1

STABLE ISOTOPIC AND FATTY ACID EVIDENCE FOR UPTAKE OF FISH FARMING INDUCED ORGANIC

POLLUTANTS BY FILTER-FEEDING MUSSELS (PERNA VIRIDIS) IN A POLYCULTURE SYSTEM

Kevin Q F Gao1, S G Cheung1, G H Lin2,3; S P Chen2; Paul K S Shin1

1Department of Biology and Chemistry, City University of Hong Kong.2Laboratory of Quantitative Vegetation Ecology, Institute of Botany, the Chinese Academy of Sciences.

3Department of Global Ecology, Carnegie Institution of Washington, USA.

2

Introduction: Fish farming is an important economic activity world-wide.

3

Introduction: Fish farming leads to pollution due to uneaten feed, faeces and excretion.

4

Introduction: Bivalve mussels can filter particulate matter in high efficiency.

5

Introduction: Polyculture, combining fish and mussels, can achieve an environmental and economic Win-Win solution.

Canadian Mussel Export Values (X106US$)

0

5

10

15

20

25

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

Year

Ex

po

rt V

alu

e

6

Introduction: Trophic markers

Stable Isotopes:

Changes in stable isotope ratios (e.g., 13C/12C and 15N/14N) are predictable when matter is transported along trophic levels; they can thus be used as markers to trace matter flow: food or pollutant sources and fates.

7

Introduction: Trophic markers

Fatty Acid Profile

Sink-specific and conservative in transportation and transformation

Use of Multiple Markers

Improve the accuracy of determining source and sink

8

Objectives

1 To quantify the contribution of potential food sources to the mussel ration.

2 To evaluate the feasibility and capability of filter-feeding bivalves as biofilters for organic wastes from fish farming activities in a polyculture system.

9

Experimental site: Kau Sai marine fish culture zone - a semi-enclosed bay

10

Methods

1 Mussels transplanted to fish rafts and a reference site (without effects from fish farms).

11

Methods

2. Sampling from fish raft and reference site: mussels, particulate matter, fish feed and fish faeces after 3 months in the field.

3. Sample analysis: 2 aliquots for all samples

Aliquot 1 for stable isotope ratios (13C/12C and 15N/14N) with EA-IRMS;

Aliquot 2 for fatty acid profiles with GC-FID

4. Data analysis:

Comparison: Mussel tissue between fish raft and reference site with t-test.

Isotope mixing model: Contribution of food sources to mussel tissue.

Principle Component Analysis (PCA) ordination: For fatty acid profiles.

12

Results: Stable Isotopes

Comparison of stable isotope values in mussel tissue between fish raft and reference site

-25

-20

-15

-10

-5

0

5

10

15

Reference site

Fish Raft

δ13C (‰)

δ15N (‰)

δ13C=[(13C/12C)smpl/ (13C/12C)std-1]X1000‰

δ15N=[(15N/14N)smpl/ (15N/14N)std-1]X1000‰

13

Results: Stable Isotopes

5

6

7

8

9

10

11

12

13

14

15

-22.0 -21.0 -20.0 -19.0 -18.0 -17.0 -16.0

δ13C (‰)

δ15N

(‰

)

mussel

POM

fish feed

fish feces

Dual isotope plot showing the food source of mussels at fish raft site

Contributions of food sources to mussel ration:

Based on isotope mixing model,

POM: 68.3%;

Fish feed: 27.5%;

Fish faeces: 4.2%,

14

Results: Overall Fatty Acid Profiles

Fatty Acids MFR MRS PFR PRS FFD FFC

Saturated Fatty Acids

11:0 0.00 0.00 0.00 0.00 0.01±0.00 0.00

12:0 0.00 0.01 0.00 0.00 0.17±0.02 0.00

14:0 7.55±0.51 5.96±0.45 3.41±0.35 3.06±0.22 5.27±0.88 1.17±0.68

15:0 0.90±0.22 0.71±0.03 0.24±0.02 0.42±0.09 0.72±0.06 0.23±0.01

16:0 30.31±3.82 35.04±3.22 29.41±2.33 24.34±2.15 32.70±1.66 8.80±1.11

18:0 10.59±0.78 7.53±0.46 2.48±0.30 4.26±0.48 9.16±1.10 7.72±0.35

17:0 1.73±0.55 2.36±0.55 0.46±0.03 0.90±0.08 1.01±0.05 0.41±0.02

20:0 0.97±0.08 0.55±0.06 0.49±0.07 0.00 0.83±0.07 0.75±0.06

21:0 0.13±0.01 0.76±0.05 0.00 0.02 0.00 1.24±0.16

22:0 0.00 0.00 0.24±0.01 0.00 0.00 0.00

subtotal 52.18±1.85 52.92±1.66 36.72±1.58 33.00±1.55 49.87±1.34 20.32±1.22

MFR-mussel of Fish Raft, MFS-Mussel of Ref. Site, PFR-POM of Fish RaftPFS-POM of Ref. Site, FFD- Fish Feed, FFC-Fish faeces (meanSD, N=3-9)

