Biology

Field trip Report

Mangroves in Ting Kok

2008Tin Ka Ping Secondary

6S Ho Cheuk Ming

6S Hung Chun Hin

6S Lee Wang Kei

6S Leung Ka Wai

6S Suen Hue Man

6S Tze Wun Ting

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Contents Aims and introduction 2

Introduction of the field site –Ting Kok 3

Equipment of field work 4

Procedures of field work 5-6

Laboratory works 7-8

Discussions

A. Abiotic factors 9-13

B. Dominant species 14-18

C. Unusual observations 19

D. Improvements 19

Conclusions 19

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Title : Study of Mangrove Ecosystem in Ting Kok

Aims:

1. To identify the plants and animals that found in the mangroves

2. To investigate the zonation pattern of the plants and animals in

mangrove ecosystem

3. To investigate how the abiotic factor affect the distribution of the

animals and plants in mangroves

4. To identify the dominant species of animals and plants in

mangroves

5. To identify and interpret adaptive features of the dominant

species of animals and plants in mangrove ecosystem

6. To learn the techniques of field studying

Introduction

Mangroves are the habitat that the saline coastal habitats grow

with tree and shrubs. They are most common found in the tropics and

subtropics and also marks the transition between the sea , the estuary

and the land. Therefore most of the mangroves are in the brackish

water region and the salinity is relatively higher than the inland. The

tides in mangroves not only give a gentle gradient to the mangroves

but also affect the humidity of the soils periodically. Further more the

aerobic and anaerobic condition of the soil are also affected.

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Introduction of the field site – Ting Kok

Date of study: 20th Feb, 2008 (Wednesday)

Time of study: 1:15 p.m.

Weather conditions: Sunny day the temperature is about 25oC

Wave Action: Gentle

Location of the study: Tai Po, Ting Kok

A map showing the location of mangroves in Ting Kok

Ting Kok has a mangrove which is along the coastal line of Tolo Habour.

The species in the mangroves’ area are quite abundant. The inner

coast avoids the strong wave from the Pacific Ocean. The Ting Kok is

less polluted and a good field site for studying mangroves.

Field

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Equipment of field work

50m transect line 1 roll

Quadrat (50x50 cm) 2 pc

Measuring Tape (60 inches) 1 pc

Light meter 1 pc

Digital thermohygrometer 1 pc

Abney level and supporting

frame

1 set

Trowel 2 pcs

Plastic bag 3 pcs

Forcep (Blunt) 2 pcs

Forcep (Fine) 2 pcs

Magnifying glass 2 pcs

Compass 1 pc

White plastic tray 2 pcs

Blue plastic tray 1 pc

Metal sieve 2 pcs

Counter 1 pc

Map 1 pc

Ruler (30 cm) 1 pc

Water sampling bottle 2 pcs

Digital anemometer 1 pc

Soil thermometer 1 pc

Thin nylon thread 1 pc

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Procedures of field work

A. Vegetations Analyzing

a. Transect was put across the site and was about half on the

beach and half in the mangrove community

b. The presence of plants which touch, overlie or underlie the

transect line was recorded

c. The plants were identified according to the field guide

d. A leaf was removed from each plant species and was brought

back to the laboratory for further study

B. Measurement of physical factors

a. The direction of wind was found by letting a light nylon thread

blow by wind and using compass, and recorded.

b. The speed of wind was found by holding digital anemometer

against the wind

c. The temperature and the humidity in the air and under the

canopy of plants were recorded every 10 minutes at the

same position and found by digital thermo-hygrometer, the

average was recorded

d. The sediment temperature at 0m, 6m, 12m, 18m, 24m, 30m

and 36m point of the transect line was found by the soil

thermometer.

