Mangrove

Mangrove Ecosystems

• Intertidal coastal wetland ecosystem in sheltered tropical / subtropical shores. • marks the transition between the sea or an estuary and the land • relatively gentle gradient, high temperature, fluctuated salinity, alternating aerobic and anaerobic conditions, periodic wet and dry soils, and unstable and shifting substratum. • is a woody plant or plant community which lives between the sea and the land in areas which are inundated by tides.

• Hong Kong has about 60 mangrove stands which cover a total area of about 510 ha. They are distributed in six districts: Sai Kung, Northeast New Territories, Tolo Harbour, Deep Bay, Lantau Island and Hong Kong Island.

Study Of Mangrove Ecosystem

Background • Mangrove habitat is a swampy mud flat which marks the transition between the sea or an estuary and the land .It is alternately exposed and covered by the tides and is inhabited by special ecological groups of tropical plants and animals which are adapted to living in intertidal regions of muddy shores

• In HK which lies in the sub-tropical zone and the temperature is therefore low in winter. Mangroves here are rather small and not very extensive and they are considerable human interference

Abiotic factors (Problems in Mangrove)

Unstable substratum

slow water movement allows fine sediment particles to settle and accumulate to form mud →soft unstable mudflat

Fluctuating salinity High : input of seawater at high tides which bring salt and nutrients Low : input of freshwater at low tides which remove salt

Tidal movement ebb and flow twice a day → substratum unstable → affects salinity

Anaerobic environment fine soil particles → easily waterlogged → low oxygen content in soil

Fluctuating temperature fluctuate with tidal movement → high due to exposure to sunlight at low tides

Water dehydration under intense exposure to the sun at low tides

Adaptations of Plants •

1) Adapt to Unstable substratum -branched, looping aerial roots ( 氣根 ) └ arise from trunk/ lower branched └ trap mud during tidal movement └↑amount of soil

-prop roots ( 柱根 ) └ supply air to underlying roots └ provide stability for plant by broadening the base

Adaptations of Plants •

-buttress roots ( 板根 ) └ aerial branch roots: provides support └ thicken unevenly └ flattened blade-like structures

-cable roots ( 纜狀根 ) └ spread horizontally+ laterally just below soil surface └ anchor the plant firmly in soil

Adaptations of Plants •

2) Adapt to Anaerobic Condition

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-pneumatophores ( 呼吸根 ) └ erected aerial roots └ extend upwards into air at intervals from cable roots └ facilitate gas exchange between submerged roots and atmosphere └↑lenticels on root surface →↑efficiency of gas exchange

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-knee joints ( 根膝 ) └ arches of prop roots └ grow above soil surface for gas exchange

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↑lenticels on pneumatophores , knee joints and prop roots →↑efficiency of gas exchange

Adaptations of Plants •

3) Adapt to High Salinity

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-halophytic properties └ accumulate low molecular carbohydrates └ keepΨof root cells< surrounding water └ overcome difficulty of water absorption └ draw water in

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-store excess salts in leaves └ leaves shed when old └ reduce salt content inside plant

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-salt glands in leaves └ secret excess salts

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-active pump mechanism └ prevent salts from entering root xylem

Adaptations of Plants •

4) Adapt to Reproduction

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-droppers └ seeds will germinate inside this fruit └ when droppers detach from plants └ roots already in the early stage of development └ establish rapidly in substratum └ elongated+ heavier at lower tip→ stick to substratum in upright position └ hypocotyls of droppers: help dropper float+ disperse+ carried by H2O └ until reaching a region that H2O is shallow enough to contact substratum

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-produce ↑amount of seeds └ enhance reproductive success

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- spongy outer layers on seeds └ for floating + dispersal

Adaptations of Plants • •

•

5) Adaptation to dehydration Leaves └ thick cuticle epidermal hairs and sunken stomata └ reduce transpiration └ reduce water loss store water in special multilayered water storage tissues

Animals in Mangrove • We can find them in

Prop roots

Water pools

creek

canopy

Mud surface

Invertebrates • Soft substratum : small ground-dwelling invertebrates digging / boring holes • Feed on: detritus in mud

Invertebrates---- diff Groups Dominant gps: • Molluscs → gastropod → bivalves • Crustaceans

Invertebrates---- where to live? • Attach on mangrove plants / stones • Gastropods: roots, trunks of trees e.g. Littoraria • Bivalves : mangrove root/stone e.g. Gafrarium

Invertebrates---- where to live? • Crustaceans (relatively large-sized) • E.g. Uca (fiddler crab) Alpheus (snapping shrimp) → hollow up mud → live in large open burrows √ √ √ √ √

O2 to enter deeply into subs. changes in temp. changes in salinity refuges from predation breeding places

Vertebrates • Mudskipper (Periophthalmus) - bony fish √ diff. tidal levels: exposed to air / complete submersion - pectral fins √ walk / hop on mud surface - When hold up body, tail fin = gill √ gas exchange

Vertebrates • Reptiles - snakes, lizards • Amphibians - Frogs

Vertebrates • Mammals - nocturnal e.g. Civet cats - live in thick scrub, densely wooded area

Vertebrates • Birds – over 400 species - nest-breeding (in colonies on trees - migrating birds - food: from gei wai / mudflats of Mai Po

-detritus : consist of fallen leaves, twigs & dead trees  provide food to support a large variety of mangroves animals -↑productivity refuge & nursery grounds for juvenile fishes, crabs, shrimps & mollusks nesting & migratory sites for birds -retain nutrients  cycling of materials -refines waste water (e.g. heavy metal)  natural water & waste water treatment plants

-maintain stability & ecological balance of coastal & marine ecosystems -Mangrove plants: land-builders roots ~ trap sediment build up & extend mangrove habitats -Protect shorelines from erosion due to currents, waves ,wind & storms -Sustainable for food production (for man)

1.Species diversity 2.Species rarity 3.Representativeness (typicalness) 4. Current protection 5.Protection disturbance and hazard Other Values: -Recreational -Scientific -Educational -Aesthetic -Historical/ geographical -Naturalness

-legally protected under Marine Park Ordinance and Country Park Ordinance -44 mangroves in HK— 5 categories: -1.Extremely important and must be conserved immediately -2. Very important and should be conserved -3. Important and worth to conserve -4. Can be conserved -5. Relatively low priority for conservation

1. Enforcement of existing ordinances 2. Designation of new SSSIs 3. Set up buffer zones 4. Good Management for SSSIs

Mangrove Ecosystems

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