Figure 1.
Spatial characteristics of the coupled models.
(a) Annual primary production (in gC.m−2.d−1) in the upper 65 m simulated by ROMS-N2P2Z2D2 (adapted from [36]) and (b) spatial extent of fish individuals modeled in OSMOSE, aggregated over species, ages and seasons with delimitation of the 200 m and 500 m bathymetry.
Figure 2.
Processes represented within and for coupling the model components.
Processes modelled within a time step (15 days) in OSMOSE (left hand side) and fluxes represented between functional groups in N2P2Z2D2 (right hand side). Coupling of models occurs through the predation process, where plankton biomass serves as a prey field for fish schools (arrow 1), and an explicit fish-induced predation mortality is applied as feedback on plankton groups (arrow 2).
Figure 3.
Simulations plan and combination of climate and fishing forcing factors.
The blue cell (1;1) corresponds to the current situation of fishing and wind stress forcing. Orange cells correspond to one forcing factor varying and the other factor kept at its current level, i.e. separate effects of fishing (horizontal orange line) and of climate (vertical orange line). The circles represent the simulation of combined effects: the lower half circle represents the bottom-up wind stress forcing, and the upper half circle the top-down fishing pressure. For each half circle, white codes for a negative direct effect (decreased wind stress leads to lower primary production, increased fishing pressure leads to lower biomass of top predator fish), whereas black codes for a direct positive effect.
Figure 4.
Change of biomass of the four main trophic groups for the 25 sets of simulations.
Biomasses are expressed relatively to the baseline situation. Fishing pressure on top predator fish and wind forcing vary according to a multiplier of the baseline values. Blue and red bars represent positive and negative responses, respectively.
Figure 5.
Model II regressions between adjacent trophic levels.
Model II regressions are examined between phytoplankton and zooplankton biomass, between zooplankton and small fish biomass, and between small fish and top predator fish biomass. In red, the regression line estimated using major axis regression (MA), and in grey its confidence intervals. On the last graph, coloured dots show the increase of fishing pressure on top predator fish from 0 (dark blue dots) to heavily exploited (red dots). Schematic trophic pyramids are inset top of each plot - model groups regressed are indicated in darker shading.
Figure 6.
Comparison of combined effects versus separate effects of fishing and climate for each trophic group.
Each panel shows relative change of biomass of a trophic group (A: phytoplankton, B: zooplankton, C: small fish, D: top predator fish) when fishing pressure and wind stress act simultaneously (combined effect, y-axis) versus relative change of biomass computed from scenarios of wind stress and fishing pressure acting separately (x-axis). The 1∶1 line represents combined effects equal to the sum of separate effects, i.e. neither synergism nor dampening of effects. The symbols used are the same as in figure 3, each circle corresponding to one of the combined scenarios simulated: the lower half circle represents the bottom-up wind stress forcing, and the upper half circle the top-down fishing pressure. White half-circles code for a negative direct effect (decreased wind stress leads to lower primary production, increased fishing pressure leads to lower biomass of top predator fish), whereas black half-circles represent a direct positive effect. In the yellow area of the plot, the combined effects are amplified compared to the addition of isolated effects; in the purple area, the combined effects are dampened, and in the white area, the combined effects are antagonistic to additional effects.