The ocean largely contributes to human wellbeing but is increasingly threatened by human action and climate change [1]. Marine Protected Areas (MPA) are advocated as a key strategy for simultaneously protecting biodiversity and supporting coastal livelihoods [2,3]. They are now part of the Convention on Biological Diversity and the Sustainable Development Goals. Their level of protection encompasses fully protected areas where all activities are prohibited to a range of “partially protected MPA” that allow activities to different degrees [4, 5]. The formers are known to deliver ecological benefits [6, 7, 8] whereas the latter assume that conservation will be achieved through cooperation in the social space [9].
While scientific evidence shows that most benefits including biodiversity conservation, food provisioning and carbon storage stem from fully or highly protected areas, most established MPA are of lower protection levels because of lobbying from current users and political bias towards creating many rather than highly protected areas [6, 7, 8, 10]. Thus, potential benefits and beneficiaries have to be highlighted and understood at a local level to discuss trade-offs and address the ecological, social and economic requirements of sustainability.
However, guiding principles are lacking on how to manage trade-offs in specific social-ecological systems (SES) [11]. Even if conceptual models of SES have been elaborated to characterize human-nature interactions and inform decision-making [12, 13, 14, 15, 16, 17, 18], effective science-policy interfaces in marine environments are scant [8].
There is room for more effective and inclusive science-policy frameworks, including dedicated modelling approaches. Each step of a collaborative prospective modelling from elaborating narratives to interpreting simulation results, including model conception, may help exploring ecological, social and economic consequences of management alternatives at a local level and in the context of on-going climate change.
For decision-makers, there is a growing awareness that integrating valuable scientific knowledge and stakeholders during the management process can offer better outcomes [19, 20, 21, 22, 23, 24, 25, 26] and is less likely to result in the collapse of the resource [27, 28]. But it raises three main challenges for science. First, collaboratively develop narratives that break with the usual approach based on ongoing trends, which has failed to mobilize transformative change [29]. Second, shift from resources toward ecosystem-based management, addressing interactions among scales within SES [30]. Third, better align the modelling practice illustrating trade-offs with the decision-making process ultimately setting management rules [19].
We argue that bridging the gap between what the literature recommends and what is done on the field requires an innovative science-policy framework which identify potential benefits, tackles necessary trade-offs and promotes collective deliberation on management goals and rules. To test this, we hybridized research and decision-making through collaborative prospective modelling in the case of a French Mediterranean marine park. Hence, scientists, policy-makers and stakeholders involved in the management of the MPA conducted this research. Here, we describe how we were collectively able to (i) build contrasting narratives for the future addressing biodiversity conservation, food provisioning and economic activity in the context of climate change; (ii) explore resulting strategies with a science-based SES model illustrating trade-offs; (iii) share common understandings of management issues and raise new concerns.
Findings
Building disruptive narratives to open the range of possible futures (342 words)
Very recent scientific works suggest that we need to move beyond classical scientific studies depicting future trajectories of decline which have failed to mobilize transformative change [19]. Exploring different futures through narrative scenarios prove to be helpful to address MPA management issues in a constructive manner [31]. Lubchenco and Gaines notably emphasize how narratives help in framing our thinking and action [32]. Indeed, like in mythology or literature, these act as a reference frame to which one can refer to make decisions adapted to unpredicted but pictured context. Here, the challenge is to extend or amend our reference scheme by imagining transformative futures.
In our project we did so by inviting scientists, stakeholders and decision-makers to participate in three workshops led by a specialist in building prospective scenarios. Each time, participants were split into three groups for progressively writing a narrative about the Gulf of Lion Marine Natural Park by 2050. It led to the writing of three original and transformative narratives (table 1). 2050 was considered close enough to fit with real political deadline, i.e., the completion of two management plans, and far enough to deal with some expected effects of climate change so as the decline of primary production in marine ecosystems.
Each group focused on fostering one of the three ecosystem service considered: regulation, provisioning or cultural ecosystem service. Ecosystem services are acceptable indicators to assess MPA sustainability in providing a common semantic for all participants with diverse backgrounds. They allow to work on interactions between biodiversity conservation and economic development. Proxys used and related to ecosystem services are also aligned with the ones used in the park management plan, which helps for science-policy dialogue.
