Conservation strategies in coastal wetland: compromise based on habitat conflicts between mangroves...

Conservation strategies in coastal wetland: compromise based on habitat conflicts between mangroves and the fiddler c

rab, Uca formosensis in Taiwan

Hwey-Lian Hsieh, Po-Fen Lin*, Chang-Po Chen

Institute of Zoology, Academia Sinica, Taipei, Taiwan

Research Center for Biodiversity, Academia Sinica, Taipei, Taiwan

Outline

1. Taiwanese fiddler crab, Uca formosensis.

2. Why mangrove is important to Taiwan coastal zone?

3. The habitat characteristics of mangroves and Uca formosensis.

4. How mangroves could change the habitat of Uca formosensis?

5. Conservation Strategies

IntroductionThe fiddler crab Uca formosensis is endemic to Taiwan

Uca formosensis Other Uca species

The habitats of Uca formosensis : Non-vegetated, high tidal zones in firm mud intertidal flats

Life history stageZoea and Megalop stageSpread/distribution

Juvenile

Feeding/growth

Adult

Burrowing/breeding

Competition between fauna

Aspect of organism

Micro- habitat

Temperature, humidity, sediment salinity, oxygen content, water content, quantity and quality of food, toxic materials, etc.

Coastal environments

erosion/siltationemerging/sinking

Macro- habitat

support

Aspect of habitat

Sediment

particle sizetopographyelevation

mangrovebenthic microalga

e

VegetationWater influence

estuarytideflow tidal level

Water column

influence

influence

Benthic environment

Benthic environment

120°E 121°E 122°E

25°N

24°N

23°N

23°N

Distributional records of Uca formosensis (from 1918 to 1997)

Black stars represent areas with active population of U. formosensis

Open stars represent areas where the population of U. formosensis has extinguished.

(Shih,1999)

Threats to fiddler crabs: Land reclamation, dike and road construction

Another threat to fiddler crabs: Improper planting of mangroves on the Uca formosensis habitats

Goals of this study: To examine the habitat characteristics of bot

h U. formosensis and mangroves To provide a scientific basis for conserving t

he diversity of intertidal habitats and populations of U. formosensis

To propose conservation strategies for the protection of intertidal habitats in coastal wetlands of Taiwan

Material and Methods

Hsinchu City

Taipei City

Changhua County

Kuantu (KT)

Tachuang mangrove (TCS)

Haishanku Mangrove (HS)

Tatu (TT)

Jenchang Lake (JCL)

Tachuang Creek North Shore (TCN)

Haishanku-1(HSI)

Haishanku-2(HSII)

Haishanku-3(HSIII)

Sedimentary substrates of microhabitats Grain size (Silt/Clay content) Total organic carbon and nitrogen content Water content pH Salinity of interstitial water Depth of the oxidation layer Benthic macroinvertebrates

Depth of the oxidation layer

JCL TCN HS I HSII HSIII DD HS TCS GD

Silt

/Cla

y C

on

ten

t(%

)

0

20

40

60

80

100

Results and Discussion

○ The habitat of Uca formosensis (△mean±S.E.) ● The habitat of mangroves(▲mean±S.E.)

TTJCL TCN HSI HSII HSIII HS TCS KT JCL TCN HS I HSII HSIII DD HS TCS GDD

ep

th o

f O

xid

ati

on

La

yer(

cm

)0

10

20

30

40

50

60

70

TTJCL TCN HSI HSII HSIII HS TCS KT

JCL TCN HS I HSII HSIII DD HS TCS GD

Wat

er C

on

ten

t(%

)

0

10

20

30

40

50

JCL TCN HS I HSII HSIII DD HS TCS GD

pH

0

2

4

6

8

10

○ The habitat of Uca formosensis (△mean±S.E.) ● The habitat of mangroves(▲mean±S.E.)

TTJCL TCN HSI HSII HSIII HS TCS KT TTJCL TCN HSI HSII HSIII HS TCS KT

JCL TCN HS I HSII HSIII DD HS TCS GD

TN

(%)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

JCL TCN HS I HSII HSIII DD HS TCS GD

TO

C(%

)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

TTJCL TCN HSI HSII HSIII HS TCS KT TTJCL TCN HSI HSII HSIII HS TCS KT

JCL TCN HS I HS II HS III TT HS TCS KT

Den

sity

of

infa

un

al c

om

mu

nit

y (i

nd

ivid

ual

s/m

2 )

0

5000

10000

15000

20000

25000

○ The habitat of Uca formosensis (mean±S.E.) (including polychaetes, insects and crabs )

● The habitat of mangroves (mean±S.E.) (including polychaetes, insects, crabs and oil

gocheates)

Potential negative impacts on U. formosensis caused by mangrove intrusion

A. Alternation of sediment characteristics

Siltation increases

Depth of oxidation layer decreases

pH decreases

B. Direct effects by mangrove trees Shading effects (Hsieh,1999; Hsieh et al.,2002; Wainright et al., 2000)

Productivity of benthic microalgae declines

Aboveground structures Stems and branches block crabs’ view and movement Leaves shaken by wind may scare crabs

Underground structures Roots become obstacles to crabs’ burrowing

C. Benthos changes (Shih,1999; Hsieh et al.,2002)

Helice formosensis, H. wuana, U. arcuata prefer

mangrove habitats

Helice formosensis U. arcuata

Accelerate studies on the habitat characteristics of each stage of the life history of U. formosensis

Apply ecological engineering practices to restore habitats of U. formosensis

Monitor the impacts of mangroves on estuarine ecosy

stems and manage mangroves accordingly

Conservation Strategies

Conserve coastal wetlands which

1) retain those still sound function,

2) improve those that have been disturbed, and

3) restore those that have been destroyed.

We try to connect these three types of habitats to form a “Coastal Wetlands Conservation Greenway along Taiwan’s Western Coastal Zone” (Hsieh et al., in press)

Promote the wise use of coastal wetlands

Mangrove trees

Uca formosensis reserve

Buffer zones

Mangroves should be eliminated from U. formosensis reserve areas.

For examples: remove mangroves from Uca formosensis reserve and buffer zones

Carry out public education on biodiversity and habitat diversity.

When U. formosensis encounters mangroves

Summary

The invasion of mangroves into U. formosensis habitats has a negative impact on the fiddler crab’s population.

Mangroves on estuarine ecosystems and coastal zones should be managed properly in Taiwan.

Future coastal management should emphasize on maintaining biodiversity and habitat diversity.

Acknowledgements

Funding agencies

Institute of Zoology Academic Sinica

Research Center for Biodiversity Academia Sinica

Hsinchu City Government

Assistants and Graduate studentsYuan-Hsien Chen, Hsin-Yi Yeh, Hsiao-Hui Yang, Tai-An Chen, Song-Lin Wu, Wu-Hsiung Ou, Shu-Ting Lin, Feng-Lin Wang, Chang-Hao Hoa, Ming-Che Yang, Meng-Jeng Guo.

Thanks!