Elkhorn corals, Acropora palmata , are important reef-building coral species that once dominated the Caribbean ecosystem. They are known to produce anther-like shape colonies hence the name Elkhorn corals. In 1991, the National Marine Fisheries Service (NMFS) identified this coral as a candidate for listing under the Endangered Species Act (ESA) (federalregister.gov, 2006). In 1997, this species was removed from the candidate list since there was no sufficient data regarding threats level to guarantee their entry to the candidate list. In 1999, however, the species was listed in the candidate list after the data from 1998 analysis showed that they had declined substantially. In 2004, the Elkhorn coral attained the status of “species of concern” showing that they truly qualified for the listing. As of 2005, NMFS established that A. palmata might be endangered in the future. This made the species be listed as “critically threatened” under the U.S. ESA in 2008 (Chamberland et al., 2015). The current report illustrates the importance of the A. palmata to the ecosystem, events that caused their decline, and current measures being undertaken to conserve them.
Elkhorn corals are reef-building corals that comprise of genetically similar animals living together. They are pale brown or golden tan with white tips. These species get their color from algae that are found growing within their tissues (Meaghan et al ., 2011). A. palmata have frond-like structures with rounded tips that project from the central trunk. The colonies can grow upwards to about 6 feet with a diameter of about 12 feet (Meaghan et al ., 2011). Moreover, the colonies can grow in dense strands and develop tickets, a framework of interlocking strands (fisheries.noaa.gov, n.d). A single colony comprises of multiple individual polyps that grow as a unit. The polyps are clones implying that they are made of the same genetic materials.
Delegate your assignment to our experts and they will do the rest.
Elkhorn corals are hermaphrodites implying that they possess both male and female garments, sperm and eggs respectively. This also shows that they can reproduce sexually. Under this type of reproduction, various colonies release their gametes simultaneously through a process called broadcast spawning (fisheries.noaa.gov, n.d). It is noteworthy that the male gametes, however, cannot fertilize the female gametes from the same colony. After the fertilization process, the fertilized egg hatches quickly, and the young coral spends a couple of days in water before it settles on the reef to start forming a new colony. Elkhorn corals can also reproduce asexually through a process known as fragmentation. During stormy periods, colonies break apart, and the fragments reattach to the reef and start to grow again. These processes coupled with rapid growing abilities made Elkhorn coral dominate the Caribbean reefs.
Chamberland et al., (2015) showed that A. palmata were crucial to the Caribbean ecosystem. The authors stated that these species created a habitat for organisms that play a role in essential ecological processes including those involved in calcification and nitrogen fixation. Elkhorn corals also offer a complex habitat for many species of animals including parrotfishes, Caribbean spiny lobsters, and tube blennies among others (fisheries.noaa.gov, n.d). In that regard, a decline in Elkhorn coral implies that these organisms would be exposed o predators and other harsh conditions that these corals help them avoid. In the end, sea organisms used by humans as food would reduce significantly or become extinct.
A report by fisheries.noaa.gov (n.d) also showed that Elkhorn corals protect ocean lines from strong water waves. As noted previously, these corals can grow upwards forming a mass of genetically identical projections. When these structures are abundant, they protect shorelines against storms and waves. Nationalgeographic.org (2016) claimed that coral reefs are important because 25% of flora and fauna in the oceans depend on it. The article was quick to acknowledge that little is known about how humans depend on corals. However, it showed that ocean-side communities depend on these animals for protection against storms as well as support for the fishing industry. Nationalgeographic.org (2016) also indicates that scientists have also discovered the medical opportunities provides by these animals and are exploring how these animals could b used for medical advancement.
A report by Vardi et al. (2012) indicated that Elkhorn corals were not historically rare or restricted to a particular geographical area. The report shows that before they started declining, A. palmata dominated 80% of shallow waters in the Caribbean region. In 1983, their dominance dropped to 40%, and in the 1990s, its percentage fell further to an estimated 20%. This decline continued until 2005 when surveys showed that the percentage of Elkhorn corals was at 2 to 20% of the figures reported in the 1970s (Vardi et al., 2012). The lower diversity in the Caribbean coupled reduced ability to recover, resulted in listing A. palmata as an endangered species in the Red List of Threatened Species (Chamberland et al., 2015). The decrease in the prevalence of Elkhorn coral is attributed to many factors including temperature anomalies and bleaching, diseases, pollution, and loss of diversity among others (Vardi et al., 2012).
