14 April 2021.
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.
- 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.