Marine Invertebrates of Bermuda Grooved Brain Coral (Diploria labyrinthiformis) By Kate Rossi-Snook and Dr. James B. Wood and Kim Zeeh - Editors Abstract  Taxonomy  Habitat  Ecology  Recent Research  Commercial Importance  Bermuda Laws  Personal Interest  References  Links

Abstract

Diploria labyrinthiformis, also known as the grooved brain coral, is a brown or yellow hemispherical-shaped reef-building coral occurring in the Caribbean, the Bahamas, southern Florida, and Bermuda (Humann, 1993). It is most commonly found on offshore reefs at depths between 1 and 30 meters, growing to about 2 meters in diameter (Sterrer, 1986). Bermudian brain corals such as D. labyrinthiformis grow upward at a rate of about 3.5 millimeters per year (Sterrer, 1992). Like many other anthozoans, D. labyrinthiformis is host to symbiotic dinoflagellate algae called zooxanthellae. These zooxanthellae are supplied with protection and nutrients from the coral animal, while the coral is supplied with nutrients and energy for calcification and growth (Savage et al., 2002). Recent research has involved studying the increased incidences of coral bleaching and disease (Kuta and Richardson, 2002; Nugues, 2002; Cook et al., 1990; Brylewska, 2003). This is being done in an attempt to understand the causes of the degradation of coral reefs.


Taxonomy

Phylum: Cnidaria
  Class: Anthozoa
    Subclass: Hexacorallia
      Order: Scleractinia
        Suborder: Faviida
          Family: Faviidae



Habitat

Diploria labyrinthiformis is a reef building coral that, along with numerous other coral species, aids in creating a biodiversity-rich habitat for innumerable other coral reef animals. It is found in the Caribbean, the Bahamas, southern Florida, and Bermuda (Humann, 1993). In Bermuda, D. labyrinthiformis most commonly occurs on outer and offshore reefs, and has a broad depth range, occurring anywhere between 1 to 30 meters (Sterrer, 1986).

The distinction between depth occurrences relies heavily on water quality. Here in Bermuda, the expansive area of relatively shallow, nutrient-limited water surrounding most of the island offers prime conditions in which D. labyrinthiformis, and other coral species, may thrive. However, as the population of Bermuda increases, the coral habitat is threatened. D. labyrinthiformis once flourished in Castle Harbour, but with the construction of the airport in the early 1940’s, landfills, dredging, and increased turbidity depleted most of the D. labyrinthiformis population in that area (Sterrer, 1992).


Ecology

Diploria labyrinthiformis is identified by its characteristically brain-like hemispherical-shaped heads, and deep, interconnected polyp-bearing valleys which are separated by broad, grooved ridges (Humann, 1993). Coloring ranges from varying degrees of yellow and brown, and growth can reach up to about 2 meters in diameter (Sterrer, 1986). Like other scleractinian species, D. labyrinthiformis is a sessile animal, with the only locomotion involved in its life cycle found in its planktonic larval stage (Sterrer, 1986).

Because of its strictly benthic behavior, the colonial D. labyrinthiformis polyps depend mostly on suspension feeding methods to obtain nourishment. By using their tentacles and extruded mesenterial filaments, the polyps prey primarily on zooplankton and bacteria (Sterrer, 1986). The polyps are equipped with nematocysts that, when triggered, immobilize and hold prey. Mucus and cilia then aid in the capture and transport of these food particles to the mouth (Sterrer, 1986).

D. labyrinthiformis also receives nutrients from symbiotic dinoflagellate algae, or zooxanthellae, located in its polyps’ endodermal tissue layer. The zooxanthellae receive protection and nutrients in the form of waste products from the coral animal (Sterrer, 1986), while in return, the zooxanthellae provide the coral with photosynthate for energy to complete basic life processes such as calcification and growth, and reproduction (Savage et al., 2002). Because of their location in typically oligotrophic waters, scleractinians, such as D. labyrinthiformis, greatly depend on such symbiotic relationships as with nitrogen-fixing bacteria (Shashar et al., 1994) and photosynthetic zooxanthellae.

