BIOLOGY 457/657 PHYSIOLOGY OF MARINE & ESTUARINE ANIMALS. March 8, 2004 Physiological Adaptation to the Deep Sea. FEATURES OF THE DEEP SEA. Area: The deep benthos and its overlying waters occupy a large area and a huge volume . FEATURES OF THE DEEP SEA.
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March 8, 2004
Physiological Adaptation to the Deep Sea
Area: The deep benthos and its overlying waters occupy a large area and a huge volume
Light: essentially absent, except for bioluminescence
Temperature: low (~4°C) and constant
Salinity: constant (~35°%)
Oxygen: generally adequate (may
be depleted near substratum)
Pressure: greatly elevated (can
exceed 1000 atm)
Food supply: extremely
limited (except near
Diversity is great: invertebrates may be very unusual
Density is very low (except at hydrothermal vents)
Energy content of animals is unusually low
Metabolic rates also tend to be very low
Sizes of animals can be unexpectedly large
Light: enlarged eyes, photophores, black or red coloration, transparency
Temperature: maintain low metabolic rates
Salinity: no adaptation required, since it is constant & reliable
Oxygen: no special adaptations normally required
Pressure: numerous special adaptations of enzymes and membranes
Food supply: must cope with the scarcity of food, its low energy content, and the risk of being detected. Food sources include land runoff, molts, fecal pellets, “marine snow”, dissolved organic matter, bacteria, vertical migrators
Reproduction: mates are infrequently encountered; must have special means of communication (while reducing risk of predation)
Biological Effects of Pressure
Water is essentially incompressible
Effects on gas-filled spaces can be severe
All biochemical effects result from volumechange
(3) Polymerization/Subunit dissociation
(4) Enzyme kinetics (activation volumes)
Physiological processes affected by pressure:
(1) High-pressure neurological syndrome (HPNS)
(2) Membrane fluxes (effects on ATPases)
(3) Muscle contraction (cytoskeletal effects)
(4) Synaptic transmission (generally inhibited)
(5) Membrane fluidity
Ligand-binding events often involve changes in conformation and hydration, leading to increased volume
Pressure adaptation may require only minor sequence change
Pressure adaptation often leads to greater protein stability (resistance to denaturation)
Pressure-adapted systems often have lower rates of catalysis
Note that in bothfish and crustaceans, aerobic metabolic rates (and presumably typical anaerobic rates as well) decrease considerably with habitat depth.
Hydrothermal vents represent very unusual deep-sea benthic habitats because they are sites where energy is abundant, due to chemicals supplied by “black smokers” – sources of abundant mineral sulfur.
The ultimate source of energy is H2S, which is oxidized by bacteria. The energy thus derived is used to operate the Calvin-Benson cycle of carbon fixation.
Sulfide is highly toxic at µM concentrations (it poisons cyt-c). Tubeworms (Riftia) detoxify it by binding it to Hb. Other vent organisms have various sulfide-binding proteins.
Most vent animals contain endosymbiotic bacteria, which actually produce their nutrients.
An additional problem faced by thermal vent organisms is the extreme transience of the vent habitat; any one site may have a lifetime measured in tens of years. Thus, efficient dispersal and navigation by larvae is essential.
(Photo: Bythograea thermydron)