Teachers, scroll down for a quick list of key resources in our Teachers Toolkit.
- New research indicates our bias toward pretty pictures may influence our perception of coral reefs. What are coral reefs?
- Coral reefs are incredibly biodiverse ecosystems made up of multicolored limestone ridges built by tiny sea animals called corals. The corals’ hard exoskeletons are what make up coral reefs.
- “Coral reefs are the most species-rich ecosystems in the ocean, providing food for people, habitat for hundreds of thousands of marine species, coastline protection from wave exposure, and recreational and cultural heritage benefits.”
- In addition, coral reefs generate ecosystem services valued at up to a million dollars per hectare per year. “This estimate is greater than any other ecosystem on the Earth and highlights the importance of coral reefs in terms of ecosystems services and associated benefits they provide to human society.”
- The ecosystem benefits provided by coral reefs rely largely on their dazzling colors. Why are corals so colorful?
- They’re not, really. Corals and their exoskeletons are actually clear or translucent.
- Corals can synthesize pigments. These pigments benefit a type of algae known as zooxanthellae. Zooxanthellae live inside the coral, and have a mutualistic relationship with their host organism.
- “The coral provides the algae with a protected environment and compounds they need for photosynthesis. In return, the algae produce oxygen and help the coral to remove wastes. Most importantly, zooxanthellae supply the coral with glucose, glycerol, and amino acids, which are the products of photosynthesis. The coral uses these products to make proteins, fats, and carbohydrates, and produce calcium carbonate” to make their exoskeletons. Photosynthesizing zooxanthellae lend corals their brown and dark-green colors.
- Corals’ brightly colored pigments protect zooxanthellae by acting as sunscreen and shielding the algae from harmful UV rays.
- That sunscreen is costly: “[T]he enhanced protection offered by the sunscreening pigments costs the corals a lot of energy that might be diverted away from growth or reproduction. Therefore, being brightly coloured might not be a good investment for corals settling in more shady parts of the reefs.”
- Deep-water corals, less dependent on pigments, are usually greyish, brownish, or white.
- Coral reef coloration is dependent on genetics. The production of pigments is a complex, energy-intensive process involving multiple copies of one gene. The process may vary radically across corals exposed to the same light and environmental conditions.
- Why is it “unrealistic” to expect a healthy coral reef to be colorful?
- Photographers and filmmakers frequently only show the most colorful coral reefs, leading to the popular assumption that all healthy reefs are colorful. They’re not—healthy reefs may be greenish, yellowish, or brownish.
- Photographers and filmmakers can also augment the colors in a reef: “The use of artificial lighting, pumped up colors, and heavy editing in documentaries and photography pushes these boundaries even further. This may affect which reefs people want to protect.”
- In other words, fake news: Many citizens “are used to only seeing heavily photoshopped ‘perfect’ reefs.”
- Why is the appearance of a healthy reef possibly as important an actually healthy reef?
- Criteria for UNESCO World Heritage Sites such as the Great Barrier Reef include “exceptional natural beauty” and “aesthetic importance.”
- Both the tourism industry and conservation organizations benefit from beauty. Visitors and donors are more likely to value “unhealthy and beautiful” reefs over “healthy and less-beautiful” ones.
- When corals are stressed (often due to ocean acidification), they can no longer divert energy to supporting zooxanthellae, and expel their algae partner. These “coral bleaching” events are signs of an unhealthy ecosystem: without algae, the corals lose a major source of nutrients are more susceptible to disease. How can you tell the difference between an uncolorful reef that has undergone a bleaching event and an uncolorful “healthy and less-beautiful” reef? Take a look at this guide from EcoMar for some help.
- Healthy corals are consistently olive green, brownish, and pale yellow. The waters surrounding healthy coral reefs are rich in biodiversity; just take a look at our downloadable illustrations for a peek at a coral reef food web. Fish, plankton, sea turtles, fish, snails, sea stars, crustaceans, marine mammals, worms, shrimp, clams, seagrass, and sponges are just a few of the organisms that may be found in a healthy coral reef ecosystem.
- Bleached corals are white, although the reef as a whole is often inconsistently colored. In fact, a smatter of “[b]right coloring is common in the early stages of a bleaching event.” A reef that has undergone a bleaching event does not support a food web.
Nat Geo: Coral Reefs: Ecosystems Full of Life
Nat Geo: Coral Reef Food Web
EcoMar: Healthy v. Unhealthy Coral
The Conversation: Revealed: why some corals are more colourful than others
(extra credit!) Royal Society Open Science: Using virtual reality to estimate aesthetic values of coral reefs