Lecture 9 - Mangroves

Question 1

What are mangroves?

Answer 1

Coastal communities, tropical equivalent of salt marshes, sheltered habitats sediment accumulation, found on 60-75% of tropical coastline

Question 2

What are the six conditions needed from mangrove growth

Answer 2

> water needs to be shallow (intertidal)
Sedimentation deposition occurs (low energy)
Adequate light (photosynthesis)
Water temperature >5oC
Air temp high
High rainfall, controls salinity

Question 3

Explain the type of biota in mangroves

Answer 3

Mangrove trees are exposed to tidal emersion and partial immersion, due to the specialised habitat associated life has a low diversity, not totally marine some organisms are terrestrial. Water column and sediments are truly marine

Question 4

Explain zonation on the mangrove shore

Answer 4

Zonation is a function of tollerance to tidal regime, salinity, anoxic sediments, stability and the main adaptions and roots are mechanisms of salt loss goes from (sea to shore) 
Red magrove
black mangrove
white mangrove
buttonwood

Question 5

How can zonation vary from location to location

Answer 5

Its though to be due to environmental conditions such as tide (macrotidal they can be dench) and other factors such as rainfall etc

Question 6

Explain the four factors of the tidal regime

Answer 6

> Landward areas dry out resulting in desiccation and high salinity
Tidal flushing washes away salt crystals and hydrates the sediment, less effective inshore
tidal immersion also provides suspending nutrients
anoxic sediments release sulphides, removed by tide

Question 7

Explain how anoxic sediments form in mangroves

Answer 7

Colonisation by plants stabilise sediment, immersion by tide limits O2 exchange, high detrital input from plants leads to high bacterial mineralisation rates, which leads to anoxic sediment

Question 8

what are the four root forms mangroves have to deal with anoxic sediments

Answer 8

> Pneumatophores
Prop roots
Kneed roots
Plank roots

Question 9

Pnuematophores explantation

Answer 9

-ve geotropic, roots grow up to 3m in length and go under the substrate and emery protruding out vertically, can take oxygen out of the air

Question 10

Prop roots explanation

Answer 10

These hold the tree base out of the sediment and therefore can be emmersed allowing for oxygen absorption

Question 11

What are Lenticles

Answer 11

Pores which allow gas exchange but not water and solutes enable oxygen to be transported through channels in the Aerenchyma tissues (found in both prop and pneumatophores)

Question 12

Knned roots explanation

Answer 12

Look like little knees coming out of the sand, no lenticles

Question 13

Plank roots explanation

Answer 13

minimise amount of tree under the ground like the ones you see in the rainforest, no leticles

Question 14

What are the tree mangrove adaptations to saline environment

Answer 14

> Salt secretions
root membranes
Non-salt secretions

Question 15

Explanation of salt secretions

Answer 15

Salt is taken in by the plant roots and is transported to the leaves in the sap, the sap is normally at 1/10th of the water column, sap is then excreted through glands in the leaves

Question 16

Root membranes as an adaption again saline environments

Answer 16

Semi-permeable membrane excludes most salt ions, limiting uptake

Question 17

Explanation of non secretors

Answer 17

Complex ultra-filtration system that is not fully understood in the following order in the root system (radial filtration)

a. Na+ / K+ ions pumps in the xylem (active transport)
b. Na+ / K+ ion pumps in the leaves (active transport)
c. Salt is stored in ion saturated cells, sealed of by suberin coating
d. These cells are lost when leaves are shed and are pushed back down by plant growth

Question 18

Mangrove reproduction stages (3)

Answer 18

1. Viviparous seeds (germinate before detachment) develop onto the parent plant - vivipary
2. Embryo grows out through the seed coat and fruit wall - Cryptovivipary
3. Embryo only grows out through the seed coast and not the fruit wall before it splits open

Question 19

what occurs after germination of the vivipary

Answer 19

Seed drops out of fruit and is already ready to grow in a suitable habitat, it is either washed away of falls straight into the mud - has competition with parent plant in that case

Question 20

Explain mangal fauna

Answer 20

Similar to other soft shore sediment communities in types of organisms, i.e molluscs, decapods etc..

Question 21

What are the five key types of mangal fauna

Answer 21

Molluscs
Crustaceans (decapods and cirrpidiia) 
Chelicerates (spiders and horseshoe crabs)
Fish
Birds

Question 22

What are the human uses of mangrove swamps?

Answer 22

Timber, paper, cattle fodder, tobacco substitute, wine etc…