Spillover refers to the ecological and socio-economic benefits generated by a protected area, particularly a marine protected area (MPA), that extend beyond its boundaries or are received from neighbouring protected areas within a connected landscape or seascape.

Description

Ecological spillover (see ES - Support) occurs when species within a MPA increase in abundance, size or reproductive output, and then disperse outside the MPA through adult movement, juvenile migration or larval export. These processes can operate in two directions: an MPA may actively deliver spillover benefits to surrounding areas, or it may receive ecological inputs from neighbouring MPAs, particularly where there is ecological connectivity, to deliver spillover benefits.

Socio-economic spillover (see ES – Provisioning) arises when these ecological processes lead to improved catches, greater species diversity or larger fish in neighbouring fishing grounds. This supports local livelihoods.

In the context of IMET analysis, spillover can be understood as an ecosystem service provided by the marine protected area. It functions as a supporting service because protection measures within the MPA enhance key ecological processes, such as reproduction, biomass recovery and ecological connectivity with surrounding areas. At the same time, spillover constitutes a provisioning service as these locally generated or externally reinforced ecological processes produce tangible benefits for fishers and coastal communities, such as increased catches, improved species composition and larger average fish size

How to assess spillover in IMET

First, document the evidence
Before classifying spillover, IMET users should complete both analytical sections.
- Supporting ecosystem services (ecological spillover): assess evidence related to ecological processes, such as reproduction, biomass recovery, adult movement, juvenile migration or larval export.
- Provisioning ecosystem services (socio-economic spillover): assess evidence related to the benefits for fishers and communities, such as changes in catches, species composition, fish size or CPUE.
Base your classification on the evidence, not your assumptions
After completing both sections, select the most appropriate classification:
- Supporting only: ecological processes are evident, but socio-economic benefits are not demonstrated.
- Provisioning only: benefits to livelihoods are reported, but the ecological mechanisms are not documented.
- Supporting and provisioning: both ecological processes and socio-economic benefits are supported by evidence.
Link spillover to management effectiveness
The selected classification informs IMET analysis across:
- C1.5 – Ecosystem services (importance and prioritisation);
- I1 - Basic information
- PR7 - Management of key values and threats (management actions).
- O/C2 - ecological outcomes and/or O/C3: Effects on local quality of life.

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