Marine Heatwaves

Why in news?

• Marine heatwaves are rising in Indian Ocean says study.

More about the news:

• The Western Indian Ocean region experienced the largest increase in marine heatwaves at a rate of about 1.5 events per decade, followed by the north Bay of Bengal at a rate of 0.5 events per decade.
• From 1982 to 2018, the Western Indian Ocean had a total of 66 events, while the Bay of Bengal had 94 events.

What are Marine Heatwaves?

• Marine heatwaves are periods of extremely high temperatures in the ocean.
• These events are linked to coral bleaching, seagrass destruction, and loss of kelp forests, affecting the fisheries sector adversely.
• Study showed that 85% of the corals in the Gulf of Mannar near the Tamil Nadu coast got bleached after the marine heatwave in May 2020.
• The most common drivers of marine heatwaves include ocean currents which can build up areas of warm water and air-sea heat flux, or warming through the ocean surface from the atmosphere.
• Winds can enhance or suppress the warming in a marine heatwave, and climate modes like El Niño can change the likelihood of events occurring in certain regions.

What are the impacts of Marine Heatwaves?

• Affect ecosystem structure:
  • Marine heat waves affect ecosystem structure, by supporting certain species and suppressing others.
  • It has been associated with the mass mortality of marine invertebrates, and may force species to change behaviour in a way that puts wildlife at increased risk of harm.
• Change habitat ranges of certain species:
  • Marine heatwaves can change the habitat ranges of certain species, such as the spiny sea urchin off southeastern Australia which has been expanding southward into Tasmania at the expense of kelp forests which it feeds upon.
• Economic Losses:
  • Marine heatwaves can cause economic losses through impacts on fisheries and aquaculture.
• Affect Biodiversity:
  • Biodiversity can be drastically affected by marine heatwaves.
  • In 2016, marine heatwaves across northern Australia led to severe bleaching of the Great Barrier Reef.
• Increase the risk of deoxygenation and acidification:
  • Often they occur alongside other stressors such as ocean acidification, deoxygenation, and overfishing.
  • In such cases, MHWs not only further damage habitats, but also increase the risk of deoxygenation and acidification.

PRACTICE QUESTION:

With reference to ‘Marine Heatwaves’, consider the following statements:

1. They are periods of extremely high temperatures in the ocean.

2. Marine heatwaves can change the habitat ranges of certain species

Which of the statements given above is/are correct?

(a) 1 only

(b) 2 only

(c) Both 1 and 2

(d) Neither 1 nor 2

Answer