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Acropora cervicornis: Staghorn Coral
By: Madison Stuckenschneider
Scientific Classification
About Staghorn Coral
Staghorn coral is one of the most important reef building species, along with elk horn coral! They are known as some of the fastest growing corals in reefs. This is important because they should be able to recover quicker than other corals after an event (bleaching, hurricane, etc.) and makes them prime candidates for restoration projects such as coral nurseries. They create important habitats for many other reefs animals such as fish. Staghorn corals share a symbiotic relationships with unicellular photosynthetic algae (zooanthellae), where the two benefit each other. The algae is given a place to live and grow and the coral is provided with food and oxygen.
The algae also give corals their beautiful colors! However coral bleaching is an event that causes the corals to expel their important algae, which also takes away their beautiful color. The images below show a comparison of a healthy coral and a bleached coral. Without this zooanthellae corals are weaker, grow slower, have weaker immunity to disease and these factors can lead to coral mortality.
Healthy coral with zooanthellae Bleached coral lacking zooanthellae
Coral bleaching occurs when the coral is stressed due to changing environmental factors such as the changing ocean temperatures, more extreme weather events as well as the changing salinity known as ocean acidification. Ocean acidification is simply described as the phenomenon that decreases the pH of the ocean due to an increase in the amount of carbon dioxide absorbed from the atmosphere(The ocean and the ocean are constantly trying to equilibrate). These factors can all be connected to global climate change. Other factors threatening staghorn corals include unsustainable fishing, pollution and human disturbances.
Characteristics
The name Acropora means porous stem or branch. These are true stony or hard corals. Staghorn corals typically have light brown, branching tubes with pale pointed tips. The two body forms under the order cnidaria include polyp and medusa. Corals are under the polyp body plan, and have many individual polyps that make up the coral as shown in the image below. A few defining characteristics (not just for staghorn corals but for all species under the class Anthozoa) includes the following;
Absence or loss of a medusa stage
Circular mitochondrial DNA
Carnivorous (some staghorn corals have been seen capturing fish with nematocycts)
Presence of a siphonoglyph (ciliated grooves used to create water currents)
Absence of operculum (gill cover)
Absence of cnidocil (causes the stinging in jellyfish!)
Planula larva (Pechenik, 2015)
Reproduction and Life Cycle
Research
A few summaries on interesting research topics regarding staghorn corals:
Diverse Staghorn Corals (Acropora) in High-Latitude Eocene Assemblages: Implications for the Evolution of Modern Diversity Patter of Reef Corals by Carden C Wallace and Brain R Rosen
Currently staghorn corals are some of the most diverse reef building species in the world today. It is evident that the history of these corals could suggest the evolution and biodiversity about our present day Acropora species and how they will respond to climate change.
It is proposed after looking at Eocene fossils from Southern England and Northern France, that their rapid diversification and pre-existing diversity is important in present day corals.
This is important since many corals are critically endangered; can they keep up with climate change and evolve in future generations to keep up with this phenomenon?
2. Fish Communities on Staghorn Coral: Effects of Habitat Characteristics and Resident Farmerfishes by Michele K. Johnson et.al.
Staghorn corals are vital for many species such as the Farming damselfishes, giving them shelter, habitat and food in which they actively defend against other fish. Is the decline in Staghorn corals affecting the fish?
The value of staghorn coral was assessed for native fish, as well as how the territoriality of the damselfish affects the assemblage of fishes.
Damselfish are aggressive towards non predators, and not aggressive towards predators. Does this behavior change if their habitat is removed?
185 Acropora (staghorn) patches surveyed
The fishes habitat is the most important when looking at fish diversity and assemblage.
The effect of the patch area being removed (the staghorn coral), showed that there was a positive co variance between the damselfish and other fish on staghorn corals.
Fish acted more aggressively when patch area was removed...this could be due to limited resources and a dependence on resources from these staghorn corals.
This study shows the importance of these corals on fish communities!
Conservation
Over the last 30 years, staghorn corals have significantly declined by over 80 percent in the Caribbean (Charteirs, M. 2017). According to a study done in 2015 by Alex E. Mercado-Molina, Staghorn corals will reach quasi-extinction in sixteen years or greater. It is now listed as Critically Endangered (CR) on the IUCN (International Union for Conservation of Nature) Red List and listed on Appendix II of CITES. Here are a few things that are being done to preserve these corals:
Protecting the habitats of coral reefs (forbid fishing, cruise ships, pollution etc. in these areas)
Promote education and research
Breeding staghorn corals in nurseries and when they are mature enough plant them into the wild.
