Topic 7: Oceans on the Edge 7.1 How and why are some eco-systems threatened with destruction? How are human activities degrading and destroying marine ecosystems on a global scale? Mangrove removal- over half of the world s Mangrove Swamps have been cleared in countries such as Vietnam to make room for prawn farming. Prawn aquaculture in mangrove swamps causes pollution from antibiotics to surrounding fish and sea. They are also cleared to allow coastline for tourist developments; transport is easier and access to the coast is better for tourists without Mangrove swamps. Deforestation- this is the large scale removal of trees. When this happens more soil is washed into the rivers with surface run-off, this increases the amount of silt from rivers going to reefs, which can kill coral. Overfishing- taking too many fish from the sea can destroy food chains and lead to an imbalance causing extinction of species. Fishing in the North Sea has led to the numbers of cod reducing by 90% since 1960. Food Web Imbalance- the Crown of Thorns Starfish is eaten by sea snails; when there are not enough sea snails to eat them they get out of control. Until 2003 sea snails were harvested from the Great Barrier Reef, and sold. Crown of Thorns Starfish eat the coral reefs (they snack on the plant part inside the coral); food web imbalance can lead to coral destruction. Eutrophication- fertilisers used on farms run off into rivers, which then take the nitrates to the sea. Too many vitamins means lots of algae grown, taking oxygen out of the water and leading to the death of fish and crabs. Climate change- with seas becoming warmer this can kill off plankton and lead to a food shortage in the sea. Carbon dioxide is dissolving into sea water leading to the water becoming more acidic; this can kill coral reefs and is known as bleaching as the coral turns white. 95% of the great barrier reef s coral will be lost by 2050 if this carries on.
Pollution and waste disposal from land sources- Pacific Garbage Patches are enormous areas of the Pacific Oceans full of rubbish; with up to one million pieces of floating plastic in a square mile. They are near the USA and Japan and repeatedly circle in the North Pacific Gyre; a circular ocean current. This is a big, thick rubbish soup; and can only be tackled by reducing litter and banning plastic bags which make up half of the garbage patches. Pollution and waste disposal from ocean sources-. Internationally The Law of The Sea is banning ships from rinsing out oil from their tanks with sea water, and single hull oil tankers (which rupture easily causing spills) are now banned after the Prestige spilled oil on the Spanish coast. Tourism- Tourism is leading to the large scale clearance of Mangrove Swamps (see mangrove removal for details). Snorkelling is disturbing marine wildlife and tourist boat trips to coral reefs can damage the reefs if the water is shallow. Tourists can also cause the death of coral if they touch it, and coral is taken as souvenirs; people do not realise it is a living animal. Coastal development- Building on the coast is leading to the large scale clearance of Mangrove Swamps (see mangrove removal for details). Developing coastal areas for agriculture has lead to increased siltation and eutrophication. It has also lead to increased pollution with beach litter and leaks of untreated sewage. The increased carbon emissions in previously undeveloped areas are contributing to coral bleaching.
What is the global pattern of either coral reefs or mangrove swamps, and how it has changed in the past 50 years? The map above shows where coral reefs are found in the world. The amount of coral in the world has fallen by around 50% in the last 50 years due to global warming and a range of human and natural factors. The number of mangrove swamps has halved due to human clearance. Unsustainable use of marine eco-systems leads to the disruption of food webs and nutrient cycles and can lead to extinction. See notes on food web imbalance and overfishing above. Whale and shark populations will never recover to their original sizes due to whale hunting and on-going shark fishing by the Japanese for shark fin soup.
Investigate physical processes in marine eco-systems, including marine food webs and nutrient cycles. How can food webs and nutrient cycles can be disrupted through overfishing, eutrophication and siltation, as well as the impacts of climate change, including bleaching and species migration? The nutrient cycle is the reuse of substances such as nitrogen in an ecosystem. Fish eat the nitrates as part of plants and algae, fish waste products are made into ammonia and nitrates by bacteria and algae reabsorb the nitrates, which the fish then eat. It is a never ending cycle, however less fish leads to algae overgrowth and too many nitrates in the ocean.
Disruption to food webs and the nutrient cycle: Overfishing- disrupts the nutrient cycle as the however less fish leads to algae overgrowth and too many nitrates in the ocean. Overfishing disrupts the food web as there are less big fish, predators (such as sharks) have less food. There are no big fish to eat the medium fish, this means the large number of medium fish eat too many small fish. There is then an overgrowth of bacteria, plankton and algae due to the lack of smaller fish. Eutrophication- leads to an overgrowth of algae and an excess of nitrates in the nutrient cycle. This cannot all be consumed by fish and leads to a nitrate build up, disrupting the nutrient cycle. The excess algae depletes the water of oxygen and disrupts the food web as it causes crabs and shrimp to die. Siltation-run off from land washing soil into rivers and the sea. This buries underwater plants killing sea grasses and sea weed as they can t get light to photosynthesise. This leads to a build up to nitrates (not absorbed due to lack of plants) disrupting the nutrient cycle. It also disrupts the food web as there is no plants for small fish to eat.
