Ocean Ecosystems


Open ocean habitats exist beyond the reef where water depth is 100m or more.  Open ocean habitats may vary according to oceanographic factors such as currents, water temperature, and light transmission. The open ocean is home to the largest and fastest marine creatures. Some of the animals that are found in the open ocean are large pelagic fish such as marlins, sharks, turtles, dolphins and whales. The open ocean plays an important role in renewing the water in the lagoon and along coasts during high tides, providing water that is clean, cool and rich in oxygen. Ocean currents transport, nutrients, plankton and coral and fish larvae thereby linking marine ecosystems.


The open ocean hosts only about 10 percent of all marine species but is home to some of the fastest and largest marine animals, those that can dive the deepest and can migrate the furthest. The open ocean is relatively unproductive: organic debris produced in the epipelagic zone located between the surface and 200 meters depth tend to sink to the seafloor, limiting therefore the amount of nutrients available for photosynthesis. Nevertheless, because of its vastness, it has more overall primary production than any other marine habitat. Furthermore, some areas of the worlds’ oceans have upwellings, where deep water currents rise bringing nutrients from the depths and making some of the most biologically productive areas in the world. The open ocean is home to the majority of the world’s marine mammals, as well as large pelagic fish such as billfishes, tunas, jellyfishes, sharks, and many other groups.


Ecosystem benefits

The open ocean is vital to keeping the lagoon and coral reef healthy, by providing water that is clean, cool and rich in oxygen during incoming tides. It plays a crucial role in the water cycle, with vast amounts of water evaporating from the ocean to create clouds and rain. It is estimated that the microscopic phytoplankton that live in the ocean waters and photosynthesise, are responsible for at least 50% of the oxygen found in the atmosphere. Ocean waters also absorb and dissolve vast amounts of carbon dioxide (CO2), produced over the last two hundred years and absorbs the heat from the sun. The open ocean thus plays a vital role in regulating climate and attenuating the effects of increased levels of greenhouse gases in the atmosphere. 


Threats and management

Pollution, shipping, overfishing and destructive fishing practices, climate change and lack of protection are some of the most pressing issues affecting the health of ocean systems. The Accumulation of waste in some oceans of the world is equal to the size of countries and continents. Managing the inflow of waste from land to the ocean is the first step in preventing this problem. Global warming is altering ocean chemistry and many oceanic processes, and it is affecting and threatening many marine animals that cannot cope with higher water temperatures and acidic waters. In many parts of the world overfishing is a major problem that is depleting fish stocks and threatening the survival of many marine species. Many countries have created marine protected areas, but more and larger areas need to be conserved to protect the biodiversity of the oceans.