Singapore Green Guardians Blog

In this series, we showcase the diversity of rare, peculiar, and fascinating native flora and fauna in Singapore. We enthusiastically invite you to explore our nature reserves and gardens, urging you to pause and observe your surroundings—whether by looking up or down—to see if you can catch a glimpse of these unique wonders.

Are corals rocks, plants, or animals?

Montipora coral. Image: Ryan McMinds

Coral reefs are diverse underwater ecosystems that play a critical role in maintaining the health and balance of marine environments. These living structures serve as foundation keystone species and ecosystem engineers, providing habitat and shelter to a multitude of marine species. Despite occupying less than 1% of the marine floor, coral reefs support over 25% of the world’s marine life.

Although corals permanently attach themselves to the ocean floor and “take root” like most plants do, and they don’t have distinct faces or body parts like most animals do, they are animals. 

As foundation species, hard corals play a transformative role in shaping their surrounding environments by building coral reefs that many other organisms use. Coral reefs are made up of hundreds to thousands of small, delicate marine organisms known as coral polyps. These tiny coral polyps secrete a hard outer skeleton of calcium carbonate that attaches to rock or the dead skeletons of other polyps. Over time, as the calcium carbonate accumulates and corals reproduce, the size of a coral reef grows. They are built over hundreds of thousands of years. 

Mushroom coral skeleton. Image: Jon Zander

Coral polyps live in a symbiotic relationship with a specific type of algae called zooxanthellae that live in their tissues. The coral provides the plant-like organism with a protected environment, sufficient sunlight, and nutrients in the form of the coral’s metabolic waste for photosynthesis, the process by which plants make their food. In return, the zooxanthellae produce oxygen, remove wastes, and supply the coral with the organic products it needs to grow and thrive. 

Not all corals are reef builders; soft corals do not build stony skeletons and don’t have a symbiotic relationship with algae. 

Flowerpot coral. Image: Peter Young

Corals are communal animals related to sea anemones and jellyfish. Each tiny coral polyp uses their stinging tentacles to capture creatures like zooplankton or organic debris that float by. Their symbiotic relationship with zooxanthellae allows them to get additional energy. Remarkably, the zooxanthellae transfer approximately 90% of the organic material they produce to the host coral tissue, enhancing the coral’s nutrient intake.

A symbiotic relationship is a close long-term relationship between two species, where one or both species benefit from the interaction. There are four main symbiotic relationships, mutualism, commensalism, parasitism, and competition.

Coral polyps. Image: Ryan McMinds

Threats faced by coral reefs

Despite their many strengths, coral reefs are fragile and extremely sensitive to environmental conditions. They need clean, clear water to survive and have been especially vulnerable to a diverse range of human activities, including coastal changes and pollution. Today, the challenges faced by coral reefs are further exacerbated by two global trends: increasing sea surface temperatures and ocean acidification, primarily caused by climate change.

Zooxanthellae, in addition to supplying corals with vital nutrients, contribute to the distinctive and vibrant colours observed in many stony corals. When corals undergo physical stress, such as high temperatures, they expel their symbiotic zooxanthellae, losing their main food source. They also lose their colour, resulting in a bleak white appearance. This is commonly described as “coral bleaching”. Prolonged periods without zooxanthellae (and if bleaching events happen too frequently) can lead to the death of the coral colony.

Coral bleaching. Image: EcoCafePranburi

The first global bleaching event occurred in 1998 and killed about 8% of the world’s coral. In the last four decades, there has been a noticeable decrease in the abundance of corals, accompanied by a more frequent occurrence of bleaching incidents and an increase in algae levels within our oceans, which suggest a decline in the overall health of coral reefs. Recent studies, however, have found that reef systems do not respond uniformly to bleaching events and post-bleaching recovery can occur at different degrees. 

What do we know about coral reefs in Singapore?

Much of Singapore’s coral reefs have experienced significant impact due to extensive land reclamation and coastal development over the past five decades. From 1922 to 1993, the extent of coral reef areas was reduced by nearly 50%. Consequently, these activities led to a rise in levels of turbidity and sediment in the marine environment.

Surprisingly, Singapore’s waters host a remarkably diverse array of marine life, boasting a diverse range of over 250 species of reef-forming hard corals that are habitat to over 100 species of reef fishes. Most of the coral reefs are found along the southern shores of Singapore––surrounding the islands, on tidally-exposed areas along the Singapore Straits, and along the last remaining rocky shore on Labrador Beach. There has also been unexpected diversity along man-made seawalls, which cover over 70% of Singapore’s coastline. 

Distribution of coral reefs shaded in purple. Image: Lim et al., Intertidal Marine Species in Singapore

Turbid coral reefs, characterised by high levels of turbidity, are often found in shallow coastal waters close to urban areas like Singapore. They have shown an incredible ability to endure and survive under chronic sediment stress and low-light environmental conditions. It has also been suggested that Singapore’s urbanised reefs can recover quickly from thermal stress events, compared to reefs in more remote areas. 

As climate change continues to drive increases in ocean temperatures, the frequency and intensity of marine heatwaves and severe bleaching events are also on the rise. Additionally, rising sea levels are resulting in deeper waters above shallow reefs, reducing the amount of light that reaches the corals, and potentially threatening reefs around the world.

Exposed reef. Image: Yeowatzup

While our coral reefs demonstrate remarkable resilience and adaptability in coping with challenging conditions of reduced light and high temperatures, there can still be negative impacts on their overall health and growth. The survival of these vital marine ecosystems depends on our proactive and innovative measures and solutions to mitigate the effects of climate change. By acting now, we can work towards preserving and safeguarding these valuable ecosystems.

How can you contribute to protecting and conserving our coral reefs?

• Practice responsible snorkelling and diving. Avoid touching or stepping on corals and maintain a safe distance from marine life
• Choose reef-friendly sunscreen. Use mineral-based sunscreen that is free of harmful chemicals known to cause coral bleaching.
• Reduce pollution and waste to prevent pollutants from entering the marine environment.
• Support sustainable seafood practices to reduce the demand for destructive fishing practices.
• Contribute to reef restoration efforts. Volunteer or donate to organisations that actively work towards restoring damaged reefs and promoting their conservation. Explore WildSingapore’s list of opportunities for individuals to contribute their assistance.
• Respect marine protected areas. Observe and adhere to regulations when visiting Sisters’ Islands Marine Park. 

If you come across coral reefs in the wild, we encourage you to (safely and respectfully) capture photos and document your observations. We especially recommend using the local SGBioAtlas app, or the iNaturalist app, which enables you to share and validate your findings within the community.

Discover the wonders of nature, observe the intricacies of the world around you, and let curiosity be your guide. Happy exploring!

📷 Post your findings on social media and tag us on Instagram or Facebook.

Further reading:

🇸🇬 100,000 corals to be planted in Singapore waters, Big Sister’s Island to reopen in 2024

📋 Scientists Are Learning How to Help Coral Reefs Save Themselves