Hard Corals

A major new assessment by the Global Coral Reef Monitoring Network (GCRMN) has reported a dramatic decline in hard coral populations across the Caribbean region. The report highlights the increasing vulnerability of coral reef ecosystems due to climate change, coral diseases, and ecological imbalance.

About Hard Corals

Hard corals, also known as stony corals, are marine invertebrate animals that form the structural foundation of coral reefs. They grow in large colonies and are therefore commonly referred to as reef-building corals. These corals belong to the phylum Cnidaria.

Key Features of Hard Corals

Hard corals are made up of thousands of tiny organisms called polyps. Each polyp secretes calcium carbonate (CaCO₃), which forms a hard limestone skeleton. Over long periods, the accumulation of these skeletons turns into rock-like structures that create the physical framework of coral reefs. This framework provides a stable surface on which new coral larvae can settle and grow.

Symbiotic Relationship with Zooxanthellae

Hard corals have a mutually beneficial (symbiotic) relationship with microscopic algae known as zooxanthellae, which live inside their tissues. The corals provide the algae with shelter and nutrients, while the zooxanthellae supply the corals with food through photosynthesis. This relationship is essential for coral growth, energy supply, and reef productivity.

Major Threats to Hard Corals

One of the most serious threats to hard corals is coral bleaching, which occurs due to extreme sea surface temperature rise. Bleaching leads to the expulsion of zooxanthellae, causing corals to lose their color and primary food source.

Another major threat is Stony Coral Tissue Loss Disease (SCTLD). This disease has spread across more than 30 countries and is responsible for unprecedented levels of coral mortality in the Caribbean and nearby regions.

The loss of key herbivores, particularly the Diadema sea urchin, has further worsened coral reef health. Their decline has resulted in an approximately 85% increase in macroalgae, which competes with corals for space, sunlight, and nutrients, thereby inhibiting coral recovery.

Conclusion

The sharp decline in hard coral populations underscores the urgent need for global climate action, disease management, and ecosystem restoration. Protecting hard corals is vital, as they form the backbone of coral reef ecosystems, which support marine biodiversity and coastal livelihoods.