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Marine Biology > Lecture 7 - Tropical Ecosystems > Flashcards

Lecture 7 - Tropical Ecosystems Flashcards

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1
Q

When have corals been present since?

A

The Ordovician period.

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2
Q

What corals are reefs dominated by?

A

Scleractinian corals (hard, reef-forming, stony corals that lay down skeleton)

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3
Q

How old is the Great Barrier Reef?

A

0.5 million years old

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4
Q

What are the two classes of corals?

A
  • Hermatypic (reef-building)

- Ahermatypic (non reef-building)

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5
Q

How do cnidarians feed?

A

Catch food with nematocysts in tentacles and pass to the central mouth.

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6
Q

Describe coral growth.

A

The polyp constantly moves upwards, secreting a calcium carbonate skeleton behind it.

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7
Q

How many dinoflagellate cells are there per unit squared of a coral?

A

1 million

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8
Q

What are zooxanthellae?

A

Unicellular dinoflagellates taken up by the coral and hosted in the surface tissue

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9
Q

Describe the role of zooxanthellae.

A
  • Fix CO2

- Provide up to 90% of energy to coral in return for protection and nutrients.

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10
Q

Where are corals found?

A

30 degrees North and South

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11
Q

What are some requirements for corals?

A
  • Require clear water less than 50m, to ensure photosynthesis is possible
  • Temperatures 18-36 degrees
  • Full salinity water (33-35ppt)
  • Hard substrate
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12
Q

What is the optimum temperature for corals?

A

26-28 degrees

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13
Q

Why is coral biomass low at the West Coast of Southern Africa?

A

Very intense upwelling, giving cold water and thus low coral density.

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14
Q

How do corals reproduce?

A

Asexually by budding.

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15
Q

How do corals disperse long distances?

A

By planulae via sexual reproduction.

Release buoyant eggs and sperm.

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16
Q

Give the three sexual categories of corals.

A
  • Gonochoric (male or female)
  • Simultaneous hermaphrodites (produce both eggs and sperm)
  • Sequential hermaphrodites (produce eggs for a while, and then sperm)
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17
Q

Give the four stage life cycle of corals.

A

1) 1-3 day larval stage
2) settlement to hard rock
3) Metamorphosis and secretion of the basal plate
4) Zooxanthellae acquisition

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18
Q

Describe the work of Charles Darwin.

A

Wrote a book on reefs before Origin of Species; noticed that not all corals were the same, and could form different structures.

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19
Q

Name and describe three different coral reefs.

A
  • Fringing reefs; corals growing on the edge of an island.
  • Barrier reefs; lagoon between reef and edge of the island.
  • Atoll; rings of corals growing out of the depths.
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20
Q

When do corals form fringing reefs?

A

On young land masses, where corals establish themselves on the edges of islands

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21
Q

When do barrier reefs form?

A

When islands sink back into the sea, and coral continues to grow upwards forming sand-filled lagoons

22
Q

When are atolls formed?

A

When islands sink below the sea altogether.

23
Q

What is the typical net growth rate of coral?

A

3mm per year

24
Q

How much do individual corals grow per year?

A

20cm per year

25
Q

How much limestone a year can coral reefs deposit?

A

4,200 tons of limestone per km per year

26
Q

What are the two sources of coral erosion?

A
  • Physical; e.g. hurricanes, storms, tidal effects.

- Grazing; parrotfish, urchins and boring by sponges and bivalves.

27
Q

How much more surface area do corals provide compared to a seabed?

A

15% more

28
Q

What percentage of marine species do coral reefs provide ecological niches for?

A

25%

29
Q

How many reef building corals are there?

A

About 800

30
Q

Give four theories for the coral triangle.

A
  • Centre of origin; lots of new species evolving, and gradually spread away from centre.
  • Centre of overlap; species evolving all over Pacific Ocean, but where species overlap we have the highest number of species.
  • Centre of survival/refuge
  • Centre of accumulation; diverse habitat, and over time species accumulate in the area.
31
Q

How many species of fish can be found in the Coral Triangle?

A

2,000

32
Q

What did studies show on the coral triangle?

A
  • Older populations closer to the coral triangle
  • Youngest populations found further away from the triangle
  • Therefore is the centre of origin or refuge.
33
Q

How much a year do coral reefs provide in ecosystem goods and services?

A

$375 billion per year

34
Q

How many people rely on reefs for food and livelihoods?

A

500 million people.

35
Q

Why are reefs important ecologically?

A
  • Act as a buffer zone between land and sea, providing coastal protection from the power of the ocean.
  • Play role in waste processing, through uptake of CO2 and removal of nutrients from the water.
36
Q

If present rate of destruction continues, what percentage of the world’s reefs will be destroyed by 2050?

A

70%

37
Q

What percent of the world’s coral reefs are threatened by human activities at the local level?

A

60%

38
Q

When coupled with global threats, what percentage of the world’s reefs are threatened?

A

75%

39
Q

What are the only true marine angiosperms?

A

Seagrasses

40
Q

How long have seagrasses been around?

A

100 million years

41
Q

Explain the role of seagrasses.

A
  • Have a rhizome and root system

- Fix nitrogen and stabilise soft sediments.

42
Q

Why are seagrasses so important?

A

Important for coastal protection, through stabilisation of mobile sediment.

43
Q

What depth can seagrasses be found?

A

From intertidal to 10m

44
Q

How many shoots per metre squared do seagrasses produce?

A

1,200

45
Q

What are mangroves?

A

Trees or shrubs that form extensive mangals in high salinity waters.

46
Q

Give the three types of mangrove.

A
  • Riverine
  • Tide-dominated
  • Basin
47
Q

How do mangroves obtain oxygen?

A

From lenticles in aerial / knee roots.

48
Q

What are pneumatophore roots?

A

Roots that stick up out of the sand/mud.

49
Q

Name the seagrass species that can excuse salt uptake by roots.

A

Avecinnia

50
Q

Describe a method that seagrasses are adapted to cope with high salinities.

A

Excreting excess salt in bark or leaves.

51
Q

How are mangroves adapted to cope with high temperatures?

A

Leaves are held at angles to the sun to avoid excess transpiration.
Can regulate temperature of the leaves.

Marine Biology (19 decks)

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