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Occasionally, the ocean takes on a blood-like hue, with numerous dead fish floating to the surface. While it may seem like a disaster from an ancient story, the cause is far more simple—it's algae.
Red tides, or harmful algal blooms, happen when certain algae species multiply rapidly, becoming visible to the naked eye. These blooms aren't always red; they can also be blue, green, brown, or purple. They happen worldwide. In the Gulf of Mexico, red tides are typically caused by a microscopic algae called Karenia brevis. This algae produces a toxic substance that impacts the nervous system of marine life like fish, sea turtles, manatees, and dolphins, often leading to death. Along with creating this neurotoxin, K. brevis can become airborne, causing symptoms in humans such as coughing, skin irritation, and watery eyes [PDF]. However, not all algal blooms release toxins harmful to humans or animals.
Algal blooms can occur naturally or be exacerbated by runoff from farming and coastal development that flows into rivers and streams, eventually reaching the ocean. Specifically, agricultural runoff, which may include fertilizers and livestock waste, often contains large amounts of nitrogen, promoting rapid algae growth. These blooms can suffocate marine life by blocking sunlight and depleting oxygen in the water, causing fish and other creatures to suffocate.
One of the most devastating red tides occurred in 2018, when a massive algae bloom lingered along Florida’s gulf coast for over a year. Hotels on the popular Captiva and Sanibel islands lost $8 million due to canceled bookings, while the state of Florida spent $14.5 million to clean up beaches contaminated with dead wildlife.
