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Coral Reproduction

Corals can reproduce asexually and sexually (NOAA 2005; Richmond andHunter 1990).Many coral species are either simultaneous or sequential hermaphrodites, meaning that they produce both sperm and eggs either simultaneously or during different times of the year (NOAA2005; Richmond and Hunter 1990; Edwards 2010). Sexual reproduction and fertilization can occur externally via broadcast spawning or internal lyvia brooding (NOAA 2005; Richmond and Hunter 1990; Edwards 2010).

Broadcast spawning corals, like the lobed star coral (Orbicella annularis) simultaneously release large amounts of sperm and eggs into the water column where fertilization takes place (NOAA 2005; Richmond and Hunter 1990; Edwards 2010). This process produces massive amounts of coral larvae called planulae (NOAA 2005; Richmond and Hunter 1990; Edwards 2010). Corals that fertilize their eggs internally are called brooding corals and include coral species such as the mustard hill coral (Porites astreoides) (NOAA 2005; Richmond and Hunter 1990; Edwards 2010). Brooding corals produce less planulae than broadcast spawning corals do, however, brooding coral larvae have a better chance of survival since they emerge from the colony fully developed (NOAA 2005; Richmond and Hunter 1990). As a result, coral recruitment rates are much higher for brooding corals than they are for broadcast spawners (NOAA 2005; Richmond and Hunter 1990). This is one reason why recruitment rates for Porites astreoides corals are much higher on Caribbean coral reefs than they are for Orbicella annulariscorals (Richmond and Hunter 1990).

Post development, planulae swim towards the surface of the water where they are transported by ocean currents to a suitable settlement location (NOAA 2005; Richmond andHunter 1990; Edwards 2010). During this time period, planulae encounter various hazards such as increased predation (NOAA 2005; Richmond andHunter 1990). As a result, planulae mortality is highest during the period between development and settlement (NOAA 2005; Richmond and Hunter1990).Once settled, the coral larvae will begin to metamorphosize into a coralpolyp that over time will continue to grow as a solitary or colonial coral(NOAA 2005; Richmond and Hunter 1990; Edwards 2010).The amount of time it takes for planulae to settle varies among species and can range from 2 days to three weeks (NOAA 2005; Richmond and Hunter 1990).Corals can also reproduce asexually by a variety of mechanisms including polyp budding, fragmentation and asexual planula development (NOAA2005; Richmond and Hunter 1990).

Coral colony growth occurs through asexual polyp reproduction called “budding”. This process is initiated once a coral polyp becomes newly settled (Edwards 2010).Fragmentation as a means of reproduction is common among species of Acropora such as Acropora cervicornis, Acropora palmata and Acroporaprolifera (Highsmith 1982; Lirman 2000; NOAA 2005; Richmond andHunter 1990).The extensive fields of elkhorn corals (Acropora palmata) and staghorn corals (Acropora cervicornis) once seen in the Caribbean were a result of colony fragmentation (Highsmith 1982; Lirman 2000; NOAA 2005; Richmond and Hunter 1990). Certainspecies of brooding corals can also produce planula larvae asexually(Richmond and Hunter 1990).