The Ocean's Rainforests

Coral reefs are among the most biodiverse ecosystems on Earth. Despite covering less than 1% of the ocean floor, they are home to an estimated quarter of all marine species. They provide critical habitat for fish, crustaceans, molluscs, and countless other organisms — many of which are not found anywhere else.

Beyond biodiversity, reefs provide enormous value to human societies: protecting coastlines from storm damage, supporting fishing communities and food security, underpinning tourism economies, and offering potential medical compounds from their unique organisms.

What Is Coral Bleaching?

Coral bleaching is a stress response triggered when sea temperatures rise above a coral's tolerance threshold — even by just 1–2°C above normal summer maximums for an extended period. Under heat stress, corals expel the symbiotic algae (zooxanthellae) that live within their tissues and provide them with up to 90% of their energy through photosynthesis. Without these algae, the coral turns white — "bleached."

Bleached coral is not immediately dead, but it is severely weakened. If temperatures return to normal quickly enough, coral can recover. If the stress continues, the coral starves and dies.

Mass bleaching events — affecting large portions of reef systems simultaneously — are becoming more frequent and severe as average ocean temperatures rise.

The Key Threats to Coral Reefs

Ocean Warming

Rising sea temperatures driven by climate change are the primary threat to reefs globally. As global temperatures increase, bleaching events that were once rare are now occurring far more frequently, leaving reefs insufficient time to recover between episodes.

Ocean Acidification

The ocean absorbs a significant portion of the CO₂ emitted by human activity. This CO₂ reacts with seawater to form carbonic acid, lowering the pH of the ocean — a process called ocean acidification. As acidity increases, it becomes harder for corals (and other organisms like oysters and sea urchins) to build and maintain their calcium carbonate skeletons.

Local Stressors

  • Overfishing — Removing key species like herbivorous fish disrupts the reef ecosystem, allowing algae to overgrow corals.
  • Coastal pollution — Agricultural runoff carrying nutrients and sediment can smother reefs and fuel algal blooms.
  • Destructive fishing practices — Dynamite fishing and bottom trawling cause direct physical damage.
  • Tourism pressure — Careless snorkelling, boat anchoring, and sunscreen chemicals containing oxybenzone can harm reef structures directly.

What Is Being Done to Protect Reefs?

Marine Protected Areas (MPAs)

Designating reef ecosystems as MPAs reduces local stressors by restricting fishing, development, and pollution. Well-managed MPAs allow reef ecosystems to build resilience, making them better able to withstand climate-driven bleaching events.

Coral Restoration

Coral restoration projects — including coral gardening, where fragments are grown in nurseries and transplanted onto degraded reefs — are expanding globally. Researchers are also working to develop heat-tolerant coral strains that can survive in warmer waters.

Climate Action

Ultimately, the future of coral reefs depends on the trajectory of global greenhouse gas emissions. Limiting warming gives reefs the best chance of survival. Reef systems can recover if given time and reduced local stressors — but this window is narrowing.

What You Can Do

  • Choose reef-safe sunscreen (mineral-based, free of oxybenzone and octinoxate) when swimming near reefs.
  • Avoid buying coral jewellery or souvenirs made from reef species.
  • Support organisations working on reef conservation and restoration.
  • Reduce your carbon footprint — every fraction of a degree of warming matters for reef survival.
  • If you dive or snorkel, follow responsible reef etiquette: no touching, no standing on coral, careful buoyancy control.

A Future Worth Fighting For

Coral reefs have survived millions of years of planetary change. The current crisis is the fastest and most severe challenge they have ever faced. But reefs are also resilient when given the chance — the same qualities that make them extraordinary also give them the capacity to recover. Protecting that chance is one of the most important conservation goals of our time.