Many ocean animals cannot tolerate the low salinity of inshore waters and so many of the animals and plants found on Gray's Reef are different from the ones found nearer the Georgia coast. The amount of oxygen dissolved in sea water is another factor that determines where particular marine organisms can live. Animals, plants, and bacteria all use up oxygen in their respiration. The oxygen in sea water comes from photosynthesis by marine plants and from the mixing of air and water at the surface of the sea. There is usually more oxygen in the water in winter since more oxygen will dissolve in cold water than in warm water.
Respiration is also at a lower level in the winter.
Oxygen levels are high enough for animals life in most parts of the ocean. However, a few places, particularly shallow waters polluted by sewage and with little tidal movement, are anaerobic, areas without oxygen where only a few species of bacteria can survive. The waters at Gray's Reef are well oxygenated. Oxygen is not a limiting factor for the organisms of the Reef. Put several water samples of different temperatures in beakers.