The red tide organism, Karenia brevis or K. brevis, produces toxins that can kill fish and other vertebrate species that ingest them by affecting the central nervous system.
Environmental impacts include massive fish kills; marine mammal, sea turtle and sea bird mortalities; and impacts on benthic communities including sea grass and coral community die-offs.
Red tide is also dangerous for humans. Eating shellfish contaminated with the K. brevis toxin can cause neurotoxic shellfish poisoning, with symptoms like vomiting and nausea and a variety of neurological difficulties.
Regulators ban recreational shellfish gathering during red tide events and commercial shellfish operations strictly monitor for red tide. But people can also be exposed through the air, causing respiratory and eye irritation, particularly in those with severe or chronic respiratory conditions such as emphysema or asthma. The algae’s airborne spread has shown to be affecting people as far as 10 miles away.
Blue-green slime is also toxic to wildlife and humans. Touching or ingesting water containing this cyanobacteria can cause symptoms such as skin rashes, runny nose, sore throat, allergic reactions, severe gastroenteritis, liver or kidney toxicity, and neurological problems.
The International Agency for Research on Cancer, a specialized division of the World Health Organization, has determined that microcystin, one of four major toxins made by blue-green algae outbreaks, is possibly carcinogenic to humans.
Toxic algae outbreaks have also killed pet dogs in Florida and elsewhere.
Florida set a grisly record for manatee deaths in 2021, with more than 1,000 manatees found dead in Florida waters, mostly in the Indian River Lagoon on the southeast coast. The manatees starved because algae outbreaks killed off the seagrass beds they depend on for food. Only an estimated 5,700 manatees exist in Florida.