e. The light intensity inside and outside the mangrove

community, also above and below the canopy was recorded

by the light meter

6f. 1Kg of soil sample was obtained with the aid of trowel

g. 2 bottles of water sample were taken from the sea

h. The slope along the transect was recorded by Abney level

and supporting frame every several meters

C.Animals Analyzing

a. Quadrat was placed on the 0m, 6m, 12m, 18m, 24m, 30m and

36m point of the transect

b. Animals found on the soil in the quadrat were captured and

transferred to the white plastic tray

c. The animals were identified according to the field guide and

the number of each species was recorded

d. The surface of soil (about 5 cm) was removed

e. Animals found in the soil in the quadrat were captured and

transferred to the white plastic tray

f. The animals were identified according to the field guide and

the number of each species was recorded

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Laboratory works

A. Sediment analysis

‧ Aims: To analyze the colour, smell, text and composition of the

sediment in mangrove.

‧ Materials：500ml~600ml sediment、Water

‧ Apparatus: 1000ml measuring cylinder、cover、crucible、oven、

electric balance、gas burner

‧ Procedures:

1. The colour, smell, and text of the sediment were studied by our

eyes, nose and hands. The results were recorded.

2. 500ml of sediment were added into a 1000ml measuring

cylinder.

3. Water was added into the cylinder until it reaches the 1000ml

mark.

4. The mouth of the cylinder was covered with covered.

5. It was shaken vigorously and then the mixture was settled for

overnight.

6. The proportion of each component(gravel, coarse sand, fine

sand, silt, clay, humus) was estimated.

7. The crucible was weighted and then 3/4 full of sediment was

put into it.

8. The sediment was dried in an oven which operating at 105℃.

9. When it was dried, it was weighted and burnt it by using the

gas burner for about 20minutes.

10. After it was cooled, it was weighted again.

11. The amount of organic matter present in the sediment was

calculated.

Data：Please refer to the attachment.

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B. Water analysis

‧ Aims：To analyze the composition of water that collected in

mangrove.

‧ Materials: water sample

‧ Apparatus: pH meter、refractometer、filter paper、filter funnel、

measuring cylinder、conical flask、oven

‧ Procedures：

1. pH of the water sample was measured by a pH meter.

2. Salinity of the water sample was measured by a refractometer.

3. 100ml water sample was measured by measuring cylinder.

4. The water was poured into conical flask.

5. Then, it was filtered by a dry filter paper.

6. The filter paper was dried in oven and then was weighted.

7. The amount of total suspended solids was calculated.

Data: Please refer to the attachment.

C. Detailed study of specimen

‧ Aims：to study the micro-organism in the water and in the sediment

under a microscope. Also, to identify the collected animals and

plants

‧ Materials: the collected animals and plants

‧ Apparatus: microscope、watching dishes

‧ Procedures:

1. The collected animals were put into the watching dishes.

2. The dishes were placed under the microscope.

3. The microscope was adjusted and then the animals were

observed.

4. The morphology of the living organisms was studied.(Adaptive

features: respiratory organs, feeding organs, organs for

attachment, locomotion, organs for defending and preventing

desiccation.)

5. The collected mangrove leaves were cut and observed under

high power microscope.

6. Their adaptive features were examined.

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Discussions

Interpretation of results

E. Abiotic factors

i) Sediment temperature

Refer to the graph showing the trend of sediment temperature

along the transect, from 0m to 18m, the sediment temperature

increases gently and from 18m to 36m, the sediment temperature has

a general trend of decreasing. The increase may be caused by the

decrease of amount of water in soil when it is away from the sea. And

the decrease may be caused by the increase of density of mangroves

so that the shading area has lower sediment temperature.

Since the distribution of animals was found to be varying along

the transect, sediment temperature is believed to be one of the

factors affecting this because most of the animals stay underground

during the sun time. For example, from our data, there are totally 16

Scopimera globosa(圓球股窗蟹) from 12m to 18m while we could not

find any of them at other places. The sediment temperature at 12m to

18m may be suitable for them to live.

