Marine protected areas and ecological restoration strategies are complementary tools to support the conservation of ecosystems and recovery of the ecosystem services that they provide. MPAs are designated areas in the ocean that receive protection to safeguard biodiversity from threats and range from full to minimal protection (Grorud-Colvert et al., 2021). They aim to protect biodiversity and productivity of a defined area of value (natural, cultural and/or social) from degradation. 

Ecological restoration seeks to assist in the recovery of an ecosystem that has been degraded, damaged or destroyed. Restoration activities may be conducted within or outside of marine protected areas and may complement MPA management measures. Restoration activities outside of protected areas can be designed to reduce threats in unmanaged areas to allow for natural recovery or involve active interventions such as planting vegetation, re-establishment of locally extinct species, or the removal of invasive species.

Currently, marine protection and restoration are rarely applied together, missing key opportunities to achieve multiple benefits. Including protection and threat mitigation as core components of protected area management (MPAs, OECMs), and utilizing restoration projects to jumpstart recovery in protected areas has significant potential to improve marine conservation successes. In many situations, agencies have adopted the position of “protect first, restore second,” prioritizing protection over restoration due to the challenges that restoration efforts face in comparison to MPAs (i.e., high cost per unit area and perception of more immediate outcomes). Consequently, restoration has been perceived as a lower priority conservation tool as compared to protection (Possingham et al., 2015).

While prevention is always better than cure, restoration may benefit the quality of the ecosystems being protected. Recent studies have revealed that the perceived challenges facing restoration can be minimized through careful planning and newer cost-effective restoration methodologies and tools (e.g., automated underwater cameras and vehicles for monitoring, automated and remote hatchery set-ups, citizen science initiatives - oyster gardening) (Abelson et al., 2020). 

The process of establishing MPAs and restoration projects follow similar steps (planning and design, implementation, monitoring and evaluation, all within an adaptive management context) (Gann et al., 2019). This is particularly helpful when implementing restoration projects and MPAs together. Keenleyside et al., 2012 proposed a framework for planning and implementing ecological restoration within MPAs. This framework can be applied at any time within well-established MPAs that require ecological restoration to improve their ecological value and/or to stop further degradation of the ecosystem. The framework could also be used concurrently when designing and implementing new MPAs.

MPAs often face similar challenges to restoration (poor implementation and management, lack of short-term benefits, not achieving desired social or ecological goals and global change increasing pressures). Therefore, there is a need and an opportunity to better combine protection and restoration efforts to maximize conservation outcomes. Carefully planned and implemented marine restoration projects within MPAs will become increasingly necessary to maintain biodiversity and ecosystem services in the face of increasing environmental threats including climate change. When protection and restoration are applied in an ecosystem, the net outcomes are increased, and the ecosystem services provision is maximized (Possingham et al., 2015). While MPAs can reduce human impacts and help stop ecosystem degradation from occurring, restoration can help to increase the condition and total area of the ecosystem, increasing habitat and ecological connectivity within the MPA and increasing ecosystem services enhancing resilience to climate change. 

It is critical to note that just because restoration is implemented in an MPA does not mean that local threats are effectively addressed. Despite the major increase in MPAs over the last several decades, most are failing to meet their management objectives. This is often due to lack of funding or technical capacity to manage MPAs, or an inability to effectively manage local stressors including those that occur outside the boundaries of the MPA. Less than 3% of MPAs are considered to be effectively managed and marine habitats and species within MPAs continue to decline. Much like with restoration outside of MPAs, understanding the potential to effectively address local threats within an MPA prior to implementing a restoration project is key.

Whether, When, and Where to Restore Within MPAs

Decisions about whether, when, and where to restore need to be made thoughtfully. Marine restoration projects are costly, and if not designed and implemented correctly, can have a high rate of failure.

Whether to restore

In some cases, the best choice is not to implement restoration activities. For example, an MPA manager may notice coral reefs at their site have been damaged by illegal blast fishing. They may consider implementing a coral reef restoration project to support recovery. However, if there are suitable conditions present for natural recovery (i.e., the cause of degradation, is controlled and there is adequate coral larvae supply, good water quality, available substrate for coral larvae to settle on), natural recovery may occur without any additional intervention - i.e., direct restoration actions are not needed because the corals can recover on their own. 

