Learning Objectives

• Describe the structure of corals and what coral reefs are made of.

• Explain the environmental conditions needed for healthy coral reefs to grow and thrive.

• Analyze the causes and consequences of the coral bleaching phenomenon on reefs.

• Evaluate the importance of coral reefs and identify methods for their protection.

Key Vocabulary

Coral Polyp

An individual coral animal, related to jellyfish, that lives in a colony forming a reef.

Zooxanthellae

Tiny plant algae living in coral tissue in a symbiotic relationship called mutualism.

Coral Bleaching

A process where corals expel algae due to stress, revealing their white skeletons.

Fringing Reef

A type of coral reef, which is the oldest, that grows near the coastline.

Calicle

The hard, protective limestone skeleton of a coral that anchors it to the seafloor.

What is a Coral Reef?

• A coral reef is a calcareous organic reef, often called the sea's rainforest.

• It consists of coral colonies, made up of many tiny animals called polyps.

• Polyps secrete a hard limestone skeleton (calcium carbonate, CaCO₃) called a calicle.

• Each polyp has a central mouth and stinging tentacles used to capture small prey.

Solved Example 1
If a coral reef grows at an average rate of 0.8 cm/year, how many years would it take for the reef to grow 20 cm in height? This does not account for erosion or other factors.

Step 1: Analyze and Sketch the Problem

Solved Example 1
If a coral reef grows at an average rate of 0.8 cm/year, how many years would it take for the reef to grow 20 cm in height? This does not account for erosion or other factors.

Step 2: Solve for the Unknown

Solved Example 1
If a coral reef grows at an average rate of 0.8 cm/year, how many years would it take for the reef to grow 20 cm in height? This does not account for erosion or other factors.

Step 3: Evaluate the Answer

• To verify, multiply the time by the growth rate: 25 years * 0.8 cm/year = 20 cm.

• The answer is logical and the units are correct.

Types of Coral Reefs

Fringing Reefs

• ​These reefs grow very close to the coastline of continents and islands.

• ​​They are the most common and youngest type of all coral reefs.

• ​A shallow lagoon may sometimes separate it from the nearby shore.

Barrier Reefs

• ​These are found further from shore, creating a wide, deep lagoon.

• ​​This lagoon separates the barrier reef from the mainland or island coast.

• ​They are much larger and older than the common fringing reefs.

Atolls

• ​Atolls are ring-shaped coral reefs that encircle a central lagoon completely.

• ​​They usually form on top of submerged volcanic islands in the ocean.

• ​Smaller patch reefs can often be found inside the atoll's lagoon.

A Symbiotic Relationship: Feeding and Survival

• Corals share a mutualistic relationship with tiny algae called zooxanthellae living in them.

• The algae provide the coral with oxygen and 90% of its food.

• In return, the coral provides the algae with protection and essential nutrients.

• Corals also capture zooplankton from the water using their tentacles for food.

Coral Bleaching: A Stress Response

• It is a stress response where corals expel symbiotic algae called zooxanthellae.

• This process reveals the coral’s white skeleton, making it look bleached.

• The primary cause is high water temperature, an increase of just 1-2°C.

• Bleached corals can starve and are more vulnerable to disease and death.

Solved Example 2
The average summer water temperature on a reef is 29°C. If the temperature rises to 30.5°C, what is the temperature increase and is the coral at risk of bleaching?

Step 1: Analyze and Sketch the Problem

Solved Example 2
The average summer water temperature on a reef is 29°C. If the temperature rises to 30.5°C, what is the temperature increase and is the coral at risk of bleaching?

Step 2: Solve for the Unknown

• Calculate the temperature increase: 30.5°C - 29°C = 1.5°C.

• The temperature increase is 1.5°C.

• Corals are known to bleach when temperatures rise 1-2°C above the average.

• Since 1.5°C is within this range, the coral is at risk of bleaching.

Solved Example 2
The average summer water temperature on a reef is 29°C. If the temperature rises to 30.5°C, what is the temperature increase and is the coral at risk of bleaching?

Step 3: Evaluate the Answer

• The calculation is a simple subtraction, and the result is correct.

• The conclusion is based on the fact provided in the lesson that a 1–2°C increase causes bleaching. The answer is consistent with the lesson content.

Reef Importance and Protection

Why Reefs Matter

• Coral reefs provide habitat for 25% of the world's marine species.

• They protect coastlines from erosion and the damage caused by large storms.

• Reefs provide food and income for communities through tourism and fishing activities.

• They are a source for compounds that are used to create new medicines.

Reef Protection

• Corals can recover from bleaching, but this process can take several decades.

• We can help by reducing stressors like pollution to improve water quality.

• Shading and cooling reefs during heat waves can also help to protect them.

• Coral nurseries grow new colonies that are transplanted to damaged reef areas.

Common Misconceptions About Corals

Summary

• Coral reefs are ecosystems built by animal polyps that form limestone skeletons.

• Reefs require warm, shallow, clear, and sunlit tropical waters to thrive.

• A vital symbiotic relationship with algae provides corals with food and oxygen.

• Coral bleaching is a stress response where corals expel their symbiotic algae.

• Reefs support marine biodiversity, offer coastal protection, and sustain human livelihoods.

• Protecting reefs includes reducing stressors and using coral nurseries to aid recovery.