1. THE USE OF ECO-EXERGY IN OCEANOLOGY: APPLICATION TO POSIDONIA OCEANICA MEADOWS
Dorothée Pête, Branko Velimirov & Sylvie Gobert
PhD student, University of Liège

2. Introduction What a mystification! It’s metaphysics! Are you crazy?
Exergy = « Useful work a system can perform when brought into equilibrium with its environment » (Szargut et al., 1988)
= distance from thermodynamic equlibrium
Applying this theory to understand ecosystems and to detect environmental perturbations
What a mystification!
It’s metaphysics!
Are you crazy?

3. Thermodynamic theory for Ecosystems (S. E. Jørgensen)
Thermodynamic equilibrium = Inorganic soup

4. Thermodynamic theory for Ecosystems (S. E. Jørgensen)
Take energy in:
Matter
Storage in biochemical constituents
 Trends to keep away from thermodynamic equilibrium when becoming more complex (Prigogine, 1980)
Loose energy:
Matter
Maintenance
Trophic webs

5. Exergy index or eco-exergy: a practical way to apply the exergy theory to ecosystems
Ex (kJ/volume or surface)
= distance between the system and the thermodynamic equilibrium
  when the ecosystem is moving away from thermodynamic equilibrium
  when the ecosystem is getting closer from its climax, its ecological optimum
= « work capacity possessed by organisms and ecological networks of organisms due to biomass and information embodied in their genome and the amino acid sequence of proteins » (Jørgensen et al., 2010)

6. Exergy index or eco-exergy
Formula:
βi:
β-factor of the ith organism
defined on a genetic basis: enzymes and proteins, defined by DNA, are driving life processes (Jørgensen et al., 2005)
kind of approximation of organisms complexity
higher for « specialised » organisms
expressed relatively to detritus (no genetic information, only free energy of the organic matter, ≅ 18,7 kJ.g-1)
ex: β = 1 for detritus, 8,5 for bacteria and 133 for nematods
Ci: Biomass of the ith organism

7. Specific exergy (Structural exergy, Silow, 1998)
Exsp = expresses the presence of more specialised organisms in the ecosystem
Ex = informations on the capacity of the ecosystem to develop and get more complex
Exsp = information on the « quality » of the biomass

8. Use of Ex and Exsp in Oceanology
2 main uses:
Modeling of ecosystems development (plankton dynamics)
Indicators of environmental quality

9. Use of Ex and Exsp in Oceanology
2 main uses:
Modeling of ecosystems development (e.g. plankton dynamics)
Indicators of environmental quality
Interest as indicators:
Complete part of an ecosystem  Global
 More sensitive ?
- Reflect ecosystem development and complexity.

10. Can we use them to detect a perturbation in a marine ecosystem early?
Focus ecosystem = Posidonia oceanica meadow
- What?
Posidonia oceanica = endemic seagrass of the Mediterranean Sea
Exportation of vegetal biomass
Production of vegetal biomass
Production of animal biomass
Biodiversity hot spot
Basis for food webs
Spawning and breeding ground
Hydrodynamic protection
Stabilization of the bottom
Trapping of suspended particules

11. Can we use them to detect a perturbation in a marine ecosystem early?
Focus ecosystem = Posidonia oceanica meadow
Why?
P. oceanica = descriptor of the quality of the Mediterranean coastal zone
University of Liege:
- Tradition of marine research (Biology, chemistry, physics, modeling)
- Research station in Calvi Bay, Corsica: STARESO (STAtion de REcherche Sous-marine et Océanographique)
- Years of experience in the Mediterranean Sea with a special focus on the Posidonia oceanica ecosystem
In Calvi Bay, pristine and perturbated meadows are well known.
 Good zone to test the use of Ex and Exsp

12. Can we use them to detect a perturbation in an ecosystem early?
Posidonia oceanica meadow has a low turnover.
Sediment = final container of pollutants (sedimentation)
Microbenthic loop: organic matter (OM), microphytobenthos (microscopic algae), meiofauna (microscopic animals), bacteria
Important sub-system in P. oceanica meadows
 High turnover

