Future habitat suitability for coral reef ecosystems under global warming and ocean acidification

Abstract. To better predict how ocean acidification will affect coral reefs, it is important to understand how biogeochemical cycles on reefs alter carbonate chemistry over various temporal and spatial scales. This study quantifies the contribution of shallow porewater exchange (as quantified from advective chamber incubations) and fresh groundwater discharge (as traced by 222Rn) to total alkalinity (TA) dynamics on a fringing coral reef lagoon along the southern Pacific island of Rarotonga over a tidal and diel cycle. Benthic alkalinity fluxes were affected by the advective circulation of water through permeable sediments, with net daily flux rates of carbonate alkalinity ranging from −1.55 to 7.76 mmol m−2 d−1, depending on the advection rate. Submarine groundwater discharge (SGD) was a source of TA to the lagoon, with the highest flux rates measured at low tide, and an average daily TA flux of 1080 mmol m−2 d−1 at the sampling site. Both sources of TA were important on a reef-wide basis, although SGD acted solely as a delivery mechanism of TA to the lagoon, while porewater advection was either a sink or source of TA dependent on the time of day. This study describes overlooked sources of TA to coral reef ecosystems that can potentially alter water column carbonate chemistry. We suggest that porewater and groundwater fluxes of TA should be taken into account in ocean acidification models in order to properly address changing carbonate chemistry within coral reef ecosystems.

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Ocean acidification impacts in select Pacific Basin coral reef ecosystems

Regional Studies in Marine Science ◽

10.1016/j.rsma.2019.100584 ◽

2019 ◽

Vol 28 ◽

pp. 100584

Author(s):

Marine Lebrec ◽

Stephanie Stefanski ◽

Ruth Gates ◽

Sevil Acar ◽

Yimmang Golbuu ◽

...

Keyword(s):

Coral Reef ◽

Ocean Acidification ◽

Pacific Basin ◽

Coral Reef Ecosystems

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Altered States: What Will Coral Reefs Look Like in the Future?

The Paleontological Society Papers ◽

10.1017/s1089332600002497 ◽

2011 ◽

Vol 17 ◽

pp. 131-137

Author(s):

Joanie A. Kleypas

Keyword(s):

Climate Change ◽

Coral Reef ◽

Coral Reefs ◽

Ocean Acidification ◽

Large Scale ◽

Altered States ◽

Starting Point ◽

The Future ◽

Coral Reef Ecosystems ◽

Bounce Back

Future environmental conditions for coral reefs are rapidly approaching states outside the ranges reefs have experienced for thousands to millions of years. Coral reef ecosystems, once thought to be robust to climate change because of their ability to bounce back after large scale physical impacts, have proven to be sensitive to both temperature rise and ocean acidification. Predicting what coral reefs will look like in the future is not an easy task, and one that is likely to be proven flawed. The discussion presented here is a starting point for those predictions, mostly from the perspective of reef building and ocean acidification.

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Changes in coral reef communities across a natural gradient in seawater pH

Science Advances ◽

10.1126/sciadv.1500328 ◽

2015 ◽

Vol 1 (5) ◽

pp. e1500328 ◽

Cited By ~ 62

Author(s):

Hannah C. Barkley ◽

Anne L. Cohen ◽

Yimnang Golbuu ◽

Victoria R. Starczak ◽

Thomas M. DeCarlo ◽

...

Keyword(s):

Coral Reef ◽

Ocean Acidification ◽

Benthic Communities ◽

Coral Community ◽

Low Ph ◽

Coralline Algae ◽

Negative Effects ◽

Skeletal Density ◽

Coral Communities ◽

Coral Reef Ecosystems

Ocean acidification threatens the survival of coral reef ecosystems worldwide. The negative effects of ocean acidification observed in many laboratory experiments have been seen in studies of naturally low-pH reefs, with little evidence to date for adaptation. Recently, we reported initial data suggesting that low-pH coral communities of the Palau Rock Islands appear healthy despite the extreme conditions in which they live. Here, we build on that observation with a comprehensive statistical analysis of benthic communities across Palau’s natural acidification gradient. Our analysis revealed a shift in coral community composition but no impact of acidification on coral richness, coralline algae abundance, macroalgae cover, coral calcification, or skeletal density. However, coral bioerosion increased 11-fold as pH decreased from the barrier reefs to the Rock Island bays. Indeed, a comparison of the naturally low-pH coral reef systems studied so far revealed increased bioerosion to be the only consistent feature among them, as responses varied across other indices of ecosystem health. Our results imply that whereas community responses may vary, escalation of coral reef bioerosion and acceleration of a shift from net accreting to net eroding reef structures will likely be a global signature of ocean acidification.

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Acclimatization of massive reef-building corals to consecutive heatwaves

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2019.0235 ◽

2019 ◽

Vol 286 (1898) ◽

pp. 20190235 ◽

Cited By ~ 11

Author(s):

Thomas M. DeCarlo ◽

Hugo B. Harrison ◽

Laura Gajdzik ◽

Diego Alaguarda ◽

Riccardo Rodolfo-Metalpa ◽

...

Keyword(s):

Global Warming ◽

Heat Stress ◽

Coral Reef ◽

Thermal Tolerance ◽

New Caledonia ◽

Thermal Thresholds ◽

Early Twenty ◽

Coral Reef Ecosystems ◽

Late Twentieth ◽

Mortality Projections

Reef-building corals typically live close to the upper limits of their thermal tolerance and even small increases in summer water temperatures can lead to bleaching and mortality. Projections of coral reef futures based on forecasts of ocean temperatures indicate that by the end of this century, corals will experience their current thermal thresholds annually, which would lead to the widespread devastation of coral reef ecosystems. Here, we use skeletal cores of long-lived Porites corals collected from 14 reefs across the northern Great Barrier Reef, the Coral Sea, and New Caledonia to evaluate changes in their sensitivity to heat stress since 1815. High-density ‘stress bands’—indicative of past bleaching—first appear during a strong pre-industrial El Niño event in 1877 but become significantly more frequent in the late twentieth and early twenty-first centuries in accordance with rising temperatures from anthropogenic global warming. However, the proportion of cores with stress bands declines following successive bleaching events in the twenty-first century despite increasing exposure to heat stress. Our findings demonstrate an increase in the thermal tolerance of reef-building corals and offer a glimmer of hope that at least some coral species can acclimatize fast enough to keep pace with global warming.

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