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

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?

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

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

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)

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

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

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

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.

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

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

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

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

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

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

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

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

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

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

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

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

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.

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

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

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

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…

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…

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,…