It deals with all forms of life in the oceans, from viruses so small they can be seen only with the most powerful electron microscopes to whales, the largest living animals. Living things are found in all parts of the ocean, from the shores where waves splash onto the land to the deepest points of the ocean floor. Because people have always been able to visit the seashore at low tide and observe marine life, studies of marine biology began in shallow-water regions. Early marine biologists studied plants and animals from deep waters by using nets and other devices to collect samples. The development of scuba diving equipment has enabled biologists to observe marine organisms in their natural habitats, especially in the clear tropical waters along coral reefs.
Scientists also can visit the deepest parts of the ocean in special underwater craft.
Marine biologists who usually study life in deepwater regions are called biological oceanographers. What marine biologists do. Marine biologists describe and classify marine organisms. They try to determine how these organisms develop, how they obtain food, how they reproduce, how they interact with other organisms, and why particular groups of organisms live in different regions of the ocean. The work of marine biologists becomes increasingly important as people use more and more of the ocean's resources for food and recreation.