In another example, if a mangrove forest has been degraded due to a local community overharvesting mangroves for firewood, an MPA manager may consider implementing a mangrove restoration project. However, if the restoration project does not have the support of the local community, they are likely to continue to harvest the replanted mangroves due to a lack of other resource options. In this instance, it would be important to work with the community to identify other sources of revenue (e.g., alternative livelihoods) that could replace the need to harvest the mangroves. It may also be important to implement communication campaigns or behavior change campaigns to build local support for protecting and restoring mangroves.

Key factors to consider before implementing a restoration project include (Keenleyside et al., 2012): 

• Whether direct restoration actions or improved management of threats passive is needed (e.g., whether removing the pressure would result in natural recovery or more active human-interventions are required)

• Whether all factors limiting recovery have been removed, minimized or mitigated

• Whether restoration is feasible based on cost, local capacity, regulatory environment, local support 

• Consideration as to whether there are risks of harmful side effects from restoration activities that could adversely affect local communities or remaining habitats (e.g. sediment resuspension from active re-construction, increasing erosion rates, ecological impacts on endangered species). This might imply the need for an environmental impact assessment before restoration activities are implemented.

An MPA manager may consider implementing a restoration project for a number of reasons:

• An MPA may not be meeting its social or ecological objectives. 

• One or more MPA metrics may have fallen below a key threshold and restoration might be required to recover them. 

• Restoration may be needed to recover a critical species, habitat, or ecosystem service.

• Legal requirements to support restoration may be imposed (e.g., following a disaster such as a ship grounding or an oil spill or when a degraded area is gazetted for protection). 

• The need for climate change mitigation or adaptation may be required that could be achieved through restoration. For example, the restoration of coastal habitats, such as shellfish and coral reefs, may be needed to protect coastal communities from erosion, storms and wave energy. Projects that restore mangroves, seagrasses, and saltmarshes can provide valuable carbon storage benefits to support climate mitigation. 

Before implementing a restoration project, it is important to understand the threats in the area, how well they are being managed, and the local level of support for active restoration activities. It is essential to remember that if MPA management is not able to effectively address local stressors, it does not make sense to implement a restoration project there due to the high potential for failure. 

Guidance for when and where to restore can be found in best practice manuals (coral reefs, shellfish reefs, mangroves, seagrasses, kelp, and saltmarsh) for marine ecosystems and should be informed by the location of habitats prior to damage or degradation, assuming current conditions at the site support ecosystem recovery.

When to restore

As global and local threats to marine ecosystems intensify, MPA managers increasingly need to use restoration to achieve social and ecological goals of MPAs. MPA managers often face limited budgets to support management activities. Therefore, decisions about when to implement restoration are based on prioritizing limited funding between management and active restoration activities. Assessing the full costs of restoration before implementing a restoration project is essential to avoid implementing a project that lacks sufficient funds to deliver the intended restoration outcomes. There are many examples around the world of failed restoration projects that ended when the grant supporting the project finished, did not deliver the desired outcomes, or in some cases, led to damage to adjacent ecosystems. 

Timing is another key consideration to support successful restoration efforts within MPAs. It is important to consider the time of year when restoration will yield the highest benefit (e.g., coinciding with spawning and recruitment seasons for target species; avoiding outplanting during hurricane season; nutrient availability and growing seasons for kelp and seagrass). It may also be important to consider whether implementing a new restoration project could align with when an MPA management plan or zoning plan is being revised or following legislative or policy changes that support restoration.

Where to restore

The decision for where to restore can be based on many factors: 

• Current or historical presence of habitat

• Proximity to existing habitat 

• Ecological and biological factors favoring restoration success 

• Presence of stressors (water quality, shoreline alterations); potential of future climate change impacts

• Human use (boating, harvesting, tourism, subsistence livelihoods) including minimizing potential conflicts 

• Ecosystem services expected to be enhanced from restoration (e.g., coastal protection, biodiversity, etc.)

• Feasibility of conducting restoration - access and logistics

Improper site selection is one of the most commonly cited reasons for restoration failure. To inform site selection, it is important to identify the historical distribution of the restoration targets (species, habitats) and the factors that affect their dispersal and distribution (and therefore, may limit their natural recovery). It is generally not desirable to restore a habitat where it did not previously exist. 

