Species Description: The northern cup coral, Astrangia poculata, is a large-polyped stony coral found in and around the Indian River Lagoon. Colonies are arranged in rough, irregular white clumps of cups (Kaplan 1988). The polyps are translucent and have a fuzzy appearance when extended. Colonies with polyps harboring microscopic algae, called zooxanthellae, are brownish in appearance (Ruppert & Fox 1988). See below for more information on the symbiotic relationship between A. poculata and zooxanthellae.
Potentially Misidentified Species: A. poculata may be confused with the southern cup coral, A. solitaria, from Bermuda to Brazil (Kaplan 1988). However, the polyps of the A. solitaria are often brownish in color, and form clumps or isolated cups that are each up to 4 mm wide and bear 36 septa.
Habitat & Regional Occurrence: The northern cup coral is found subtidally from Cape Cod, Massachusetts to Florida and the Gulf of Mexico. Clumps are often seen on wrecks and rocks in deep waters (Kaplan 1988). Dead colonies are known to wash ashore.
Size & Growth: The northern cup coral is a small species. Encrusting growth forms grow in patches that generally do not exceed 5 cm in diameter (Ruppert & Fox 1988). Growth occurs by budding of new polyps at the margin of the colony (Ruppert & Fox 1988). Colonies of A. poculata grow faster in warmer months, with an increase of about 2.5 polyps per week for corals studied in the temperate waters around Rhode Island (Dimond & Carrington 2007). A. poculata growth will slow or cease entirely in colder temperatures, and colonies can frequently lose polyp tissue, increasing their vulnerability to fouling by other organisms.
Reproduction: The northern cup coral reproduces in the summer months by broadcasting eggs and sperm into the water column, where fertilization takes place (Ruppert & Fox 1988). Fertilized eggs develop into larvae called planulae, each measuring less than 0.1 mm long. Larvae eventually settle onto hard surfaces and metamorphose into the first polyps of a new colony.
Temperature: The northern cup coral is described as a species tolerant of a wide range of environmental conditions (Peters et al. 1988). In the northern part of its range, colonies of A. poculata can withstand seasonal temperature fluctuations of -1°C to over 25°C (Diamond & Carrington 2008).
Carbon Dioxide & Ocean Acidification: Due in part to its ability to thrive under a wide range of environmental conditions, A. poculata has been used to explore the effects of ocean acidification on corals. Holcomb et al. (2012) found that coral colonies exposed to elevated carbon dioxide levels experienced lower calcification rates. The authors also found that, among colonies maintained at warmer temperatures, females exhibited greater decreases in calcification than males. This phenomenon may reflect decreased skeletal growth as a result of the greater energy investment required for egg production among females, relative to sperm production in males.
Trophic Mode: A. poculata is a facultatively symbiotic coral (Dimond & Carrington 2008). When water temperatures are warm and/or light levels are high, the coral obtains energy via photosynthesis from symbiotic zooxanthellae in its tissues. However, when light and water temperatures are low, the zooxanthellae that were once beneficial symbionts can become too costly to maintain. In such conditions, A. poculata expels the zooxanthellae and derives all of its energy from plankton and other particles that it catches from the water column.
Dimond J & E Carrington. 2007. Temporal variation in the symbiosis and growth of the temperate scleractinian coral Astrangia poculata. Mar. Ecol. Prog. Ser. 348: 161-172.
Dimond J & E Carrington. 2008. Symbiosis regulation in a facultatively symbiotic temperate coral: zooxanthellate division and expulsion. Coral Reefs 27: 601-604.
Holcomb M, Cohen AL & DC McCorkle. 2012. An investigation of the calcification response of the scleractinian coral Astrangia poculata to elevated pCO2 and the effects of nutrients, zooxanthellae and gender. Biogeosci. 9: 29-39.
Kaplan EH. 1988. A field guide to southeastern and Caribbean seashores: Cape Hatteras to the Gulf coast, Florida, and the Caribbean. Houghton Mifflin Co. Boston, MA. USA. 425 pp.
Peters, EC, Cairns SD, Pilson MEQ, Wells JW, Jaap WC, Lang JC, Vasleski CEC & LSP Gollahon. 1988. Nomenclature and biology of Astrangia poculata (= A. danae, = A. astreiformis) (Cnidaria: Anthozoa). Proc. Biol. Soc. Wash. 101: 234-250.
Ruppert E & R Fox. 1988. Seashore animals of the Southeast: a guide to common shallow-water invertebrates of the southeastern Atlantic Coast. University of SC Press. Columbia, SC. 429 pp.