The Stinging Fire Corals of Belize

What is Fire Coral?

The term “fire coral” is used for organisms of the genus Millepora. Despite their name, fire corals are not actually coral, but rather belong to a group known as hydrocorals. They are more closely related to hydrozoans, such as the freshwater jellyfish and Portuguese man-o’-war, than to true corals.

Image of yellow fire coral surrounded by small orange fish.
Image Credit: Derek Keats. Used with Creative Commons Attribution 2.0 Generic license.

Due to similarities in appearance, however, fire corals are easily mistaken for true corals. What seems to be a single fire coral is actually a colony of polyps that have built a rigid, hollow “skeleton”. Fire corals are usually yellow, green, or tan- not red as their name may suggest! The name “fire coral” actually comes from the colonies’ nematocysts (defensive hair-like cells), which, much like jellyfish, can deliver a painful sting to predators and unwary divers. Fire corals are sometimes also referred to as “stinging corals.”

A fire coral colony exists in a symbiotic relationship with zooxanthellae, a type of tiny, single-celled algae, which provide food for the colony via photosynthesis. Because of this, fire corals can only be found in waters shallow enough for sunlight to penetrate; their typical range is up to 10 meters (33 feet) below the surface, though some fire coral species can be found at depths up to 50 meters (164 feet). Additionally, fire corals can stun and capture prey- usually microscopic organisms such as phytoplankton or zooplankton- with their stinging nematocysts. The prey is then engulfed and digested.

Image of fire coral (Millepora alcicornis) taken underwater.
Image Credit: Fernándo Herránz Martín, 23 August 2005. Used under GNU Free Documentation License.

Fire corals have a complicated, multi-stage reproduction. To create more fire coral colonies, the polyps first asexually produce medusae, which are tiny, free-swimming structures that look similar to jellyfish. The medusae, which live for only a few hours, then engage in sexual reproduction by releasing egg and sperm cells into the surrounding water. A fertilized egg, in the right conditions, can then become a new colony. 

Fire corals can also engage in asexual growth, often to repair damaged branches. This allows colonies to regrow both skeletal and soft tissues. Reproduction by fragmentation can also occurl this involves a branch of a colony growing into a new colony through asexual reproduction. Fragmentation is especially important in laboratory settings, as it allows researchers and conservationists to grow new colonies of endangered coral or hydrocoral species in safe, controlled environments. This is often used as a response to- as discussed below- incidents of coral bleaching and coral reef pollution that threaten coral and hydrocoral populations. 

Coral Reefs of Belize

Belize is home to the Belize Barrier Reef, the second-largest coral reef on Earth. This massive, beautiful reef system contains at least three known species of fire coral (Millepora alcicornis, Millepora complanata, and Millepora striata), alongside hundreds of species of true corals, fish, and other marine wildlife.

Branching fire coral surrounded by various fish.
Branching fire coral from Fernandez Bay, offshore from the western shoreline of San Salvador Island, eastern Bahamas. Image Credit: James St. John, 24 March 2011. Used under Creative Commons Attribution 2.0 Generic License.

However, the Belize Barrier Reef is currently under threat from pollution, habitat destruction, and the effects of climate change. 

One such effect is coral bleaching. Coral bleaching is a phenomenon in which corals- or, in this case, hydrocorals- come under so much stress, often from rising ocean temperatures or ocean acidification, that they expel their zooxanthellae, leaving the colonies with pale white colorations. Frequent, severe bleaching can kill large amounts of coral and hydrocoral and permanently damage the reef. Though fire corals have been seen to recover quickly from short-term bleaching, repeated bleaching events still cause widespread damage and death to fire coral colonies. 

Bleaching is far from the only threat to Belize’s fire corals, though its effects are some of the hardest to prevent. This, however, has not stopped scientists, conservationists, and a dedicated public from working hard to protect the Belize Barrier Reef. This commitment towards preserving Belize’s reefs is not new; after the devastation caused by Hurricane Iris in 2001, followed by repeated bleaching events over the next few years, scientists and locals worked together in replanting lab-grown coral colonies to repair large portions of the reef, with an almost 90% long-term success rate by 2017. Restoration efforts for damaged Belizean reefs continue into the present. Other organizations, including our partners at the Tobacco Caye Marine Station, engage the public in collecting coral population data for the citizen science program CoralWatch, organized by the University of Queensland. The information gathered by Tobacco Caye’s scientists, interns, and volunteers is used to help predict, prevent, and repair damage to reefs from bleaching events. 

The devotion of Belize’s scientists and citizens has paid off. In 2018, the Belize Barrier Reef was removed from the United Nations list of endangered sites. Though the reef still faces threats and challenges, public involvement can make, and has already made, a difference for these reefs and all the organisms within them. 

To learn more about Belize’s reefs, schedule a virtual tour at Marine Biology Live!

Article by Kayla Windelspecht. : Kayla is a biologist and science writer specializing in ecology and conservation. She is a graduate from North Carolina State University and project manager for Inspire EdVentures since 2020.

References and Further Reading

Biodiversity in Belize. “Corals of Belize”, 2009. (http://biological-diversity.info/corals.htm)

Lamar University Department of Biology. “Fire Coral”, 2011. (https://www.lamar.edu/arts-sciences/biology/study-abroad-belize/marine-critters/marine-critters-1/fire-coral.html)

John B. Lewis, Biology and Ecology of the Hydrocoral Millepora on Coral Reefs, Advances in Marine Biology, Academic Press, Volume 50, 2006, Pages 1-55, ISSN 0065-2881, ISBN 9780120261512, https://doi.org/10.1016/S0065-2881(05)50001-4. (https://www.sciencedirect.com/science/article/pii/S0065288105500014)

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