Explanation:

All of the above codes are correct.
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.

Impacts of Marine Heatwaves

• Affect Ecosystem Structure: Marine heat waves affect ecosystem structure, by supporting certain species and suppressing others.
• 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.
• Affect Biodiversity: Biodiversity can be drastically affected by marine heatwaves.
• 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.

Hence option 3rd is correct.