To reach the objectives of the narratives, participants were especially requested to give indications about considering climate change impact or not, fishing effort evolution, spatial sea-users’ rights (FPA), facilities planning (artificial reefs, floating wind turbines, harbors and breakwaters, multi-purpose facilities) and ecological engineering (reintroduction of species), the main features of the socio-ecological representation on which we all agreed (see figure 1). [see methods A].
Table 1 – Co-designed visioning narratives built in workshops
Narrative 1: protecting the ecological heritage and strengthening the marine food web in order to promote regulation ecosystem services.
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Starting point: it reports the progressive deficiency of top predators and keystone species (grouper, sharks…) and its corollary: the impoverishment of the whole trophic chain [59]. But this scenario considers the uncertainties surrounding the idea of good ecological status [60] and shifting baselines [60, 61, 62]. Hence, specifying an ideal ecological state to achieve didn’t make so much sense for the participants, who focused on preserving key habitats, keystone species, and enhancing the actual food chain [63]. This strategy was inspired by the ecological concept: the more diversity there is, the greater the resilience of the system [64, 65].
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Management rules: the participants imagined extending full protection up to 30% of the MPA. This ratio was chosen to echo the most ambitious existing target worldwide: the International Union for the Conservation of Nature recommendation that at least 30% of the entire ocean should benefit from strong protection. Participants also proposed stabilizing fishing effort and re-introducing top predators like groupers in the suitable habitats.
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Climate change
Decline of primary production in marine ecosystems
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Fisheries
Constant fishing effort but no fishing on existing reefs & in fully protected areas
Diving
Constant number of divers but no access to fully protected areas
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Fully protected areas
Level:
most ambitious existing target
Location:
most important natural areas all over the rea
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Facilities & ecological engineering
- No development but no removal of artificial reefs
- Acceptation of a small experimental wind farm to evaluate its impacts
- Reintroduction of heritage species
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Narrative 2: upgrading the artisanal fishery in order to promote food provisioning ecosystem services.
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Starting point: it is a strong awareness among the members of the group of the climate change expected consequences on marine primary production, being the first level of the food chain [66, 67]. They figured a decline of primary production due to climate change may be driven by the decrease of nutrients flows due to dams on rivers and partial closure of estuaries. In order to increase the biomass of commercial species, stakeholders proposed actions to be taken on land to avoid the expected decline of marine primary production. They also got inspired by "slow food" movements and invented a "slow fishing" style, in the sense that fishing should respect life cycles of different species and marine habitats, in terms of harvesting gears and anchoring systems. It would still be profitable enough for fishermen because the products would be eco-labeled and valued as such.
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Management rules: only this narrative allows increasing the fishing effort while artificial reefs for productive purpose are favored and commercial species are reintroduced. The share of fully protected areas is kept to current level (2% of the MPA). Climate change leads to a decline of primary production in marine ecosystems, that would be counterbalanced by a spatial development improving the circulations between lagoons, rivers and sea.
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Climate change
Decline of primary production in marine ecosystems counterbalanced by improved circulation between lagoons, rivers and sea
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Fisheries
Increased fishing effort but no fishing on any reefs & in fully protected areas
Diving
Constant number of divers but no access to fully protected areas
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Fully protected areas
Level:
actual MPA’s target
Location:
most important natural areas surrounding the existing marine reserve
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Facilities & ecological engineering
- Increased density of existing artificial reefs villages and creation of new reefs
- Development of a commercial wind farm
- Reintroduction of commercial species
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Narrative 3: fostering a new economy promoting cultural ecosystem services.
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Starting point: it lies in the climate change expected consequences on the coastline and the consideration of a possible radical transformation in coastal livelihoods due to the loss of biomass of the sea induced by a primary production decrease [67]. Even if the sea level rise consequences exceeded our time frame, participants considered it as a major driver of change. They presumed management would fail to prevent sea level rise and decided to put their efforts in making the best of the new resulting land/sea-scape. They invented a new economic model for the park area, valuing marine underwater seascapes, eco-friendly tourism around artificial reefs and wind turbines, or even an underwater museum around aesthetical artificial reefs.
