Lecture 8 Flashcards
What is a mangrove forest?
Sheltered, depositional coastal environments e.g. estuaries or inlets, characterised by mangroves
Found in tropical and sub-tropical areas
What is a mangrove?
A woody tree or shrub adapted to saline environments
What are the features of a mangrove environment?
- Low oxygen
- High and variable salinity
- High temperature
What causes mangrove environments to have low oxygen?
There is a large amount of leaf litter from the trees
It is broken down by high densities of fungi and bacteria
This creates a very high oxygen demand
Why is zonation observed in mangrove environments?
Tides create an environmental gradient
Gradient creates zonation of plants, based on their tolerance to immersion
Four key genera of mangrove forests
- Red mangrove (Rhizophora)
- Black mangrove (Avicennia)
- White mangrove (Laguncularia)
- Mangrove apple (Sonneratia)
What is the zonation of the different mangrove genera in Florida?
White mangrove found furthest from the sea
Black mangrove intermediate
Red mangroves more tolerant to brackish water so closest to sea
Adaptations of plants to cope with low oxygen
- Pneumatophores: upward growing extensions of the roots that help aerate the tissue
- Lenticels: pored in bark and/or pneumatophores
- Prop roots: help support the plant, but may also be covered in lenticels to obtain more oxygen
Plant root adaptations to cope with high salinity
- Some mangroves develop greater amounts of root biomass to increase water uptake
- Roots are also adapted to prevent excessive salt intrusion - operating an ultra-filtration mechanism to exclude salt
Plant leaf adaptations to cope with high salinity
- Salt secretion glands in leaves to secrete excess salt
- Xylocarpus moluccensis is deciduous and drops all leaves at one
- Waxy cuticle can reduce transpiration loss
- Leaves can orientate themselves to reduce evaporation
- Stomata can remain closed during the heat of the day
How do plants combat the issue of seed germination in high salinity low oxygen environments?
Viviparity: seeds or embryos germinate on the parent plant, and only drop off once the propagules are large enough
What animals are found around mangroves?
Ants Termites Mosquitoes Sponges Oysters Sea anemones Barnacles Crabs
What two major families of crabs are found in mangrove ecosystems?
Grapsidae
Ocypodidae
How does the fiddler crab help mangrove ecosystems?
Keystone species
Bioturbation
It is a detritivore and shovels sediment into its mouth to sift for food
The sediment is formed into a ball called a pseudofaecal pellet and placed at the entrance to the burrow
Helps to aerate then surface increasing bacterial breakdown of organic matter
Fiddler crabs also burrow, preventing the buildup of anoxic substances in the mud. Burrowing allows oxygenated water into the mud, enabling nitrification to occur
Why is the mud lobster important in mangrove ecosystems?
Thalassina sp.
Excavated mud mounds
Brings buried organic material to the surface and helps facilitate succession in mangrove plants
Also an ecosystem engineer
Features of mudskippers
Fin modification
Amphibious
Protruding eyes
Burrow modification to protect themselves from predators and rear young. Also protects from high temperatures
Heavily vascularised to maintain oxygen supply
Able to maintain a pocket of air in burrow even at high tide to breathe
How did the Scarlet Ibis affect mangroves?
Caroni swamp contaminated with Mercury
Adult ibis lives in mangrove but moves to freshwater to rear young as they cannot tolerate salinity
Mercury contamination of freshwater bioaccumulate in young birds
Shed feathers, contaminating the mangrove and damaging the plants
Threats to mangroves
- Boat traffic
- Oil spills
- Pollution (pesticides, heavy metals)
- Sea level rise
What have 1/3 of world’s mangroves been lost to in last 50 years?
Aquaculture and agriculture
Why is it important to protect mangroves?
They have primary production rates equal to those of tropical evergreen forests
Play a key role in human sustainability and livelihoods
Offer protection from tsunamis, cyclones and dampen shoreline erosion (Alongi, 2008)
