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Heat stress more dangerous to corals than ocean acidification

  • Category
    Ecology and Environment
  • Published
    20th Jan, 2023


Global warming poses a more significant threat to coral growth and reef accretion than ocean acidification (OA), according to a new study. 

How heat stress affects corals more than ocean acidification?

  • Ocean acidification slows the rate at which coral reefs generate calcium carbonate, thus slowing the growth of coral skeletons.
  • Heat stress directly affects coral performance in hospite exacerbation of light stress in the symbionts, whereas ocean acidification induces moderate effects on coral metabolism, some of them even positive.
  • As temperatures rise, mass coral bleaching events and infectious disease outbreaks are becoming more frequent.

Role of corals: 

  • Corals are animals. Coral reefs boost biodiversity, buffer storms and support the livelihoods of over one billion people.
  • Coral reefs do not absorb carbon and do not play a direct role in climate change mitigation. However, they are important for climate adaptation.
  • In the last decade, the world lost about 14 per cent of its coral reefs.

What is Coral Bleaching?

  • It occurs when abnormal environmental conditions, such as warmer sea temperatures, cause coral polyps to expel algae (zooxanthellae) living in their tissues, causing the coral to turn completely white.
  • Normally, coral polyps live in an endosymbiotic relationship with this algae crucial for the health of the coral and the reef as the algae provides up to 90% of the coral's energy.
  • When a coral bleaches, it is not dead. Corals can survive a bleaching event, but they are under more stress and are subject to mortality.
  • Corals can recover if the water temperature drops and the algae are able to recolonise the coral reefs.

Factors responsible for Coral Bleaching:

  • Increased water temperature (most commonly due to global warming), or reduced water temperatures
  • Oxygen starvation caused by an increase in zooplankton levels
  • Increased solar irradiance (photosynthetic active radiation and ultraviolet light)
  • Increased sedimentation (due to silt runoff)
  • Bacterial infections
  • Changes in salinity
  • Herbicides
  • Extreme low tide and exposure
  • Cyanide fishing
  • Pollutants such as oxybenzone, butylparaben, octyl methoxycinnamate, or enzacamene: four common sunscreen ingredients that are nonbiodegradable and can wash off of skin
  • Ocean acidification due to elevated levels of CO2 caused by air pollution
  • Being exposed to Oil or other chemical spills

Required measures:

  • A better understanding of the underlying mechanisms that enable corals to tolerate heat can significantly improve coral reef conservation and restoration efforts.

Understanding the terms:

  • Heat Stress: Thermal stress is a term to describe a temperature change that is severe enough to cause unfavourable and even lethal conditions to aquatic organisms, their populations, community structure, or the ecosystem.
  • Ocean acidification: Ocean acidification describes the lowering of seawater pH and carbonate saturation that results from increasing atmospheric CO2 concentrations.

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