Marine Invertebrates of Bermuda

Mustard Hill Coral (Porites astreoides)

By Ashley Rowland
James B. Wood (Ed)

Abstract Taxonomy  Habitat  Ecology  Recent Research  Commercial Importance  Bermuda Laws  Personal Interest  References  Links 

Mustard Hill Coral, Porites astreoides


Porites astreoides, also known as the mustard hill coral, is a flat coral with a hemispherical shape. It is typically a yellow to brown color covered with small bumps with and is mainly found in Florida, Bahamas, the Caribbean, and the Bermuda (Sterrer, 1986). Colony growth mainly occurs on reefs and open inshore waters from half a meter to 15 meters (Sterrer, 1986). P. astreoides grows at an average of 3.5 mm per year in Bermuda and depending on other locations and conditions, it can grow anywhere from 3.0 mm per year to 4.75 mm per year (Sterrer, 1992). Like many other scleractinian corals, P. astreoides has a symbiotic relationship with dinoflagellate zooxanthellae from which it gets nutrients and energy for growth and calcification (Lasker, 1981). Recent studies on P. astreoides have focused on coral bleaching (Souter and Linden, 2000).


Phylum: Cnidaria
  Class: Anthozoa
    Subclass: Hexacorallia
      Order: Scleractinia
        Family: Poritidae

Porites astreoides displays all the characteristics that are unique to the phylum Cnidaria. These characteristics include the presence of stinging cells called cnidae, a gut cavity, and a polyp body form (de Putron, 2007). More specifically,it belongs under the coral class Anthozoa and subclass Scleractinia because it is a stony coral with a hard calcium carbonate skeleton where the polyps always bear six tentacles (de Putron 2007). The family Poritidae displays characteristics of small corallites filled with septa that tend to be 0.6 to 1.3 mm.


Porites astreoides is an abundant stony coral found mainly in Florida, Bahamas, Caribbean, and Bermuda (Humann 1993). Stony corals are reef building corals that inhabit tropical and subtropical waters in temperatures ranging from 70 to 85 degrees Fahrenheit (Humann, 1993). P. astreoides most commonly grows in depths ranging from .5 meters to 15 meters and settle on all reef types. In Bermuda, colonies grow mainly in inner and outer reefs and open inshore waters (Sterrer, 1986). Occasionaly, P. astreoides will grow as a free-living colony by settling on loose pieces of dead coral, mollusk shells, calcareous algae, and rocks (Rodriquez-Martines and Jordan-Dahlgren, 1999).


Porites astreoides can be found in both shallow and deep waters and their shape varies with depth. They are typically flat and encrusting in shallow waters and grow more vertically into a dome shape in deeper waters (Humann, 1993). Colonies range in color from yellow- brown to green to grey and the extension of their polyps makes it appear soft (Humann, 1993). The surface is typically bumpy with corallites, Calcium Carbonate holes set close to one another (Humann, 1993).

P. astreoides uses suspension feeding to capture prey. They feed primarily at night, when there is a decrease in predation, using tentacles and mesentery filaments to capture prey. Zooplankton and Bacteria are the main prey and P. astreoides opens its polyps for optimal capture ability. It also produces a mucus, consisting of a carbohydrate-protein complex, in the mouth used for ingestion of the captured prey (Coffroth, 1990). This mucous is also a source of 40 to 60% of the photosynthetically-fixed carbon that is released into the water and nitrogen that can be used by other corals (Coffroth, 1990).

All Scleractinian corals are hermatypic, relying on their symbiotic relationship with the dinoflagellate zooxanthellae (Lasker, 1981). P. astreoides provides protection and nutrients to the zooxanthellae in the form of waste released by the coral. In return, the zooxanthellae provide the photosynthate for energy in the form of amino acids, sugars, and carbohydrates. The photosynthate acquired by the coral is essential for growth and calcification (Lasker, 1981). This symbiotic relationship creates a highly successful base of coral reef environments in which many other animals inhabit (Lasker, 1981).

P. astreoides is a unique brooding coral in which half the colonies are hermaphroditic, meaning it has both male and female gametes, while half are female (Chornesky and Peters, 1987). Brooding corals internally fertilize the egg with sperm within the polyps. The egg and spermary of the hermaphroditic corals develop within the same mesentery before they are released into the open water (de Putron, 2007). The hermaphroditic colonies tend to sexually reproduce at smaller sizes than the female colonies and are capable of self-fertilization (Heyward and Babcock, 1986). Female colonies differ from hermaphroditic colonies because they must use cross-fertilization to create offspring. These two different modes of fertilization can create a difference in the offspring’s genetic composition and diversity (Chornesky and Peters, 1987). Both forms of reproduction are based on lunar cycles, season, and the polyp location within the colony. April to August is the most successful time for reproduction, which usually occurs six to eighteen days around the full moon when water temperatures are between 24.5 to 27.5 C (Maguire, 1998). Male gametes are typically spawned prior to the new moon and then the larvae are released during the full moon. Female gonads, however, can take more than a month to mature (Koji and Quinn, 1984).

