The answer is “dinoflagellates”.
Dinoflagellates are a group single celled eukaryotes from the kingdom Protista. Dinoflagellates are often photosynthetic and can produce their own food by photosynthesis. Some dinoflagellates are parasitic. When there is a large number of dinoflagellates during the warmer seasons (also known as an “algal bloom”), the body of water will change into a rusty red color called red tide. Red tide occurs because dinoflagellates produce a neurotoxin called saxitoxin which manifests as paralysis. When humans eat affected fish, they will experience a non-specific syndrome with nausea and vomiting called ciguatera. On the other hand, when humans eat affected shellfish; then there will be paralysis, confusion, poor mental status, etc. and this is called paralytic shellfish poisoning.
