Coral Reefs

Coral Reefs

High School

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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

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Coral Polyp

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

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Zooxanthellae

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

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Coral Bleaching

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

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Fringing Reef

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

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Calicle

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

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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.

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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.

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Step 1: Analyze and Sketch the Problem

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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.

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Step 2: Solve for the Unknown

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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.

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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.

Multiple Choice

What is a 'coral' fundamentally composed of?

• A type of marine plant that grows in shallow water.

• A large collection of different types of rocks and sand.

• Colonies of animals called polyps with a limestone skeleton.

• A single, large organism that resembles a sea anemone.

Types of Coral Reefs

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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.

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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.

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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.

Multiple Choice

Which of the following is the primary abiotic factor that determines where a coral reef can be located?

• Temperature

• Substrate type

• Water Turbidity

• Salinity

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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.

Multiple Choice

What is the primary benefit that corals receive from their mutualistic relationship with zooxanthellae?

• The ability to anchor to the sea floor.

• Approximately 90% of their food.

• Protection from predators like fish.

• Help in capturing zooplankton with their tentacles.

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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.

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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?

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Step 1: Analyze and Sketch the Problem

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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?

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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.

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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?

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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.

Multiple Choice

What is the direct cause of a coral turning white during a bleaching event?

• A white-colored fungus grows over the entire coral colony during periods of high temperature.

• The coral is producing a white chemical as a defense mechanism against stress.

• The coral is covered by an excess of white sand and sediment due to strong currents.

• The coral's tissue becomes clear, revealing its white skeleton after expelling its symbiotic algae.

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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.

Multiple Choice

According to the slide, which of the following is a key reason why coral reefs are important for humans?

• They are the primary source of salt for the world's oceans.

• They create sandy beaches by breaking down rocks.

• They provide food, income through tourism, and protect coastlines.

• They help regulate the Earth's climate by absorbing carbon dioxide.

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Common Misconceptions About Corals

Misconception	Correction
Corals are just rocks or plants.	Corals are colonies of tiny animals called polyps.
A bleached coral is a dead coral.	A bleached coral is alive but under stress and can recover.
Coral reefs recover from bleaching quickly.	Reefs need decades to fully recover from a severe bleaching event.

Multiple Choice

Why is the symbiotic relationship between corals and zooxanthellae considered crucial for the coral's survival in its nutrient-poor water environment?

• The zooxanthellae provide the coral's hard, protective limestone skeleton.

• The zooxanthellae capture all of the coral's prey with their specialized tentacles.

• The zooxanthellae help the coral attach to the hard substrate on the seafloor.

• The coral derives the vast majority of its food and oxygen from the zooxanthellae.

Multiple Choice

Based on the conditions required for their development, why are coral reefs typically found in shallow, clear, tropical waters?

• Because this is where the water has the highest turbidity, which brings more nutrients.

• Because these locations have the freshest water, which corals prefer over high salinity.

• These areas provide the warm temperatures and strong sunlight that corals and their symbiotic algae need.

• Because these areas lack the strong currents and waves that can damage the reef structure.

Multiple Choice

A coral reef experiences a prolonged period where the water temperature is 2^oC higher than the summer average. What is the most likely sequence of events for this reef?

• The coral polyps will reproduce at a much faster rate, creating a larger and more robust reef.

• The zooxanthellae will thrive in the warmer water, causing the coral to grow darker and healthier.

• The reef will be unaffected as corals are highly resistant to minor temperature fluctuations.

• The corals will expel their zooxanthellae, bleach, and become highly vulnerable to disease and death.

Multiple Choice

A coastal community relies on its local coral reef for tourism and coastal protection. If the reef suffers a severe, long-lasting bleaching event, what are the potential long-term consequences for both the community and the reef structure?

• The reef will recover within a year, and the community's income will see a temporary dip before returning to normal.

• The reef will be replaced by a different, more resilient ecosystem like a kelp forest, providing new tourism opportunities.

• The community's tourism income will likely decline, and the coastline could become more vulnerable to erosion as the dead reef structure is worn away by bioerosion.

• The local fish population will increase as their predators are driven away, boosting the fishing industry.

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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.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

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• 3

• 4