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This feature on oceans was transferred to the Cool Planet website from On the Line. Much of the information here relates to the time when the millennium dawned.
Life began in the oceans. Covering two-thirds of the Earth’s surface, the oceans in the twenty first century remain crucial for our survival; for regulating climate, providing us with resources like fish and minerals, and potentially offering us cures for disease.
The oceans are home to half the world’s biodiversity, and new species are being found almost daily. In fact, we know more about the moon than we do about the deep ocean. Marine life has adapted to exploit every niche, from the poles to the tropics, and from estuaries to the deep ocean.
We take a look at the oceans and seas along the meridian, their importance to man, the diversity of wildlife that inhabit these waters, and some important conservation issues.
Oceans on the Line
The meridian line cuts through the Arctic, North and Mediterranean Seas in the northern hemisphere, and the South Atlantic Ocean and Southern Ocean, in the southern hemisphere.
The Mediterranean Sea is an enclosed sea, covering 2,500,000 km2 with an average depth of 1,500m. The Sea is connected to the world’s oceans at its western end by the Straits of Gibraltar. The coastline extends 46,000km and runs through 22 countries.
The Mediterranean Sea represents only 1% of the world’s marine cover yet it contains approximately 6% of its marine species. Some of the world’s most endangered species, such as the monk seal, can be found in the Mediterranean. Fish stocks are down to 20% of natural levels in some areas, and the region is now a net importer of fish.
The Mediterranean Action Plan was established by the bordering countries in 1975, which in turn led to the development of a number of specific conventions notably the Barcelona Convention in 1976. Further action, however, is still necessary to provide protection for wildlife and to reverse destructive trends.
The Atlantic Basin stretches between the continents of Europe, Africa and the Americas. Few of the mineral deposits of the Atlantic are commercially viable, an exception being oil and gas reserves in the North Sea. In addition, massive exploitation of oil and gas reserves take place in both the marine and terrestrial region of West Africa - 150 million tonnes compared with 44 million tonnes in the North Sea. Further, some of the finest diamonds in the world are extracted from the coast of South West Africa.
The North Atlantic is the world’s most heavily fished ocean area, and many fish stocks suffer from over-fishing. In the North-East Atlantic, for example, 40 out of 60 commercial fish species are being fished unsustainably due to fisheries mismanagment. In the southern hemisphere, rich fisheries, comprising shrimp, lobster, sardine, anchovy and tuna occur along the West African coast as a result of the upwelling of cold, nutrient-rich water in the region.
The Southern Ocean encircles the Antarctic continent. This polar sea is incredibly productive during the short Antarctic summer. The drifting plankton (tiny plant and animals) support squid, fish, seals, whales and birds such as albatross and penguin. Lack of ownership or international agreement concerning the exploitation of resources in this area was one reason for the dramatic declines in wildlife resources over the course of the twentieth century. International treaties now aim to regulate the use of living and mineral resources.
The oceans along the meridian line are home to a diversity of habitats and wildlife. Inshore habits like estuaries, mudflats and mangroves offer feeding and roosting areas for birds, and provide sheltered nursery areas for fish and shellfish. Offshore, fish species like tuna, toothfish and sharks, and birds like albatross and petrels patrol the vast oceanic expanses.
Phytoplanton (the marine equivalent of terrestrial grasslands), seaweeds and seagrasses form the base of the food web. In the Southern Oceans the stark seasonality provides a bounty of plant and animal plankton. The estimated production of phytoplankton in the surface waters of the Southern Ocean is 610 million tonnes a year. Zooplankton (the marine equivalent of insects) feed on the phytoplankton and support abundant schools of squid, fish, and consequently a variety of larger marine creatures like seals, seabirds and whales. Half the zooplankton in the Southern Ocean are krill, a shrimp-like animal. Several species of filter feeding whale like humpbacks feed directly on krill. In 1994 the Southern Ocean was declared a sanctuary for the great whales.
A number of human impacts threaten the wellbeing of the oceans and marine life:
Pollution: Litter, sewage, run-off of nutrients from agriculture and mariculture practices, and oil resulting from extraction processes and shipping incidents pose a threat to marine wildlife. In addition, persistent toxic chemicals from industrial processes can accumulate in wildlife. In particular, top predators are at risk as many of theses chemicals are known to increase, or bioaccumulate, up the foodchain.
Fisheries: Over-exploitation of fish stocks has left many of the world’s fisheries severely depleted. In particular, the demise of inshore fisheries has led to declines in coastal fishing communities.
Further, fishing activities result in the death of thousands of marine animals. For example dolphins and turtles caught in nets, and birds, such as albatross, caught on long lines of baited hooks.
Climate change: A number of impacts are likely to result from climate change, including rising sea levels, increased storminess, changes to oceanic currents, and an increase in sea temperature affecting the types of plants and animals found in a specific region. In particular, changes to plankton species, their abundance and distribution are extremely worrying as they form the fundamental basis of the marine food chain.
Coastal development: Development for industry, aquaculture, ports, coastal defences and tourism can result in losses of important wildlife habitats such as wetlands.
By taking an ecosystem approach i.e. one that considers the importance and interrelationship of oceanic process and wildlife, and the repercussions that a range of human activities have on our oceans, it will be possible to promote the sustainable use of our oceans.
Facts + figures
Did you know that?
1. How much of the eath's surface is covered by oceans?
2. Name the seas the grenwich meridian line runs through.
3. Which is the most fished ocean in the world?
4. What is krill, and why is it important to humpback whales?
5. How many tonnes of phytoplankton (plant plankton) grow in the Southern Ocean every year?
6. Which types of sea creatures are most at risk from pollutants?
7. How many tonnes of fishes are caught by marine fisheries every year? And what other creatures get caught in their nets?
8. What is the deepest place in the ocean?
Oceans quiz answers
1. 71% of the eath's surface is covered by water, over two thirds of the planet's surface.
2. The Greenwich Meridian Line runs through the Arctic Sea, the North Sea, the Mediterrannean sea, the South Atlantic Ocean and the Southern Ocean.
3. The North Atlantic is the world's most heavily fished ocean area.
4. Krill is a shrimp-like zooplankton (animal plankton), and it is important to Humpback whales because they eat it.
5. Around 610 million tonnes of phytoplankton (plant plankton) grow in the Southern Ocean every year.
6. Top predators are most at risk from pollutants because many polluting chemicals bioaccumulate (build up) up the food chain.
7. Around 80 million tonnes of fish are caught every year by marine fisheries. Other creatures at risk from fishing include dolphins and turtles cuaght in nets, and sea birds, such as albatrosses, which get caught on long lines of baited hooks.
8. The deepest known point in the ocean is the Mariana Trench, which reaches depths of over 36,000 feet (11,000 metres).