Assessment and interpretation of temporal or spatial differences in shellfish productivity of typical French ecosystems

Transcription

1 Assessment and interpretation of temporal or spatial differences in shellfish productivity of typical French ecosystems Joseph Mazurié, Patrick Soletchnik Michel Ropert Pierre-Gildas Fleury from Isabelle Auby Daniel Maurer C.Bacher... and - providers of qualified data from surveys - managers of data banks and designers of internet data (

2 «quant aux principales circonstances dont [la nature ] se sert encore chaque jour pour varier ses productions, les principales naissent de l évolution des climats, des variations de température de l atmosphère et de tous les milieux environnants, de la diversité des lieux de celle des actions, enfin de celle des moyens de vivre, de se conserver, de se multiplier, etc» Jean LAMARCK, 1800

3 Oyster Farms Ecosystem GENERAL FRAME OF ANALYSIS (3 levels) HYDRO- GEOGRAPHY CLIMATE TERRESTRIAL HUMAN ACTIVITY HYDRO-BIO Factors - Water renewal - Primary production Food Turbidity, Temperature OYSTER FARMER MANAGEMENT STOCK of FILTER- FEEDERS Food consumption Individual oyster production (mortality, growth ) Collective oyster production

4 Source of data : «Rephy» network => surveys Phytoplankton ( 11 common stations NORTH BRITTANY AB Brest BR SOUTH BRITTANY EL AY GM PF QB PB PAYS DE LOIRE BO POITOU- CHARENTES RE Remora network => monitors oyster growth ( MX 13 02Morlaix NM SM PL Channel Atlantic Ocean AQUITAINE AR CA NORMANDY CO national points LEGEND IFREMERlaboratories SV BV Port-en -Bessin Mediterranean Sea MEDITERRANEAN Thau TH

5 Assessment and interpretation of temporal or spatial differences in shellfish productivity of typical French ecosystems 1- SHELLFISH CULTURE PERFORMANCES HYDRO- GEOGRAPHY CLIMATE HYDRO-BIO Factors - Water renewal - Primary production Food Turbidity, Temperature TERRESTRIAL HUMAN ACTIVITY OYSTER FARMERS MANAGEMENT STOCK of FILTER- FEEDERS Food consumption Individual oyster production (mortality, growth ) Collective oyster production

6 temporal Mortalités huîtres 1 an Mortalités huîtres 2 ans spatial 1 year-old (left) 2 years-old (right) oysters Mortality QUESTION : what determines higher mortalities of 1yr-oysters in some sites, and of 2 yr-oysters some years? MV01 BV01 BV02 BV03 SV01 SV02 SV03 CO01 CO02 CO03 CA02 PL03 MX02 PZ01 AB02 BR03 EL02 QB01 QB02 AY01 AY02 GM02 GM05 PF02 PB02 BO01 BO02 BO03 BO04 RE01 RE02 RE03 FO01 MA01 MA02 MA03 MA04 MA05 AR01 AR03 AR04 TH01 MV01 BV01 BV02 BV03 SV01 SV02 SV03 CO01 CO02 CO03 CA02 PL03 MX02 PZ01 AB02 BR03 EL02 QB01 QB02 AY01 AY02 GM02 GM05 PF02 PB02 BO01 BO02 BO03 BO04 RE01 RE02 RE03 FO01 MA01 MA02 MA03 MA04 MA05 AR01 AR03 AR04 TH01

7 Interpretation of oysters performances, from close, surrounding medium 2- WATER QUALITY & SHELLFISH CULTURE HYDRO- GEOGRAPHY CLIMATE HYDRO-BIO Factors - Water renewal - Primary production Food Turbidity, Temperature TERRESTRIAL HUMAN ACTIVITY OYSTER FARMERS MANAGEMENT STOCK of FILTER- FEEDERS Food consumption Individual oyster production (mortality, growth ) Collective oyster production

8 Spatial differences in water quality : Example from 2 well-known oyster basins Principal Component Analysis (common to all sites) on monthly water parameters (TEMP, SAL, CHL, PHE, TURB) (means ) => site-specific trajectories second axis second axis turbidity Sud Jan turbidity Feb Dec Bassin d' Mar Marennes-Oléron ARCACHON pheophytin Apr Nov pheophytin chlorophyll a May June July Oct first axis chlorophyll a first axis Sept Aug temperature salinity Terrestrial influence Oceanic influence temperature salinity

9 WATER QUALITY AND OYSTERS PERFORMANCES : effective link though food (and temperature) FOOD (& TEMP) CHL /TURB spring CHL/TURB year long T C, CHL/TURB) summer CHL /TURB summer/spring GONADAL MATURATION LARVAE and SEED SURVIVAL 1 st year 2 nd year GROWTH (developed next )

