Measuring respiration, in this case the amount of oxygen (O2) consumed by animals, can teach researchers about how deep-sea life functions, and can also show what levels of food inputs are needed to sustain or alter the dynamics of populations. Respiration takes place in humans when air is breathed into the lungs where O2 is taken up by the blood and delivered to individual cells. At the cellular level O2 is then used to help transform food (Glucose - C6H12O6 where the C is carbon and H is hydrogen) and eventually into energy. During that process carbon dioxide (CO2) and water (H2O) are released. The CO2 is then taken up by the blood delivered to the lungs and exhaled.
Basic aerobic respiration: C6H12O6 + 6 O2 = 6 CO2 + 6 H2O
During our investigations we’re making respiration measurements of a sea cumber in the genus Peniagone (see picture, see also 8 July 2009: Sea cucumbers- animal, vegetable or mineral?). These Peniagone are among the most abundant animals observed in the many photos and video in the Whittard Canyon. You may not have seen one before, but sea cucumbers like these populate the vast expanses of deep-seafloor that make up the majority of Earths surface. Although the organs and circulation fluids are different, they respire in the same basic way as people. By measuring how much O2 they use we can estimate, using the above formula, how much food they use and how much CO2 is produced in the process. The size of the animal and the water temperature are also important factors in respiration. Generally warm water and smaller body sizes are associated with increased respiration. Once size and temperature have been taken into account, the data collected here can be compared with respiration data collected in other oceans.
Left: A Peniagone sea cucumber on the seafloor at ~3,700 m depth (about 2.3 miles deep). Most are about 10 cm in length. This one is moving from left to right feeding on marine snow on the sediment.
Also important is the abundance and respiration of smaller fauna. These animals are counted using samples of the muddy seafloor from cores (see 9 July 2009: A muddy story...) and their respiration is measured using systems that enclose a small area of seabed and measure changes in oxygen (see 23 June 2009: Measuring the respiration of deep-ocean life).
The carbon-rich food supply for these animals either sinks from the sunlit surface waters above, or is transported down the canyon axis in virtual underwater rivers. While it may initially seem bizarre to measure a sea cucumbers ‘breath’, understanding how food is used has important connections to understanding how much carbon the ocean can absorb during climate change. CO2, a key greenhouse gas, can be transferred from the atmosphere into the ocean, incorporated into marine phytoplankton, and subsequently sink to the seafloor two miles below all within a matter of weeks to months. Seafloor animals influence the carbon budget mainly by eating and respiring the sinking food supply. Their movements on the seafloor also mix part of the food supply into the sediments where it’s effectively removed from oceanic circulation for millions of years. So researching these animals, which are so far from normal human experience, helps us understand the fate of greenhouse gas, something we produce every day.
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