Coral Reefs

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.

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.

There is no population estimate for Dichocoenia stokesii, however the species is considered common.

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.

Vulnerable (VU) 2012.2 IUCN Red List

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.

 

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.

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.

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 > 17^th December 2012.

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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.