Marine biologists study the whole area of marine, or sea, life including plants and animals that inhabit the oceans. Their studies include the interaction between the plants and animals and the ocean life environment. Any animal that depends upon saltwater for life is studied by marine biologists. The animals range from the large mammals, like whales, to the smallest animals in the oceans.
Three distinctive types of mammals live their lives in a marine environment. Marine biologists study all three types, but usually specialize in one particular mammal. The first classification, called cetacea, spend their entire lives in the ocean. They include whales, dolphins and porpoises. Another group, pinnipedia, include seals, sea lions and walruses that spend part of their lives in the ocean and part on land. The final classification, sirenia, includes manatees who spend their entire lives in water and are the only herbivores.
Marine biologists have over 16,000 species of fish available for study, according to the University of Georgia. For example, the study of sharks focuses on the primitive nature of the animal. It lacks a swim bladder and its body is composed of cartilage instead of bone. The shark must swim at all times to stay afloat. Its predatory habits provide ample opportunities for study. Among other fish their habitats and range offer interesting topics of study.
Crustaceans include crabs, lobsters and shrimp. These sea creatures are arthropods who are related to spiders and insects. Crustaceans have a hard exoskeleton and range in size from tiny shrimp to large lobsters. Marine biologists study this group of animals due to their importance as a source of food for humans and also to learn what environmental forces impact their survival.
This category covers a wide range of animals including molluscs. Molluscs include such creatures as clams, mussels, oysters, octopi and squids. The giant squid, which inhabits deep ocean areas, is the largest of the group with a reported length of up to 90 feet. Other invertebrates include primitive animals like sponges, anemones, corals and jellyfish. A marine biologist can choose to become an expert on jellyfish: their physical makeup, areas of concentration, dangers to humans and issues surrounding their long-term viability.