Implementation of marine spatial planning in shellfish aquaculture management: modeling studies in a Norwegian fjord

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Abstract:

Shellfish carrying capacity is determined by the interaction of a cultured species
with its ecosystem, which is strongly influenced by hydrodynamics. Water circulation controls
the exchange of matter between farms and the adjacent areas, which in turn establishes the
nutrient supply that supports phytoplankton populations. The complexity of water circulation
makes necessary the use of hydrodynamic models with detailed spatial resolution in carrying
capacity estimations. This detailed spatial resolution also allows for the study of processes that
depend on specific spatial arrangements, e.g., the most suitable location to place farms, which
is crucial for marine spatial planning, and consequently for decision support systems. In the
present study, a fully spatial physical-biogeochemical model has been combined with scenario
building and optimization techniques as a proof of concept of the use of ecosystem modeling
as an objective tool to inform marine spatial planning. The object of this exercise was to
generate objective knowledge based on an ecosystem approach to establish new mussel
aquaculture areas in a Norwegian fjord. Scenario building was used to determine the best
location of a pump that can be used to bring nutrient-rich deep waters to the euphotic layer,
increasing primary production, and consequently, carrying capacity for mussel cultivation. In
addition, an optimization tool, parameter estimation (PEST), was applied to the optimal
location and mussel standing stock biomass that maximize production, according to a
preestablished carrying capacity criterion. Optimization tools allow us to make rational and
transparent decisions to solve a well-defined question, decisions that are essential for policy
makers. The outcomes of combining ecosystem models with scenario building and
optimization facilitate planning based on an ecosystem approach, highlighting the capabilities
of ecosystem modeling as a tool for marine spatial planning.