Question: Which group of organisms is most commonly responsible for red tides?

Disambiguated questions and answers:
context: No context provided
question: Which broad group of organisms is most commonly responsible for red tides?
short_answers: protozoans and unicellular algae

algae

algal blooms

dinoflagellates and diatoms

aquatic microorganisms

context: No context provided
question: Which species of organisms is most commonly responsible for red tides?
short_answers: Gymnodinium nagasakiense

context: HABs occur in many regions of the world, and in the United States are recurring phenomena in multiple geographical regions. The Gulf of Maine frequently experiences blooms of the dinoflagellate "Alexandrium fundyense", an organism that produces saxitoxin, the neurotoxin responsible for paralytic shellfish poisoning. The well-known "Florida red tide" that occurs in the Gulf of Mexico is a HAB caused by "Karenia brevis", another dinoflagellate which produces brevetoxin, the neurotoxin responsible for neurotoxic shellfish poisoning. California coastal waters also experience seasonal blooms of "Pseudo-nitzschia", a diatom known to produce domoic acid, the neurotoxin responsible for amnesic shellfish poisoning. Off the west coast of South Africa, HABs caused by "Alexandrium catanella" occur every spring. These blooms of organisms cause severe disruptions in fisheries of these waters as the toxins in the phytoplankton cause filter-feeding shellfish in affected waters to become poisonous for human consumption.
question: Which species of organisms is most commonly responsible for red tides in Florida?
short_answers: Karenia brevis
wikipage: Algal bloom

context: HABs occur in many regions of the world, and in the United States are recurring phenomena in multiple geographical regions. The Gulf of Maine frequently experiences blooms of the dinoflagellate "Alexandrium fundyense", an organism that produces saxitoxin, the neurotoxin responsible for paralytic shellfish poisoning. The well-known "Florida red tide" that occurs in the Gulf of Mexico is a HAB caused by "Karenia brevis", another dinoflagellate which produces brevetoxin, the neurotoxin responsible for neurotoxic shellfish poisoning. California coastal waters also experience seasonal blooms of "Pseudo-nitzschia", a diatom known to produce domoic acid, the neurotoxin responsible for amnesic shellfish poisoning. Off the west coast of South Africa, HABs caused by "Alexandrium catanella" occur every spring. These blooms of organisms cause severe disruptions in fisheries of these waters as the toxins in the phytoplankton cause filter-feeding shellfish in affected waters to become poisonous for human consumption.
question: Which group of organisms is most commonly responsible for red tides off California?
short_answers: Pseudo-nitzschia
wikipage: Algal bloom

Long answers:
knowledge: content: Red tides are a phenomenon of discoloration of sea surface.
wikipage: Red tide

content: It is a common name for harmful algal blooms occurring along coastal regions, which result from large concentrations of aquatic microorganisms, such as protozoans and unicellular algae (e.g. dinoflagellates and diatoms).[1][2]
wikipage: Red tide
long_answer: Red tides are a phenomenon of discoloration of sea surface. It is a common name for harmful algal blooms occurring along coastal regions, which result from large concentrations of aquatic microorganisms, such as protozoans and unicellular algae. Gymnodinium nagasakiense is most commonly responsible for red tides.  The well-known "Florida red tide" that occurs in the Gulf of Mexico is a HAB caused by "Karenia brevis", another dinoflagellate which produces brevetoxin, the neurotoxin responsible for neurotoxic shellfish poisoning. California coastal waters also experience seasonal blooms of "Pseudo-nitzschia", a diatom known to produce domoic acid, the neurotoxin responsible for amnesic shellfish poisoning.