Deadly algae kill 4,000 tonnes of Salmon in Chile.

14 April 2021.

Introduction:

More than 4,000 tonnes of Salmon in Chile have been killed by deadly algae.The algal bloom in the water reduced the amount of oxygen suffocating the salmon fishes.

Highlights:

  • More than eighteen salmon fish farms that produce 26% of world salmon have been affected.
  • The presence of urea and ammonia in the salmon farms have  led to the algal bloom. Three different types of harmful algae were detected in eighteen farms.
  • Chile is the second largest producer of Salmon in the world after Norway.
  • It exported more than 4.4 billion USD of fish in 2020. Chile produces more than 26% of world Salmon.

About Algal Bloom:

  • Algal Bloom is rapid increase of algal population in marine water or fresh water.
  • It occurs due to the nutrients from phosphorous or nitrogen fertilizers run off.
  • They create harmful effects such as blocking of sunlight.
  • This causes depletion of oxygen level in water.

Dissolved Oxygen in Water

  • The Dissolved oxygen in water is the most important water quality factor. A pond supporting an aquatic ecosystem will have more than 10 ppm oxygen dissolved in it.
  •  On the other hand, atmosphere has 200,000 ppm of oxygen.
  • The oxygen concentrations below 3 ppm will stress the species of fish in the water.
  •  The oxygen concentrations below 2 ppm will kill the fishes.
  • Oxygen dissolves in water in two ways.
  • One is through atmospheric contact that happens at the surface.
  • The other primary source of dissolved oxygen is from algae.
  • The algae add dissolved oxygen to the water by photosynthesis, thereby supporting lives in the water system.
  • In that case, how did the algal bloom in Chile kill thousands of fishes?

How does Algal Bloom kill fishes?

  • During day, the algae produce oxygen through photosynthesis.
  • While at night, in the absence of sunlight, it stops photosynthesis and starts respiring just like other organisms in the water system.
  • Respiration is taking in Oxygen and releasing carbon dioxide.
  • Thus, during night the dissolved oxygen drops too low suffocating the fish in the water system.
  • Also, as the algal bloom increases, it forms thick blanket over the water surface.
  • This prevents sunlight from penetrating the water.
  •  Hence the second source of oxygen where the oxygen dissolves in water at the surface contacts is blocked.

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