When carbon dioxide reacts with water it produces carbonic acid that lowers the water's pH. The ocean absorbs enormous amounts of carbon dioxide from the atmosphere, put there by the many combustion reactions that power daily life on Earth. As a result, the world's oceans have begun to acidify just enough to cause some damage to marine life. Many marine organisms count on calcium to build their internal or external skeletons and the presence of carbonic acid interferes with this process. Phytoplankton, microscopic organisms that are the basis of most marine food chains, depend on calcification to build exoskeletons to protect them from their natural predators. If they are unable to accomplish this, the entire complex food web of the ocean will be disrupted.
Salinity is a measure of the salt content in ocean water. Sodium and chlorine, the components of salt, account for approximately 85 percent of the things dissolved in the oceans. The average salinity of ocean water is 35 parts per 1,000. Salinity is what gives ocean water its salty taste. Salt also affects the types of plants and animals that live in a particular habitat; it also prevents the oceans from freezing. Weather, currents, changing of the seasons, climate of an an area and location in the ocean can all fluctuate salinity. Animals and plants living in the ocean have adapted to be salt tolerant. Less tolerant or intolerant organisms will live in outlying areas such as at the mouth of rivers emptying into the ocean or along the shoreline.
Sunlight will penetrate the ocean to a depth of approximately 200 meters (65 feet). Approximately 90 percent of all marine life inhabits this part of the ocean. Photosynthetic organisms such as phytoplankton and algae require sunlight to complete energy synthesis and are essential to the survival of many other organisms. Animals and plants that live in the depths of the ocean are adapted to survive in the dark and thrive in cooler temperatures. However, they still benefit from the light absorbing photosynthetic organisms in the upper layers of water.