Grooved Brain Coral, Diploria labyrynthiformis

Grooved Brain Coral, Diploria labyrynthiformis. Underwater photograph taken in the coastal waters off Bonaire, Caribbean Netherlands, December, 2019. Photograph and identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny:  The Grooved Brain Coral, Diploria labyrynthiformis (Linnaeus, 1758), is a hexacoral in the Faviidae Family of Brain Corals. The genus Diploria is one of ten genera in this family. This is the only species in this genus.

Morphology:  Grooved Brain Coral  polyps have radial symmetry, a hollow digestive cavity, and specialized stinging structures in tentacles surrounding the mouth. Their polyps have a flower-like appearance and produce a hard, calcareous skeleton. They live in tightly packed colonies. The colonies grow in a spherical shape, marked with maze-like valleys and ridges, giving it the appearance of a human brain. The valleys are 5 mm (0.2 inches) to 1.0 cm (0.4 inches) wide, up to 6 mm (0.25 inches) deep and U-shaped in a cross section. The ridges are wider than valleys being up to 1.5 cm (0.6 inches), and have a concave profile with edges that are 2 mm (0.1 inches) to 4 mm (0.2 inches) higher than the rest of the ridge. Grooved Brain Coral can be a variety of colors including tan, yellow, and gray. Colonies of Grooved Brain Coral can be one to two meters in diameter.

Habitat and Distribution:  Grooved Brain Coral grows on hard and looser substrates. They are able to become established on softer substrates than most corals. Because of its need for sunlight it lives in shallow water and can be found at depths between 1 m (3 feet) and 30 m (100 feet). Grooved Brain Coral is a tropical West Atlantic species that are found in Mexican waters of the Gulf of Mexico and the Caribbean from Paraiso, Tabasco to Belize.

Diet: Grooved Brain Corals are zooxanthellate. They have a symbiotic relationship with single-cell dinoflagellates, known as zooxanthellae. Zooxanthellae live within certain coral polyps, sea anemones, jellyfish, and nudibranchs. The zooxanthellae produce energy, during daylight, by means of photosynthesis. This energy is passed along to their hosts, sometimes providing up to 90% of the host’s total energy needs. In return, the host provides nutrients, carbon dioxide, and a secure, sunlit, platform for the zooxanthellae. During periods of chemical or thermal stress the corals can eject the zooxanthellae, to reduce metabolic stress. This causes the coral to appear white. This process is known as coral bleaching. Coral bleaching can be an indicator of an unhealthy environment, or a natural response to a short-term condition such as El Niño. The coral can replace the zooxanthellae after the stress is resolved, or it can acquire a different species of zooxanthellae that is better accommodated to the new environment. In either case, the polyp risks starvation if it is unable to replace the zooxanthellae quickly enough. Grooved Brain Corals supplement the energy provided by zooxanthellae by using their tentacles to capture amphipods and other plankton from the surrounding water. The tentacles then pass the food to the mouth. Because these polyps cannot change location, they are found in areas where moving water, caused by wave action or current, brings them more food.

Predators:  Grooved Brain Corals are preyed upon by various fishes including parrotfish, polychaetas, sea stars and sea urchins.

Reproduction:  Grooved Brain Coral is hermaphroditic. Reproduction can be asexual, through budding, or sexual. Sexual reproduction involves broadcast spawning, with internal fertilization. The eggs hatch into planktonic planulae larvae, which settle on an appropriate substrate, where asexual reproduction begins. Secondary polyps are formed, which develop to adult polyps. The typical spawning season of grooved brain coral is from late May to late June.

Ecosystem Interactions: In addition to the symbiotic relationship with  zooxanthellae, Grooved Brain Coral may also have a symbiotic relationship with the Long-spined Sea Urchin, Diadema antillarum. Grazing by the urchin, on, and around, the coral,  may benefit the coral by reducing macroalgal growths and shading. Grooved Brain Coral has an endoparasitic and ectoparasitic relationship with the Brevibrachium Copepod Corallovexia brevibrachium, which contributes to Black Band Disease in the coral.

Human Interactions:  Historically, Grooved Brain Coral  have been significantly harmed by human activities such as dredging, anchoring of vessels, water pollution, and aquarium and curio collecting. The Grooved Brain Coral are now protected throughout most of its range and most of these threats have lessened.  All corals, including Grooved Brain Corals may be damaged by being covered by sediment or by being handled or stepped on by snorkelers, divers, or other beach goers. Any form of contact with Grooved Brain Coral by humans should be avoided. From a conservation perspective the Grooved Brain Coral is currently considered to be Critically Endangered.

Synonyms:  Coeloria labyrinthiformis, Coeloria labyrinthiformis var. tenera, Diploria cerebriformis, Diploria geographica, Diploria truncata, Madrepora implicata, Madrepora labyrinthiformis, Maeandra (Platygyra) cerebriformis, Maeandra cerebriformis, Maeandra implicata, Maeandra labyrinthiformis, Maeandra labyrinthiformis var. stokesii, Maeandrina (Coeloria) labyrinthiformis, Maeandrina labyrinthiformis, Maeandrina sinuosa, Meandrina cerebriformis, Meandrina laberintiformis, Meandrina truncata, Montastraea truncata, and Platygyra cerebriformis.