L8 Mangroves

Question 1

3 facts about mangrove ecosystems

Answer 1

1. Plants colonise which are tolerant to saline conditions, unusual of large plants to adapt to harsh conditions.
2. Less productive than salt marshes or seagrass beds.
3. Leaves contain tannins, toxins and are unpalatable.

Question 2

Why are mangroves often anoxic environments?

Answer 2

Large amount of leaf litter from trees, difficult to decompose. Done by fungi and bacteria causes massive O2 demand and rapidly becomes anoxic

Question 3

What abiotic factors make thriving in mangroves difficult?

Answer 3

High temperature, High and variable salinity, low O2.

Life may be less abundant than in other muddy environments. (bacteria are abundant).

Question 4

How is some research in mangroves carried out?

Answer 4

Use electrochemical sensors on fragile electrodes inserted into mud to see microprofiles of dissolved O2, H2S, pH, salinity to see changes in upper layer of sediment. Micromanipulator to insert into mud bu increments of 0.1mm.

Question 5

What causes zonation in mangrove plants

Answer 5

tolerance to immersion

tides

Question 6

4 key genera

Answer 6

Red mangrove - Rhizophora
Black mangrove - Aucennia
White mangrove - Laguncularia
Mangrove apple - Sonneratia

Question 7

Describe some variation in patterns of mangrove zonation

Answer 7

Florida - White and black above red
Malaya - Red above black
E.Africa - Black > red> apple
Indo west pacific has most extensive mangrove forests!

Question 8

What are 2 adaptations to low O2 which mangroves show?

Answer 8

Pneumatophores - Tall tree can have 1-10,000. Upward growing extensions of roots to help aerate tissue, poke out of mud/water surface. Covered in lenticels(pores in bark)
Prop roots - also covered in lenticels, help support plant.

Question 9

2 examples of extensive roots

Answer 9

Kneed roots of Bruguiera cylindrica

Plank roots of Xylocarpus granatum

Question 10

What are some mechanisms to cope with high salinity?

Answer 10

Sometimes greater biomass in roots developed in high salinity to increase water uptake
Adapted to prevent excessive salt intrusion. Ultra filtration mechanism to exclude salt.
Roots also use reverse osmosis.
Salt secretion glands on leaves to secrete excess salt.

Question 11

3 ways to reduce transpiration losses in mangroves.

Answer 11

Waxy cuticle
Stomata remain closed most of the day
Leaves can orientate themselves to reduce transpiration.

Question 12

How is reproduction of mangroves adapted?

Answer 12

Seed germination is a problem in high salinity and low O2, so capable of viviparity. Embryos germinate on parent plant and drop off once the propagules are large enough.

Question 13

For those species with seeds, what are 2 adaptations for dispersal?

Answer 13

Cannon ball mangrove - fruit ~20cm diameter, contain up to 18 seeds. Fruit explodes and disperses seeds into the sea.
Looking glass mangrove - Prominent ridge on seed acts as a sail to aid dispersion

Question 14

4 groups of mangrove fauna

Answer 14

1. truly arborial - insects, tree snakes, iguanas
2. animals positioned between surface and hard bottom - sponges,oysters, anemones, sea squirts, barnacles
3. Animals under the mud - uca (fiddler crab), gobies
4. Marine fauna which visits at high tide

Question 15

What 2 families of crabs are common in mangroves and why are they important?

Answer 15

Grapsidae, Ocypodidae
Cause bioturbation by working surface sediments furiously all the time - take leaves and place in burrows. recycling nutrients within the mangrove - without breakdown of leaves there is no nitrification :(
Increases heterogeneity.

Question 16

How are fiddler crabs (uca) ecosystem engineers? 2 ways

Answer 16

Detritivore, sifts sediment for food and shovels into mouth. Produces pseudofaecal pellets, sediment formed into ball and placed at burrow entrance. Helps aerate surface to help breakdown of organic matter by microbes.

Burrows prevent accumulation of anoxic substances in mud by having oxygenated water flowing through. Allows nitrification and nutrient cycling to occur. measures of sediment quality and forest productivity are significantly lower when crabs are removed.

Question 17

How is the mud lobster, Thalassina, an ecosystem engineer?

Answer 17

Excavates mud mounds, up to 3m. brings buried organic material to the surface to help facilitate succession in mangroves, as mounds are higher than tidal HW.

Question 18

How are mudskippers adapted to mangroves

Answer 18

1 Pectoral fins modified for walking, caudal fin fanned out to act as thrusting mechanism.
2 Breathes through skin, lack of O2 is less of an issue.
3 Protruding eyes can retract back into eye socket. Can see much more on land as water is v turbid.
4 Highly vascularised, complex capillary network to cope with gas exchange.

Question 19

3 aspects of muskipper behaviour

Answer 19

More dominant if can open mouth wider and enlarged dorsal fin.
Burrow has a rapid O2 gradient - 80% at surface, <3% at bottom. Air pocket forms in breeding chamber where eggs are laid on roof and encased in air pocket. Gives protection from hot environment and predators.
Climb up pneumatophores to spot predators

Question 20

How did Scarlet Ibis cause mercury contamination of Caroni swamp, Trinidad?

Answer 20

adult ibis is a mangrove resident but moves to FW as the young cant tolerate salinity.
Mercury contamination of young bioaccumulated in young birds, who shed feathers into mangroves, contaminating them with mercury and damaging plants.

Question 21

what are 6 threats to mangroves?

Answer 21

1. Boat traffic
2. Oil spills
3. Pollution by heavy metals
4. Pesticides
5. Agriculture and aquaculture - causes loss of 1/3 worlds mangroves over 50 years
6. deforestation rate similar to tropical deforestation rate. Adds 10% of total C emissions from deforestation.

Question 22

Why dont mangroves occur in temperate climates?

Answer 22

Ultrafiltration of salts is an energy expensive process, needs warm highly productive environment.