Lecture 10 - Polar Ecosystems

Question 1

How North is the Arctic Circle?

Answer 1

66 degrees

Question 2

Which is the enclosed ocean; the Arctic or the Antarctic?

Answer 2

The Arctic

Question 3

Give the three pieces of land that surround the Arctic.

Answer 3

• Siberia
• Alaska
• Northern Canada

Question 4

Define the Arctic.

Answer 4

The extent of the midnight sun and the polar night.

Question 5

Why is the Arctic described as the position oft he treeline?

Answer 5

North of the treeline is where it is too cold for trees to grow.

Question 6

Where is the coldest place on the planet?

Answer 6

A mountain in Antarctica, goes down to -90

Question 7

What is the range of winter temperatures at the coast of the Antarctic?

Answer 7

0 to -30 degrees

Question 8

How much of the Earth’s surface can pack ice cover at its maximum extent?

Answer 8

13%

Question 9

What is the dominant feature influencing both polar ecosystems?

Answer 9

Sea ice dynamics

Question 10

In the Arctic, when is the

a) Maximum sea ice extent?
b) Minimum sea ice extent?

Answer 10

a) Maximum = end of winter; March

b) Minimum = end of summer, September

Question 11

In the Antarctic, when is the

a) Maximum extent?
b) Minimum extent?

Answer 11

a) Maximum = November

b) Minimum = February

Question 12

Give the three polar habitats.

Answer 12

• Sea-ice realm
• Pelagic realm
• Benthic realm

Question 13

How does sea ice form?

Answer 13

• Once it begins to freeze, salt is excluded from the ice crystal in brine rejection.
• Surrounding seawater becomes saltier and denser, and sinks.

Question 14

What is the difference between first year and multi year ice?

Answer 14

• First year ice contains pockets of brine that form channels within the ice where brine is collecting and dropping out of the bottom.
• Multi-year ice; brine channels drop out and ice consolidates and becomes denser.

Question 15

Describe primary production in polar environments.

Answer 15

Comes in short, sharp pulses.

Question 16

Where in polar environments are there changes in seawater temperature?

Answer 16

Towards the edge of the environment

Question 17

When do plankton peak in polar environments?

Answer 17

In the early spring

Question 18

How much of the total annual primary production does primary production in the Arctic sea ice contribute?

Answer 18

Over 50%

Question 19

True or false:

Production in first year ice is greater than multi-year ice.

Answer 19

TRUE.

This is true because there are more channels in first year ice.

Question 20

What are sympagic species?

Answer 20

Ice-associated flora and fauna

Question 21

What are the most common invertebrates in the Arctic sea ice?
How do they feed?

Answer 21

Calanoid copepods and amphipods.

Eat diatoms that sink to the sea floor upon ice melt.

Question 22

What temperature can sea ice bacteria and algae survive up until?

Answer 22

-25 degrees

Question 23

Describe how antifreeze proteins work.

Answer 23

Bind ice crystals as they start to form and lower the freezing point in thermal hysteresis.

Question 24

Describe the winter-spring transition in the Arctic

Answer 24

• Sun rises a few hours a day from March to April
• April-May, 24 hours of sunlight
• Ice thins, forming more channels, and nutrients drop out, leading to blooms of phytoplankton.
• Invertebrates then increase in abundance.

Question 25

Describe the peaks in algal blooms at

a) 70 degrees North
b) 75 degrees
c) Higher

Answer 25

a) 70 degrees = two peaks of algal blooms
b) 75 degrees = a single peak
c) Peaks become smaller

Question 26

How are calanoid copepods adapted to cope with seasonal pulses of primary production in the polar environments?

Answer 26

Overwinter with high lipid reserves.

Have a lipid sac which grows through primary production period.

Question 27

Give the three key calanus species in the Arctic.

Answer 27

• C. hyperboreus; specialises in deeper parts of the Arctic.
• C. glacialis; in the Arctic shelf
• C. finmarchicus; in the Atlantic.

