Quick Facts

Species Type



Alexandrium monilatum is a warm water marine species.


Found in the Atlantic Ocean, Gulf of Mexico, Caribbean Sea and Chesapeake Bay. Alexandrium monilatum wasn’t found in the Chesapeake Bay until 2007, but has become increasingly common. It occurs most commonly in the late summer.

Conservation Status



Alexandrium monilatum is a dinoflagellate—a type of single-celled algae with thread-like flagellum that help them move. It generally forms chains of between two and 80 cells. This species is bioluminescent and glows blue-green when stimulated at night, often by waves or boats.


Alexandrium monilatum is photosynthetic. Excess nutrients in the Bay can fuel the growth of algae blooms, when populations of algae like Alexandrium monilatum grow rapidly. Dead zones form when these algae blooms die and decompose. Because the decomposition process removes oxygen from the water faster than it can be replaced, the decomposition of an algae bloom creates hypoxic or anoxic conditions that can suffocate marine life and shrink the habitat available to fish, crabs and other critters.


Planktonic algae like Alexandrium monilatum is at the base of the food chain and is an important food source for small fish and other wildlife.

Reproduction and Life Cycle

Alexandrium monilatum is able to reproduce both asexually and sexually.

Did You Know?

  • Alexandrium monilatum populations have recently expanded and intensified in the Chesapeake Bay. This algae is toxic and blooms can cause fish kills and the deaths of oysters.
  • While it isn’t well documented, it is possible that bioluminescent dinoflagellates like Alexandrium monilatum can cause sand crabs to glow. Sand crabs are filter feeders, so as they filter the water, bioluminescent algae can stay in their bodies, causing them to glow.

Sources and Additional Information