P. astreoides utilize stinging cells called nematocysts as a form of protection from predation (de Putron, 2007). Common predators include reef fish, Gastropods, Polychaetes, and Asteroids (Sterrer, 1986). While nematocysts can protect from predation, they cannot protect from overgrowth or overtopping from other corals and algae. If there is a nutrient increase in the water, algal blooms will occur and block out the light necessary for photosynthesis to occur (de Putron, 2007). Competition for space on a reef is important for successful growth and the overgrowth of a stronger coral can be deadly (de Putron, 2007).

Recent Research

Coral bleaching has become a major issue on coral reefs throughout the world in the past two decades. Recently research has been conducted to determine what could be causing this reef disruption.

Bleaching mainly occurs due to a rise in temperature above the corals threshold of 30 C (de Putron, 2007). Studies have shown that anthropogenic threats are the main cause of coral bleaching (Souter and Linden 2000). High amounts of carbon dioxide are emitted into the atmosphere everyday through the use of cars, industrial plants, etc. (Alexiadis, 2006). Carbon dioxide emitted is a primary element in the greenhouse gas effect, which captures light in the atmosphere and causes temperatures to rise. The carbon dioxide also breaks down the ozone layer allowing a higher penetration of UV light into the atmosphere. The higher temperatures and penetration of UV light are two of the main factors in the disappearance of about 10% of the world’s coral reefs (Souter and Linden, 2000). Souter and Linden (2000) predict that if anthropogenic threats continue at the rate they are going, 20% of the worlds reefs will be gone within the next two decades.

Other anthropogenic causes of death that have recently been studied include smothering from sedimentation and overexploitation of the reefs (Souter and Linden, 2000). Sedimentation occurs mostly in coastal areas due to coastal developments from human colonization. It is believed that 58% of the world’s coral reefs are at a high risk of destruction due to these coastal developments, pollution, and overexploitation (Souter and Linden 2000). Building airports, industrial buildings, and housing developments increase sedimentation which reduces light penetration or smothers the corals.

Commercial Importance

Porites astreoides is one of the most common reef builders in Bermuda coral reefs, creating a habitat for many other animals (Sebens, 1994). The wide variety of fish which inhabit the coral reefs are important for, not only the fishing industry, but for tourists and scientists as well. SCUBA diving and snorkeling are the best ways to see the coral reefs first hand, and are popular with vacationers and scientists.

Tourism is especially important in Bermuda because it creates many jobs for the people who live there. However, such a wide influx of people has been damaging to the coral reef through the creation of airports, cruise ships stirring up sediment, and runoff (Sebens 1994). Scientists from all over the world come to Bermuda to study these anthropogenic effects on coral reefs and other aspects of coral reef ecology.

Bermuda Laws

While there are no laws put forth in Bermuda specifically for Porites astreoides, they are protected under the Coral Reef Preserve Act of 1966 and the Fisheries Protected Species Order of 1978. The Coral Reef Preserve Act states that the marine flora and fauna within coral reef preserves may not be removed or damaged. The most important areas protected by this law is the North Shore and South Shore marine protected areas. Similarly, the Fisheries Protected Species Order states that the removal of all coral types is prohibited anywhere within the exclusive economic zone.

Personal Interest

Prior to coming to Bermuda, I knew very little about coral reefs. I chose to study Porites astreoides because it is one of the most common scleractinian corals found in Bermuda and throughout all coral reef environments, researching this coral not only taught me about it specifically, but how it effects the entire coral reef. P. astreoides is one of many scleractinian species that have to deal with the threat of coral bleaching. Studying the direct and indirect effects global warming and human activities have on coral reefs intrigues me and I hope to study them further.


Alexiadis, A. 2006. Global warming and human activity: a model for studying the potential instability of the carbon dioxide/temperature feedback mechanism. Ecological Modelling, 203: 243-256.

Chornesky, E. A., Peters, E.C. 1987. Sexual Reproduction and Colony Growth in the Scleractinian Coral Porites astreoides. Biol. Bull., 172: 161-177.

Coffroth, M. A. 1990. Mucous sheet formation on poritid corals: an evaluation of coral mucus as a nutrient source on reefs. Marine Biology, 105: 39-49.

Heyward, A.J., Babcock, R.C. 1986. Self- and cross-fertilization in scleractinian corals. Marine Biology, 90: 191-195.

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

Koji, B.L., Quinn, N.J. 1984. Seasonal and depth variation in fecundity of Acropora palifera at two reefs in Papua New Guinea. Coral Reefs, 3: 165-172.

Lasker, H. R. 1981. Phenotypic Variation in the Coral Montastrea covernosa and its Effects on Colony Energetics. Biol. Bull., 160: 292-302.

Maguire, M.P. 1998. Timing of larval release by Porites astreoides in the northern Florida Keys. Coral Reefs, 17: 369-375.

de Putron, S. 2007. Lecture Notes Fall 2007 Semester.

Rodriquez-Martinez, R.E., Jordan-Dahlgren, E. 1999. Epibiotic and free-living Porites astreoides. Coral Reefs, 18: 159-161.

Sebens, K.P. 1994. Biodiversity of coral reefs: What are we losing and why? American Zoologist, 34: 115-133.

Souter, D.W., Linden, O. 2000. The health and future of coral reef systems. Ocean and Coastal Management, 43: 657-688.

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. Highsmith and maguire


Bermuda Laws online
Environmental Protection Agency Coral Site