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Management rules: participants assumed a commercial wind farm would be created allowing for a multifunctional exploitation of the water column, including educational sea trips. Artificial reefs villages would be densified to create a relief zone for the rocky coast diving sites. These reefs would have a cultural function, like an underwater museum. Their design would rely on ecological and aesthetical requirements. An intermediary target for fully protected areas was set after Member States Parties to the Convention on Biological Diversity (CBD) agreement to cover 10% of their coastal and marine areas with MPAs by 2020 (CBD Aïchi target 11).
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Climate change
Decline of primary production in marine ecosystems
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Fisheries
Constant fishing effort but no fishing in fully protected areas only
Diving
No access to fully protected areas but increased number of divers with the creation of new recreational reefs
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Fully protected areas
Level:
intermediary target
Location:
most important natural areas but first those surrounding the existing marine reserve
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Facilities & ecological engineering
- Increased density of existing artificial reefs villages and creation of new recreational reefs
- Development of a commercial wind farm
- Sea trips around the farm & diving around recreational reefs
- No reintroduction of species
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Ecosystem-based modelling to address SES complexity (638 words)
Tackling the whole issues marine spaces are confronted to requires MPA managers to adopt an integrated Ecosystem Based Management (EBM) that considers the entire ecosystem, including humans. While fishing affects target species, marine food-webs and habitats (depending on fishing and anchoring gears), climate change is expected to influence the dynamics of all marine organisms in terms of growth and spatial distribution (including primary production).
EBM focuses on maintaining a healthy, productive and resilient ecosystem so it provides the services humans want and need. It requires transdisciplinary approach that encompasses both the natural dimension of ecosystems and the social aspects of drivers, impacts and regulation [33].
Whether “end-to-end models” are recommended by marine scientists to study the combined effects of fishing and climate change on marine ecosystems, using one of these tools was beyond the scope of the project [see methods B]. We looked for alternative ways and built on knowledge and data from the park management plan and on past research conducted on the area: ecosystem-based quality indexes (EBQI) describing the functioning of specific ecosystems and mass-balance models analyzing the overall ecosystem structure and fishing impacts (Ecopath with Ecosim) [see methods C].
We map four major park habitats (see figure 2): “sandy&mud” (31 species), “rock” (18 species), “posidonia” (17 species), “coralligenous” (15 species). Here (group of) species are represented in aggregate form (biomass density) and linked together with diet ratios (see table SM2 a-d).
This ecosystem-based representation is at the core of our modelling exercise. To simulate ecosystem dynamics, we used the ecosystems food-webs as transmission chains for the type of controlling factors described in the narratives [34]: bottom-up control (climate, management), top-down control (fisheries, management). For each (group of) species, biomass variation results from the equal combination of two potential drivers on a yearly basis: the abundance of prey (bottom-up control, positive feedback) and the abundance of predators (top-down control, negative feedback) [see methods D].
To link this food-web modelling with the driving factors described in the narratives, we adopted an agent-based modeling (ABM) framework. ABM are already used for SES applications and science-policy dialogue [see methods E].
We then developed a spatially explicit model for the main dimensions of the MPA described in the narratives. To set up agents and their environments, we used data from the ecosystem-based representation and geographic information systems (GIS) layers provided by the MPA team. To model space, we used a regular grid, the size of each cell being related to the average size of an artificial reef village (0,25 km2). In accordance with our prospective horizon, simulations ran by 2050 with an annual time step.
The food-web model is located at the cell level with previous year's outputs as input data for each new year. Other human and non-human agents are also represented at the cell level. At this stage we model temporal dynamics but lack important spatial dynamics such as adaptive behaviors of human and non-human agents re-locating their activities as a result of management measures. For now, interactions between agents are mostly made of spatial-temporal co-occurrence with restricted mobility.