Question 28

What percentage of the total mesoplankton biomass in the Arctic is made up of Calanus species?

Answer 28

50-80%

Question 29

Describe reproduction of Calanus species in the Arctic.

Answer 29

• Suppress metabolic rate in Winter.
• Enough lipid reserve to form eggs before they feed, timing release of eggs with algal blooms.
• Larvae have food to eat as soon as they hatch, but must grow quickly due to short summer period.

Question 30

In stead of Calanus, what occupies the primary consumer niche in the Antarctic?

Answer 30

Krill

Question 31

Ho many tonnes of krill are there in the Southern ocean?

Answer 31

500 million tonnes

Question 32

Describe the lifecycle of krill in Antarctica.

Answer 32

• Begin life feeding on algae beneath the sea ice.

- In summer, leave the ice and form swarms with millions of individuals (feed by swimming upside down).

Question 33

Why are krill a keystone species in Antarctic ecosystems?

Answer 33

• Key source of food for many other animals

- Release high levels of iron - Antarctic is iron-limited.

Question 34

Compare the differences in production in the Arctic and Antarctic environments.

Answer 34

• Strong stratification of water column in Arctic due to high freshwater input, not in Antarctic.
• Primary prduction nutrient-limited in Antarctic, but iron-limited in the Antarctic.

Question 35

What structures the benthos in polar ecosystems?

Answer 35

• Ice scour
• Effective at removing attached intertidal organisms
• Holds environment in early successional stages.

Question 36

What is the polar benthos dominated by?

Answer 36

Suspension feeders such as crinoids and brittle stars

Question 37

What is the polar benthos dominated by?

Answer 37

Suspension feeders such as crinoids and brittle stars

Question 38

Describe the Antarctic benthos.

Answer 38

• Modern skeleton-crushing predators e.g. sharks, rays, lobsters, crabs; rare, if not present. Too cold for them.
• Slow-moving invertebrates, e.g. echinoderms, are the top predators.
• Soft-bodied suspension feeders evolved in the absence of crushing predators.

Question 39

Describe an Antarctic invasion.

Answer 39

• Crabs mostly lacking from Antarctica, but invasion of King Crabs into Antarctic shelf seas.
• King crabs from warmer deeper waters migrating to shallow waters due to warming.
• Could have ecological impacts, as benthic invertebrates are not evolved to protect themselves from crushing predators.

Question 40

Why are invertebrates slow moving in polar environments?

Answer 40

Aerobic capacity is low

Question 41

How can polar fish maintain aerobic scope for fast swimming?

Answer 41

They have more mitochondria.

Question 42

Why is gigantism common in polar environments?

Answer 42

They live much longer, due to slower growth rates and higher oxygen content.

Question 43

How many more times species does the Antarctic have compared to the Arctic?

Answer 43

1.5-6 times

Question 44

Why is there higher endemism in the Antarctic species?

Answer 44

Due to isolation of Antarctica from the rest of the world’s oceans.

Question 45

How did the Arctic benthos arise?

Answer 45

From invasions from the Pacific in the last 2 million years.

Question 46

How many species of marine fish are found in the Arctic marine waters?

Answer 46

240

Question 47

Name a commercially important species in the Arctic.

Answer 47

Arctic cod.

Uses ice revises to hide and avoid predation.

Question 48

What two groups of fish dominate the Antarctic?

Answer 48

• Notothenoids (icefish)
• Liparids
• Do not have strong jaws for crushing

Question 49

Describe an adaption of notothenioids in the Antarctic

Answer 49

Lost heat shock proteins and haemoglobin due to stable temperatures and high levels of oxygen.

Question 50

Give some charismatic megafauna found in the Antarctic.

Answer 50

• Leopard seals
• Penguins
• Walruses
• Killer whales

Question 51

Give some charismatic megafauna found in the Arctic.

Answer 51

• Polar bears
• Migratory whales
• Seals