[1] One species, Karenia brevis, is known to cause respiratory distress and neurotoxic shellfish poisoning (NSP) in humans.

[2] It is relatively sporadic in abundance, but it can form large blooms in the summer or fall which can have severe ecological and economical consequences.

[2] Karenia is known to divide very slowly, but are able to form dense blooms probably due to their ability to swim quickly, which likely allows them access to higher concentrations of nutrients.

[8] When a large bloom occurs, resources become limited, and this means greater competition for space and sunlight between several marine organisms—as the genus Karenia start dying they release their neurotoxins, which can kill fish and other organisms.

[8] Karenia brevis also causes distress in humans in the form of neurotoxic shellfish poisoning (NSP) which gets biomagnified up the food chain.

Karenia follow the typical life cycle of a dinoflagellate with a motile, haploid, asexual cell with regular mitotic divisions.

[1] Karenia, like all organisms in the dinoflagellate group, are characteristic for their unique permanently condensed chromatin that lacks nucleosomes and histones.

[1] Karenia brevis is of particular importance to humans because it also can cause neurotoxic shellfish poisoning (NSP) and respiratory distress through accumulation of toxins in tissue.

[10] They work by activating voltage-sensitive sodium channels and causing them to remain open for excessive amounts of time, which leads to uncontrolled depolarization of the neural membrane.

[10] No deaths have been recorded in association with brevetoxin, but severe effects have been noted, such as nausea, vomiting, and slurred speech.