Mangroves: their importance and vulnerability Flashcards
What is a mangrove?
Mangroves are inter-tidal habitats along sheltered coastlines of the sub-tropics.
Mangroves are regions of high deposition of riverine sediment giving them high levels of organic matter.
Mangroves are restricted to being near the sea.
Why are mangroves considered a harsh environment?
Mangroves are highly variable environments due to them being inter-tidal. This makes temperature, salinity, sediment, tides and dissolved oxygen vary daily.
Mangroves can get hyper-salinity pools when the tide goes out and the water evaporates.
How do mangroves stay stable in the loose mud?
They have extensive aerial root systems.
What are the main features of a mangrove root?
Main stem
Anchor roots
Modified cable roots
Knee roots
Nutritive roots
What are the main roles and services mangroves provide?
Habitat function
Offshore fisheries
Shoreline protection
Carbon storage
Sediment and nutrient traps
Aquaculture and food
Chemicals and medicines
Forestry and products
What fauna live in the canopy and roots of a mangrove?
Canopy: Birds, insects, spiders, reptiles and mammals.
Roots: Covered by encrusting organisms e.g algae, barnacles, hydroids, bryzoans, sponges, bivalves and tunicates.
What macro and meiofauna live in the mud of a mangrove?
Meiofauna: Flatworms, nematodes, harpacticoid copepods, ciliates, foraminifera, bivalves, oligochaetea, polychaetes, hydrozoa, amphipods, cumaceans
Meiofauna feed on: Bacteria, detritus which are in turn good food for snails, crabs, gastropods, juvenile fish and birds.
What organisms can be found in mangrove sub-tidal water?
Prawns, shrimps, crabs, crocodiles, turtles and fish including juvenile deep water fish.
What are the two main groups of crabs that inhabit mangroves?
2 main groups – grapsy crab and fiddler crabs inhabit mangroves. Both slightly unusual.
Grapsy crab climbs up and down the trees and try collect the newly formed leaves or seeds (propogoules).
Fiddler crabs Live on the intertidal flat, asymmetric claws. Use the massive claw to shovel in mud to filter the food. In some ways they are deposit feeders. The big claw is also for show and defence.
Why do many organisms use mangroves as a nursery?
High primary productivity and organic matter. Low risk of predation due to physical barriers of roots and cloudiness of water.
What are the economic values of the ecosystem services supported by mangroves?
Water quality maintenance (biofilter function):
$5820 per hectare per year.
$1193 per hectar per year.
- 4 amd 21.6 ha of mangroves needed to remove nitrate and phosphorous, respectively, in effluents per ha of intensive shrimp pond.
- 8-5.4 ha of mangroves needed to remove nitrate in effluents per ha of shrimp pond.
Environmental disturbance prevention:
Storms: $4700 per ha
Flood: $3679 per ha
Erosion control: $120 per household
Carbon sink: 155kg C per ha
1500kg C per ha
(source: Walters et al., 2008)
What products have been made using the red mangrove Ryzofera
Wood for building. Ryzofera (red mangrove) is normally cut down due to high levels of tannins which is a toxic material so it’s resistant to rotting. They’ve isolated a chemical which can be used to provide medicine with stomach ulcers.
Mangroves are cut for charcoal for barbeques.
What are the main threats to mangroves?
Cutting and clearing for agriculture/ development. (Last 20 years 35% mangroves have been lost. Losing 2.5% per year. The main threat is being cut down, due to them being in prime building locations.)
Land management, erosion, sediment, and pollution. (Normal amount of sediment laid down is less than 5mm. Due to construction work, the release of sediment from the works covered the pencil roots and caused deaths of many black mangroves.)
Climate change; increasing sea level, storms, increased precipitation, temperature, local hydrology - circulation patterns etc.
Where are the most vulnerable regions of mangrove?
Low-lying areas are most vunerable where rising sea levels are affecting them. Also in areas of low levels of sedimentation so trees aren’t as adaptable if there is a sudden increase in sediment. Or in areas where they can’t retreat. Mangroves near forest, agriculture or building, the mangroves can’t retreat from rising sea levels.
List the main ways to ensure mangrove restoration, use case studies to illustrate your answer.
- Manage and protect (national parks, MPAs)
The protected mangrove forest reserve in Santa Marta, Colombia suffered 70% loss due to altered hydrology (road and dike construction.) - Ecological engineering ‘aided natural regeneration’
- Determine reason for decline.
- Propagule limitation (removal of mangroves or hydrologic restrictions) In general mangroves live on a raised slope, being inundated by tidies for 30% of the time.
- Depth, duration and frequency of flooding do matter.
Case study Florida (Lewis, 2005) - Construction of appropriate slope and tidal creeks. After 7 year the mangrove was restored and no more planting was required.
- Restoration ‘planting’
- Most successful sites are where mangroves have previously existed.
Case study Malaysia (Hashim et al., 2010)
- History of logging, clearing, erosion, mangroves declining 1% per year.
- A constructed detached breakwater deployed to enhance sedimentation.
- Seedlings in coir logs planted (density 10,000 per ha)
- Phase one ~ 6,000 Avicennia propagules planted - phase 2, Bruguiera and Rhizophora to be planted.
- 30% of transplants survived in 8 months which is considered successful.
