Deep-Sea Survival

You have compared traits that affect mating success. Here, compare how pressure affects gas spaces and cell chemistry. Much of the deep sea is dark, cold and under high pressure. Gas compresses as pressure rises and expands as pressure falls. Water-rich tissues compress much less. Many deep-sea animals lack large gas spaces, but some fish regulate gas-filled swim bladders. A sealed, flexible gas space changes volume when surrounding pressure changes.

Little tissue compression does not mean pressure leaves cells unaffected. Pressure can alter proteins' shapes and activity. Enzymes are molecules that speed up chemical reactions. Adaptations in proteins and other cell chemicals help deep-sea reactions continue. There is no single rule that every protein must become harder or more flexible.

Antarctic icefish have antifreeze glycoproteins in their blood. These attach to small ice crystals and limit further growth. They do not heat the blood or melt large crystals. This protection helps fish survive icy seawater below the freezing point their body fluids would otherwise have.

Wood frogs tolerate partial freezing. Ice forms mainly outside cells. Glucose, a sugar, builds up as freezing begins and helps protect cells from freezing and water-loss damage. Under suitable conditions, up to about two-thirds of body water may freeze. Recovery depends on temperature and duration. Unlike icefish, these frogs tolerate substantial body ice; both adaptations reduce ice-related damage.

Some tardigrades tolerate gradual drying by entering cryptobiosis, a reversible state with extremely low metabolism. They retract their legs into a tun and lose most of their water. Protective molecules limit damage. If the animal survives, adding water can allow activity to return. Recovery time varies, and recovery is not guaranteed.

Some dried tardigrades have survived limited experimental exposure to vacuum, radiation or extreme temperatures. Results depend on species, preparation and exposure duration. They do not feed or grow in space. Drying does not make them indestructible, and surviving one exposure does not prove survival under harsher conditions.

Thermophiles grow well at high temperatures. Some microbes grow in hot water near hydrothermal vents, where hot fluid mixes with cooler seawater. Halophiles grow well in very salty environments. Some microbes tolerate several extremes, but heat tolerance alone does not prove salt tolerance. Active growth in heat differs from a tardigrade's dormant survival.