Elliptical star coral
(Dichocoenia stokesii)
VU
Overview
The elliptical star coral is a distinct and attractive coral whose morphology varies within the vast range of depths in which it grows. Commonly, colonies are spherical in shape and possess long meandering corallites with pronounced, ridged edges. In some conditions however, colonies will instead form thickened plates and feature rounded corallites.

Endemic to the Western Atlantic, this species is under considerable threat from coral diseases such as white plague and also sedimentation resulting from coastal developments. The former threat in particular is deemed to be responsible for a severe decline in this species population number and has resulted in the species being listed as vulnerable in the IUCN Red List.
Urgent Conservation Actions
There is currently no species specific conservation for Dichocoenia stokesii.
Distribution
The elliptical star coral is found throughout the Caribbean including the Gulf of Mexico, Caribbean Sea and the Eastern Pacific

 
Fact
In the Florida Keys the population of Dichocoenia stokesii has declined by 75% since 1995.
Associated Blog Posts
11th Jan 11
EDGE launches a brand new conservation project: EDGE Coral Reefs! Scientists have highlighted 32 coral species that are on the EDGE of Existence. ...  Read

Media from ARKive
ARKive image - Elliptical star coral, close up
ARKive image - Elliptical star coral, close up
ARKive image - Elliptical star coral
ARKive image - Elliptical star coral
ARKive image - Elliptical star coral in natural habitat
ARKive image - Elliptical star coral
ARKive image - Elliptical star coral
ARKive image - Elliptical star coral
ARKive image - Elliptical star coral in coral reef habitat
Evolutionary Distinctiveness
Order: Scleractinia
Family: Meandrinidae
Dichocoenia stokesii is the only species in its genus and is part of the small Meandrinidae family. Four genera in the family including Dichocoenia spp. are restricted to the Atlantic while the three remaining family members are restricted to the Indo-Pacific. Fossil records for this species date back to the Eocene period which occurred between 33 and 55 million years ago. Molecular analysis has confirmed this genus is monospecific and it is placed in a clade with three other genera from the Meandrinidae family.

 
Description
Size: 
>160cm2
Dichocoenia stokesii forms attractive, often spherical colonies that are a distinct orange-brown in colour. Colonies are adorned by numerous conspicuous corallites, the exoskeletons of coral polyps. These corallites vary in shape but are typically long and meandering in shallower waters and rounded in at increased depths. Each is bordered by white ridged structures known as septo-costae, which are pronounced and attractive. In some cases, colonies may appear as thickened plates rather than spherical.

Colonies can grow to medium sizes. For successful reproduction to occur colonies must be at least 160cm2, or roughly 10-15cm across.
Ecology
An overview of hard coral ecology can be found here.

As a colonial, Scleractinian coral, Dichocoenia stokesii growth contributes to reef development. As the individual animals (polyps) of this species grow, they exude calcium carbonate to form exoskeletons (corallites) for protection. Specific oceanic conditions are required for polyps to synthesize and exude calcium carbonate

As a zooxanthellate coral Dichocoenia stokesii obtains the majority of its energy from a symbiotic relationship with algae called zooxanthellae. Zooxanthellae live in the tissue of coral and require sunlight for photosynthesis, a process that produces energy for the algae and its host coral. Additional nourishment is provided through the catching of prey using fleshy polyps which this species extends day and night.

In terms of its reproductive characteristics, this species is predominantly gonochoric, meaning that polyps are either male or female. A small proportion of polyps however have been found to be hermaphroditic and therefore capable of producing both eggs (female) and sperm (male) for sexual reproduction. As a spawning species, Dichocoenia stokesii colonies release eggs and sperm into the water column en masse for external fertilization. The synchronization of this release is thought to be the result of the corals colonies responding to an external trigger related to full moon events.
Habitat
Dichocoenia stokesii can be found in most reef environments including back and fore reef, lagoons and channels. The species can withstand a high range of depths, ranging between 2 and 72m. Hemispherical structures are most commonly found on shallow reefs between 5-20m where sunlight is available for the zooxanthellae that require light for photosynthesis.
Distribution
Dichocoenia stokesii is found in the western Atlantic Ocean, the Caribbean Sea and Gulf of Mexico.

