NORWECOM.E2E is a merger of several models; an Nutrient-Phytoplankton-Zooplankton Detritus (NPZD) model for nutrient cycling and the lower trophic levels (Aksnes et al. 1995; Skogen et al. 1995; Skogen et al. 2007) and different Individual Based Models (IBMs, Grimm and Railsback 2005) developed initially for fish (Huse and Giske 1998; Strand et al. 2002; Huse et al. 2004; Huse and Ellingsen 2008; Utne et al. 2012) and zooplankton (Huse 2005; Samuelsen et al. 2009; Hjøllo et al. 2012; Hjøllo et al. submitted). NORWECOM.E2E is one of very few bottom-up models world-wide where IBMs for different trophic levels are two-way coupled and used to simulate food web dynamics of a large regional sea, and the only model system to run for the Norwegian Sea. At present, IBMs for adult pelagic fish (mackerel, herring, blue whiting), Calanus finmarchicus, Calanus hyperboreus and krill (Meganyctiphanes norvegica) are running, while there is ongoing work to include IBMs for capelin, mesopelagic fish and fishing vessels. The model system also has modules for ocean acidification (Skogen et al. 2014) and contaminants (Green et al. 2011). Through NORWECOM.E2E, all these models are now being integrated into a fully coupled model system running in offline mode using physical fields (salinity, temperature, velocities, etc.) from the ROMS model (Shchepetkin and McWilliams 2005). The model system has also been used to study climate effects through downscaling of global climate models (Skaret et al., 2014).
The 3D IBMs implemented for Calanus and krill take into account the entire life cycle and main life-history features such as growth, mortality, movement and reproduction, as well as adaptive traits which control the interaction with the environment (Huse 2005). Vertical movement is an emergent property resulting from many generations of evolution using a genetic algorithm. The models are linked so that the IBM receives input on phytoplankton and zooplankton densities from the NPZD model. Both Calanus and krill individuals then feed on the plankton and the local plankton abundance is updated continuously in the model. The krill, considered an omnivorous species, may also feed on the Calanus population. All Calanus biomass removed by foraging krill is continuously added as mortality in the Calanus population so that mass balance is achieved.
The three species of pelagic fish included in the model are herring, blue whiting and mackerel, which are dominant in terms of biomass in the region. The model cycle starts at the overwintering area, followed by spawning migrations, feeding migrations and migrations back to the overwintering area. The model includes the adult and juvenile stage of the life cycle, and there are ongoing work to extend these to full life cycle models. The pelagic fish module includes processes such as movement, feeding, growth and mortality. The pelagic fish are feeding on the Calanus through a two way coupling, and Utne et al. (2012) showed how linking the Calanus IBM with the pelagic fish IBMs changed the spatial distribution of C. finmarchicus in the upper 400 m towards higher abundances in the northern Norwegian Sea and lower values along the Norwegian coast compared to running the Calanus IBM with a uniform fish predation.
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