Lecture 14

Question 1

What are coral reefs?

Answer 1

Large underwater structures composed of the skeletons of colonial marine invertebrates called coral.
The largest living structure on the planet, and the only living structure to be visible from space.

Question 2

What are corals?

Answer 2

They are marine invertebrate within the kingdom of Animalia (animals) and the phylum Cnidaria, which includes jellyfish.

Diverse array of shapes and colours.

Question 3

What are the two types of corals? Describe them.

Answer 3

The difference lies in their structural makeup.

1. Hard corals.
   - produce rock-like skeleton.
   - produce calcium carbonate to create a hard, durable exoskeleton that protects their soft, sac-like bodies.
2. Soft corals.
   - flexible organisms often resembling plants and trees.
   - produce smaller amounts of calcium carbonate that helps them keep their sharp.
   - do not produce reefs by may live on them.

Question 4

How is a marine reef an ecosystem?

Answer 4

The calcified exoskeleton of reef-building corals, attached to the sea floor provides a 3D shelter or stable anchor for many other organisms.

Question 5

Why are marine reefs so important?

Answer 5

1. Biodiversity.
   - most diverse marine ecosystem.
2. Provide habitat, shelter, and food for many marine organisms.
3. Protect coastlines from the damaging effect of wave actions and tropical storms.
4. Support marine food chains.
   - strong source of nitrogen and other essential nutrients for marine food chains.

Question 6

What is a polyp and what is its importance?

Answer 6

Each individual coral animal is called a polyp - many form a colony.

A polyp has a sac-like body and an opening, or mouth, encircled by tentacles.

The polyol uses calcium and carbonate ions from seawater made of calcium carbonate. This skeleton protects the soft, delicate body of the polyp.

Question 7

How do corals grow?

Answer 7

Polyp multiplies and eventually die, adding their limestone skeletons to the reef.

Coral polyps live on the calcium carbonate exoskeletons of their ancestors, adding their own exoskeleton to the existing coral structure.

As the centuries pass, the coral reef gradually grows, one exoskeleton at a time.

Question 8

How fast do corals grow?

Answer 8

Different species of coral grow at different rates depending on water temperature, salinity, turbulence, and the availability of food.

Question 9

Where do coral reefs grow?

Answer 9

Mostly grow in shallow topical and subtropical waters - within 30 degrees of latitude from the equator.

Both temperature and salinity affect calcification, restricting tropical coral reefs to waters between 23-29C and in salinity range of 32-40%.

Question 10

How to corals interact with their physical environment?

Answer 10

Local environmental conditions (wave actions, light levels, nutrient levels, sediment) affect the shapes and size of coral communities.

Strong waves: encrusting.
Quiet water: branching, plate-like.

Question 11

What are the 2 ways that corals feed?

Answer 11

1. Depend on algae called dinoflagellates to provide energy via photosynthesis.
   - most hard corals are photosynthetic through the symbiotic algae living within them.
2. Some species catch small marine life, like fish and plankton, by using the stinging tentacles on the outer edges of their bodies.
   - most soft corals are non-photosynthetic.

Question 12

Explain the symbiotic relationship between corals and algae.

Answer 12

Algae live inside the coral polyp’s boys where they photosynthesize to produce energy for themselves and the polyps. The algae provide the coral with their lively colour.

The polyps provide a home and CO2 for the algae.

Question 13

Why does the symbiotic relationship between algae and corals limit the habitat for corals?

Answer 13

Photosynthesis requires light and the dependence of corals on algae limits corals to shallow depths.

Question 14

When did corals first appear? How were they affected?

Answer 14

The late Cambrian period.

Corals have experienced a number of extinctions due to warming due to rising GHGs (CO2 and CH4) and ocean acidification.

Question 15

Explain the Ordovician-Silurian extinction event of corals.

Answer 15

The supercontinent Pangea was beginning to form and the circulation of the world’s oceans was being affected by drifting land masses = ice age.

Sea levels and ocean temperatures dropped as glaciers grew.

Resulted in the disappearance of corals and marine life.

Question 16

When did corals reappear following their extinction?

Answer 16

Corals re-appeared during the Devonian period.

These early corals reefs were predominantly composed of coral-like stromatoporoids (reef forming sponges). First “stony” corals appeared.

Devonian coral reefs were present on nearly every continent and left abundant limestone depositions.

Question 17

What is limestone?

Answer 17

A sedimentary rock which is often composed of the skeletal fragments of marine organisms such as corals.

Question 18

Explain the late-Devonian period extinction of coral reefs.

Answer 18

The Devonian Period ends with a series of mass extinction that wipe out coral reefs and most invertebrates species.

The Devonian experiences super GHG climate conditions - it was very warm and there was a lot of CO2 in the atmosphere.

Question 19

What are the theories behind the Devonian extinction?

Answer 19

Both theories have to do with a rapid reduction in atmospheric CO2 that led to the earth cooling and the extinction of many organisms.

Plants expanded and depleted CO2 in the atmosphere.

Question 20

What are the threats to coral reefs?

Answer 20

1. Natural phenomena such as hurricanes and diseases.
2. Local threats such as overfishing, destructive fishing techniques, coastal development, pollution.
   - plastics in the ocean.
3. global effects of climate change.
   - warmer waters.
   - coral bleaching.
   - ocean acidification.

Question 21

What is coral bleaching?

Answer 21

Under environmental stress, the algae-coral symbiotic relationship becomes unhinged.
- affected by factors like temperatures changes, pollution and overfishing.

When corals overheat, they react to the stress by expelling their algae, which results in coral bleaching = corals begin to starve - dies off.

Question 22

How do plastics in the ocean threaten corals?

Answer 22

When coral reefs come into contact with plastic waste, the incidence of disease rises 20-fold.

Scientists speculate that bacteria on the plastic can infect the coral and plastic can block the needed sunlight.

Question 23

How does ocean acidification threaten corals?

Answer 23

Acidification reduces the ocean’s carrying capacity for calcium carbonate that corals need to build their skeletons.

There are fewer carbonate ions available in more acidic seawater, making it harder for corals to accurate skeletons.