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All marine life is immersed in water, the matrix and womb of life itself. [7] Water can be broken down into its constituent hydrogen and oxygen by metabolic or abiotic processes, and later recombined to become water again. While the water cycle is itself a biogeochemical cycle, flow of water over and beneath the Earth is a key component of the ...
In response to decreasing dissolved oxygen level in the environment, fish swim up to the surface of the water column and ventilate at the top layer of the water where it contains relatively higher level of dissolved oxygen, a behavior called aquatic surface respiration (ASR). [33]
Sea slugs respire through a gill (or ctenidium). Aquatic respiration is the process whereby an aquatic organism exchanges respiratory gases with water, obtaining oxygen from oxygen dissolved in water and excreting carbon dioxide and some other metabolic waste products into the water.
Hypoxia occurs when dissolved oxygen (DO) concentration falls to or below 2 ml of O 2 /liter. [2] When a body of water experiences hypoxic conditions, aquatic flora and fauna begin to change behavior in order to reach sections of water with higher oxygen levels. Once DO declines below 0.5 ml O 2 /liter in a body of water, mass mortality occurs.
Organisms, both microbial and multicellular, use oxygen in respiration throughout the entire depth of the ocean, so when the supply of oxygen from the surface is less than the utilization of oxygen in deep water, oxygen loss occurs. This phenomenon is natural, but is exacerbated with increased stratification and increasing ocean temperature.
The concentration of oxygen in water is lower than air and it diffuses more slowly. In a litre of freshwater the oxygen content is 8 cm 3 per litre compared to 210 in the same volume of air. [7] Water is 777 times more dense than air and is 100 times more viscous. [7] Oxygen has a diffusion rate in air 10,000 times greater than in water. [7]
Natural decomposers present in the water begin decomposing the dead algae, consuming dissolved oxygen present in the water during the process. This can result in a sharp decrease in available dissolved oxygen for other aquatic life. Without sufficient dissolved oxygen in the water, animals and plants may die off in large numbers.
This decomposition process consumes oxygen, depleting the supply for other marine life and creating what is referred to as a "dead zone." Dead zones are hypoxic, meaning the water has very low levels of dissolved oxygen. This kills off marine life or forces it to leave the area, removing life from the area and giving it the name dead zone.