13. Precise, early and global method
Goals
Clarification and validation of the use of Ex and Exsp as descriptors of anthropogenic perturbations in P. oceanica beds
Effects of nutrients and organic matter inputs which are the main perturbations in the Mediterranean coastal zone
 New method to measure and detect perturbations affecting P. oceanica meadows
Precise, early and global method

14. Sampling What? - sediment cores (vertical profile)
- Biomass determination for every component of the microbenthic loop.
- sediment and environment parameters

15. How to validate an index and a method?
Spatial heterogeneity at small scale
Comparison between a pristine and a perturbated site
In situ experiments

16. Sampling sites Seasonal variations 10 m, 22 m Small scales Alteration
Shading
= Reference site
Seasonal variations
From STARESO SA
Perturbated site
Fish farm
22 m
From STARESO SA
Adapted from Vermeulen et al., 2011

17. Spatial heterogeneity
125 cm
3 grids
March, June, November 08, March 09
12 nodes/grid (uniform random)
3 cores/node
STARESO
25 cm

18. Results : DIVA analysis Biomass of bacteria
120
130
Heterogeneity and « hot spots » of biomass 40 50
0-1 cm
1-2 cm
240
260
140
140 60 60
2-5 cm
5-10 cm

19. Spatial heterogeneity : Estimation of Ex & Exsp
For 10 cm
Median ± range
Important heterogeneity especially for the 1st cm of the sediment
Most dynamic slice, exchanges with the water column
BUT probably the most affected by environmental perturbations
The less heterogenous slice is the 5-10 cm
Less dynamic slice and no exchanges with the water column
Anoxic conditions for most samples
BUT « old » sediment
Choose the 5-10 cm to prevent heterogeneity effects
For 1 cm

20. Spatial heterogeneity : Ex & Exsp 5-10 cm
Median ± range
Important heterogeneity in spite of the choice
No real seasonal variability
 Seems stable along the year

21. STARESO vs. Fish farm: 5-10 cm
Median ± range
This estimation is not able to catch the difference in EX between sites.
In November 2008, Ex STARESO>Ex Fish farm
STARESO is closer from the ecosystem climax than the fish farm.
No difference in Exsp.
No difference in the « complexity » of organisms living in the ecosystem.
The ecosystem is able to adapt itself to this perturbation (Silow, 1998).
Awaited results for November 2008 only
 Not an estimation…
No difference in Exsp
 No difference in biomass « quality » between sites

22. In situ experiments: Sediment alteration
Site: STARESO, 10 m depth.
Duration: 3 months (from end of May to end of August 2009).
Alteration (mimic pollution by fish farms or dredging):
- 500 ml of sediment were added once a week on 21 marked points in a 3x3 m frame.

23. In situ experiments: Shading
Shading ( in turbidity because of  in nutrients concentration, fish farms, sewages, land farms):
- 3 nets (3x1 m, mesh size: 0,5 mm2) about 50 cm from the canopy.
- Light extinction: 52 ± 1,6 %
- Cleaning once a week to avoid fouling

24. In situ experiment : Ex 5-10 cm
No difference between periods
Estimation?
Too short experiment?
Median ± range

25. In situ experiment : Exsp 5-10 cm
No real difference between periods
Estimation?
Too short experiment?
Median ± range

26. Conclusions Spatial variability
Important heterogeneity BUT less important in the 5-10 cm sediment depth zone
Choice of the 5-10 cm sediment horizon to compare samples even if it is maybe less precise
Fish farm vs. STARESO
Ex STARESO>Ex Fish farm in November 2008 for the 5-10 cm horizon
 Ex seems able to dicriminate both sites
In situ experiment
No difference along the experiment.
 Too short experiment to see an impact…

27. Conclusions
Use of Ex and Exsp as a tool to detect perturbations in the Mediterranean coastal zone is not easy to validate in this part of P. oceanica ecosystem.
Important to link the results with environmental parameters to understant why it works or not.
Work in progress…

28. Thank you!
Tanks to Loïc Michel, Renzo Biondo, Gilles Lepoint, Sylvie Gobert, Branko Velimirov, people of the STARESO, students, cleaning team, spreading team, repairing team,…