Elkhorn coral (Acropora palmata)

TAXONOMY AND NAMING

Class: Anthozoa
Order: Scleractinia
Family: Acroporidae
Genus: Acropora
Common names:
English: Elkhorn coral
Spanish: Coral cuerno de alce
French: Corail corne d’élan

Elkhorn coral (Acropora palmata)© Nick Hobgood

MORPHOLOGY AND LIFE HISTORY

Elkhorn coral (Acropora palmata) is an important reef-building coral in the Caribbean. The species has a complex structure with many branches which resemble that of elk antlers; hence, the common name. The branching structure creates habitat and shelter for many other reef species. Elkhorn coral can reproduce both sexually and asexually, though asexual reproduction is much more common and occurs through a process called fragmentation.

Elkhorn coral’s primary source of nutrients comes from photosynthetic algae, zooxanthellae, that live inside the coral’s cells. Therefore, Elkhorn coral are highly dependent on the sunlight for sustenance, leaving Elkhorn coral vulnerable to increased turbidity or water clarity. Elkhorn coral colonies live for centuries. These colonies grow 5-10 cm (2-4 inches) each year, reaching maximum size in 10 to 12 years.

DISTRIBUTION AND ABUNDANCE

Elkhorn coral live in shallow habitats, which give them abundant access to light. Like all animals, Elkhorn coral requires oxygen to survive, most of which they obtain through special, photosynthetic algae living in their tissues called zooxanthellae.

Elkhorn coral are one of three Caribbean corals, primarily found in the southeast region of the world. These corals are found throughout the Bahamas, Florida, the Caribbean, and beyond to the northern shores of Venezuela. Characteristically found in shallow, turbulent water ranging from 1 to 5 meters, Elkhorn coral thrive best in high-energy zones where wave action is frequent.

Elkhorn coral (Acropora palmata) geographic range©IUCN red list

THREATS

Elkhorn coral face many global threats such as climate change, ocean acidification, and overfishing.
When water temperatures warm, Elkhorn coral expel their zooxanthellae. Without their zooxanthellae, Elkhorn coral first lose their prime oxygen source, then color, and then usually die.[citation needed] In addition, climate change increases the severity and prevalence of storms, which can decimate Elkhorn coral populations.

Overfishing affects Elkhorn coral by reducing fish populations that feed on harmful macroalgae. Macroalgae damage Elkhorn coral by producing toxic chemicals and by decreasing the nearby available oxygen. Macroalgae can further harm Elkhorn coral by facilitating pathogen growth. Also, macroalgae reduce the amount of suitable areas where Elkhorn coral larvae attach, reducing the ability for Elkhorn reefs to recover. Local water pollution, also known as wastewater, negatively impacts Elkhorn coral by increasing the prevalence of white pox disease, the abundance of macroalgae, and by increasing water cloudiness.

ABUNDANCE AND CONSERVATION STATUS

Since the 1980s, Elkhorn coral populations have rapidly declined by an estimated 97%. It has been listed as critically endangered by the IUCN. Some conservation efforts are now in place to protect the species and promote increased genetic variability among the species.

International conventions for the protection of elkhorn coral© personal source

Bibliography
Crabtree, R. E (2014). Endangered Species Act - Section 7 Consultation Biological Opinion. United States Corps of Engineers, 17-28.
Fisheries, NOAA (December 30, 2019). "Elkhorn Coral | NOAA Fisheries". NOAA. Retrieved April 14, 2020.
"Species Profile". ecos.fws.gov. Retrieved April 14, 2020.
"Welcome to the NOAA Institutional Repository |". repository.library.noaa.gov. Retrieved April 15, 2020.
Zanevald (June 7, 2016). "Overfishing and nutrient pollution interact with temperature to disrupt coral reefs down to microbial scales". Nature Communications. 7: 11833. Bibcode:2016NatCo...711833Z. doi:10.1038/ncomms11833. PMC 4899628. PMID 27270557.