MC Polar Ecosystems

Polar communities

Marine ecosystems in the Arctic and Antarctic characterized by extreme cold, sea ice, and strong seasonality

Major environmental factors

Cold temperatures (-2 to ~6°C), extensive sea ice, extreme seasonal light, strong ice formation/melt cycles

Light seasonality in polar regions

24 hours daylight in summer and 0 hours in winter, strongly controlling primary production

Why few reptiles/amphibians in polar regions

They are ectothermic and cannot maintain body temperature in extreme cold

Why mammals and birds dominate

They are endothermic and can regulate internal temperature

How fish/invertebrates survive freezing

They produce antifreeze compounds to prevent cellular freezing

Thermal tolerance of polar benthic organisms

Many cannot survive above ~10°C

Sea ice importance

Provides habitat, affects nutrient cycling, and controls food web structure

Seasonal ice pattern Arctic

Summer ice ~half of winter ice extent

Seasonal ice pattern Antarctic

Summer ice ~1/6 of winter ice extent

Primary producers in polar systems

Phytoplankton, especially diatoms

How ice preserves nutrients

Diatoms get trapped during ice formation and release nutrients when ice melts

Result of ice melt + sunlight

Large single phytoplankton bloom in summer

Polar bloom pattern

One major summer bloom instead of multiple seasonal blooms

Benthic-pelagic coupling

Strong connection between surface processes (ice/phytoplankton) and bottom communities

Arctic food web base

Diatoms/phytoplankton

Antarctic food web base

Diatoms, but strongly routed through krill

Key difference Arctic vs Antarctic food webs

Arctic is diverse; Antarctic is heavily krill-dependent

Role of fish in Arctic

Important intermediate trophic level (e.g., cod, capelin)

Role of fish in Antarctic

Less prominent than in Arctic systems

Krill classification

Zooplankton (planktonic crustaceans)

Role of krill

Central link connecting phytoplankton to higher trophic levels

Animals dependent on krill

Penguins, whales, squid, seals, birds

Apex predators Arctic

Polar bears and orcas

Apex predators Antarctic

Orcas (no polar bears)

Penguins vs polar bears

Penguins = Antarctic; polar bears = Arctic

Why Antarctic food web is vulnerable

Heavy reliance on one key species (krill)

Antarctic benthic community composition

Sponges, bryozoans, hydrozoans, ascidians, echinoderms

Why suspension feeders thrive in Antarctic benthos

Less sediment clogging feeding structures

Unique Antarctic benthos trait

Lack of shell-cracking predators

Possible reason for missing predators

Extreme cold limits predator distribution

Antarctic benthos compared to others

More primitive/Paleozoic-like and less predation-driven

Disturbance in polar benthos

Ice scour from glaciers/icebergs scraping the seafloor

Effect of ice scour

Removes organisms and resets succession

Recovery after disturbance

Very slow (can take over a decade)

Does RSP apply to polar systems?

No, does not fit well

Why RSP does not apply

No monopoly-forming competitor and no keystone predator suppressing it

Competition in polar systems

Exists but forms hierarchies rather than monopolies

Keystone predator presence in benthos

Not clearly identified in polar systems

Main disturbance driver in polar systems

Ice scour rather than biological interactions

Tolerance importance

Extreme cold limits which species can survive

Top-down control definition

Predators regulating lower trophic levels

Bottom-up control definition

Nutrients and primary production controlling the food web

Dominant control in polar systems

Strong bottom-up control from ice, light, and nutrients

Example of bottom-up control

Ice → diatoms → krill → higher trophic levels

Top-down effects in polar systems

Present (e.g., orcas) but less dominant than bottom-up forces

Climate change effect on temperature

Polar regions warming rapidly (especially Arctic)

Effect of warming on seasons

Longer summers, shorter winters

Effect of warming on ice formation

Ice forms later in the year

Why delayed ice formation matters

Fewer diatoms are trapped in the ice

Effect on nutrient storage

Reduced nutrient availability in ice

Krill life cycle timing

Larvae rely on ice-associated food during winter

Effect of reduced diatoms on krill

Less food for larvae → lower survival

Result for krill populations

Decline in abundance (also influenced by overharvesting)

Impact on Antarctic food web

Reduced krill affects many species

Adelie penguin trend

Declining populations

Chinstrap penguin trend

Declining populations

Gentoo penguin trend

Not declining significantly

Why gentoo penguins are less affected

More generalist diet (not strictly krill-dependent)

Other climate impacts

Reduced ice affects breeding and habitat

Additional threat: overharvesting

Krill fishing reduces food availability

Additional threat: invasive species

Warming allows new predators (e.g., king crabs)

Potential effect of king crabs

Increased predation on benthic organisms

Pollutants in polar regions

PCBs and PBDEs

How pollutants reach poles

Global distillation (evaporate → travel → condense in cold regions)

Global distillation definition

Movement of volatile pollutants toward colder latitudes

PCB source

Industrial insulators and flame retardants (banned but persistent)

PBDE source

Flame retardants in electronics and plastics

Key property of PCBs/PBDEs

Lipophilic (accumulate in fat)

Do PCBs and PBDEs biomagnify?

Yes, increase in concentration up the food web

Biomagnification definition

Increase in toxin concentration at higher trophic levels

Example of high contaminant levels

Orcas (top predators)

Effects of PCBs

Endocrine disruption, neurotoxicity, carcinogenic effects

Effects of PBDEs

Toxicity and disruption of biological systems

Why top predators are most affected

They accumulate toxins from all lower trophic levels

Human relevance example

High PCB levels found in Arctic populations due to diet

Big picture rule of polar communities

Physical factors (ice, temperature, light) dominate over biological interactions