Graph showing the trend of sediment temperature along the

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transect

ii) Air temperature and humidity

Refer to the graph comparing the air temperature and humidity in

mangrove, the air temperature is lower and the humidity is higher

below the canopy. Both differences may be mainly caused by the

presence of mangroves. Mangroves shed the light so to reduce the

air temperature below the canopy. The lower light intensity and

temperature below the canopy result in higher humidity. This provides

a more suitable environment for animals because lower temperature

and higher humidity can prevent the occurrence of desiccation.

Ｇraph comparing the air temperature and humidity in mangrove

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iii) Tidal movement

There are high tides and low tides

during the day. High tides bring nutrients

up to the substratum and the water stirs

up the sediment so to assist the animals

hide from natural predators. This results in

relatively large biodiversity and amount

of animals. For example, from the table

showing the distribution of animals, we

could find 20 Saccotstrea cucullata(石蠔）

from 0m to 10m but 0 from 15m to 25m. Similarly, we found 17 Slithon

sp.（彩螺）from 0m to 10m but 0 from 15m to 25m. These distributions of

animals may be resulted from the tidal movement.

Another example is the droppers. Most of the droppers are away

from the mother plants by the tidal movement. This can allow the new

plants to obtain sufficient light for photosynthesis to grow well and

expend the habitat of mangroves.

iv) Sediment

The composition of sediment cause different abundance of

organisms in different depth. Most of the animals have a larger

amount near the sediment surface. This may because the oxygen

content is higher due to the larger size of the surface soil particles. But

some of the animals have larger amount in the lower layers of

sediment. For example, all larva of Chironomous sp. (紅蟲) found are

from the lower part of sediment. This may because they are well

adapted for underground

Saccots trea cucullata(石蠔）

Sli thon sp.（彩螺）

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v) Wind

Wave action : gentle

Wind in the shore: 1.7 m/s to NW

Wind in the mangroves

Above the canopy: 1.2m/s to NW

Under the canopy: 0.42m/s to NW

Table showing the wind speed and direction in the site

The data shows that wind speed in the shore is faster than above the

canopy. It may because the wind experienced resistance on the path.

Also, the data shows that wind speed above canopy is faster than

under canopy. It may because the high density of mangroves’ trunk

caused very high resistance.

vi) Light intensity Above canopy: 74600 lux

Below canopy: 12600 lux

Table showing the light intensity in mangroves

Refer to the data of light intensity, the light intensity above canopy is

much larger than that below canopy. Obviously, it is because the

mangroves shed the light.

It inhibits the growth of other plants under the canopy. There, there is a

few of plants growing under the mangroves. So this can protect their

nutrients from other types of plants. Mangroves have more nutrients

for growth.

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vii) Salinity

The salinity of sample is 2.0%

Since the salinity of sea water is 5% and of fresh water is about 0.02%,

it proves the site is at the border between the sea and fresh water

stream. This salinity provides a suitable habit for a wide range of

organism to live in there. The diversity of organisms in mangrove is

quite big. There are total 14 kinds of organisms including plant and

animal along the transect line.

viii) pH

The pH of water sample is 8.48

It shows that the water is alkaline and it is abnormal.

This may be caused by the pollutants produced by human activities or

decomposition of organic matter.. It may inhibit the growth of

organisms. There, the original amount of organism and biodiversity

should be greater than what we had found.

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B. Dominant species

SAND SNAILS: BATILLARIA SPP.灘棲螺

BATILLARIA SPP in Tin Kok mangroves

i) Adaptation to strong wave action:

A Broad flat muscular foot

In order to prevent sand snails being washing away by the strong

wave action, it possess a broad flat muscular foot for attach firmly

onto the substratum.

Ragged calcareous shells

Sand snails have a calcareous shells to protects them from physical

damage such as forceful water wave action

ii) Adaptation to dehydration:

Ragged calcareous shells

Sand snails have a calcareous shells to protects them from

dehydration by reduce water loss in directly evaporation.

