Is the study of all aspects of the biology of the oceans particularly in the context of their physical and chemical environments, so that it overlaps with marine biology in many respects. The range of living organisms extends from the smallest living things, like viruses and bacteria, to the largest animal ever to have lived on earth, the blue whale (Balaenoptera musculus). This vast size range also reflects a wide range of life cycles—a bacterium's lifetime may be just a few hours during which it experiences the conditions in just a few millilitres of water, whereas a whale, which may live 50 years, will have repeatedly migrated halfway round the world. Techniques used to study bacteria and whales are totally different, yet the aim is to blend information for all organisms into an overall conceptual understanding of life in the oceans.
Life occurs at all depths, and there is 180 times more living space in the oceans than in terrestrial habitats. On land one can stand on a hilltop and survey the landscape, whereas oceans are remote, out of sight, and difficult to study. The classical questions investigated by biologists are: what species live where and when? How big are the populations? How are these species organized into communities? What are the dynamics of these populations and how do they cope with their environment's challenges? How are they responding to mankind's activities? Such questions cannot be studied in isolation from the other disciplines in oceanography. Biological processes not only respond to physical and chemical processes but also play a central role in many biogeochemical cycles, especially the fate of pollutants and the dynamics of the carbon cycle (see environmental issues). It is important to understand how marine communities are responding to fluctuations in ocean climate, how changes in the morphology of ocean basins have been reflected in the zoogeographical distribution of species today, and what the micro-fossils in ocean sediments can tell us about the climate changes of past eras.
Whether a study focuses on a single species, like a whale or a species of fish, or takes the broader approach of focusing on communities and how they change throughout the year, the organisms need to be sampled and quantified. Sampling the tiniest organisms (viruses, bacteria, and marine plants like phytoplankton) involves collecting samples of water and filtering them. The extracts are either examined by microscopy or plated out to grow cultures. The volume of water processed may be less than a litre, so studies of these micro-organisms are akin to studying the whole of the Sahara Desert by examining a few grains of sand. Living cells have to be distinguished from the abundant inanimate particles and aggregates if they are to be counted. The surfaces of bacteria suspended in the water are highly active chemically. The total surface area of bacteria, suspended in the water or attached to particles, greatly exceeds that of the inanimate particles, so bacteria play a major role in many aspects of water chemistry.
The tiniest animals, protozoans and their relatives, are equally hard to sample, identify, and quantify, and yet their activities are the key to understanding how the sun's energy fixed by the phytoplankton gets passed through to all parts of the oceanic ecosystem. Plankton is sampled with various types of nets. Small fine-meshed nets are used to catch animals about a millimetre in length, and much larger coarser-meshed nets to catch the faster-swimming Crustacea like shrimps, and small fishes a few centimetres long. Larger animals can swim faster and so can dodge slowly towed nets. Even so, many of the abundant species are gelatinous and fragile, and when caught disintegrate and so are essentially ‘invisible’ to us. They have to be collected individually by underwater vehicles or photographed in situ. In contrast, the larger animals, game fishes like tuna and marlin, sharks and whales, are too large and too fast to be caught in conventional nets.
Subjects: Maritime History.