DOI: 10.5061/dryad.ghx3ffbmq
title: Combining seascape connectivity with cumulative impact assessment in support of ecosystem-based marine spatial planning

description: 1. Cumulative impact assessment (CIA) is a promising approach to guide
 marine spatial planning (MSP) and management. One limitation of CIA is the
 neglect of seascape connectivity, which may spread the impact of localised
 pressures to ambient areas, e.g. through lost dispersal and recruitment of
 organisms. 2. We here, for the first time, incorporate seascape
 connectivity into a traditional CIA model using a connectivity matrix,
 exemplified by dispersal of propagules estimated through biophysical
 modelling. Two connectivity impactsare identified:
 the source impact represents downstream areas losing
 recruits because of reduced larval dispersal from sites affected by the
 pressure, and the sink impact represents loss of
 recruits originating from upstream areas prevented from settlement in the
 site affected by the local pressure. 3. By including seascape connectivity
 into the Swedish MSP-guiding CIA tool Symphony we demonstrate how to
 practically account for remote effects of local environmental impact. Our
 example on blue mussel shows how reducing mussel fitness in a given area
 may have impacts on mussels far from the acting pressures. Overall,
 results indicate that connectivity impact for blue mussels plays a minor
 role in most areas, less than 10% of the ordinary cumulative impact.
 However, in some smaller areas, e.g. on offshore banks and the Danish
 Straits, seascape connectivity may increase ordinary cumulative impact
 with 20-30%. In an example of scenario-based CIA analyses of MSP
 projections, we demonstrate how impacts of particular management actions,
 e.g. shipping rerouting and wind power developments, can be tracked far
 from the original area of influence. 4. Depending on the dispersal ability
 of ecosystem components, a local pressure may impact a considerable area
 through seascape connectivity, transgressing management units and national
 borders. Although the mean connectivity impact may be modest for a single
 ecosystem component, the consideration of seascape connectivity across
 multiple ecosystem components may significantly alter the mapping of
 cumulative impact and the assessment of different MSP scenarios. 5.
 Synthesis and applications. Our extension of Cumulative Impact Assessment
 offers a new method for mapping and practically integrating seascape
 connectivity with ecosystem-based MSP and other spatial instruments for
 policy making, such as marine protected areas.
description: The article by Jonsson et al. in Journal of Applied
 Ecology presents an extended model for the estimate of marine Cumulative
 Impact Assessment (CIA) that includes seascape connectivity. We use a new
 CIA model (Symphony) based on spatial data layers of human pressures and
 ecosystem components (e.g. mussel reefs, seagrass beds, and photic soft
 sediments), which covers the Swedish Exclusive Economic Zone in the North
 Sea and the Baltic Sea. This CIA model is combined with modelled seascape
 connectivity to show how estimates of connectivity can be implemented into
 a model of CIA. As a demonstration we here consider the connectivity of
 blue mussel (Mytilus edulis/trossulus) habitats represented by the
 dispersal of planktonic mussel larvae. Dispersal was estimated with a
 biophysical model, which simulates the dispersal trajectories of larvae in
 the seascape from release to settlement. Dispersal probability between all
 gridded locations in the seascape was summarised into a connectivity
 matrix. With a set of Python and Cuda scripts the ordinary cumulative
 impact was compared to the cumulative impact when also seascape
 connectivity was considered.