7.2 How should eco-systems be managed sustainably? The pressure to use marine eco-systems is growing, due to rising populations and resource demand, creating difficult choices for humans. The world population has gone over 7 billion. We need to use undersea resources, but doing this damages the oceans. The main areas creating pressure are: Overfishing- to feed the world s population more fish than nature can easily replace are being taken from the ocean. This is classified as unsustainable fishing. Eutrophication- fertilisers are needed to make plants grow the feed the world s population, these run off into the sea causing eutrophication. Energy- we need electricity, drilling for oil can lead to oil spills (such as in the gulf of Mexico) and off- shore wind farms destroy fish s breeding grounds when they are built into the sea bed. Drilling for gas also disrupts fish species and habitats on the ocean floor. Global warming an coral bleaching- both of these are being caused by carbon dioxide emissions from burning fossil fuels to meet the world s needs.
What are the pressures on a named marine ecosystem and what conflicts are there about its management? Named Ecosystem: Firth of Clyde Summary: The Firth of Clyde is a 60 km stretch of water along the west coast of Scotland. The Isle of Arran is where Lamlash Bay is located. 20,000 animal and microbe species live there. Tourists are mainly nature lovers; there are seals, harbour porpoises, basking sharks, leatherback turtles and killer whales. Pressures Fishing-Active fishing (ships driving in circles using large nets) have lead to a crash in cod populations. Fishing with nets (bottom trawling) has damaged maerl (a relation to coral that makes up the sea bed). Dredging machinery (chains and rollers) have been used to harvest scallops, destroying the maerl where fish go to have babies. Passive methods of crab and lobster pots and traps are also used on the sea beds. Tourism and Leisure-Locals rely on tourism due to falling farming and fishing incomes. Yachting, snorkelling and kayaking attract tourists but disturb wildlife. Sewage Disposal- Limited sewage disposal facilities in the past meant sewage was released straight into the sea. New laws has led to this stopping. Military testing-the Royal Navy test submarines in the Firth of Clyde, a nuclear accident would wipe out the entire ecosystem. Conflicts COAST (Community of Arran Seabed Trust) established no take zones where there is no fishing and the maerl can recover. They are also promoting the area to tourists to bring an income to the area. Fishermen want to fish everywhere so they can make money, without being able to fish they cannot feed their families. Not all locals want a large amount of tourists in their peaceful area. Tourism could bring problems including road traffic and overcrowding.
Future Conflicts over the Firth of Clyde There are plans to make the Firth of Clyde into a Coastal Marine Park, this is the same status as a National Park and the area would be protected by law against oil drilling and fishing. The area could have oil and gas or be used for a wind farm. With a growing need for energy this could lead to further damage of the area. Sustainable management is needed locally and globally if the oceans are to be protected from further degradation.how are international laws protecting our seas? Locally No take zones in the Firth of Clyde allow fish stocks to replenish and habitats to recover. They prevent fishing in breeding grounds, reducing the risk of baby fish being caught as by catch. Coastal Marine Parks can protect breeding grounds of important species such as dolphins allowing numbers of these species to recover. Sustainable management in the coral triangle (located in the south Pacific) is vital as three quarters of the world s coral species are found there. The governments in this area are locally protecting coral by having marine protected areas where species cannot be caught or harvested, fish quotas and climate change adaption plans.
Globally CITES- This international law makes it illegal to buy or sell endangered species of plants and animal, this included coral and the sturgeon fish (sturgeon fish eggs are used to make caviar). Law of the Sea (UNCLOS)- The international law of the sea has imposed fish quotas (to stop overfishing), banned the washing out of ship s tanks with sea water (as this pollutes the ocean with oil) and has lead to the phasing out of single hulled oil tankers (which leak easily, like the Prestige which caused large scale damage on the Spanish coast in 2002). IWC (International Whaling Convention)- It was made illegal to commercially hunt whales in 1986, this means whales cannot be hunted and sold for profit (although some people break this law). Compare two located case studies of marine management establish the tensions between achieving economic and environmental sustainability. Indonesia and Malaysia (the coral triangle) balance marine protected areas where species cannot be harvested with allowing tourists to visit the reefs to make up for lost fishing income. Fishing is allowed in other areas to meet food and economic needs, the hope is that the no fish zones will aid the replenishment of stocks. The Firth of Clyde (Isle of Arran) has a no fish zone to ensure marine species remain in the area, this will help to attract tourists and make sure the area can make an income. Fishing is allowed in the surrounding seas, by protecting some marine areas (as a marine park) fishermen will have fish to catch in the future. Fish Stocks in the North Sea- Fishing boats are given quotas under the law of the sea which states you shouldn t take more than nature can replace. Random boat searches enforce these quotas. Boats often throw back dead fish if they are over quota.