Stable isotopes:
can they serve as tracers of
fish farm effluents in all
environments?
prepared by
Sonja Lojen
Department of Environmental Sciences, Jožef Stefan
Institute, Ljubljana, Slovenia,
with great support of all Biofaqsers
Podgorica
Ljubljana
Piran
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
What we wanted to do:
Trace the debris from fish cages in the sediment (δ13C)
X•δ13CA + Y•δ13CB = δ13CA+B, X+Y=1
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)
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 sample



 1   1000
 R s tan dard

‰
Number of replicate analyses: 1 -12
POM collected at the cages =
fish food + faeces + “background” POM
X faeces + Y pellets
X + Y = 1; X, Y = ?
Assumed the
same as at the
control site
Go to library
Ye et al., 1991, salmonid farm: 55% faeces, 45% pellets
Lefebvre et al., 2001, sea bass farm: 37% faeces, 63% pellets
Results I.: suspended material
13
CRETE
 C
15
At the farm
control
13
OBAN
15
 N
-20,1
-20.5*
8.7
7.6*
-22.3
7.3
-20.1
7.0
-20.2
5.8
V.01: -22.3 12.3
V.02: -24.0 7.8
VII.01:-22.5 5.0
V.01:
XI.01:
III.02:
V.02:
-22.3
-22.7
-21.2
-20.0
V.01: -22.4
V.02: -24.2
VII.01: -21.1 3.2
V.01:
XI.01:
III.02:
V.02:
-21.8 7.0
-23.1 4.0
-20.8 5.7
-20.0 4.0
9.7
9.5
1.8
 C
15
 C
FAECES
POM
EILAT
 N
FOOD
 N
13
7.1
3.0
5.6
2.9
13
PIRAN
 C
-24.4
15N
8.0
8.7*
4.5
VII.02: NA
7.6
VIII.02: -22.8 6.3
IX.01: - 22.1 4.6
VIII.02: -21.3 4.4
IX.02: -23.0 7.1
VII.01:
VIII.01:
IX.01:
XI.01:
IX.02:
NA 5.8
-22.0 5.6
-21.8 0.5
-21.6 4.6
-22.9 6.0
Theoretical isotopic composition of
POM deriving from fish cages
13C
15N
1
CRETE1
EILAT1
OBAN2
PIRAN1
No data
for faeces
-20,1
8,1
-21,5
6,7
7,1*
Lefebvre et al., 2001; 2Ye et al., 1991
Who has DATA
on F:P ratio
in debris
released from
fish farms?
Results II. : sediment
CRETE
EILAT
OBAN
PIRAN
13C
15N 13C
15N 13C
15N 13C
15N
At the
farm
-18,7
5,4
-23,2
4,9
-22,1
6,9
-21,3
3,9
control
-20,4
2,4
-21,7
4,3
-21,6
6,6
-21,6
4,4
Influence of debris and
effluents from fish cages
influence of terrestrial debris
transported by the river with
15N about +1‰
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:
 Oban: predominantly tunicates
 Piran: predominantly bryozoa
 Crete: predominantly bryozoa
 Eilat: tunicates, mussels, worms, sponge, sea
anemone, Thyroscopus fructisosus
Results: fouling organisms, Piran
Bryozoa
At the farm
VII.01:
IX.01:
XI.01:
Control
VII.01:
IX.01:
XI.01:
Tunicate
13C
15N
-23,0
-22,5
-22,7
4,6
6,3
5,7
-20,8
-20,3
-21,3
Influence of
13C depleted fish food,
terrestrial input?
13C
15N
-21,2
10,3
7,5
6,8
6,4
Influence of 15N depleted
riverine input of POM
8,0
7,5
15
 N (‰ air)
7,0
6,5
6,0
5,5
5,0
control site
at the cages
4,5
4,0
-23,5 -23,0 -22,5 -22,0 -21,5 -21,0 -20,5 -20,0 -19,5 -19,0
13
 C (‰ V-PDB)
Stable isotope composition of bryozoans collected in Piran
Bryozoans - cage
Bryozoans - control
POM - cage
POM - control
food pellets
-20,0
-20,5
-21,5
-22,0
-22,5
-23,0
13
 C (‰ V-PDB)
-21,0
-23,5
-24,0
-24,5
-25,0
July 2001
September 2001
November 2001
Temporal variations of 13C of particulate organic matter and bryozoans
collected in Piran
9
15
 N (‰ vs. air)
8
7
6
5
4
3
Bryozoans - cage
Bryozoans - control
POM - cage
POM - control
food pellets
2
1
0
July 2001
September 2001
November 2001
Temporal variations of 15N of particulate organic matter and bryozoans
collected in Piran
Results: fouling organisms, Crete
Bryozoa
13C
15N
XI.01:
VII.02:
VII.02:
-20,7
-20,9
-20,1
6,9
5,8
6,6
Control
IX.01:
-19,4
4,0
At the
farm
Indirect influence
of fish farm
effluents
Results: fouling organisms, Oban
Tunicate
At the farm
IX.01:
XI.01:
XII.01
V.02:
Control
IX.01:
XI.01:
XII.01:
Scalops
13C
15N
-18.8
-20.6
-19.8
-20.0
11.6
9.2
11.2
7.8
-18.3
-21.1
-19.4
13C
15N
-20,8
6,3
9.7
9.1
11.7
No significant differences due to turbulent environment
Results: fouling organisms, Eilat
P.
aegiptiaca
13C
At the farm
V. 01:
IX.01:
V.02:
V.02:
Control
V. 01:
IX.01:
V.02:
V.02:
-19.4
15N
Tunicate
13C
15N
Worms
13C
15N
Sponge
13C
15N
Bryozoa
13C
15N
-20.0
-19.5
4.2
2.2
-19.2
3.5
2.3
2.1
-18.8
-21.6
-19.9
enrichment
in average
13C
15N
T.
fructicosus
13C
15N
3.8
-20.7 5.1
-22.1
-20.7
Sea
anemone
7.3
-22.4
6.0
-21.9
3.3
4.9
-16.6
-19.7
5.7
-22.5
4.0
Similar effect
as in Piran
-21.5
2.8
5.3
-20.9
1.8
-20.5
1.9
2.6
Sensitive to
dissolved
nitrogen
-19,0
13
 C (‰ vs. V-PDB)
-19,2
-19,4
-19,6
-19,8
-20,0
-20,2
cage
reference
-20,4
-20,6
-20,8
-21,0
-21,2
1,8
2,0
2,2
2,4
2,6
2,8
3,0
15
 N (‰ vs. air)
13C vs. 15N of Pteria aegiptiaca, collected in Eilat in April 2002
3,0
2,8
15
 N (‰ vs.air)
2,6
2,4
2,2
2,0
at the cage
reference
1,8
1,6
1
2
3
4
5
6
7
8
9
10
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
 findings consistent with data from literature
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
Conclusions - fouling organisms
effective consumption of farm-POM by sponge
and worms
 partially effective: tunicates, mussels
questionable effect of bryozoans
Need data on average isotopic
composition of POM for each
growing period
need data on increase of
biomass in each growing
period
then we could estimate
the amount of debris
retained by biofilters
Thank you!