Heat stress more dangerous to corals than ocean acidification
Ecology and Environment
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
- 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
- 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.