Question: Which group of organisms is most commonly responsible for red tides?
Disambiguated questions and answers: question: Which broad group of organisms is most commonly responsible for red tides?
Which species of organisms is most commonly responsible for red tides?
Which species of organisms is most commonly responsible for red tides in Florida?
Which group of organisms is most commonly responsible for red tides off California?
answer: protozoans and unicellular algae
algae
algal blooms
dinoflagellates and diatoms
aquatic microorganisms
Gymnodinium nagasakiense
Karenia brevis
Pseudo-nitzschia
Natural Questions answer: dinoflagellates (from the Wikipedia article "Red tide")