One of the major threats to the health of Elkhorn coral is temperature changes (Vardi et al., 2012). Scientific studies show that global temperatures are rising due to increased accumulation of greenhouse gases such as carbon (IV) oxide and methane. The increase of these gases in the atmosphere depletes the ozone layer thereby insulating the earth against losing excess heat. This results in an elevated temperature that affects the ecosystem. According to Williams (2017) changes in temperatures, nutrients, or light have adverse effects on corals. They stress corals forcing them to expel the algae (zooxanthellae) that live in their tissue (Nationalgeographic.org, 2016; Williams, 2017). As a result, they turn completely white a phenomenon scientists refer to as coral bleaching. Climate change has been associated with other conditions such as flooding, El Niño, and El Niña among others.Nationalgeographic.org (2016) indicates that El Niño was the primary cause of coral bleaching throughout the world in 2016. Coral bleaching has become common in recent times due to the rise in temperatures. Scholars have projected that most of the corals in the world would be affected by mass bleaching in the next two decades if the current rate of emitting greenhouse gases persists (Nationalgeographic.org, 2016).
Another cause of Elkhorn coral reduction is ocean acidification. Ocean acidification refers to a condition in which ocean waters acidifies after absorbing carbon (IV) oxide (Mollic et al ., 2018). The effects of ocean acidification are felt throughout the food web in the marine ecosystem since calcifying organisms such as sea urchins and oysters experience difficulties in creating their skeletons and shells (Mollic et al ., 2018). This makes them vulnerable to damage and predation. Like in the calcifying organisms, this process impairs the ability of corals to build their protective structures.
Diseases and pollution have also been associated with a decline in the prevalence of Elkhorn corals. A report by fisheries.noaa.gov (n.d) noted that diseases affect both the sexual and asexual potential of Elkhorn corals. The diseases that affect these organisms depend on the interactions between the environment, host, and pathogens. Coral diseases, according to Kemp (2018), usually produce severe tissue loses. Common diseases that affect these animals include white plague and white band diseases (Macintyre and Toscano, 2007; Rodriguez-Martínez et al ., 2014). Sutherland (2011) and Kemp (2018) also found that pathogens that cause diseases in humans caused diseases to coral reefs. They identified Serratia marcescens as one of the organisms that cause diseases to coral reefs. In Florida, for instance, Vibrio bacteria of known pathogenicity caused white pox disease outbreak in Elkhorn corals. Importantly, these studies show that coral diseases are increasing globally and are the major contributors to the decline in coral reefs.
Research by Hernández-Delgado et al . (2015) also acknowledged that certain human activities polluted water bodies thereby creating conditions that impede both the growth and reproduction of A. palmata . The researchers asserted that poor execution of beach renourishment activities coupled with an increase in sewage and non-point sources of pollution had negative impacts on coral reefs in the Caribbean. Such practices, typically, affect the overall ecological function, cause diseases, and increases deaths in many coral reef ecosystems (fisheries.noaa.gov, n.d).
After listing the Elkhorn corals as an endangered species, initiatives have been initiated to conserve the species. The fisheries.noaa.gov (n.d) leads by implementing multiple regulatory, conservation and restoration measure. That includes protecting, designing a habitat for the animals, breeding the species in nurseries, and taking them back into the wild. The organization also embraces research ideas to boost the ability of Elkhorn corals to resist the effects of climate change. Fisheries.noaa.gov, (n.d) also indicates that it is committed to rescuing A. palmata that sustained injury following ship grounding or major catastrophic event. Petersen et al . (2008) shared similar views by showing that scientists have successfully fertilized Elkhorn eggs in vitro and transfer over 800 juvenile corals to public aquaria in 2007 alone. This made Chamberland et al. (2015) and Petersen et al . (2008) to suggest that zoological gardens and public aquaria serve a crucial function in the conservation of endangered and threatened animal species.
