Lecture 10 - Polar Ecosystems Flashcards
How North is the Arctic Circle?
66 degrees
Which is the enclosed ocean; the Arctic or the Antarctic?
The Arctic
Give the three pieces of land that surround the Arctic.
- Siberia
- Alaska
- Northern Canada
Define the Arctic.
The extent of the midnight sun and the polar night.
Why is the Arctic described as the position oft he treeline?
North of the treeline is where it is too cold for trees to grow.
Where is the coldest place on the planet?
A mountain in Antarctica, goes down to -90
What is the range of winter temperatures at the coast of the Antarctic?
0 to -30 degrees
How much of the Earth’s surface can pack ice cover at its maximum extent?
13%
What is the dominant feature influencing both polar ecosystems?
Sea ice dynamics
In the Arctic, when is the
a) Maximum sea ice extent?
b) Minimum sea ice extent?
a) Maximum = end of winter; March
b) Minimum = end of summer, September
In the Antarctic, when is the
a) Maximum extent?
b) Minimum extent?
a) Maximum = November
b) Minimum = February
Give the three polar habitats.
- Sea-ice realm
- Pelagic realm
- Benthic realm
How does sea ice form?
- Once it begins to freeze, salt is excluded from the ice crystal in brine rejection.
- Surrounding seawater becomes saltier and denser, and sinks.
What is the difference between first year and multi year ice?
- 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.
Describe primary production in polar environments.
Comes in short, sharp pulses.
Where in polar environments are there changes in seawater temperature?
Towards the edge of the environment
When do plankton peak in polar environments?
In the early spring
How much of the total annual primary production does primary production in the Arctic sea ice contribute?
Over 50%
True or false:
Production in first year ice is greater than multi-year ice.
TRUE.
This is true because there are more channels in first year ice.
What are sympagic species?
Ice-associated flora and fauna
What are the most common invertebrates in the Arctic sea ice?
How do they feed?
Calanoid copepods and amphipods.
Eat diatoms that sink to the sea floor upon ice melt.
What temperature can sea ice bacteria and algae survive up until?
-25 degrees
Describe how antifreeze proteins work.
Bind ice crystals as they start to form and lower the freezing point in thermal hysteresis.
Describe the winter-spring transition in the Arctic
- 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.
Describe the peaks in algal blooms at
a) 70 degrees North
b) 75 degrees
c) Higher
a) 70 degrees = two peaks of algal blooms
b) 75 degrees = a single peak
c) Peaks become smaller
How are calanoid copepods adapted to cope with seasonal pulses of primary production in the polar environments?
Overwinter with high lipid reserves.
Have a lipid sac which grows through primary production period.
Give the three key calanus species in the Arctic.
- C. hyperboreus; specialises in deeper parts of the Arctic.
- C. glacialis; in the Arctic shelf
- C. finmarchicus; in the Atlantic.
What percentage of the total mesoplankton biomass in the Arctic is made up of Calanus species?
50-80%
Describe reproduction of Calanus species in the Arctic.
- 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.
In stead of Calanus, what occupies the primary consumer niche in the Antarctic?
Krill
Ho many tonnes of krill are there in the Southern ocean?
500 million tonnes
Describe the lifecycle of krill in Antarctica.
- 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).
Why are krill a keystone species in Antarctic ecosystems?
- Key source of food for many other animals
- Release high levels of iron - Antarctic is iron-limited.
Compare the differences in production in the Arctic and Antarctic environments.
- 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.
What structures the benthos in polar ecosystems?
- Ice scour
- Effective at removing attached intertidal organisms
- Holds environment in early successional stages.
What is the polar benthos dominated by?
Suspension feeders such as crinoids and brittle stars
What is the polar benthos dominated by?
Suspension feeders such as crinoids and brittle stars
Describe the Antarctic benthos.
- 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.
Describe an Antarctic invasion.
- 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.
Why are invertebrates slow moving in polar environments?
Aerobic capacity is low
How can polar fish maintain aerobic scope for fast swimming?
They have more mitochondria.
Why is gigantism common in polar environments?
They live much longer, due to slower growth rates and higher oxygen content.
How many more times species does the Antarctic have compared to the Arctic?
1.5-6 times
Why is there higher endemism in the Antarctic species?
Due to isolation of Antarctica from the rest of the world’s oceans.
How did the Arctic benthos arise?
From invasions from the Pacific in the last 2 million years.
How many species of marine fish are found in the Arctic marine waters?
240
Name a commercially important species in the Arctic.
Arctic cod.
Uses ice revises to hide and avoid predation.
What two groups of fish dominate the Antarctic?
- Notothenoids (icefish)
- Liparids
- Do not have strong jaws for crushing
Describe an adaption of notothenioids in the Antarctic
Lost heat shock proteins and haemoglobin due to stable temperatures and high levels of oxygen.
Give some charismatic megafauna found in the Antarctic.
- Leopard seals
- Penguins
- Walruses
- Killer whales
Give some charismatic megafauna found in the Arctic.
- Polar bears
- Migratory whales
- Seals
