Scientists have believed for many years that less oxygen is dissolved in deeper layers of the ocean compared to shallower layers. what experimental method would best test this hypothesis, and why? send a robot to measure how much oxygen is dissolved in ocean water at various depths, because the amount of oxygen dissolved in water changes with pressure add oxygen into a sample of ocean water and measure the percentage of oxygen that stays dissolved, because this allows you to control how much oxygen is added capture fish from various ocean depths and measure how much oxygen is found in their tissues, because this most directly measures the oxygen available to living systems grow photosynthetic plants at various ocean depths and determine how much oxygen those plants, produce, because all oceanic oxygen has to come from plants