In conclusion, Elkhorn corals were once dominant animal species in the Caribbean. These organisms can reproduce both sexually and asexually. Nonetheless, temperature changes, diseases, pollution, and ocean acidification have impaired their ability to grow and multiply. Today, however, they are scarce and highly susceptible to extinction. This explains their listing in the United States ESA. Without careful conservation practices, these Elkhorn corals could be lost entirely. Scientists are now exploring biotechnological techniques such as in vitro fertilization to produce these animals and then release them to the wild. The use of such methods has proved to be successful in conserving and restoring these Caribbean reef-building corals.
References
Chamberland, V. F., Vermeij, M. J., Brittsan, M., Carl, M., Schick, M., Snowden, S. & Petersen, D. 2015. Restoration of critically endangered elkhorn coral (Acropora palmata) populations using larvae reared from wild-caught gametes. Global Ecology and Conservation , 4 , 526-537.
Federalregister.gov. Endangered and threatened species. Final listing determinations for Elkhorn coral and Stahgorn coral. 5 September 2006 https://www.federalregister.gov/documents/2006/05/09/06-4321/endangered-and-threatened-species-final-listing-determinations-for-elkhorn-coral-and-staghorn-coral [Accessed 2018 October 31].
Fisheries.noaa.gov. Elkon coral . n.d. https://www.fisheries.noaa.gov/species/elkhorn-coral. [Accessed 2018 October 31].
Hernandez-Delgado, E., Hutchinson-Delgado, Y. M., Laureano, R., Hernandez-Pacheco, R., Ruiz-Maldonado, T. M., Ohms, J., and Diaz, P. L. 2011. Sediment stress, water turbidity and sewage impacts on threatened Elkhorn Coral (Acropora palmata) Stands at Vega Baja, Puerto Rico. Proceedings of the 63th Gulf and Carribbean Fisheries Institute. 83-92 pp.
Kemp, K.M. 2018. Abundance and multilocus sequence analysis of vibrio bacteria associated with diseased elkhorn coral (Acropora palmata) of the Florida Keys. Appl Environ Microbiol . 84:e01035017. https://doi.org/10.1128/AEM.01035-17.
Macintyre, I. G., and Toscano, M. A. 2007. The Elkhorn coral Acropora palmata is coming back to the Belize Barrier Reef. Coral Reefs , 26 (4), 757-757.
Meaghan, E., Caitlin, L., Erich, B., Iliana, B. B., David, S. G., Elizabeth, A. L., Diego, L., Margaret, W. M., Ken, N., & Schopmeyer, S. Caribbean Acropora Restoration Guide: Best Practices for Propagation and Population Enhancement. 2011. https://nsuworks.nova.edu/occ_facreports/71 [Accessed 2018 October 31].
Mollica, N. R., Guo, W., Cohen, A. L., Huang, K. F., Foster, G. L., Donald, H. K., and Solow, A. R. 2018. Ocean acidification affects coral growth by reducing skeletal density. Proceedings of the National Academy of Sciences , 115 (8), 1754-1759.
Nationalgeographic.org. Coral restoration research findings bring positive news for the future of coral reefs. 6 January 2016. https://blog.nationalgeographic.org/2016/01/06/coral-restoration-research-findings-bring-positive-news-for-the-future-of-coral-reefs/ [Accessed 2018 October 31].
Petersen, D., Carl, M., Borneman, E., Brittsan, M., Hagedorn, M., Laterveer, M., & Schick, M. 2008. Noah’s Ark for the threatened Elkhorn coral Acropora palmata . Coral Reefs , 27 (3), 715-715.
Rodríguez-Martínez, R. E., Banaszak, A. T., McField, M. D., Beltran-Torres, A. U., & Alvarez-Filip, L. (2014). Assessment of Acropora palmata in the Mesoamerican reef system. PLoS One , 9 (4),1-7
Sutherland, K. P. 2011. Human pathogen shown to cause disease in the threatened Elkhorn coral Acropora palmata. PLoS ONE. 6(8):e23468. https://doi.org/10.1371/journal.pone.0023468
Vardi, T., Williams, D. E., and Sandin, S. A. 2012. Population dynamics of threatened elkhorn coral in the northern Florida Keys, USA. Endangered Species Research , 19 (2), 157-169.
Williams, D. E. 2017. Thermal stress exposure, bleaching response, and mortality in the threatened coral Acropora palmata. Marine Pollution Bulletin . 124(1):189-197. https://doi.org/10.1016/j.marpolbul.2017.07.001.