10 Water Quality and REPRODUCTION (1) : REPRODUCTION «EFFORT» as (MEAT / INTERNAL WEIGHT OR VOLUME) L & S INDEX in JUNE Lawrence & Scott CONDITION INDEX of ARCACHON OYSTERS in JUNE R 2 = MEAN CHLOROPHYL FROM FEB. TO JUNE (µg/l) Auby, Maurer (2004) => Gonade size linked to spring food concentration

11 LN (% Nb of MEAN / Nb of SMALL Larvae) Water Quality and REPRODUCTION (2) Survival of larvae SURVIVAL of LARVAE as a function of water TEMPERATURE in "BASSIN d'arcachon" R 2 = TEMPERATURE Auby, Maurer (2004) => Survival of larvae is linked to summer water temperature

12 WATER QUALITY & 2 YEAR-OLD OYSTERS GROWTH CHLOROPHIL a Annual GROWTH of 2 year-oysters from 11 sites x 12 years ( ) as a function of TURBIDITY (ntu) and CHLOROPHYL-a (annual means) Oyster growth depends on chlorophyll (phytoplankton ) and turbidity (particulate organic and inorganic matter) OPTICAL TURBIDITY (NTU)

13 Annual mean Growth «PHYSIOLOGICAL» GROWTH MODEL OF C.GIGAS (1) 2D representation Annual GROWTH MODEL of 2 YEAR-OYSTERS from TROPHIC INDEX : CHL / (TURB ) (11 stations Remora-Rephy x 10 years) Trophic index y = 26.5x R 2 = 0.41 Quality of ingested food (Phytoplancton / Tot. Partic. Matter) TROPHIC INDEX (CHL/TURB) x f 0-1 with f 0-1 = TURB / (TURB + 1.2) TURB : Turbidity (NTU) Quantity ingested (% of maximum flux) (Arrhenius fonction in Kooijman DEB model)

14 «PHYSIOLOGICAL» GROWTH MODEL OF C.GIGAS (2) 3D representation quality of ingested food (CHL/TURB) OYSTER GROWTH as a function of QUANTITY AND QUALITY OF FOOD INGESTED 25 FOLD 3D graph : circles surface is proportional to growth 2 FOLD quantity ingested as a fraction of maximum f= TURB/(TURb+1.2) Arcachon Bourgneuf Brest Baie des Veys Cancale North-Marennes South-Marennes Morlaix Paimpol Quiberon Thau Moderate ingestion of high energy food High ingestion of low energy food

15 WATER QUALITY & 1-YEAR-OLD OYSTERS MORTALITIES (mean annual data) Matrice de corrélation : CHLA PHEO SAL Teau NTU Tair Pluvio Insol CHLA PHEO SAL Teau NTU Tair Pluvio Insol En gras, valeurs significatives (hors diagonale) au seuil alpha=0.050 (test bilatéral) F2 : 24.0 % SAL F1 et F2 : % Pluvio PHEO Mort 1an NTU CHLA Teau Tair Insol F1 : 41.3 % 1 year-oysters mortality TEMP, CHL, TURB = factors with high spatial differences

16 WATER QUALITY & 2-YEARS-OLD OYSTERS MORTALITIES (annual means) Matrice de corrélation : CHLA PHEO SAL Teau NTU Tair Pluvio Insol CHLA PHEO SAL Teau NTU Tair Pluvio Insol En gras, valeurs significatives (hors diagonale) au seuil alpha=0.050 (test bilatéral) Variables (axes F1 et F2 : %) 2ans P 1P 2 Pluvio SAL NTU PHEO CHLA axe F 1 (41.20 %) --> Insol Tair Teau 2 year-oysters mortality RAIN, SALINITY = factors with high temporal (inter-annual) differences empirical statistical correlations however! => eventual lack of pertinent non linear combination of parameters

17 LOOKING FOR PERTINENT NON LINEAR PARAMETERS seasonal variation Déposer champs of trophic de page index Ici => MORTALITY? TROPHIC INDICE monthly evolution Trophic Index = Food quality (CHL/TURB) x Food quantity Somme I-TRO Libellé point quadrige Boyard Teychan MARENNES OLERON : high mortality ARCACHON : low mortality mois

18 SEASONAL CHANGE IN FOOD QUALITY => 1 YEAR-OLD OYSTERS MORTALITY % MORT ANNUAL MORTALITY (1 year-oyster) as a function of TROPHIC INDEX (summer / spring) QB BV CA AR PL BR MX BO MAS MAN ITROPH2-678/345 Mean Trophic Index summer (month 6-7-8) / Mean Trophic Index spring (month 3-4-5) R 2 = 0.38 Trophic index = CHL/(TURB +1.2) (Seasonal change between spring and summer = at the end of gonadal maturation)

19 Oyster Ecosystem Environment II- Upper explanatory levels : Hydro-Geo & Human HYDRO- GEOGRAPHY CLIMATE HYDRO-BIO Factors - Water renewal - Primary production TERRESTRIAL HUMAN ACTIVITY Food Turbidity, Temperature OYSTER FARMERS MANAGEMENT STOCK of FILTER- FEEDERS Clearance Individual oyster production (mortality, growth ) Collective oyster production