This species is distributed widely through the Caribbean and Central American Region and further north around Bermuda.
Population Estimate
There is no population estimate for Dichocoenia stokesii, however the species is considered common.
Population Trend
The population of Dichocoenia stokesii is declining. Population surveys carried out in the northern Florida Keys, following a white plague type II disease outbreak in 1995, showed a 38% mortality of Dichocoenia stokesii in 1995 and an ensuing 75% decline in mean number of colonies. Research also showed that in the seven years following the disease outbreak there was no new recruitment, indicating the surviving corals were not reproducing. Declines of the overall coral cover on Caribbean reefs have been estimated at 80% over the past 30 years and from this information we can infer that the wider population of Dichocoenia stokesii is declining.
Status
Vulnerable (VU) 2012.2 IUCN Red List
Threats
The most significant current threat to this species is that of coral disease. In particular Dichocoenia stokesii is highly susceptible to white plague, epidemics of which have led to serious declines in populations of the species. Outbreaks of white plague type II disease in Florida Keys for example was found to result in the mortality of 75% of colonies. Even 7 years later, no coral recovery was reported for the species in this area. In addition to this disease, the species is also susceptible to Black Band disease.

Whilst Dichocoenia stokesii colonies are not particularly susceptible to thermal induced coral bleaching, the prevalence of diseases such as white plague seem to correlate with increased temperatures and as such global warming is likely to increasingly impact this species.

Dichocoenia stokesii is also susceptible to sedimentation and has been found to exhibit physiological stress at turbidity levels considered acceptable within the US state of Florida. Whilst this stressor is unlikely to result in localized extinctions of the species alone, they will contribute to reducing the species resilience to additional threats such as thermal stress.

Coral cover in the Caribbean has plummeted by 80% over the past 30 years and this is due both to the above stressors and a multitude of additional threats. These additional threats, most of which affect a range of coral species, can be viewed here.

To date, natural predation and collection for the aquarium trade has not posed a significant threat to this coral.

 
Conservation Underway
Dichocoenia stokesii, as with all corals is offered some protection through their inclusion in CITES Appendix II which manages the export of threatened species.

Additionally parts of the species range do overlap within marine protected areas (MPAs). In many regions, there is a drive to upscale MPAs and form networks from them.

This coral will also be offered some protection through regional conservation initiatives such as the Caribbean Challenge. This programme was initiated in 2008 and involves 8 countries, each of which have pledged to effectively manage and protect 20% of their coastal areas by 2020. They will achieve this by creating networks of MPAs and a trust fund to provide sustainable funding to be used for MPA management, expansion and scientific monitoring.
Conservation Proposed
With no suggested conservation measures, the species would benefit from further research into all aspects of its ecology, therefore allowing for scientifically informed conservation proposals.

The continued development of new marine reserves as well as the enhancement and improved management of existing areas would also benefit this species.

More must also be done to curb global emissions of greenhouse gases in order to prevent climate change and ocean acidification.
Associated EDGE Community members

NGO dedicated to working with local communities to conserve threatened marine environments.

Links
References
Aronson, R., Bruckner, A., Moore, J., Precht, B. & E. Weil 2008. Dichocoenia stokesii. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 19 December 2012.

CITES national export quotas. Accessed < www.cites.org > 17th December 2012.

Borger, J. L. and Steiner, S. C. C. 2005. The spatial and temporal dynamics of coral disease in Dominica, West Indies. Bulletin of Marine Science. 77(1): 137-154

Gardner, T.A. et al. (2003) Long-Term Region-Wide Declines in Caribbean Corals.Science 301:958-960

Richardson, L.L. and Voss, J.D. (2005) Changes in a coral population on reefs of the northern Florida Keys following a coral disease epizootic. Mar Ecol Prog Ser 297: 147-156

Telesnicki, G, J. and Goldberg, W. M. 1995. Effects of turbidity on the photosynthesis and respiration of two South Florida reef coral species.Bulletin of Marine Science. 57(2): 527-539

Veron J.E.N. 2000. Corals of the World. Volume 2. Townsville. Australian Institute of Marine Science

Wagner, D. E. et al. 2010. Species composition, habitat and water quality influence coral bleaching in Southern Florida. Marine Ecology Progress Series. 408: 65-78

Wilkinson, C. 2008. Status of coral reefs of the world: 2008. Global Coral Reef Monitoring Network and Center, Townsville, Australia.

if you can provide new information to update this species account or to correct any errors, please email us at info@edgeofexistence.org


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