15

Results: Overall Fatty Acid ProfilesMonounsaturated Fatty Acids

15:1n5 0.00 0.00 0.84±0.03 1.79±0.01 0.04 0.00

17:1n7 0.21±0.01 0.68±0.02 3.16±0.16 7.25±0.22 0.60±0.03 0.64±0.03

16:1n7 10.65±0.68 8.47±0.56 17.76±1.23 17.73±1.33 8.28±1.02 8.67±0.89

18:1n9 4.66±0.16 2.27±0.09 2.38±0.09 2.11±0.11 12.75±1.35 24.86±1.88

18:1n7 3.85±0.11 3.52±0.15 7.67±0.22 9.78±0.36 3.89±0.11 3.55±0.15

20:1n9 2.35±0.08 3.21±0.18 0.00 0.00 0.16±0.02 0.00

22:1n9 0.45±0.05 0.61±0.03 0.00 0.00 0.00 0.39±0.05

subtotal 22.16±1.55 18.75±1.63 31.80±2.15 38.66±2.30 25.71±2.10 38.11±1.59

Polyunsaturated Fatty Acids

18:2n6 1.46±0.12 1.50±1.08 1.58±0.15 0.35±0.01 0.91±0.09 1.47±0.12

18:3n6 0.20±0.01 0.00 0.00 0.00 0.05 0.28±0.01

20:2n6 0.72±0.03 0.48±0.05 0.21±0.02 0.00 0.00 0.00

20:3n3 0.14±0.01 0.20±0.01 0.21±0.01 0.00 0.00 0.00

20:4n6 3.30±0.22 2.97±0.36 0.77±0.05 0.00 3.42±0.25 5.26±0.26

20:5n3 8.24±0.22 12.21±1.23 16.06±1.25 14.37±1.36 7.00±0.79 7.74±0.88

22:2n6 0.00 0.92±0.05 0.25±0.02 0.00 0.00 0.00

22:6n3 11.59±0.98 10.04±0.88 12.41±1.23 13.62±1.33 13.07±1.56 26.84±2.32

subtotal 25.66±1.52 28.32±2.21 31.48±3.32 28.34±2.35 24.45±2.01 41.59±3.32

16

-5

-4

-3

-2

-1

0

1

2

3

-1.5 -0.5 0.5 1.5 2.5

PC1 (34.9%)

PC

2 (

21

.8%

)

MFR

MRS

PFR

PRS

FFD

FFC

-5

-4

-3

-2

-1

0

1

2

3

-1.5 -0.5 0.5 1.5 2.5

PC1 (34.9%)

PC

2 (

21

.8%

)

MFR

MRS

PFR

PRS

FFD

FFC

-5

-4

-3

-2

-1

0

1

2

3

-1.5 -0.5 0.5 1.5 2.5

PC1 (34.9%)

PC

2 (

21

.8%

)

MFR

MRS

PFR

PRS

FFD

FFC

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

-1.2 -1 -0.8 -0.6 -0.4 -0.2 0

MFR

MRS

FFD

Results: Overall Fatty Acid Profiles

PCA ordination plot showing the Overall fatty acid profiles of mussels and their food sources

POM at reference site

POM at fish raft

Fish feed, fish raft only

Fish feces, fish raft only

Mussels at fish raft

Mussels at reference site

17

0

5

10

15

20

25

30

35

40

45

14:0 18:0 18:1n9 20:5n3 16:0 18:1n7 22:6n3

Fat

ty a

cid

conc

(%

)Results: Single Fatty Acids

Effects of fish feed fatty acids on mussel tissue

No effectS

ources identical

Negative

Effect

Positive Effect

Mu

ssel, fish

raft

Fish

fee

d, ra

ft o

nly

PO

M, fish

raft

PO

M, re

f. site

Mu

ssel, re

f site

18

Discussion

2. Combined evidence of stable isotopes and fatty acid profiles showed that filter-feeding mussels could directly consume the organic wastes derived from fish farming activities.

1. The distinct stable isotopic and fatty acid signatures of different sources can be used as trophic markers to trace the transfer of organic matter along the food chains.

3. Eutrophic nitrogen and phosphorus could be fixed by mussel assimilation before the waste mineralization.

4. The mussels in a polyculture system can function as biofilters to reduce the nutrient released from uneaten fish feed and egested fish faeces in fish farms.

19

Acknowledgements

• Agriculture, Fisheries and Conservation Department (AFCD) of Hong Kong government for funding;

• Group colleagues for sampling assistance;

• Technicians in Institute of Botany, the Chinese Academy of Sciences;

• Department technicians

20

Thank You!