threats to mangroves

Threats to Mangroves

A2 Geography

Learning Objectives

• Understand the nature and extent of mangrove loss

• What are the drivers of change• Understand the problems associated with

Human activity within Mangroves, including exploitation

• Appreciate the consequences of climate change on Mangrove forests

Mangrove Loss

• Over 50% of the world’s original mangroves have now been lost

• A size similar to 13 UK’s• By 2007 less 15 million left hectares left• Currently the rate of loss is 1% p.a. (Roughly

the size of London)

Rates of Loss

• Thailand has lost over half of its mangroves since 1961

• The Philippines 40% were lost to aquaculture between 1918 and 1988

• By 1993 123,000 hectares were left (70% loss in 70yrs)

• Ecuador – Mangrove loss is estimated to range between 20% to 50% of the 362,000 hectares of mangrove forested coast.

Why?

• Think in groups why this might happen and write them down on the post it notes provided

• Think why do we deem this a palatable thing to do.

• Asia has lost 50% due to aquaculture (38% Shrimp. 14% fish) 25% due to deforestation. 11% to upstream freshwater diversion.

• Latin America – Mainly due to the expansion of agriculture and cattle rearing, as well as the cutting of fuelwood and building materials as well as the establishment of a shrimping industry.

Drivers of Change

• What are the main threats to biodiversity:• Habitat change• Climate change• Invasive species• Over-exploitation• Pollution

Coastal Wetlands

Habitat change

Climate change

Invasive Species

Over-Exploitation

Pollution (N, P)

SHRIMP FARMING IN THAILAND Case Study (LEDC)

Shrimping• Been done in Thailand for over 60

years• Traditional method now known as

‘Extensive production’ Shrimp (Known as ‘fry’) are trapped in salt beds and padi-fields around estuaries and harvested when mature.

• Between 1970 -1990 the coastal shrimp industry expanded massively

• With help from the govt the shrimping industry became more intensive

Why

• To help meet global demand• Exported to USA (500,000 tonnes a year – 2003)• Japan = 250,000 tonnes• France, Spain, UK and Italy = 500,000 tonnes• Since 1990’s amount consumed in Thailand has

also increased – rising incomes due to improved economic conditions

• Increase in tourist industry.

Production

Land Conversion

Shrimp farming area and Mangrove area

Impacts of the Industry

• What are the positive impacts of the industry?

• Shrimp farming has had positive impacts such as increased wealth leading to improved infrastructure and reduction in migration to Bangkok many are negative

Negatives

• Effluent from shrimp farms has to be removed before next crop cycle begins

• It is full of decaying food, shells and chemicals (Antibiotics)

• If chemicals get discharged into mangroves this can have a harmful effect on biodiversity

• Conflicts arise due to this discharge• Constant threat of disease and infection• Rice fields and channels suffer from salinisation• Depletion of biodiversity in shrimp farms and

surround areas• Loss of mangrove forest or fertile land • Degradation of the soil due to salinisation • Deterioration of water quality

Future?

• Marine shrimp culture along the coast is one of the main economic activities in the country

• It provides employment and earns national income• Without management the environment maybe

damaged beyond repair• Governments should promote the development of

marine shrimp culture along the coast but before implementation, a development plan should be formulated and good management practices should be specified

Department of Fisheries, Bangkok advice on Shrimp farming

• A land use plan should be formulated which does not allow the utilisation of mangrove for shrimp culture. The most suitable area for shrimp farming is rice fields or unused low land beyond the mangrove. The level of such land will be not over 1–2 m above the high tide level.

• To provide infrastructure which supports the shrimp culture industry such as drainage canals, roads, electricity and other necessary services.

• Control and enforcement of farm practices will be done by the official agency.• To provide education on farm and water management to farm owners and farm

operators before they start farming.• Monitoring of sea water quality along the coast will be routinely conducted and

information on water quality transferred to the farmers.• Shrimp pond wastes will not be discharged directly into natural water ways. The

waste treatment pond will be attached to the farm system and waste must be treated before discharge.

• Research on farm management, disease and parasite problems must be conducted and findings regularly transferred to the farmers

CLIMATE CHANGEThreats to Mangroves

Links to AS

• I in 10 people live less than 10m above sea level near the coast

• Asia contains 75% of these people• Global warming leads to:• Increased Arctic ice cap melt• Greenpeace predict sea levels to rise between

15 – 95cm this century• This could cause some shorelines to retreat by

upto 200m

Carbon Sequestration

• Mangroves take up about 1.5million tonnes/hectare/year

• Current removal means we are losing 220,000 tonnes of sequestration potential

• High levels of carbon in the soils is dug up and also released

• Removal of mangroves means carbon release is often 50 times higher than rate of sequestration

• By converting 2% of mangroves it effectively means all advantages of sequestration are lost

Mangrove time bomb

Mangrove Destruction

Loss of Carbon

Sequestration

Increase in Greenhouse

gases

Increased Global

warming

Rising Sea Levels

Mangrove Benefits

• Healthy mangroves can act as a buffer zone between the coastal fringes and inland areas

• Increases are expected in hurricanes and cyclones and the mangrove can help protect land

• Protect against coastal erosion

However

• Rising seas levels will swamp the forests nullifying their benefit

• Mangroves need a buffer zone themselves to develop and re-establish above the rising low tide – this too maybe lost

Over- Harvesting

• Mangrove trees serve many purposes• Fuelwood• Construction material• Wood Chip and pulp production• Charcoal• Animal fodder• Harvesting has been going on for centuries but

it is no longer sustainable

Over Exploitation of Marine Life

• Unregulated fishing is depleting fish stocks• As stocks of one become uneconomic to

exploit people are simply turning to another• Decline in biodiversity, loss of income and jobs• Over fishing alters the food chain and webs

and mangroves communities can be altered as a result

Other Threats

• Tourism

Removal for golf courses

Building of new cruise ship ports

Marinas

Hotels, apartments and restaurants

• Oil Exploration

Deforestation

Changes in Soil pH

Discharge of solids and liquid waste

Other Threats

• Domestic and Industrial waste• Waste from aquaculture• Exploration of minerals

Learning Objectives

Understand the nature and extent of mangrove loss

What are the drivers of changeUnderstand the problems associated with

Human activity within Mangroves, including exploitation

Appreciate the consequences of climate change on Mangrove forests

Homework

• Write a 500 word report• Within which you must report

on the threats to biodiversity in mangroves

• How far these are likely to change

• Whether these threats reflect people’s attitudes to mangroves and biodiversity

Links

• Shrimp Culture in Thailand • The Rise and Fall of the Blue Revolution• The Impact of International fish trade on Food

security in Thailand• Manu Potaros

, Department of Fisheries, Bangkok