Post on 04-Jan-2016
transcript
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!