Temperature Effects on Marine Animals P3
Cold Temperature Challenges in Marine Animals
A. Subzero Temperatures in the Ocean
Seawater freezes at -1.86°C due to dissolved salts.
Most marine invertebrates are osmoconformers, so their body fluids match seawater and do not freeze at 0°C.
However, some marine vertebrates (e.g., fish) have lower internal salt concentrations (~⅓ that of seawater), making them susceptible to freezing.
Threats of freezing occur in:
Polar waters (e.g., Antarctica, Arctic).
Intertidal zones in winter (exposure to freezing air temperatures).
3. Strategies for Surviving Extreme Cold
A. Freeze Tolerance vs. Freeze Avoidance
Marine animals use two primary strategies to survive freezing conditions:
Strategy | Definition | Example Animals |
|---|---|---|
Freeze Tolerance | Allow ice to form in body fluids but control its location. | Some invertebrates (e.g., bivalves, gastropods, nematodes, insects). |
Freeze Avoidance | Prevent ice formation entirely. | Most vertebrates (e.g., Antarctic icefish, polar invertebrates). |
4. Freeze Tolerance: Controlled Ice Formation
A. How Freeze-Tolerant Animals Survive Freezing
Ice nucleating proteins (INPs) promote controlled freezing in extracellular fluids.
Ice crystals form in interstitial spaces (outside cells), NOT inside cells.
Key steps in freeze tolerance:
Encourage ice formation in extracellular fluids.
Prevent ice formation inside cells (which would be fatal).
Use cryoprotectants to stabilize cells and prevent damage.
B. Role of Cryoprotectants
Cryoprotectants help cells survive freezing by:
Increasing osmotic concentration to prevent intracellular freezing.
Stabilizing membranes and proteins during ice formation.
Types of cryoprotectants:
Colligative cryoprotectants (work by concentration effects): Glycerol, sorbitol, ribitol.
Non-colligative cryoprotectants (work at low concentrations): Trehalose, proline.
Membrane stabilizers: Prevent damage when water is drawn out of cells.
C. Cellular Adaptations to Freezing
Cells must tolerate:
No oxygen supply (blood freezes).
High osmotic stress (water loss).
Anaerobic metabolism (due to lack of circulation).
Examples:
Some intertidal mollusks and insects tolerate partial freezing.
Only a few amphibians and reptiles use freeze tolerance (e.g., wood frogs).
5. Freeze Avoidance: Preventing Ice Formation
A. Supercooling in Body Fluids
Supercooling: Water can be cooled below its freezing point without solidifying, provided no ice nucleation sites are present.
Marine animals enhance supercooling by:
Avoiding ice-nucleating particles (e.g., dust, foreign objects).
Keeping body fluids free of nucleators.
Producing antifreeze proteins to prevent ice crystal growth.
Example:
Supercooled water can remain liquid at -20°C to -40°C.
B. Antifreeze Proteins & Glycoproteins
Most effective strategy for freeze avoidance.
Antifreeze proteins (AFPs) & antifreeze glycoproteins (AFGPs) prevent ice formation by:
Binding to small ice crystals to stop them growing ("adsorption inhibition").
Lowering freezing point without affecting melting point ("thermal hysteresis").
Common in:
Antarctic & Arctic fish.
Some cold-water invertebrates.
C. Seasonal Production of Antifreeze Proteins
Some fish only produce antifreeze proteins in winter to save energy.
Triggered by declining daylight (photoperiod), NOT temperature.
Example:
Winter flounder produces antifreeze proteins from October–March.
6. Endothermic Adaptations in Polar Mammals & Birds
A. Heat Loss Challenges in Cold Water
Water conducts heat 25x faster than air.
Large endotherms (e.g., whales, seals, polar bears) risk losing body heat rapidly.
How do they stay warm?
B. Strategies for Heat Retention
Large Body Size (Bergmann’s Rule)
Larger animals have a lower surface area-to-volume ratio, reducing heat loss.
Polar species (e.g., Arctic foxes, polar bears) are larger than their temperate relatives.
Insulation (Blubber & Fur/Feathers)
Blubber (thick fat layer) traps heat beneath the skin.
Fur & feathers trap air, reducing convective heat loss.
Example:
Emperor penguins have four layers of feathers for insulation.
Peripheral Vasoconstriction (Blood Flow Regulation)
Blood flow to extremities is reduced to conserve heat.
Blood shunted away from surface vessels.
Countercurrent Heat Exchange
Used in flippers, tails, and limbs to minimize heat loss.
Arteries (warm blood) run next to veins (cold blood), transferring heat before blood reaches extremities.
Example:
Seals & whales have countercurrent exchangers in their flippers and flukes.
Behavioral Thermoregulation
Huddling in groups reduces heat loss.
Example:
Emperor penguins rotate positions in huddles to share warmth.
7. Summary & Key Takeaways
A. Survival Strategies in Cold Environments
Freeze-tolerant animals allow ice formation but control its spread.
Freeze-avoidant animals prevent ice from forming using supercooling and antifreeze proteins.
B. Antifreeze Proteins in Marine Vertebrates
Found in polar fish and some invertebrates.
Prevent ice crystal growth, allowing survival in subzero waters.
C. Endothermic Adaptations to Cold
Large body size, blubber, and countercurrent heat exchange prevent heat loss.
Behavioral strategies like huddling help conserve warmth.