Biological oceanography is the study of life in the ocean, examining living organisms and their complex interactions with the marine environment. This scientific discipline focuses on the distribution, abundance, and processes of marine species, alongside the physical and chemical factors that govern their survival and development. Understanding this field is important because marine organisms regulate climate, cycle elements, and form the foundation of global food security.
Scope and Focus of the Discipline
Biological oceanography operates on vast spatial and temporal scales, investigating everything from microscopic viruses to the largest whales. The central focus is on how marine life influences and is influenced by the surrounding ocean, including temperature, currents, and water chemistry. This approach differs from marine biology, which often concentrates on the localized ecology of a single species or habitat. Biological oceanography instead addresses large-scale questions, such as the total biological production of a region or the role of organisms in the global carbon budget.
Researchers investigate how biological processes affect the planet’s climate, particularly the uptake and storage of carbon dioxide. They seek to understand the mechanisms that control the distribution of marine organisms, looking at why certain species thrive in one ocean region but are absent in another. The field also involves predicting how marine ecosystems will respond to major environmental shifts, such as ocean warming or acidification.
The Biological Components of Study
Biological oceanographers categorize marine life by its functional role and lifestyle in the water column. The smallest and most widespread group is the plankton, organisms unable to swim against ocean currents. This category includes phytoplankton, the primary producers that form the base of the marine food web. It also includes zooplankton, such as copepods and krill, which graze on the phytoplankton and serve as a crucial link to larger animals.
The nekton consists of active swimmers capable of moving independently of currents, including fish, marine mammals, and cephalopods. Nekton are primarily responsible for the vertical and horizontal movement of energy within the ocean through predation and migration. For instance, many schooling fish contribute to nutrient cycling by excreting waste products that dissolve and become available to surface-dwelling phytoplankton.
The benthos includes all organisms living on or in the seafloor, ranging from shallow coastal invertebrates to deep-sea microorganisms. Deep-sea benthic communities are often dependent on the slow rain of organic matter from the surface, known as marine snow, for their sustenance. Organisms that burrow or mix sediments, a process called bioturbation, play a part in nutrient exchange between the seafloor and the overlying water. In unique environments like hydrothermal vents, specialized benthos communities rely on chemosynthesis, deriving energy from chemical compounds rather than sunlight.
Fundamental Processes of Marine Ecosystems
A core area of study is Primary Production, the process by which organisms convert dissolved inorganic carbon into organic matter. This occurs mainly through photosynthesis by phytoplankton in the sunlit surface layer, or euphotic zone, forming the energetic foundation for nearly all marine life. The organic carbon produced at the surface is then transferred downward through the water column via the biological pump. This process involves organisms sinking after death and the production of dense fecal pellets by zooplankton.
The efficiency of energy transfer between feeding levels, known as trophic efficiency, determines the productivity of higher trophic levels, such as commercial fish stocks. In marine ecosystems, an estimated 7% to 17% of the energy from one trophic level is successfully passed up to the next. Regions with simpler food webs tend to have higher trophic efficiency than complex, open-ocean systems. The number of steps in the food chain therefore directly limits the total biomass available for top predators.
Organisms also drive Biogeochemical Cycles, recycling elements necessary for life. The nitrogen cycle, for example, is mediated by specialized bacteria and archaea that convert inert nitrogen gas into bioavailable forms through nitrogen fixation. Other elements, like phosphorus and silicon, are also cycled by marine life; diatoms, for instance, require silica to build their glassy shells. The cycling of these nutrients regulates the growth of phytoplankton and controls the overall productivity of the ocean.
The Intersection with Other Oceanographic Fields
Biological oceanography exists at the intersection of the other main oceanographic disciplines, as marine life is inseparable from its environment. Physical Oceanography provides the context for biological activity, as water movement directly controls nutrient availability. For example, wind-driven upwelling brings cold, nutrient-rich water from the deep ocean to the surface, fueling massive phytoplankton blooms. Ocean currents also act as highways for the dispersal of plankton and the migration of larger animals.
The link with Chemical Oceanography is clear, as the availability of dissolved elements dictates where life can flourish. The concentration of essential nutrients, such as nitrogen and phosphorus, or dissolved gases, limits the growth and distribution of marine organisms. The organisms, in turn, affect the chemistry by drawing down surface carbon dioxide and producing oxygen through photosynthesis.
Geological Oceanography contributes to the understanding of benthic communities, as the composition of the seafloor dictates the types of organisms that can live there. Sediment grain size and organic content influence the structure of soft-sediment communities. Rocky substrates allow for the establishment of deep-sea corals and sponges.