G. Thouzeau, S. Martin, M. Richard, J. Clavier, F. Jean, L. Guérin, J.-M. Guarini, A. Donval, A. Leynaert, J. Richard, R. Marc, E.

Transcription

1 8th International Conference on Shellfish Restoration Brest, 2-5 October 25 ta ut ho ra ut ho riz at io n IMPACTS OF FEEDING ACTIVITIES OF THE INVASIVE SLIPPER LIMPET, Crepidula fornicata, ON SILICON CYCLE IN THE BAY OF BREST: results from in situ measurements se m in at e w ith ou G. Thouzeau, S. Martin, M. Richard, J. Clavier, F. Jean, L. Guérin, J.-M. Guarini, A. Donval, A. Leynaert, J. Richard, R. Marc, E. Amice D o no td is UMR 6539 CNRS IUEM

2 ho riz at io n OBJECTIVE ho ra ut To test in situ the following hypothesis: e w ith ou ta ut Suspension feeder activity, stimulated by the proliferation of the invasive Crepidula fornicata, would be the driving force of a biologically active silicate pump which would se m in at 1) retain BSi within the Bay during spring and o no td is 2) provide the DSi necessary for diatoms during summer. D Funding: LITEAU, INVABIO 1

3 Mar. Ecol. Prog. Series 2 (2), p high low Interannual variability of river flow in early spring Differential mortality Crepidula introduction Benthos Spreading Suspension feeders (Crepidula) Sediment BSi storage Grazing? Biodeposition Grazing Si limitation Flagellates in summer Nutrient inputs (N, Si, P) Diatoms Spring: new production Summer: mainly regenerated production Advection: BSi exportation out of the Bay Dissolution «Resistance» Perturbation

4 Today: up to 4,55 ind.m-2 7,45 g DW m-2 Total biomass: 84,75 t DW ra ut ho riz 1995 no td is se m in at e w ith ou ta ut ho ++ o + D 1995 at io n Crepidula proliferation in the Bay of Brest. Photo: E. Amice

5 Crepidula distribution poster Kriging interpolation (grid: 2 x 2m; km 2 ) Density density Biomass biomass Ind.m -2 g DW m -2 Density density 2 2 Biomass biomass

6 The spatial distribution may start to converge towards a constant density model, since local carrying capacity is close to be reached in maximum patches areas in 2 Biomass (g DW m -2 ) Density (ind.m -2 ) Maximum density: 4833 ind.m -2 Maximum biomass: 781 g DW m -2

7 Habitat selection and invasion strategy From a proportional density model (without changes of patch sizes) towards a constant density model (with new patches instead of increasing patch sizes). Local density Space variable Local density Space variable

8 N Elorn river BREST Roscanvel Bay Northern basin Lanvéoc May 2: S1: 1,155 ind.m -2 S2: -3 ind.m -2 Southern basin Intertidal to -5m -5 to -1m -1 to -2m -2 to -4m > -4m 5 km Aulne river

9 Benthic flux measurements benthic chambers (.196 m 2 ) acrylic tubes and hemispheres (56-75 L) adjustable submersible pumps connected to waterproof batteries water flow = 2 L min -1 YSI 692 probes May 2 September 24 dark conditions (73 of 88 incubations) incubation time: 2h3 O 2 concentration, salinity, T C, depth water samples (nutrients, ph, TA) Macrofauna (air-lift suction sampler)

10 Results of in situ incubations Flux (µmol m -2 h -1 ) Flux (µmol m -2 h -1 ) Silicate flux - Winter y =,137x + 18,58 R 2 =, y =,854x + 76,767 R 2 =,85 Biomass (g DW m -2 ) Silicate flux - Spring Biomass (g DW m -2 ) Flux (µmol m -2 h -1 ) Silicate flux - Summer y =,2891x + 49,766 R 2 =, y =,495x + 18,39 R 2 =,7 Biomass (g DW m -2 ) Silicate flux - Autumn Flux (µmol m -2 h -1 ) Biomass (g DW m -2 )

11 S2 S1 x 1.6 Benthic silicate flux x 4.1 x 6.2 x 3. Flux (mm m -2 d -1 ) Winter Spring Summer Autumn * * 213 ind.m -2 in Sept. 24

12 March May June July September November Results of core incubations (21) S2 S1 (1719 ind./m2) ind.m -2 ) S1 S2 (26 ind.m / m2) -2 ) Biogeochemistry (in press) DSi benthic flux (mmol m -2 d -1 )

13 CONCLUSIONS This study provides further evidence of the influence of Crepidula on BSi retention at the sediment-water interface before subsequent DSi delivery to sustain diatom blooms in summer This influence may be even greater than previously found How do these data modify the silicon budget at the Bay scale?

14 SUSTAINABLE MANAGEMENT : fighting against the alien. 75 ha confinement - 1,2t of Crepidula removed Scientific survey: cleaned site + control site (2 x 1 ha)

15 SUSTAINABLE MANAGEMENT : fighting against the alien. at io n 75 ha confinement - 1,2t of Crepidula removed ra ut ho riz Scientific survey: cleaned site + control site (2 x 1 ha) o Pecten maximus ut ta ou ith w e in at se m is no td repopulation : seeding of 3 million ho benthos re-colonization biotic interactions water turbidity sediment silting Fluxes at the water -sediment interface D juveniles (3 cm shell height) Photo: E. Amice

16 Flux (mm m -2 d -1 ) S2 S1 Benthic silicate flux x 2.2 x 2.6 x 3.8 x 4.3 x 1.9 x 7.5 x 25 x 5. Winter Spring Summer Autumn Core data from the year 2 except winter (21)