Heat waves in Mediterranean Sea

Salient features of world’s physical geography.

Extreme heat has plagued the Mediterranean for weeks.

What are marine heat waves?

  • A marine heat wave (MHW) is an extreme weather event.
  • It occurs when the surface temperature of a particular region of the sea rises to 3 or 4 degree Celsius above the average temperature for at least five days.
  • MHWs can last for weeks, months or even years

Problems of high sea temperatures

  • Marine creatures are in danger of suffocating.
  • Gases like oxygen and carbon dioxide dissolve better at colder temperatures, so that means the warmer the water, the less oxygen is available to breathe.
  • Conversely, higher temperatures also cause an increase in metabolism, which in turn means animals have to breathe even more than usual.
  • That combination also heightens the risk of death by starvation for marine life.
  • The rise in temperature accelerates metabolism, and the organisms need more food to maintain this metabolic rate.
  • Algal blooms are more common in hotter waters too.
  • Such blooms can further deplete oxygen levels and produce toxins harmful for fish, marine mammals and birds.
  • High water temperatures are most harmful for animals living at the bottom of oceans, lakes or rivers.
  • These benthic species include corals, mussels, sponges, starfish and plants like sea grasses, and are often attached to rock or solid ground.
  • They can’t migrate when it gets too hot.
  • Scientists observed mass deaths of benthic species along thousands of kilometers of Mediterranean coastline between 2015 and 2019.

 Benefits to some species:

Jellyfish bloom:

  • Jellyfish are thriving because of higher temperatures, as well as nutrient run-off from farms and sewage.
  • Overfishing and loss of fish habitat mean the jellyfish have few or no predators.
  • When currents push the animals together, the Mediterranean turns into a crowded jellyfish hotspot.

Invasive species:

  • The sea also hosts around 1,000 invasive species — the highest number in the world.
  • While this is not directly linked to climate change or rising temperatures such conditions clearly favor species introduced from warmer seas.
  • Alien species can have a major impact on ecosystems.
  • For instance, invasive Rabbitfish native to the Indo-Pacific and Rea Sea feed on seaweed and have reshaped the habitat of the eastern Mediterranean.
  • Underwater deserts have replaced dense seaweed forests.

Impact of Mediterranean heat wave on humans:

Effect on fishing activities:

  • Warming seas are already affecting fishing activities in the area.
  • Fishermen are catching fewer familiar species and instead are finding more invasive fish which they have difficulty selling.

Impact on coastal ecosystem:

Habitat loss could also lead to an overall decline in fish populations, while disappearing seagrass means coasts will be more exposed to future storms.

Impact on tourism:

This could also have a knock-on effect for tourism because divers will be less likely to visit an impoverished underwater landscape.

Way forward:

One thing all the researchers agree on is that to save the Mediterranean Sea habitat, humans must stop emitting greenhouse gases.


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