Stable isotopes:can they serve as tracers of

fish farm effluents in all environments?

Sonja LojenDepartment of Environmental Sciences, Jožef

Stefan Institute, Ljubljana, Slovenia,

with great support of all Biofaqsers

prepared by

Podgorica

Piran

Ljubljana

Why stable isotopes of C and N?

tracers for material flow

enrichment in the food-chain

“You are what you eat plus 3‰” (1984)

δ15Norganism = δ15Nfood + ε

Prof. Wada

What we wanted to do:

Trace the debris from fish cages in the sediment (δ13C)

Estimate the amount of debris from the cages in POM (δ13C, δ15N)

Estimate the amount of debris from cages recycled by organisms colonising biofilters (δ15N)

X•δ13CA + Y•δ13CB = δ13CA+B, X+Y=1

δ15Norganism = δ15Nfood + ε

X•δ15NA + Y•δ15NB = δ15Nfood, X+Y=1

Sampling, sample preparation, analyses

Stable C and N isotope analyses of sedimentary organic matter, faecal material, suspended particulate organic matter (POM, collected in traps), fish food and fouling organisms at the fish cages and control sites

‰R

R

dardtans

sample 10001

Number of replicate analyses: 1 -12

POM collected at the cages = fish food + faeces + “background”

POM

X faeces + Y pellets

Assumed the same as at the

control site

Go to library

Ye et al., 1991, salmonid farm: 55% faeces, 45% pelletsLefebvre et al., 2001, sea bass farm: 37% faeces, 63% pellets

X + Y = 1; X, Y = ?

Results I.: suspended material

CRETE13C 15N

EILAT13C 15N

OBAN13C 15N

PIRAN13C 15N

FOOD 9.7 - 20,1 8.7- 20.5* 7.6*

- 22.3 7.3 - 24.4 8.0 8.7*

FAECES - 20.1 7.0 - 20.2 5.8 4.5

POMAt the farm

control

V.01: - 22.3 12.3V.02: - 24.0 7.8

V.01: - 22.4 9.5V.02: - 24.2 1.8

VI I .01:- 22.5 5.0

VI I .01: - 21.1 3.2

V.01: - 22.3 7.1XI .01: - 22.7 3.0I I I .02: - 21.2 5.6V.02: - 20.0 2.9

V.01: - 21.8 7.0XI .01: - 23.1 4.0I I I .02: - 20.8 5.7V.02: - 20.0 4.0

VI I .02: NA 7.6VI I I .02: - 22.8 6.3I X.01: - 22.1 4.6VI I I .02: - 21.3 4.4I X.02: - 23.0 7.1

VI I .01: NA 5.8VI I I .01: - 22.0 5.6I X.01: - 21.8 0.5XI .01: - 21.6 4.6I X.02: - 22.9 6.0

Theoretical isotopic composition of POM deriving from fish cages

CRETE1 EI LAT1 OBAN2 PI RAN1

13C No data - 20,1 - 21,515N for faeces 8,1 6,7 7,1*

1Lefebvre et al., 2001; 2Ye et al., 1991

Who has DATA on F:P ratio

in debris released from

fish farms?

Results II. : sediment

CRETE13C 15N

EI LAT13C 15N

OBAN13C 15N

PI RAN13C 15N

At thefarm

control

- 18,7 5,4

- 20,4 2,4

- 23,2 4,9

- 21,7 4,3

- 22,1 6,9

- 21,6 6,6

- 21,3 3,9

- 21,6 4,4

influence of terrestrial debris

transported by the river with

15N about +1‰

Influence of debris and effluents from fish cages

Whom we wish to have on biofilters

Active suspension feeders

Sessile or strongly sedentary in habit

Able to ingest and retain particles in size range released in aquaculture effluents

Able to survive and grow on a diet of non-living organic detritus

High pumping and clearance rates

What we got:

Piran: predominantly bryozoa

Crete: predominantly bryozoa

Oban: predominantly tunicates

Eilat: tunicates, mussels, worms, sponge, sea anemone, Thyroscopus fructisosus

Bryozoa Tunicate

13C 15N 13C 15N

At the farmVI I .01:IX.01:XI .01:

ControlVI I .01:IX.01:XI .01:

- 23,0- 22,5- 22,7

- 20,8- 20,3- 21,3

4,66,35,7

7,56,86,4

- 21,2 10,3

Results: fouling organisms, Piran

Influence of 13C depleted fish food,

terrestrial input?