Another relationship found among D. labyrinthiformis and other scleractinians is with the benthic dweller, Diadema antillarum, or long-spined urchin. Caribbean reefs were once dominated by scleractinian species and diminutive turf algae, but now have become overgrown by macroalgae, and are in a threatening highly degraded state (Edmunds and Carpenter, 2001). However, as the study by Edmunds and Carpenter (2001) has found, the reefs in Jamaica are beginning to show signs of localized recovery of D. antillarum populations, causing a decrease in macroalgae coverage, and an increase in the abundance of juvenile corals. It was found that specifically among Diploria spp., juvenile coral recruitment and survival occurred as a result of the urchin's algae grazing, which reduced the effect of shading and overgrowth by the macroalgae (Edmunds and Carpenter, 2001). Such findings offer good news for the rehabilitation of many of our devastated coral reefs.

D. labyrinthiformis is a hermaphroditic coral. This species reproduces sexually through brooding, which involves internal fertilization of the egg by the sperm within the polyp, and then the release of the fertilized larvae. Juvenile coral recruitment occurs once the swimming planktonic planulae larvae settle on the appropriate benthos, which is usually within 2-3 days after the brooding session (Fadlallah, 1983). Once the primary polyp settles, asexual reproduction commences, producing a secondary polyp through either intratentacular budding (a new polyp is formed by the division of a pre-existing polyp), or extratentacular budding (a new mouth and tentacles are formed in the space between tentacles of a pre-existing polyp) (Fadlallah, 1983).

Although these polyps are armed with nematocysts for protection, D. labyrinthiformis and other scleractinians are not immune to predation. Gastropods, polychaetes, echinoids, asteroids, pycnogonids, and fishes, such as Parrotfish, are the most common coral predators (Sterrer, 1986). During the day, the polyps usually withdraw their tentacles, leaving only a mucous membrane covering to minimize the effects of heaving predator grazing.


Recent Research

Unfortunately, one of the least studied aspects of the degradation of the world’s coral reefs is coral disease and bleaching, and their relationship to the environment (Kuta and Richardson, 2002). The most recent research involving Diploria labyrinthiformis is in response to the increased occurrences of bleachng and disease.

Studies have shown that both bleaching and disease, such as black band and white plague, are associated with increased seawater temperatures (Kuta and Richardson, 2002). In a study performed by Nugues (2002), D. labyrinthiformis was one of the coral species least affected by white plague in St. Lucia. However, in a previous study carried out in Puerto Rico, the affect of white plague was found to be more severe in D. labyrinthiformis than in any other scleractinian species (Nugues, 2002). These differences may be attributed to the effects of different environmental conditions and pathogens in each area.

In 1988, the reefs of Bermuda experienced its first coral bleaching incident when seawater temperatures were recorded to be their highest in 38 years (Cook et al., 1990). D. labyrinthiformis, one of Bermuda’s dominant scleractinian species, was least affected by the 1988 bleaching event (Cook et al., 1990) as well as in the 2003 bleaching event (Brylewska, 2003). As a dominant species, D. labyrinthiformis may be more resistant to environmental stresses, which may explain the limited effects during the bleaching events. This is supported by Kuta and Richardson’s (2002) observations that coral diversity was lower at black band disease sites than at healthy sites.

Additional research on D. labyrinthiformis involves the seasonal skeletal growth rates of the coral species, and how it can be tracked by analyzing the rings and striations found in slices of the coral heads (Cohen et al., 2004). Cohen et al’s (2004) study shows that with increased temperature, there is a corresponding increase in density of the skeletal striations. This may be used to project the future of coral skeletal growth as seawater temperatures continue to rise.


Commercial Importance

As a massive reef building coral, Diploria labyrinthiformis adds to the diversity of species of the coral reefs, creating a fantastic world below the surface that is rich with life. Exploring these reef ecosystems has become ever popular for the ecotourism industry. Snorkeling and SCUBA diving attracts vacationers and adventurists to countries surrounded by these beautiful coral reefs, like Bermuda.

