By Keri Murrell
Grooved Brain Corals are marine invertebrates. They are unmistakable as they appear to represent a human brain with grooved brain folds. The grooves further resemble a labyrinth, hence the scientific name Diploria labryrinthiformis. Corals consist of polyps, genetically identical animals. These secrete calcium carbonate to form the brain-like structure. Due to its hardness, the coral is classified as stony. This makes them an important reef building species.
Reproduction and Growth
Grooved Brain Coral are hermaphroditic (producing both egg and sperm) but reproduces 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 swims for two days, settles, then develops 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 photosynthesis 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 its waste, providing it nutrition. Grooved Brain Coral also filter feeds nocturnally. The polyps have tentacles with stinging cells called nematocysts, which is 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.
Due to having a widespread population, the IUCN categorises the Grooved Brain Coral as ‘least concern’. Yet, they suffer many threats. Predominantly climate change, human impact and problematic native species. Stressors such as fluctuating water temperature, low nutrients, solar overexposure, storms and pollutant runoff, causes corals to bleach. Stressors cause the expulsion of Zooxanthellae which provides the coral with their pigment, including tans, greys and yellows. Bleaching doesn’t result in death, just elevated susceptibility to other stressors, so increases mortality.