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Adaptations To The Deep Sea

by Dr. George Somero
Stanford University

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To begin Dr. Somero's talk you can click here or read this brief overview, below, that provides links to the best places in the talk for specific topics.

The physical and chemical characteristics of the deep-sea environment present daunting challenges to organisms and require a wide range of adaptations. These adaptations are of two fundamental sorts, those that effect tolerance of the environment and others that establish rates of metabolic function appropriate to the deep sea.

The high pressures of the deep sea (pressure rises by 1 atmosphere for each 10 meters increase in depth) are perturbing to physiological and biochemical processes. Selection has favored the evolution of pressure-resistant proteins which are able to sustain their native structures and activities under conditions that would seriously perturb proteins from shallow-living species. Some proteins of deep-sea fishes have unusually rigid structures. Deducing the molecular basis of this structural stability might benefit biotechnologists anxious to create proteins with higher resistance to denaturation.

Although most of the deep sea is very cold, hydrothermal vent regions present organisms with high and variable temperatures. Proteins from hydrothermal vent animals resemble those from cold-living deep-sea animals in their resistance to pressure, but unlike the latter species' proteins, they are also able to function over wide ranges of temperatures. Proteins of ultrathermophilic microbes (Archaea) in the hottest vent waters have unusually high thermal stabilities, consistent with the microbes' abilities to tolerate temperatures up to ~110 C, the highest temperatures at which life is known to occur.

Rates of life also reflect adaptation to deep-sea conditions, but these adaptations in metabolic capacity appear unrelated to the effects of high pressure and, to a large extent, to life at low temperature. For many pelagic organisms, notably fishes and crustaceans, rates of metabolic activity decrease dramatically with depth between the surface and approximately 800-1000 m. The ultimate causes of these depth-related changes in metabolic rate include the effects of near-complete darkness. For fishes and invertebrates that rely on vision in predator-prey interactions, life-in-the-dark appears to allow a large reduction in locomotory activity and, thereby, large decreases in metabolic rate. The swimming musculature of deep-sea fishes contains greatly reduced levels of enzymatic activity for generation of ATP, the cell's energy currency, consistent with reduced locomotory capacity. Invertebrates such as gelatinous species that are not visual predators do not exhibit depth-related decreases in metabolism or in enzymatic activity.

The strong correlation between enzymatic activity and rate of metabolism permits development of biochemical indices of physiological state. Thus, the quantity of enzymatic activity present in a biopsy sample of muscle tissue can serve as a proxy for the rate of oxygen consumption by the whole organism. Through measuring enzymatic activities in this way, it is possible to gauge the physiological condition of natural populations, such as deep-sea fishes that have become of major commercial importance. Analysis of deep-living rockfish suggests that some populations may live under food-limiting conditions.

Low concentrations of oxygen also present challenges to some deep-living animals. Fishes found in the oxygen minimum zone (OMZ) have elevated capacities for extracting oxygen from seawater and exhibit different patterns of gene expression for enzymes of aerobic and anaerobic metabolism than related species from high-oxygen habitats.

In summary, studies of deep-sea animals are providing new insights into issues ranging from mechanisms of evolutionary adaptation to the environment to practical concerns about gauging the status of fisheries and designing novel molecules through biotechnology.

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