Aside from its recreational role, D. labyrinthiformis creates habitats for many other organisms on which we depend (Sterrer, 1986). Mollusks, fish, and arthropods are just a few examples of food sources that are a part of the coral reef ecosystem.


Bermuda Laws

Although there lacks a law specifically protecting the species Diploria labyrinthiformis, Bermuda continues to enforce the Coral Reef Preserve Act of 1966, and the Fisheries Protected Species Order of 1978.

The Coral Reef Preserve Act states that it is an offence to remove, damage, or be in possession of plants or animals, whether dead or alive, from either the South Shore or North Shore Preserves (Wood and Jackson, 2005).

The Fisheries Protected Species Order prohibits the confiscation of any coral species, whether dead or alive, found anywhere within the stated 200 mile exclusive fishing zone (Wood and Jackson, 2005).


Personal Interest

Commonly misperceived as rocks or plants rather than animals, corals are so widely admired, yet rarely understood. The various morphologies and species create a beautifully surreal world for SCUBA divers and other reef animals alike, yet are continuously being depleted through ignorance. Corals are the cornerstone of the world’s reefs, offering both home and food for an array of organisms. It is necessary to understand and protect one of the world’s oldest, most biodiversity-rich ecosystems, and maintain its delicate balance. Through the preservation of corals, we can preserve the fish we use as food, and the many organisms we use medically, for future generations.


References

Brylewska, N. 2003. Scleractinian bleaching on the coral reefs of Bermuda, 2003. Bermuda Biological Station for Research.

Cohen, A. L., Smith, S. R., McCartney, M. S., van Etten, J. 2004. How brain corals record climate: an integration of skeletal structure, growth, and chemistry of Diploria labyrinthiformis from Bermuda. Mar. Ecol. Prog. Ser., 271: 147-158.

Cook, C. B., Logan, A., Ward, J., Luckhurst, B., Berg Jr., C. J. 1990. Elevated temperatures and bleaching on a high latitude coral reef: the 1988 Bermuda event. Coral Reefs, 9: 45-49.

Edmunds, P. J., Carpenter, R. C. 2001. Recovery of Diadema antillarum reduces macroalgal cover and increases abundance of juvenile corals on a Caribbean reef. PNAS, 98(9): 5067-5071.

Fadlallah, Y. H. 1983. Sexual reproduction, development and larval biology in scleractinian corals: a review. Coral Reefs, 2(3): 129-150.

Humann, Paul. 1993. Reef Coral Identification: Florida, Caribbean, Bahamas. Jacksonville, Florida: New World Publications, Inc. 126-127.

Kuta, K. G., Richardson, L. L. 2002. Ecological aspects of black band disease of corals: relationships between disease incidence and environmental factors. Coral Reefs, 21: 393-398.

Nugues, M. M. 2002. Impact of a coral disease outbreak on coral communities in St. Lucia: what and how much has been lost? Mar. Ecol. Prog. Ser., 229: 61-71.

Savage, A. M., Goodson, M. S., Visram, S., Trapido-Rosenthal, H., Wiedenmann, J., Douglas, A. E. 2002. Molecular diversity of symbiotic algae at the latitudinal margins of their distribution: dinoflagellates of the genus Symbiodinium in corals and sea anemones. Mar. Ecol. Prog. Ser., 244: 17-26.

Shashar, N., Cohen, Y., Loya, Y., Sar, N. 1994. Nitrogen fixation (acetylene reduction) in stony corals: evidence for coral-bacteria interactions. Mar. Ecol. Prog. Ser., 111: 259-264.

Sterrer, Wolfgang. 1986. Marine Fauna and Flora of Bermuda: A Systematic Guide to the Identification of Marine Organisms. New York: John Wiley and Sons. 159-184.

Sterrer, Wolfgang. 1992. Bermuda’s Marine Life. Bermuda: Island Press. 52-54.

Wood, J.B., Jackson, K. J. 2005. Bermuda. Caribbean Marine Biodiversity: the Known and the Unknown. Pennsylvania: DEStech Publications, Inc. 19-35.


Links

ReefBase
NOAA Coral Reef Site
EPA Coral Site
Braincoral