Creatures That Live Under the Ice | Complete Guide
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Creatures That Live Under the Ice
Antifreeze Blood, Breathing Holes, and Life That Never Sees Open Sky
Beneath the frozen surface of polar seas and glacial lakes, in water that would kill most animals in minutes, a genuinely thriving ecosystem exists. Antarctic icefish carry a natural antifreeze in their blood and, remarkably, no red blood cells at all. Weddell seals gnaw breathing holes into sea ice with their own teeth, maintaining access to air throughout the long polar winter. And researchers have even found signs of life in subglacial lakes sealed beneath kilometers of Antarctic ice for possibly millions of years. Surviving under the ice takes some of the most specialized biology found anywhere on Earth.
💡 Quick Fact
This guide covers how animals survive in subzero water, several standout under-ice species, the hidden food web that supports them, and answers to common questions.
How Life Survives Water Colder Than Freezing
Ocean water can stay liquid below the normal freezing point of fresh water due to its salt content, meaning under-ice animals often live in water genuinely cold enough to freeze their own blood without special adaptations.
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Antifreeze Proteins
Special proteins stop ice crystals from growing inside the body
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Maintained Breathing Holes
Air-breathing seals actively keep openings in the ice from freezing shut
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Ice-Algae Food Web
Algae growing on the ice’s underside supports the entire local food chain
Cold water holds significantly more dissolved oxygen than warm water, which helps make it possible for unusual species like the Antarctic icefish to survive without the oxygen-carrying red blood cells most vertebrates depend on.
°C, roughly how cold the water can get where icefish live
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minutes a Weddell seal can hold its breath on a single dive
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km of solid ice can sit above some Antarctic subglacial lakes
Standout Under-Ice Species
These species show some of the most extreme, well-documented adaptations to life beneath polar ice:
🐟 Antarctic Icefish: Blood With No Red Cells at All
Icefish are the only known vertebrates that lack red blood cells and hemoglobin entirely, relying instead on oxygen dissolved directly in their blood plasma.
Natural antifreeze: icefish also produce antifreeze glycoproteins that bind to ice crystals forming in their blood, preventing them from growing large enough to cause harm.
Large heart and gills: to compensate for less efficient oxygen transport without hemoglobin, icefish have unusually large hearts and gills relative to their body size.
Isolated evolution: this trait evolved in the extremely cold, stable, oxygen-rich waters surrounding Antarctica, a highly specific environmental condition.
🦭 Weddell Seal: Maintaining Its Own Breathing Holes
Weddell seals live farther south than almost any other mammal, using their teeth to actively gnaw and maintain breathing holes in thick sea ice throughout the Antarctic winter.
Extended dive capability: Weddell seals can hold their breath for well over an hour on deep dives beneath the ice in search of fish.
Tooth wear trade-off: the constant gnawing needed to keep breathing holes open causes significant tooth wear over a seal’s lifetime.
Acoustic navigation: Weddell seals produce a wide range of underwater calls, likely aiding navigation and communication in the dark, ice-covered water.
🦠 Subglacial Lake Microbes: Life Sealed Beneath Kilometers of Ice
Researchers drilling into Antarctic subglacial lakes, sealed beneath kilometers of solid ice for possibly millions of years, have found evidence of microbial life surviving without any sunlight at all.
Chemical energy reliance: without sunlight for photosynthesis, these microbial communities rely instead on chemical energy sources from rock and sediment interactions.
Extreme isolation: some of these lake ecosystems have likely been completely cut off from the outside world for extraordinarily long periods.
Astrobiology significance: researchers study these ecosystems partly because they may resemble conditions found on icy moons elsewhere in the solar system.
More Under-Ice Life Worth Knowing
Beyond the most extreme examples, several other species rely on the specific conditions found beneath sea ice:
🎯 Explore Another Under-Ice Species
🦐 Antarctic Krill: The Base of the Under-Ice Food Web
These small shrimp-like crustaceans feed directly on algae growing on the underside of sea ice, forming the critical base of the Antarctic under-ice food web.