Influence of 15N depletedriverine input of POM

indir

ect

ly indirectly

-23,5 -23,0 -22,5 -22,0 -21,5 -21,0 -20,5 -20,0 -19,5 -19,0

4,0

4,5

5,0

5,5

6,0

6,5

7,0

7,5

8,0

control site at the cages

15 N

(‰

air

)

13C (‰ V-PDB)

Stable isotope composition of bryozoans collected in Piran

-25,0

-24,5

-24,0

-23,5

-23,0

-22,5

-22,0

-21,5

-21,0

-20,5

-20,0

November 2001September 2001July 2001

Bryozoans - cage Bryozoans - control POM - cage POM - control food pellets

13 C

(‰

V-P

DB)

Temporal variations of 13C of particulate organic matter and bryozoans collected in Piran

0

1

2

3

4

5

6

7

8

9

November 2001September 2001July 2001

Bryozoans - cage Bryozoans - control POM - cage POM - control food pellets

15 N

(‰

vs.

air

)

Temporal variations of 15N of particulate organic matter and bryozoanscollected in Piran

Results: fouling organisms, Crete

Indirect influence of fish farm

effluents

Bryozoa

13C 15N

At thefarm

XI .01:VI I .02:VI I .02:

ControlI X.01:

- 20,7- 20,9- 20,1

- 19,4

6,95,86,6

4,0

Results: fouling organisms, Oban

Tunicate Scalops

13C 15N 13C 15N

At the farmI X.01:XI .01:XI I .01V.02:

ControlI X.01:XI .01:XI I .01:

- 18.8- 20.6- 19.8

- 20.0

- 18.3- 21.1- 19.4

11.69.211.27.8

9.79.111.7

- 20,8 6,3

No significant differences due to turbulent environment

Similar effectas in Piran

Results: fouling organisms, Eilat

P.aegiptiaca

Tunicate Worms Sponge Bryozoa Seaanemone

T.fructicosus

13C 15N 13C 15N 13C 15N 13C 15N 13C 15N 13C 15N 13C 15NAt the farmV. 01:IX.01:V.02:V.02:

ControlV. 01:IX.01:V.02:V.02:

- 19.4 3.8

- 20.0 4.2- 19.5 2.2

- 19.2 3.5

- 22.1 2.3- 20.7 2.1

- 20.7 5.1

- 19.9 4.9

- 21.6 7.3

- 19.7 5.7

- 22.4 6.0

- 22.5 4.0

- 21.9 3.3

- 21.5 5.3

- 18.8 2.8

- 16.6 2.6

- 20.9 1.8

- 20.5 1.9

enrichmentin average

Sensitive to dissolved nitrogen

1,8 2,0 2,2 2,4 2,6 2,8 3,0-21,2

-21,0

-20,8

-20,6

-20,4

-20,2

-20,0

-19,8

-19,6

-19,4

-19,2

-19,0

cage reference

13 C

(‰

vs.

V-P

DB)

15N (‰ vs. air)

13C vs. 15N of Pteria aegiptiaca, collected in Eilat in April 2002

1 2 3 4 5 6 7 8 9 101,6

1,8

2,0

2,2

2,4

2,6

2,8

3,0

at the cage reference

15N

(‰

vs.

air)

Size (cm)

15N of Pteria aegiptiaca collected in April 2002 in Eilat vs. its size

Estimation of retained N from fish cages

ε = δ15Norganism, control - δ15NPOM, control

δ15Nfood, cage = δ15Norganism, cage - ε

organism % of N deriving from the cages

Bryozoa

Tunicate 4- 60 (?)

P. aegiptiaca 6- 14

Sponge 33

Worms 41

Conclusions - particulate organic matter controversial data from the

literature it was not possible to determine the source of POM only from stable C and N isotopic composition, or to quantitatively estimate the amount of organic debris originating from the fish farm seasonal variation in carbon and nitrogen isotopic composition of phytoplankton

common scheme of production regime for modern environments: nitrate based in the spring and nitrogen fixation in summer, resulting in lower δ15N

large isotopic fractionation during degradation processes of particulate nitrogen

the suspended material is thoroughly mixed and the influence of a fish farm on the concentration and isotopic composition of suspended material is spatially very limited due to dispersion and dilution

Conclusions- sediment

the degree of remineralisation of organic particulates during sedimentation depends upon many biotic and abiotic factors - temperature, turbulence, stratification, biotic community composition and food conditions

no systematic variations in δ13C, systematic enrichment in 15N (except in Piran)

rapid remineralisation of fine POM in turbulent environments

rapid sedimentation of large particles

in environments with low organic matter content and where oxic conditions prevail during the year, the 15N of sedimentary organic matter can undergo considerable changes toward more positive 15N values with respect to the primary signal

findings consistent with data from literature

Conclusions - fouling organisms

questionable effect of bryozoans

effective consumption of farm-POM by sponge and worms

partially effective: tunicates, mussels

Need data on average isotopic composition of POM for each growing period

then we could estimate the amount of debris retained by biofilters

need data on increase of biomass in each growing period

Thank you!