Outer margin

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Outer margin is the organ that locate on the mouth of the shell, when

the sand snails withdraw their body into the shell, outer margin can

prevent water loss and thus prevent dehydration

iii) Adaptation to prevent being preyed:

Ragged calcareous shells

Sand snails can withdraw their body into the shell when danger occurs

to reduce chance of being preyed.

Camouflage

The color of the shell of sand snails is similar to the sand and rock, then

it can reduce the chance of predator to find them

The profile of the mangroves

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Kandelia obovata 水筆仔

Kandelia obovata in Tin Kok mangroves

i) Adaptation to unstable substratum:

Aerial roots

In order to establish the plant body in such a soft and unstable

substratum, Kandelia obovata develop branched, looping aerial roots

arising from the trunk and lower branches. These aerial roots trap mud

during tidal movement, and help to increase the amount of soil.

Prop roots

The prop roots of Kandelia obovata supply air to the underlying roots

also provide stability for the plant by broadening the base.

ii) Adaptations to anaerobic condition:

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Pneumatopores

Kandlia obovata produce

erected roots called

pneumatopores which extend

upwards into the air at intervals

from the cable roots.

Pneumatopores of Kandlia obovata Pneumatopores facilitate gas

exchange between the submerged roots and the atmosphere.

Knee joints

Some prop roots of Kandlia obovata form arches called knee which

grow above the soil surface for gas exchange. The knee joints bear

many large lenticels on the surface to increase the efficiency of gas

exchange.

iii) Adaptations to high salinity:

Kandlia obovata are halophytes. It can overcome the difficulty of

water absorption which arises from the high salt concentration in the

surrounding water. It can accumulate low molecular carbohydrates it

keep the water potential of the root cells even lower than that of the

surrounding water. Also Kandlia obovata can prevent salts from

entering the root xylem by an active pump mechanism.

iv) Adaptations to dehydration:

Like xerophytes, Kandlia obovata possess various adaptive features

for reducing the rate of water loss or preserving water. The leaves of

Kandlia obovata have a thick cuticle, epidermal hairs and sunken

stomata to reduce transpiration.

v) Adaptations to reproduction:

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Droppers

In order to enhance success in seedling development, Kandlia

obovata produce seeds that germinate inside the fruits. The fruits are

called droppers. When the droppers detach from the plants, the roots

are already in the early stage of development, and can establish

themselves rapidly in the substratum. The droppers have fleshy

structures called hypocotyls, which help them to float and disperse.

They are carried by water until they reach a position where the water

is shallow enough for the roots to come in contact with the

substratum.

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Unusual observations

i) Refer to the graph showing the trend of sediment temperature

along the transect, the sediment temperature has a sudden drop

at around 24m.

ii) The water sample is alkaline, which is different from the expected

pH of being neutral.

Improvements

i) We would like to have a further investigation to find out the reason

for the abnormal drop of sediment temperature at around 24m.

ii) We would also like to investigate why the water sample collected

was alkaline. We suggested that this may result from the discharge

of household detergents or the decomposition of the fallen leaves,

swigs or dead organisms to form ammonia.

iii) We could not obtain a trend of the slope of the land in our study.

Therefore, we cannot observe and look into the effect of slope on

the distribution of animals. So, further studies are needed.

Conclusions

After the study, we know more about mangroves such as the

composition of sediment and the species of organisms living there.

They provide shelter, food and substrate to support a large community

of animals. Mangroves are important habitat for many organisms,

including both animals and plants.

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Reference

Book

A Colour Guide to Hong Kong Animals;

Hong Kong Seaweeds;

Field Study Handbook - Wildlife Pictorial Guide;

Estuarine Organisms;

Hong Kong Coastal Plants

Website

http://en.wikipedia.org/wiki/Mangrove

http://chwk.huwei.com.tw/p3/redt/p3a02.htm

Others

Notes from Ho Koon Nature Education cum Astronomical Centre