Gymnodinium is a genus of dinoflagellates, which are single-celled microorganisms found in marine and freshwater environments. Some species within this genus are known for their role in harmful algal blooms, producing toxins that can affect marine life and human health. Additionally, Gymnodinium species contribute to the marine food web, serving as a food source for various organisms. They also play a role in biogeochemical cycles, influencing nutrient dynamics in aquatic ecosystems.
If you are referring to the Red Tide, then, it is a form of algae called "Gymnodinium breve". Not everyone agrees on the reason the algae booms, and causes the water to appear red, but it is said to be a natural phenomena and it's not good for the ocean life or people. you shouldn't eat fin fish that are from a red tide area, red tide produces potent neurotoxins.
George A. Rounsefell has written: 'Large-scale experimental test of copper sulfate as a control for the Florida red tide' -- subject(s): Copper sulphate, Gymnodinium breve 'Contribution to the biology of the Pacific herring, Clupea pallasii' -- subject(s): Pacific herring, Pacific herring fisheries 'Factors causing decline in sockeye salmon of Karluk River, Alaska' -- subject(s): Salmon fisheries 'A method of estimating abundance of groundfish on Georges Bank' -- subject(s): Fish populations, Groundfish fisheries, Estimates, Methodology