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
Freshwater drum of the freshwater drum's diet. In August through November, they tend to eat fish (which are primarily young-of-the-year gizzard shad). The percentage of fish in their diet at this time ranges from 52-94 percent. Other items in the drum's diet are mollusks and crayfish. Freshwater drum tend to hang out with walleye. The freshwater drum competes with several organisms. During its early stages in Lake Erie, it has been shown to compete with yellow perch, the trout-perch, and the emerald shiner. During its adult lifetime, it competes with yellow perch and silver chub in deep water, and competes with black