Marine life appeared in the form of fish, which live exclusively in water. Some of these evolved into amphibians which spend portions of their lives in water and portions on land. Other fish evolved into land mammals and subsequently returned to the ocean as seals, dolphins or whales. Plant forms such as kelp and algae grow in the water and are the basis for some underwater ecosystems. Plankton, and particularly phytoplankton, are key primary producers forming the general foundation of the ocean food chain. Marine invertebrates exhibit a wide range of modifications to survive in poorly oxygenated waters including breathing tubes (see
Marine mammals as food Marine mammals as food Marine mammals are a food source in many countries around the world. Historically, they were hunted by coastal people, and in the case of aboriginal whaling, still are. This sort of subsistence hunting was on a small scale and produced only localised effects. Dolphin drive hunting continues in this vein, from the South Pacific to the North Atlantic. The commercial whaling industry and the maritime fur trade, which had devastating effects on marine mammal populations, did not focus on the animals as food, but for other resources, namely whale oil and seal fur. Today, the consumption