Marine Heatwaves

Why in news?

• The northern Bay of Bengal has been experiencing an intense Marine Heatwave since 28th June 2023, leading to India’s usually arid northwest receiving extreme rainfall.

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
  • For example: Spiny sea urchin off southeastern Australia 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.

Add ons:

• 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.

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