Ecological aspects of the ECOBAS concept

Chowduhry, M.S.N.1,2,3, Tangelder, M.1, Ysebaert, T. 1,4, Hossain, M.S. 3, and Smaal, A.1,2

1IMARES Wageningen, Institute of Marine Resources and Ecosystem Studies, Yerseke, The Netherlands

2Aquaculture and Fisheries Group, WIAS, Wageningen University and Research Center, Wageningen, The Netherlands 3Institute of Marine Sciences and Fisheries, University of Chittagong, Chittagong, Bangladesh

4Spatial Ecology Department, NIOZ Yerseke, Royal Netherlands Institute for Sea Research, Yerseke, The Netherlands

Oyster - Crassostrea madrasensis

Food relation

Thorson, 1950

Oyster: life cycle and reef formation

Habitats

Habitat suitability

• Inundation time

• Oyster population

Habitat facilitation!

ECOBAS Phase I - substrate W

indow

pane s

hell

Liv

e o

yste

r

Oyste

r shells

Sto

nes N

um

ber

of spat/

m2

ECOBAS Phase I - substrate W

indow

pane s

hell

Liv

e o

yste

r

Oyste

r shells

Sto

nes N

um

ber

of spat/

m2

• Suitable substrates for natural spatfall and growth

• Suitable environmental conditions

• Siltation is the main threat during monsoon

• Hard and firm substrate with high vertical relief was recommended

Environmental driving forces

Water Temp. 22.5⁰C

Salinity 20.14‰

pH 7.51

Dissolved O2

TSS 1.82 g l-1

Water Current 0.22 m sec-1

ECOBAS Phase II – pilot reef

0 10,000 20,000 30,000 40,000 50,000 60,000

May

Jul

Sep

Nov

Jan 2014

Mar

May

Jul

Sep

Spat number

? How will the oyster reefs develop in the future

3 Dimensional growth

Biomass

Oyster Reef Growth Model

Oyster Reef Growth Model

Data used in the Model

Spat settlement rate

Mortality

Substrate dimension

Recruitment number

Growth of oyster

Hydrobiology

Based on DEB theory Dynamic Energy Budget Model • Describe growth, energy dynamics and reproduction • As a function of environmental conditions

(particularly temperature and food concentration)

Oyster Reef Growth Model

Model Development

4.9-12.6 µg Chal-a l-1

21.6-30.9 ⁰C

Oyster Reef Growth Model

Month

Len

gth

(cm

)

0

5

10

15

20

25

1 12 23 34 45 56 67 78 89 100 111 122 133 144

Body length, L = (V1/3)/δm

P˙G = (κ . P˙C - P˙M )

[EG]

𝑑𝑉

𝑑𝑡 =

Model simulation results: Growth (Individual Length)

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

1 5 9 13 17 21 25 29

Survival number of oyster (total individuals)

Survival number of oyster with fishing mortality (total individuals)

Oyster Reef Growth Model

Year

Tota

l nu

mb

er o

f o

yste

r in

div

idu

als

dN/dt = Z Nt

Nt/No = exp [-Zt]

Z = M+F M = 1.01 yr-1 (Amin et al. 2007) F = 0.05 yr-1 Z = 1.06 yr-1

Model simulation results: Mortality

Oyster Reef Growth Model

Model estimated

length

Surface area per

individuals

Total surface area

Total volume of the oyster

Reef height increase per

cohort

Total Reef height

Thickness of the oyster

Substrate surface

area

New Cohort

Number of alive oyster

L = (V1/3)/δm

SA= (L*δm)2

TSA= N*SA

V = N*SA*Hind

H reef=Hdead oyster (do) +Hlive oyster (lo)

dH/dt = {(Hdo1+Hdo2+Hdo3+ ........ +HdoNT)K+ HloT}

Hdo or lo = Vdo or lo /SAsub

1,2,3....N = cohort number; K = annual dissolution rate

Oyster Reef Growth Model Formulation

Oyster Reef Growth Model

Li

ve O

yste

r b

iom

ass

in r

eef

(Kg)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

1 5 9 13 17 21 25 29

Oyster biomass (Kg) before harvest Oyster biomass (Kg) after harvest harvest Harvest (Kg)

Model simulation results: Oyster Biomass

Year

Harvestable oyster biomass = 5.6 kg m-2 yr-1

0

0.5

1

1.5

2

2.5

3

1 5 9 13 17 21 25 29

Reef height increase rate (cm/year)

Reef height increase rate (cm/year) with harvest

Oys

ter

reef

gro

wth

rat

e (c

m/y

ear)

Oyster Reef Growth Model

Year

Model simulation results: Reef height

Average reef growth rate = 2 cm yr-1

Conclusions

Ecological conditions are favourable for oyster reef development in South-eastern coast of Bangladesh

Oyster reef can grow more than 2 cm yr-1 , the rate is faster than sea level rise

5.6 Kg m-2 yr-1 of oyster biomass can be harvestable from oyster reef, which will add extra income for coastal community

More oyster production can be achievable by improving the design of oyster reef substrate

Oyster reef has important ecological role in coastal habitat facilitation, which need to be addressed

Thank you ...

ECO-ENGINEER

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