How does a coral nursery work? Fragments are taken from healthy corals and hung from a line underwater. In Roatan Honduas, the marine biologists chose a spot with low human disturbance, with optimal depth and sunlight conditions. The fast growth, and importance of staghorn corals makes them great candidates for coral nurseries!
This is a picture obtained from the internet, where it is easier to see the setup of a coral nursery.
This is my own personal picture of a staghorn coral nursery (hard to see though!) This picture was taken off the island of Roatan Honduras.
Staghorn coral is known as a simultaneous hermaphrodite, meaning it is able to produce both male and female gametes. They typically do not self fertilize. Staghorn coral sexually reproduces once per year, after the full moon later in summer, where they spawn their eggs. The eggs that become fertilized develop into planula larva (a free swimming, flattened and ciliated larva). The larva that survive predators, eventually settle on a suitable surface where they can then develop into a polyp, a non motile body form, and forms new colonies. They secrete a white star like outer skeleton which eventually develops tentacles and grow into mature polyps. These are known as the founders, who were sexually produced. Staghorn can also reproduce asexually where branches grow (buds) and daughter branches form, who can also bud daughters. Staghorn coral can also grow from fragments (this is important in coral reef nurseries!). (McGregor,1974)When staghorn coral is healthy, it can grow up to 8 inches in a branch within a year. However, as we mentioned earlier, the rising ocean temperatures, ocean acidification and other factors can affect the fast growth of these corals.
Habitat
Staghorn coral is located in clear shallow tropical waters in the Caribbean, Bahamas and Florida. There are even few species located in the Great Barrier Reef (animal diversity web). Typically located at depths between 16-50 feet. Staghorn requires certain levels of light and in a warm environment of 20 degrees C and above. They live in several different reef habitats including near spur and groove formations, bank reefs, patch reefs, transitional reef habitats, limestone ridges, terraces, as well as hard bottom habitats. Staghorn corals also require very oxygenated water.
What can YOU do to help today?
Lead a more sustainable lifestyle:
use energy wisely
eat less meat
choose products wisely
Educate yourself and others (an increase in awareness in these issues has decreased greenhouse gas emissions!
Write to government representatives about taking green actions
Avoid harmful pesticides and fertilizers!
If you dive or snorkel do not touch the fish or corals
And reduce chemical and sunscreen pollution when you are in the ocean
References
Alex E. Mercado-Molina et al. “Demography of the threatened coral Acropora cervicornis: implications for its management and conservation”. Coral Reefs 2015. Retrieved at https://search-proquest-com.proxy.lib.iastate.edu/docview/1732758546?rfr_id=info%3Axri%2Fsid%3Aprimo
“Corals.” NOAA's National Ocean Service, oceanservice.noaa.gov/education/kits/corals/coral02_zooxanthellae.html.
"Coral Reef Module: Bleaching Impacts," Reef resilience, 2018. Retrieved at http://www.reefresilience.org/coral-reefs/stressors/bleaching/bleaching-impacts/
“Fish Communities on Staghorn Coral: Effects of Habitat Characteristics and Resident Farmerfishes.” Proxy Server Login, link-springer-com.proxy.lib.iastate.edu/article/10.1007/s10641-011-9802-6 Retrieved at .https://link-springer-com.proxy.lib.iastate.edu/article/10.1007/s10641-011-9802-6
Lirman et al.“Growth Dynamics of the Threatened Caribbean Staghorn Coral Acropora cervicornis: Influence of Host Genotype, Symbiont Identity, Colony Size, and Environmental Setting”. Ploseone 2014. Retrieved at http://europepmc.org/backend/ptpmcrender.fcgi?accid=PMC4182308&blobtype=pdf
"Staghorn Coral," NOAA Fisheries, retrieved at https://www.fisheries.noaa.gov/species/staghorn-coral
Vollmer, et al. “Restricted Gene Flow in the Caribbean Staghorn Coral Acropora Cervicornis : Implications for the Recovery of Endangered Reefs.” OUP Academic, Oxford University Press, 7 Dec. 2006, retrieved at https://academic.oup.com/jhered/article/98/1/40/2188406
Wallace, Carden C, and Brian R Rosen. “Diverse Staghorn Corals (Acropora) in High-Latitude Eocene Assemblages: Implications for the Evolution of Modern Diversity Patterns of Reef Corals.” Proceedings of the Royal Society of London B: Biological Sciences, The Royal Society, 22 Apr. 2006, retrieved at http://rspb.royalsocietypublishing.org/content/273/1589/975.short
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