20 HYDRO-GEOGRAPHY & CLIMATE => TEMPERATURE, SALINITY, PHYTOPLANKTON

21 HYDRO-GEOGRAPHY & CLIMATE => TEMPERATURE, SALINITY, PHYTOPLANKTON Seawifs Satellite Vilaine : 15 m 3 sec -1 Loire : 1092 m 3 sec -1 Charente 40 m 3 sec - 1 Gironde : 797 m 3 sec -1

22 HYDRO-GEOGRAPHY & CLIMATE => TEMPERATURE, SALINITY, PHYTOPLANKTON

23 (GEO-)MORPHOLOGY AND PRODUCTIVITY (1) Surface conceded (km²) Small / large, Wide open, semi-open, almost closed, oriented north, west, south 9 13 what importance?

24 OYSTER GROWTH and MORPHOLOGY OF THE REARED COASTAL AREA very wide open very wide open Degree of aperture (or surface of exchange) with ocean wide open wide open semi-open semi-open semi-open semi-open semi-closed semi-closed closed final whole weight of oysters (30g initially) = not determinant Evidence : oyster growth is not simply linked with the relative surface of exchange between farming basin and ocean Explanation : Geography determines the flux of water though the farming area (in and out) : in terms of food budget, the balance may be positive (net import) or negative (net export)

25 Oysters DENSITY at the scale of concessions influences production, but productivity / kg? Thau Quiberon Paimpol Morlaix Marennes-O Cancale Brest Bourgneuf Baie des Veys Arcachon STOCK AND PRODUCTION OF OYSTER PARKS on total conceded surface of each basin Extensive Mean SECTEUR Stock (tons/ha) individual production (g/oyster/year) oyster production (t / year / ha-conceded) Surface conceded (km²) total oyster production (tons/year) oyster production (t / year / haconceded) Intensive individual production (g/oyster/year) Stock (tons/ha) Arcachon Baie des Veys Bourgneuf Brest Cancale Marennes-O Morlaix Paimpol Quiberon Thau Value / ha / year

26 PRODUCTION (t/ha/year) No clear effect of stock density on stock productity, inter-sites relation DENSITY (or STOCK)-PRODUCTION at the scale of whole area conceded Baie des Veys Marennes Oléron y = 0.81x R 2 = mean STOCK (tons / ha) Production annuelle (tonnes) Mean P/B = 0.8 year but clear stock effect intra-marennes-ol Heral et al (1986) Relation Stock- Production d huîtres creuses dans le bassin de Marennes-Oléron Biomasse (tonnes) Crassostrea angulata Crassostrea gigas

27 Confrontation DEMAND (Clearance) OFFER (endogeneous or exogeneous Phytoplancton) Production consumable BALANCE RULE : Import Primary production PHYTOPLANKTON Clearance Filter feeders 15 t/ha of oysters (whole weight) in a 3 m water column clear daily 100% of Volume Export Stock consumable Clearance rate* < Renewal rate* + Primary production rate* * expressed as (% stock or vol.) or Clearance time* > Residence time* + Primary production doubling time* * expressed in days from Smaal, Dame, Prins( ) and common sense

28 5 days of residence RENEWAL RATE / RESIDENCE TIME

29 FOOD UPTAKE > FOOD RENEWAL (exogenous or endogeneous )? Data of renewal and primary production based on rough hypothesis => to be precised Oyster stock x individual Clearance Area considered = conceded area From size and oceanic exposure Clearance * Renewal * renewal : 10 km 2 / day affected to conceded surface primary production : moderated by turbidity Buffered by Turbidity Primary production * Clearance / (Renewal + Prim.Prod ) Indice of over-stocking Arcachon 94% 109% 158% 0.35 Baie des Veys 414% 857% 189% 0.40 Bourgneuf 131% 91% 38% 1.02 over-stocked Brest 309% Cancale 120% 167% 81% 0.48 Marennes-O 183% 38% 42% 2.27 over-stocked Morlaix 68% 221% 129% 0.19 Paimpol 145% 259% 263% 0.28 Quiberon 13% 33% 183% 0.06 understocked Thau 18% 0% 260% 0.07 understocked * expressed ICSR-2005, as % Brest of Volume daily

30 CONCLUSION Most of the observed differences in shellfish productivity of French ecosystems arise from water quality (specially food and turbidity) Coastal seawater productivity is mainly dependent on hydro-geographical traits, with climatic modulation : reactive in the vicinity of fluvial discharges, buffered by ocean elsewhere => profitability / risk choices The oyster farmers make use of this productivity, through regulation of access to this common resource (how many oysters stocked where?) : physical and social constraints generally precede food limits Land users influence on shellfish farming is another story

31 Thanks for your attention Coriolis Force : winds and currents deviated rightward in North Hemisphere