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