differences between reefs were driven by a 2-fold increase in turbidity at Hantu (typically 10–50 mg l–1), despite its similar distance offshore. Light attenuation was rapid (KdPAR: 0.49–0.57 m–1) resulting in a shallow euphotic depth of <11 m, and daily fluctuations of up to 8 m. Remote sensing indicates a regional west-to-east gradient in light availability and turbidity across southern Singapore attributed to spatial variability in suspended sediment, chlorophyll-a and colored dissolved organic matter. Net sediment accumulation rates were ∼5% of gross rates on reefs (9.8–22.9 mg cm–2 day–1) due to the resuspension of sediment by tidal currents, which contribute to the ecological stability of reef crest coral communities. Lower current velocities on the reef slope deposit ∼4 kg m2 more silt annually, and result in high soft-sediment benthic cover. Our findings confirm that vertical reef compression is driven from the bottom-up, as the photic zone contracts and fine silt accumulates at depth, reducing available habitat for coral growth. Assuming no further declines in water quality, future sea level rise could decrease the depth distribution of these turbid reefs by a further 8–12%. This highlights the vulnerability of deeper coral communities on turbid reefs to the combined effects of both local anthropogenic inputs and climate-related impacts.

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Section: Discussionsupporting

confidence: 58%

Section: Introductionmentioning

confidence: 99%

Light Limitation and Depth-Variable Sedimentation Drives Vertical Reef Compression on Turbid Coral Reefs

et al. 2020

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“…While marked sea‐level depressions result in lowered coral cover on shallow reefs, conversely sea‐level rise in the medium term (10 s of years) promotes coral cover (Brown et al, 2011; Saunders et al, 2015; Scopelitis et al, 2011). In the long term (100+ years) under extreme climatic projections (RCP 8.5), modelling of sea‐level rise on the Great Barrier Reef suggests future reef submergence (Morgan et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

The Indian Ocean Dipole and El Niño Southern Oscillation as major drivers of coral cover on shallow reefs in the Andaman Sea

Dunne¹,

Brown

Phongsuwan

et al. 2021

Global Change Biology

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Shallow reefs are a major feature of coral assemblages in the Andaman Sea. At Phuket, Thailand sheltered reefs are dominated by massive corals, together with an increasing abundance of branching species during favourable growth conditions. The growth of coral on these reefs is moderated by long‐term increases in sea temperature and relative sea level but fluctuating decadal/intradecadal climate processes of El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD), which modulate sea level and temperature, are the main drivers of coral cover. In this study, the contribution of these two climate processes was identified and also quantified. Over a 34‐year study of fluctuating coral cover, the three major reductions in cover in 1997, 2010 and 2019 were linked to overlapping positive IOD (pIOD) and El Niños in 1997 and 2019, and with an El Niño alone in 2010. Combined pIOD and El Niño depressed sea level was the major factor in reducing cover in 1997 while El Niño extreme sea temperatures were responsible for large reductions in 2010. In 2019, a bi‐phasic pIOD and El Niño resulted in lowered cover at a time of both decreased sea level and high sea temperature. Under global warming scenarios, it is projected that extreme pIODs, such as those seen in 1997 and 2019, will occur more frequently while El Niño frequencies will continue to increase even after global mean temperature stabilization. In these circumstances, and with steadily rising background sea temperatures, the future risks to the shallow reefs of the Andaman Sea are substantial, despite any temporary respite gained from climate related or land subsidence sea‐level rise. Such findings have wider implications for all reefs affected by climatic‐driven sea‐level depressions, particularly those around Indonesian shores where similar El‐Niño‐related reductions in coral cover have been reported.

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“…These different sedimentary and geomorphic settings highlight the broad range of natural environmental conditions where turbid reefs have initiated and developed and could be used to distinguish natural turbid reefs (persistent, fluctuating) from those reefs that have transitioned to turbid (or to more turbid) during the Anthropocene. [26,121,122]. This turbid nearshore shoal comprises seven disconnected fringing reef structures [14].…”

Section: Global Distribution Sources Of Turbidity and Environmental S...mentioning

confidence: 99%

Turbid Coral Reefs: Past, Present and Future—A Review

2021

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Increasing evidence suggests that coral reefs exposed to elevated turbidity may be more resilient to climate change impacts and serve as an important conservation hotspot. However, logistical difficulties in studying turbid environments have led to poor representation of these reef types within the scientific literature, with studies using different methods and definitions to characterize turbid reefs. Here we review the geological origins and growth histories of turbid reefs from the Holocene (past), their current ecological and environmental states (present), and their potential responses and resilience to increasing local and global pressures (future). We classify turbid reefs using new descriptors based on their turbidity regime (persistent, fluctuating, transitional) and sources of sediment input (natural versus anthropogenic). Further, by comparing the composition, function and resilience of two of the most studied turbid reefs, Paluma Shoals Reef Complex, Australia (natural turbidity) and Singapore reefs (anthropogenic turbidity), we found them to be two distinct types of turbid reefs with different conservation status. As the geographic range of turbid reefs is expected to increase due to local and global stressors, improving our understanding of their responses to environmental change will be central to global coral reef conservation efforts.

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Projections of coral cover and habitat change on turbid reefs under future sea-level rise

Cited by 19 publications

References 40 publications

Light Limitation and Depth-Variable Sedimentation Drives Vertical Reef Compression on Turbid Coral Reefs

Light Limitation and Depth-Variable Sedimentation Drives Vertical Reef Compression on Turbid Coral Reefs

The Indian Ocean Dipole and El Niño Southern Oscillation as major drivers of coral cover on shallow reefs in the Andaman Sea

Turbid Coral Reefs: Past, Present and Future—A Review

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