Enormous population: Antarctic krill exist in such vast numbers that their total combined weight is estimated to exceed that of the human population.
Ice-algae dependency: krill rely heavily on ice algae as a food source, especially during the winter months when other food is scarce.
Keystone species role: nearly every larger Antarctic predator, from fish to seals to whales, depends directly or indirectly on krill for food.
🐟 Polar Cod: A Key Arctic Under-Ice Fish
Polar cod thrive in icy Arctic waters and are specially adapted to tolerate near-freezing temperatures, serving as a critical link between small ice-associated organisms and larger Arctic predators.
Antifreeze proteins too: like their Antarctic counterparts, polar cod produce natural antifreeze compounds that help prevent ice crystal formation in their blood.
Under-ice shelter: polar cod often shelter directly beneath sea ice, using its underside structure for protection from larger predators.
Climate sensitivity: shrinking Arctic sea ice is a significant concern for polar cod populations, given how closely tied their life cycle is to ice conditions.
🦐 Ice Amphipods: Tiny Grazers Living Directly on the Ice
These small crustaceans live directly on and within the underside of sea ice, grazing on ice algae and forming an important food source for fish and seabirds.
Direct ice association: some amphipod species spend nearly their entire life cycle in close contact with the ice itself, rather than swimming freely in open water.
Seasonal food source: ice amphipods become an especially important food source during the long polar winter, when other prey is less available.
Sensitive indicator species: their close dependence on ice makes amphipod populations a useful indicator of overall sea ice ecosystem health.
Frequently Asked Questions
How can fish survive in water that’s below freezing?
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Certain polar fish species, like icefish and some cod relatives, produce natural antifreeze glycoproteins in their blood. These proteins bind to tiny ice crystals and prevent them from growing large enough to cause fatal cellular damage, allowing the fish to survive in water colder than the normal freezing point of blood.
How do seals breathe if the ocean surface is covered in ice?
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Ice seals like the Weddell seal use their teeth to maintain breathing holes in the ice, gnawing away new ice as it forms. They also rely on excellent underwater navigation to find natural cracks and thin spots in the ice sheet.
What is icefish blood actually made of if it lacks red blood cells?
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Antarctic icefish are the only known vertebrates that lack red blood cells and hemoglobin entirely. Instead, their blood plasma carries dissolved oxygen directly, an adaptation made possible partly by the fact that cold water holds more dissolved oxygen than warm water.
Is there life directly underneath thick glacial ice sheets?
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Yes. Researchers have found microbial life and even small aquatic animals in subglacial lakes sealed beneath kilometers of Antarctic ice for possibly millions of years, surviving without sunlight through chemical energy sources instead.
Do animals under sea ice get enough food to survive?
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Yes, though food sources differ from open water. Algae growing on the underside of sea ice supports tiny krill and other small organisms, which in turn support fish, seals, and other larger predators in a food web adapted to the ice-covered environment.
Are under-ice ecosystems affected by climate change?
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Yes. Reduced sea ice extent and thickness affects the algae that grows on ice, which forms the base of the under-ice food web, creating ripple effects for krill, fish, seals, and other species that depend on stable ice conditions.
Compare by Survival Adaptation
Different under-ice species rely on different specific survival strategies. Pick one to explore:
Conclusion: A Hidden World Beneath the Frozen Surface
From a fish with no red blood cells to a seal that gnaws its own breathing holes and microbes sealed away for millions of years, life under the ice reveals just how far biology can stretch to survive in conditions that would be instantly fatal to most other species. As polar ice conditions continue to shift, understanding this hidden, cold-adapted world has become more than scientific curiosity — it’s a direct window into how fragile and specialized these under-ice ecosystems really are.
Want to learn more?
Look into polar research programs studying under-ice ecosystems, and share which species on this list surprised you the most!
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