Site selection should consider both ecological and social objectives and be prioritized where known local stressors responsible for damage can be mitigated. Relevant environmental, biological and oceanographic conditions should be considered that affect restoration success, such as hydrodynamic patterns that affect larval and propagule dispersal, water quality and light attenuation, temperature, and growth rates of target species and habitats. It is also important to consider how human uses and current threats (i.e., recent dredging or construction of coastal infrastructure), may have affected current species and habitat distributions, and how they might limit future restoration efforts. 

Restoration actions should be “climate-smart” and consider projects and site-specific vulnerabilities to disturbances. Restoration practitioners need to consider how climate change impacts (e.g., changes in sea level, ocean temperature, precipitation patterns, ocean chemistry) may affect their restoration project and promote adaptation (Abelson et al., 2020). Ultimately, marine restoration needs to be integrated into broader coastal zone management frameworks, to help control external factors, such as pollution, that may undermine restoration efforts.

MPA managers often utilize spatial planning tools (e.g., GIS, MARXAN) to support MPA design and zoning plans. Such tools can also help inform where restoration projects should be located. These tools can help practitioners make strategic decisions about data or models needed for site selection, spatial extent (i.e., size of area to be restored), and spatial configuration of the restoration project (patch shape, connectivity, fragmentation).

Restoration suitability models are an increasingly popular spatial planning tool that can help to identify optimal areas for restoration (Jahnke et al., 2018 ; Howie & Bishop, 2021) (Figure 1). 

Restoration suitability models use geospatial data coupled with environmental variables (past, present and future) and tolerance ranges for the target species and create a composite habitat suitability index across a pre-determined area. Technical guidance has been developed for implementing restoration suitability models, primarily focused on shellfish reef restoration, but the methods are applicable to all marine habitats. Using restoration suitability models tailored to key habitats within MPAs, and under predicted future environmental conditions, will be key to predict where best to locate restoration. Ecosystem service models assess how service supply and value may be impacted by potential management actions, human activities and environmental degradation. They are increasingly used to inform site selection for restoration of marine habitats (e.g., mangroves (Adame et al., 2015), oyster reefs (Theuerkauf et al., 2019), and living shorelines).

Figure 1: Restoration suitability model for the native flat oyster (Ostrea angasi) within the Encounter Marine Park, Kangaroo Island, SA, Australia. Darker shades of blue represent higher suitability areas for oyster restoration. Grey identifies areas where restoration will not be suitable due to (1) being outside the environmental tolerance ranges for the species, or (2) being areas of conflicting use (e.g., mooring zones, aquaculture, recreational swimming areas or navigation channels). Marine park areas with different levels of protection are shown from highest to lowest: SZ: Sanctuary Zone, HPZ: Habitat Protection Zone, RAZ: Restricted Area Zone, GMUZ: General Managed Use Zone. Credits: Alice Howie, The Nature Conservancy, Australia.

Credits: Alice Howie, The Nature Conservancy, Australia

Potential challenges implementing restoration projects within MPAs

When implementing ecological restoration projects within MPAs, challenges may arise. Challenges can arise throughout MPA design, planning, stakeholder engagement and monitoring, and implementation. Usually, challenges can be mitigated through careful planning, design and meaningful inclusive engagement

identifying appropriate timing to establish protection and restoration actions, and robust stakeholder engagement processes that clarify potential adverse effects and realistic expectations. Some challenges faced when implementing restoration within MPAs include:

• Both MPA management and restoration can be expensive, so restoration may require additional long-term funding options and difficult decisions about trade-offs

• Restoration actions may impact the ecological balance of the MPA, resulting in potential negative short-term impacts to the ecosystem services provided by MPAs (increase/decrease of predators, fish abundance, species, etc.)

• Restoration actions, especially when restoring hard-substrate habitats (shellfish and coral reefs, mangrove forests) can affect the hydrodynamics of the seascape, resulting in sediment movements or change to water flow that can impact the stability of adjacent habitats. 

• Stakeholder conflicts: 

  • Restoration projects within MPAs may make certain areas off limits that previously allowed human uses to occur (e.g., zones for recreational, tourism, fishing, subsistence livelihood activities etc.)

  • Some stakeholders may perceive the restoration of certain habitats and their short-term impacts as high risk to adjacent habitats or species that the MPA is trying to protect. This may cause conflicts between the stakeholders that support the restoration versus those that are concerned it will adversely affect species protected within the MPAs.

• Restoration projects can take over a decade to achieve goals of recovering lost ecosystem structure and function.