Here's why:
Salinity: Coral reefs thrive in saltwater environments with high salinity. The Amazon River, on the other hand, is a freshwater river with low salinity. When the Amazon River water meets the ocean water at its mouth, it creates a mixing zone where the salinity fluctuates. Coral reefs cannot tolerate these fluctuations and require stable, high salinity levels.
Sedimentation: The Amazon River carries a massive amount of sediment, including silt and mud, as it flows towards the ocean. This sediment load creates high turbidity in the water near the river's mouth, reducing the amount of sunlight reaching the water's surface. Coral reefs require clear, sunlight-rich water for photosynthesis, which is essential for their survival.
Nutrient Load: The Amazon River also carries a high concentration of nutrients, such as nitrogen and phosphorus, which can stimulate excessive algae growth. This process, called eutrophication, leads to murky water conditions, further reducing the sunlight needed by coral reefs.
Water Temperature: Coral reefs are sensitive to water temperature changes. While the water near the equator, where the Amazon River is located, is generally warm, the influence of the cold Humboldt Current, which flows northward along the western coast of South America, can cause variations in water temperature near the mouth of the Amazon. These temperature changes can be stressful or even detrimental to coral growth.
In summary, the factors mentioned above, including salinity fluctuations, high sedimentation, nutrient loads, and water temperature variations, make it highly unlikely for coral reefs to grow near the mouth of the Amazon River.
