Grooved brain coral (Diploria labyrinthiformis)

Named for the system of meandering grooves and ridges on their outer surface, which resembles the appearance of the brain of higher animals, the brain corals are reef-building species that form large, rounded colonies ⁽³⁾. Like other colony-forming corals, each grooved brain coral colony is composed of numerous small polyps, which are soft-bodied animals related to anemones. Each groove contains a single, long polyp which has many mouths arranged into a row and is surrounded by tentacles that direct food into the mouths, where it is digested in a sac-like body cavity ^{(3) (4)}. One of the most remarkable and ecologically important features of some corals is that the polyps secrete a hard skeleton, called a ‘corallite’, which over successive generations contributes to the formation of a coral reef. The coral skeleton forms the bulk of the colony, with the living polyp tissue comprising only a thin veneer ⁽⁴⁾. Living colonies of the grooved brain coral range in colour from yellow to brown and grey ^{(4) (5)}.

Like many coral species, the grooved brain coral is zooxanthellate, which means that its tissues contain large numbers of single-celled algae called zooxanthellae. The coral and the algae have a symbiotic relationship in which the algae gain a safe, stable environment within the coral's tissues, while the coral receives nutrients produced by the algae through photosynthesis. By harnessing the sun's energy in this way, corals are able to grow rapidly and form vast reef structures, but are constrained to live near the water surface. While, on average, zooxanthellate coral can obtain around 70 percent of its nutrient requirements from zooxanthellae photosynthesis, the coral may also feed on zooplankton ⁽⁴⁾.  

The grooved brain coral is a hermaphroditic species and the eggs are fertilised by sperm inside the polyp walls. Larvae subsequently develop and are released into the ocean to float passively in the currents, before settling on the ocean floor, usually two to three days later. Sessile young polyps develop and immediately commence asexual reproduction, known as ‘budding’, to produce additional polyps ⁽⁵⁾.  

This coral is found in the Caribbean, the Gulf of Mexico, the Bahamas, Bermuda and off the southern Florida coast ^{(1) (5)}.

The grooved brain coral occurs in shallow reef environments down to depths of around 43 metres ^{(1) (4)}. It is often found near the shoreline in shallow waters where few other coral species occur, but it may also be a major reef building coral ⁽³⁾. In Bermuda, it is most commonly found in offshore reefs in relatively shallow waters with low nutrient levels ⁽⁵⁾.

Classified as Least Concern (LC) on the IUCN Red List ⁽¹⁾ and listed on Appendix II of CITES ⁽²⁾.

With an estimated 20 percent of the world’s coral reefs already destroyed, the grooved brain coral faces many threats that are affecting coral reefs globally ^{(6) (7)}. Worldwide there is increasing pressure on coastal resources resulting from human population growth and technological development. Consequently, there has been a significant increase in domestic and agricultural waste in the oceans, poor land-use practices that result in an increase in sediment running on to the reefs, and over-fishing, which can have ‘knock-on’ effects on the reef ⁽⁶⁾. However, the major threat to corals is global climate change, with the expected rise in ocean temperatures increasing the risk of coral ‘bleaching’, in which the stressed coral expels its zooxanthellae, often resulting in the death of the coral. Climate change may also lead to more frequent, severe storms, which can damage reefs, and rising carbon dioxide levels may make the ocean increasingly acidic. Such stresses can also make corals more susceptible to disease, parasites and predators, such as the crown-of-thorns sea star (Acanthaster planci) ^{(6) (7) (8)}. 

Despite the wealth of threats that the grooved brain coral faces, it is still relatively common throughout its range, and in places it is the most abundant reef-building species. This species’ persistence in degraded reefs also makes it fairly resilient to habitat loss ⁽¹⁾. However, two particularly severe threats to the grooved brain coral are ‘black band disease’ and ‘white plague’, both of which are caused by infectious bacteria and can cause partial or total mortality of colonies. The number of outbreaks of these diseases has increased dramatically in recent years and are most frequent in reefs already affected by pollution and degradation ^{(1) (9)}.

In addition to being listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), which makes it an offence to trade this species without a permit, the grooved brain coral also forms part of the reef community in numerous marine protected areas, including the Florida Keys National Marine Sanctuary ^{(1) (2)}. It is also protected by law in Bermuda under the Coral Reef Preserve Act and the Fisheries Protected Species Order, both of which prohibit the removal of any coral species from designated protected areas ⁽⁵⁾. To specifically conserve the grooved brain coral, recommendations have been made for a raft of studies into various aspects of the species’ biology, population status, habitat and threats to its survival ⁽¹⁾.

ARKive is supported by OTEP, a joint programme of funding from the UK FCO and DFID which provides support to address priority environmental issues in the Overseas Territories, and Defra

For further information on the conservation of coral reefs, see:

• Reef Check:
  http://www.reefcheck.org/
• Coral Reef Alliance:
  http://www.coral.org/

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Algae

Simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.

Asexual reproduction

Reproduction that does not involve the formation of sex cells (‘gametes’). In many species, asexual reproduction can occur by fission; part of the organism breaks away and develops into a separate individual. Some animals can develop from unfertilised eggs; this process, known as parthenogenesis, gives rise to offspring that are genetically identical to the parent.

Colony

Relating to corals: corals composed of numerous genetically identical individuals (also referred to as zooids or polyps), which are produced by budding and remain physiologically connected.

Fertilisation

The fusion of gametes (male and female reproductive cells) to produce an embryo, which grows into a new individual.

Hermaphroditic

Possessing both male and female sex organs.

Larvae

Stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.

Photosynthesis

Metabolic process characteristic in which carbon dioxide is broken down, using energy from sunlight. Organic compounds are made and oxygen is given off as a by-product.

Polyp

Typically sedentary soft-bodied component of cnidaria, a group of simple aquatic animals including the sea anemones, corals and jellyfish. A polyp comprises a trunk that is fixed at the base, and a mouth that is placed at the opposite end of the trunk and is surrounded by tentacles.

Symbiotic relationship

Relationship in which two organisms form a close association. The term is now usually used only for associations that benefit both organisms (a mutualism).

Zooplankton

Tiny aquatic animals that drift with currents or swim weakly in water.

Zooxanthellae

Single-celled dinoflagellates that form symbiotic relationships with hermatypic ‘reef-building’ corals.

1. IUCN Red List (September, 2010)
   http://www.iucnredlist.org/
2. CITES (September, 2010)
   http://www.cites.org/
3. Natural History Museum (September, 2010)
   http://www.nhm.ac.uk/
4. Veron, J.E.N. (2000) Corals of the World. Australian Institute of Marine Science, Townville, Australia.
5. Rossi-Snook, K. (2005) Grooved brain coral (Diploria labyrinthiformis). In: Wood, J.B. (Ed.) Marine Invertebrates of Bermuda. Bermuda Institute of Ocean Sciences. Available at:
   http://www.thecephalopodpage.org/MarineInvertebrateZoology/index.html
6. Wilkinson, C. (2004) Status of Coral Reefs of the World: 2004. Volume 3. Australian Institute of Marine Science, Townsville, Australia.
7. Carpenter, K.E. et al. (2008) One-third of reef-building corals face elevated extinction risk from climate change and local impacts. Science, 321: 560-563.
8. Miththapala, S. (2008) Coral Reefs. Coastal Ecosystems Series (Volume 1). Ecosystems and Livelihoods Group Asia, IUCN, Colombo, Sri Lanka.
9. Green, E.P. and Bruckner, A.W. (2000) The significance of coral disease epizootiology for coral reef conservation. Biological Conservation, 96: 347-361.