Grooved Brain Coral
By Keri Murrell
Reproduction and Growth
Grooved Brain Coral are hermaphroditic (producing both egg and sperm) but reproduce sexually. Their reproductive cycle occurs annually, from May through to September. Initially all Grooved Brain Corals release sperm. This coincides with environmental cues such as elevated temperature, decreased solar hours and slower wind speeds. Other colonies capture the sperm; whose polyps internally fertilise their four eggs. Considering each coral can contain hundreds of thousands, this can be a substantial number. The resulting larvae once extruded swim for two days, settle, then develop into a secondary, then adult polyp. Each secrete calcium carbonate in order to attach. Following this, the polyp multiplies asexually in order to form a new colony. They grow 1mm each year. Some have exceeded a diameter of 6ft (2m), meaning the colony is 900 years old. However, growth requires a lot of energy. This is provided through a symbiotic relationship with an alga, Zooxanthellae.
Prey and Predation
Zooxanthellae photosynthesise within the polyp, providing its host with energy; hence the coral is found in shallow waters at 50m. In return the coral gives the Zooxanthellae protection and provides it with nutrition. Grooved Brain Coral also filter feeds nocturnally. The polyps have tentacles with stinging cells called nematocysts, which are triggered when prey such as Zooplankton comes near. This holds and immobilises the prey, to allow it to be moved into the mouth. Though the polyps have nematocysts, it doesn’t allow for immunity against predators such as Parrotfish, Butterflyfish, Sea urchins and Starfish. Hence, the polyps withdraw into the grooves, which are lined with cups (holding separate polyps). They leave behind mucous, for predator consumption, minimising the effect of predation.
Threats
The IUCN categorises the Grooved Brain Coral as ‘critically endangered, predominantly due to climate change, human impact and problematic native species. Stressors such as fluctuating water temperature, low nutrients, solar overexposure, storms and pollutant runoff, cause corals to bleach. Such stressors cause the expulsion of Zooxanthellae, which provide the coral with their pigment, including tans, greys and yellows. Bleaching doesn’t result in death, just an elevated susceptibility to other stressors, which increases mortality.
