Harmful algae blooms (HAB) are the sudden proliferation of one or more species of microscopic plants (algae or phytoplankton), which live in the ocean and produce neurotoxins that can cause negative and sometimes fatal effects in shellfish, fish, birds, marine mammals, and even humans.
There are approximately 85 species of aquatic plants that can cause harmful algae blooms. In high concentrations, some HAB species can turn the water a reddish color, which is why people started calling the phenomenon “red tide.” Other species may turn the water green, brown or purple while others, although highly toxic, will not discolor the water at all.
Most species of algae or phytoplankton are beneficial, not harmful. They are essential elements in the foundation of the global food chain. Without them, higher life forms, including humans, would not exist and could not survive.
What Causes Red Tides?
Simply, red tides are caused by the rapid multiplication of dinoflagellates, a type of phytoplankton. There is no one single cause of red tides and other harmful algae blooms, but abundant nutrients need to be present in sea water to support the explosive growth of dinoflagellates.
A common source of nutrients include water pollution: scientists generally believe that coastal pollution from human sewage, agricultural runoff and other sources contribute to red tides, along with rising ocean temperatures. On the Pacific Coast of the United States, for example, red tide occurrences have been increasing since about 1991. Scientists have correlated the increase of Pacific red tides and other harmful algae blooms with a rise in ocean temperature of approximately one degree Celsius as well as increased nutrients in coastal waters from sewage and fertilizers. On the other hand, red tides and harmful algae blooms sometimes occur where there is no apparent link to human activity.
Another way nutrients are brought to surface waters is by powerful, deep currents along coastlines. These currents, called upwellings, come from nutrient-rich bottom layers of the ocean, and bring to the surface massive amounts of deep-water minerals and other nutrients. Even then, the picture is not always quite clear. It appears that wind-driven, near-coast upwelling events are more likely to bring the right types of nutrients to cause large scale harmful blooms, while current-generated, offshore upwellings seem to lack some necessary elements.
Some red tides and harmful algae blooms along the Pacific coast also have been associated with cyclical El Nino weather patterns, which are influenced by global climate change.
Interestingly, it appears that iron deficiencies in sea water may limit the ability of dinoflagellates to take advantage of the abundant nutrients present. In the eastern Gulf of Mexico off the coast of Florida, and probably elsewhere, large amounts of dust blown west from Africa's Sahara Desert, thousands of miles away, settle on the water during rain events. This dust is believed to contain significant amounts of iron, enough to trigger large red tide events.
https://www.thoughtco.com/what-causes-red-tides-1204160
--------------------------- As you can see from above the libs have to include global pollution and sea level rise etc. But truth is these things have a historic level of being around for along time. Currents are involved,nutrient levels which have a myriad of causes are involved and its a complicated “basket of deplorables” that cause red tides or algae blooms as we call them down here.
Interesting...we get red tides on the Oregon Coast...but this year, we had a similar thing happen in our (inland) city water...some time of algae bloom....you could not boil it, filter it, or anything.
Very interesting. And all along I thought it was just a bunch of toxic Alabama football fans.