Boulder brain coral  (Colpophyllia natans)

The boulder brain coral is classified as Least Concern (LC) on the IUCN Red List (1) and is listed on Appendix II of CITES (2).

The boulder brain coral (Colpophyllia natans) is named for its large, boulder-like colonies, the surfaces of which are covered in a meandering pattern of curved, brown ridges, separated by tan, green or whitish depressions, known as valleys (3) (4) (5) (6). Colonies may form large domes up to two metres in diameter, but can also grow as large, rounded plates (3) (4) (5). The boulder brain coral generally has long, wide valleys, up to two centimetres across, and wide ridges, which have a fine but distinct groove along the top (3) (4) (5) (6). Boulder brain coral colonies are often eroded at the base, forming overhangs (6).

Like all corals, the colonies of this species are composed of numerous tiny, anemone-like animals known as polyps, which possess a sac-like body and a central ‘mouth’, surrounded by tentacles (3). In the boulder brain coral, the tentacles are only extended at night (3) (4). Although generally considered to be the only species in the genus Colpophyllia, some colonies of the boulder brain coral possess short valleys containing only one to three polyps (3), and are considered by some to be a separate species, Colpophyllia breviserialis (closed-valley brain coral) (4) (5). The boulder brain coral can be distinguished from the similar Diploria brain corals by its wider valleys and ridges (3) (5).

The boulder brain coral occurs in the Caribbean, the Bahamas, the Gulf of Mexico and around Florida, USA (1) (3) (4) (7).

This coral inhabits relatively shallow reef environments at depths of up to 55 metres (1) (3) (4) (7).

The boulder brain coral is a zooxanthellate coral, meaning that it has symbiotic algae, known as zooxanthellae, living within its tissues. The zooxanthellae provide the coral with nutrients produced by photosynthesis, and in return receive a safe and stable environment in which to live. Although this limits zooxanthellate corals to living in relatively clear, shallow, warm waters where photosynthesis can take place, it allows them to grow faster and create large reef structures, formed by the laying down of the coral’s hard skeleton (3) (8). The boulder brain coral is also able to actively feed on tiny zooplankton, caught using stinging cells on the tentacles (3).

Like other corals, the boulder brain coral is able to reproduce asexually in a process known as budding, in which polyps divide into two or more new polyps. It is also capable of sexual reproduction, releasing eggs and sperm into the water for external fertilisation (3). The boulder brain coral is a hermaphrodite, meaning that each polyp produces both eggs and sperm (9). In some areas, studies have found this species to spawn in August and September, at a very specific time (shortly after sunset), which remains remarkably consistent between years (9). Fertilised eggs develop into larvae, which drift in the water column before settling and developing into polyps (3). The boulder brain coral is an aggressive species, which is able to dominate neighbouring corals by extruding filaments which digest the tissues of its competitors. This strategy helps the boulder brain coral to successfully compete for space on the reef (10).

Although the boulder brain coral is currently widespread and relatively common throughout its range, it is likely to be facing a number of threats (1). Of particular concern are coral diseases, such as black-band disease and white plague (1), which can cause large mortality in some areas (11) (12) (13). Elevated water temperatures in the Caribbean in 2005 also caused mass coral bleaching, in which the stressed corals expel their zooxanthellae, often leading to death. Although many boulder brain coral colonies initially showed signs of recovery after this event, the weakened corals were subsequently affected by an outbreak of disease (14) (15). Other specific threats to the boulder brain coral include predation by species such as the stoplight parrotfish (Sparisoma viride) and three-spot damselfish (Stegastes planifrons), as well as sedimentation (1).

The boulder brain coral is also likely to be susceptible to the many threats faced by corals worldwide, including the major threat of climate change, which can lead to more frequent and severe storms and increase coral bleaching, as well as increased ocean acidity, which can affect the ability of a coral to lay down its hard skeleton. More localised threats to corals include destructive fishing practices, human development, invasive species and pollution (1) (8) (16) (17).

All corals are listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), meaning international trade in corals should be carefully regulated (2). The boulder brain coral may also receive some protection within a number of Marine Protected Areas, such as the Florida Keys National Marine Sanctuary, Dry Tortugas National Park and Flower Garden Banks National Marine Sanctuary, USA (1). In addition, it is illegal to harvest corals commercially in US waters (1).

With an estimated 20 percent of coral reefs already lost worldwide (17), and around a third of reef-building corals threatened with extinction (16), the conservation of these vital ecosystems is now urgent. Recommended measures for protecting this and other coral species include further research and monitoring, the expansion of protected areas, building awareness, disease research and efforts to tackle global climate change (1) (8) (17).

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

To find out more about corals and coral conservation, see:

• Reef Check:
  http://www.reefcheck.org/
• The Coral Reef Alliance:
  http://www.coral.org/
• Veron, J.E.N. (2000) Corals of the World. Australian Institute of Marine Science, Townsville, Australia.