Coelastrea aspera

Lore & Background

Coelastrea aspera was first described by the American zoologist Addison Emery Verrill in 1866 as Goniastrea aspera, but it has since been determined that it should be in a different genus and its scientific name has been changed to Coelastrea aspera. Colonies are either encrusting or massive, with a honeycomb-like surface of cerioid corallites that are deep and angular with thick, straight walls. The septa are even, with long and short septa alternating in larger corallites, and budding is usually intratentacular. Paliform lobes are large and broad in protected environments but much smaller in exposed positions. On intertidal flat rocks, several colonies in close proximity may form a level expanse several metres across. The general colour is usually pale brown, and the oral discs may be a contrasting colour, often cream.

Its range extends from Madagascar and the Red Sea, through the Indian Ocean to Australia, Indonesia, Japan and the East China Sea, and the western and central Pacific Ocean. It occurs on reef flats, on reef slopes and in lagoons, at depths down to about 15 m. Coelastrea aspera is a simultaneous hermaphrodite. Packets of eggs and sperm are normally released into the water column and, being buoyant, rise to the surface for cross-fertilisation. In a different form of sexual reproduction, eggs and developing larvae are sometimes brooded in the maternal polyps, and some individual colonies have been seen adopting both breeding strategies at the same time in different parts of the colony.

C. aspera is a zooxanthelate coral, containing symbiotic unicellular photosynthetic organisms that provide nutrients and energy for the coral host. Under stress, usually high water temperature or excessive solar radiation, the coral expels some or all of these symbionts, a condition known as coral bleaching. In Thailand in 1995, on a reef flat dominated by C. aspera, a mass bleaching event occurred due to high water temperatures. Researchers found that the east side of each coral was bleached while the west side was unaffected, hypothesizing that the corals 'remembered' a previous bleaching event caused by solar radiation and had built defences on the affected side. In 2000, they detached colonies and rotated them 180°, and during a severe bleaching event in 2010, they found that rotated corals had significantly higher levels (four times as many) of zooxanthellae in the affected areas than unrotated corals, demonstrating a 'memory' of at least ten years.

Reader's Guide

Coelastrea aspera is significant as a common and widespread species in the Indo-Pacific, with a conservation status of 'least concern' according to the International Union for Conservation of Nature. Its ecological importance is underscored by its role as a zooxanthelate coral, relying on symbiotic algae for nutrients and energy, and its vulnerability to bleaching under thermal or solar stress. The species gained particular scientific attention following a 1995 mass bleaching event in Thailand, where researchers observed that only the east sides of colonies bleached, suggesting a directional memory of prior solar radiation stress. A subsequent experiment in 2000, involving rotating colonies 180°, confirmed that previously affected areas retained coping strategies for at least ten years, as evidenced by four times higher zooxanthellae levels in rotated corals during a 2010 bleaching event. This finding highlights the species' capacity for long-term acclimatization and provides insight into coral resilience. Additionally, its dual reproductive strategies—both broadcast spawning and brooding—sometimes occurring simultaneously in different parts of the same colony, illustrate its adaptive flexibility. The species' legacy lies in its contribution to understanding coral memory and stress responses, which has implications for predicting reef recovery under climate change.

Did You Know?

• Coelastrea aspera was first described in 1866 by American zoologist Addison Emery Verrill as Goniastrea aspera.
• In a 1995 bleaching event in Thailand, only the east sides of C. aspera colonies bleached, while the west sides were unaffected.
• Rotated colonies of C. aspera retained a 'memory' of past bleaching for at least ten years, showing four times more zooxanthellae on previously affected sides.
• Some individual colonies of C. aspera can simultaneously broadcast spawn and brood larvae in different parts of the colony.