Harmful algal blooms, called red tides, have sent scores of dead fish ashore in southeastern Florida in recent weeks. A similar red-tide event killed off thousands of fish in the San Francisco Bay Area last summer.
So-named because in large numbers the algae stain the water red, these toxic blooms occur when winds blowing across the ocean surface push that water away and bring deeper, nutrient-rich waters to the surface. This process, known as “upwelling,” creates the ideal conditions for algae to bloom.
The algae produce toxins that can kill fish and the seabirds that eat them, and sicken humans. They also block sunlight from reaching underwater plants, depriving the fish of oxygen.
The Environmental Protection Agency predicts that climate change will alter the “timing and intensity” of coastal upwelling, potentially leading to more algal blooms along the West Coast. Warmer waters caused by climate change could also spur other types of harmful algae, the EPA says. Toxic blue-green algae prefer warmer temperatures.
Storms and extreme weather events, which global scientists predict will worsen in the future, can also lead to algal blooms by causing nutrients to run off from the land into the water. Authorities suspect an algal bloom was responsible for dead sea animals, including sea urchins, starfish and crayfish, washing up on New Zealand’s east coast in February during a particularly stormy Southern Hemisphere summer.
It’s not just coastal environments that are at risk of harmful algal blooms, according to scientists. Droughts, which may become more frequent because of climate change, can cause marine algae to invade freshwater systems, which has happened a number of times in freshwater lakes in the United States over the past couple of decades.
Algal blooms can be caused by humans, too. A rare golden algae thought to have led to a mass fish die-off in the Oder River that runs along the border between Germany and Poland last summer may have been caused by industrial discharges into the river, according to German researchers.
