Why in news?
French vessel Tara launched an 18-month Tara Coral expedition in December 2025 to study heat-resistant corals in the Coral Triangle. Some Porites corals increased 164% amid declines, showing resilience potential.​
Key Characteristics
- Also known as stony or scleractinian corals, are marine invertebrates in the phylum Cnidaria that build rigid calcium carbonate skeletons.​
- These corals form colonies of polyps, each with a sac-like body, mouth, and tentacles equipped with stinging nematocysts for capturing prey.
- They secrete aragonite, a form of calcium carbonate, creating hard, rock-like structures that accumulate over time into reefs.
- Most species, like elkhorn and brain corals, rely on symbiotic algae called zooxanthellae for energy via photosynthesis.​
Habitat and Growth
- Hard corals thrive primarily in warm, shallow, sunlit tropical waters less than 60 meters deep, though some ahermatypic species endure cold deep-sea conditions up to 6,000 meters.
- Growth rates vary: branching types like Acropora can extend 10 cm yearly, while massive forms grow slower at 0.3-2 cm.
- Colonies expand through asexual budding, forming diverse shapes such as branches, plates, or boulders.​
Ecological Role
- As reef-builders, hard corals create foundational habitats supporting vast biodiversity, visible even from space as the planet's largest living structures.
- They reproduce via mass spawning once or twice yearly, releasing eggs and sperm synchronized by full moons.
- Vulnerabilities include bleaching from warm waters expelling zooxanthellae and threats like ocean acidification.
Key Threats
- Hard corals, have faced significant declines recently due to climate-driven threats.
- A major Global Coral Reef Monitoring Network assessment highlights a 48% drop in Caribbean hard coral cover from 1980 to 2024.​
- Mass bleaching events from marine heatwaves in 1998, 2005, and 2023-24 have starved corals by expelling symbiotic algae.
- Stony Coral Tissue Loss Disease, spreading across 30 countries since 2014, causes rapid mortality in over 30 species.
- Losses of herbivores like Diadema sea urchins have spurred an 85% macroalgae surge, outcompeting corals.​
Download Pdf
