A Research Review of Interventions to Increase the Persistence and Resilience of Coral Reefs (2019) / Chapter Skim
Currently Skimming:
5 Environmental Interventions
5 Environmental Interventions
Pages 143-162
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From page 143... ...
and serve a key purpose: reduce temperature and light stress during summer warming events where coral bleaching risk is significant (Eakin et al., 2009; Hoegh-Guldberg, 1999) and alter the chemical environment around coral reefs to reduce acidification impacts.
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From page 144... ...
Abiotic interventions to address OA fall in the category of engineering solutions using physical and/or chemical interventions that directly alter the ocean carbon chemistry toward a higher pH and aragonite saturation state (Ωa)
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From page 145... ...
Shading may cool the water column, and thereby cool the water around reef organisms. For example, if 30% of the sun's irradiance can be absorbed or scattered in the atmosphere over a coral reef at noon during summer, it would lower the energy in the system by around 10 MJ m–2 d–1 (e.g., Masiri et al., 2008)
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From page 146... ...
. Also on the Great Barrier Reef, a project is trialing a reflective polymer surface film as a potential tool to shade coral reefs during summer doldrums.2 The buoyant, monolayer 2 See announcement at https://www.barrierreef.org/latest/news/reef-sun-shield-trials show-promise-to-prevent-coral-bleaching.
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From page 147... ...
Current Feasibility Techniques that shade coral reefs to cool water and lower photo stress are at various stages of feasibility that largely relate to their intended or potential scale. Atmospheric approaches (i.e., marine sky brightening)
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From page 148... ...
Sedimentation is a common stressor on coral reefs and its use as a shading intervention would need to consider any unintended side effects such as enrichment with particulate nutrients or the smothering of benthic organisms as particles settle onto the seafloor. Bubbling would alter the gas balance, including CO2, in surface waters and such alteration of water chemistry could have risks if, for example, surface waters were enriched with CO2.
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From page 149... ...
In other words, lowering local thermal stress by shading may limit a pathway for acclimation. If shading or cooling interventions cannot be sustained, unhardened coral fauna could face rapid onset of thermal stress.
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From page 150... ...
to create artificial upwelling to replace shallow and warm with deeper and cooler water. Benefit and Goals The goal of cool water mixing is thermal stress reduction sufficient to prevent or lower the risk of coral bleaching.
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From page 151... ...
Like shading, cool water mixing is a temporary stress relief that can be focused during periodic times of environmental stress. Risk One of the technical risks associated with the pumping of deep, cooler waters to coral reefs in shallow water is that such artificial upwelling potentially leads to both nutrient and CO2 enrichment, exacerbating algal growth and OA (e.g., Feely et al., 2008; Leichter et al., 2003; Manzello, 2010)
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From page 152... ...
ABIOTIC OCEAN ACIDIFICATION INTERVENTIONS What It Is Abiotic OA interventions at the local reef scale act directly on the carbon chemistry of the seawater flowing over reefs. Interventions can be either chemical, involving the addition of a strong base to elevate pH or by interacting with the reef limestone, or physical, for example stripping CO2 from the water column.
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From page 153... ...
likely to occur in coral reef waters now and under future climate scenarios. SOURCE: Raven et al., 2005.
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From page 154... ...
. The technique builds on the principle that added CaCO3 ions consume hydrogen ions, thereby elevating pH and aragonite saturation state.
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From page 155... ...
. Logistical constraints here would be the ability to pump enough CO2-stripped air into the water body upstream of the target coral reef.
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From page 156... ...
, local control of seawater carbon chemistry over coral reefs might become more feasible, but will still be limited to the local scale and to a subset of oceanographic settings. Infrastructure The exact dosing of chemicals, air, or limestone to reefs in such a way that the marine carbon chemistry can be kept within a range that favors coral survival, growth, and reproduction requires precision technology on a massive scale.
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From page 157... ...
The first process can be achieved directly by macroalgal beds or seagrass areas upstream of the target coral reef. The extent to which these processes will work to achieve the objective (elevating Ωa of coral reef waters)
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From page 158... ...
158 A RESEARCH REVIEW OF CORAL INTERVENTIONS FIGURE 5.2 Contributions from net benthic photosynthesis and net benthic calcification to changes in aragonite saturation per unit time in shallow reef water (1-meter depth)
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From page 159... ...
However, respiration by organic matter in the sand used in this experiment offset the Ωa benefit from dissolution. In summary, the example illustrates that a dense upstream macroalgal bed the size of the coral reefs (areas are constant across benthic groups in Figure 5.2)
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From page 160... ...
. In other settings, feasibility needs to be addressed with a more general question: Is the setting such that the water body "treated" by the primary producers flows over the coral reef consistently?
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From page 161... ...
Conversely, a coral reef in a shallow embayment where water has high residence time or a reef in a coastal zone near dense seagrass beds will have the greatest scope. A key regional or local factor co-determining OA management
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From page 162... ...
Infrastructure Introduction of seagrass meadows and macroalgal beds relies on infrastructure commonly used for restoration efforts, including laboratories for propagule cultivation, and boats and divers for field transplants. Use of rhizomes has been found to be more successful than seeds or seedlings for restoration of seagrasses, along with the use of weights or staples to keep them in place (Katwijk et al., 2016)
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