Despite this, we were able to simulate the variation of any group of species in terms of biomass density in case of a change in primary production, fishing effort, artificial reefs planning or reintroduction of species. In order to disentangle the efficacy of the MPA’s management measures from climate change impact, we ran each scenario with and without climate change (figure 3). Indeed, the variation of primary production is the only difference between scenarios that does not depend on management choices at the MPA’s level. We could capture some of their propagation and final effects on indicators similar to those of the park management plan and the ecosystem services targeted by the narratives: total biomass (regulation services); harvested biomass (provisioning services); diving sites access (cultural services) [see methods F].
Discussing simulation results to inform management choices (1351 words)
No scenario perfectly reaches the objectives it was designed for (Figure 3). However, they all draw interesting perspectives like the occurrence of unexpected co-benefits. The framework we built allows i) looking at the building blocks of the scenarios and the combination of variables so as to explain the results, ii) proposing explanations and suggesting new hypotheses for enhancing the efficacy of each scenario.
Table 2 summarizes the major assumptions of the three scenarios issued by the project team from the narratives.
Table 2 - Overview of the three scenarios
Topic
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Item
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Scenario 1 – enhancing regulating services
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Scenario 2 – enhancing provisioning services
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Scenario 3 – enhancing cultural services
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Climate change - impact on primary production
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Phytoplankton biomass density
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steady decrease up to -4% by 2050
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stable
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steady decrease up to -4% by 2050
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Sea-users - fisheries
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Fishing effort
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stable
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5% increase from 2019
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stable
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Practice area
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artisanal fisheries: 0 to -200 meters; 0 to 6 miles
trawls: prohibited between 0 to 3 miles
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Access rights to FPA
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no fishing in FPA
no transfer to others areas
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Sea-users - diving
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Number of divers
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stable
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Practice area
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most popular diving sites (GIS)
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Access rights to FPA
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no diving in FPA
no transfer to others areas
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Management - FPA
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Share of FPA in the MPA
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30% by 2050 after extensions in 2020/2025/2030
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2% by 2050 after extensions in 2020/2025/2030
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10% by 2050 after extensions in 2020/2025/2030
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Location
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1 existing marine reserve (GIS)
new FPA: GIS layer scaling important natural areas
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Allocation rule
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overall extension after the level of natural value
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extension around the existing reserve
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2020: scenario 1
2025/2030: scenarios 1 & 2
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Management - artificial reefs
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Density of existing artificial reefs villages
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stable
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steady increase from 12% to 50% between 2019 and 2050
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New recreational reefs in new villages
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no
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from sandy habitat to rocky habitat with a density of 50%
colonization by marine organisms following three steps between 2019 and 2024
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Management - floating wind turbines
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Type of farm
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experimental farm of 4 turbines
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commercial farm of 80 turbines
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Location
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map of feasible and acceptable areas
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Allocation rule
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development every five years between 2020 and 2045 around more or less acceptable areas
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Management - multi-purpose facilities
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Sea trips around the commercial farm
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no
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no
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visitor attendance follows from the development of the farm
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Diving around recreational reefs
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no
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no
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visitor attendance follows from the development of recreational reefs
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Management - ecological engineering
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Reintroduction of species in existing artificial reefs villages
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2020-2025: annual release of 1 heritage specie (grouper)
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2020-2025: annual release of 2 commercial species (seabass, dentex)
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no
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Scenario 1 aimed at increasing biodiversity. Simulation results show that (see SM1):
- Undersea biomass varied little (-0.11%), despite the primary production decrease under climate change. Yet, the trophic chain structure changes with huge increase of species important in local fisheries (see biomass variation of each group in SM6 a-e). Mackerel, whiting, hake and tuna but also octopuses and soles notably increase in the muddy and sandy ecosystems; octopuses, seabass but also echinoderms and bivalves and gastropods in the coralligenous ecosystem; echinoderms, octopuses and conger in the rocky ecosystem; suprabenthos, echinoderms, octopuses, conger and scorpion fish in the posidonia ecosystem. The increase in the above listed species is balanced due to the double preys/predators constraint by a decrease in the biomass of other existing species: benthic invertebrates and fish feeding on benthic crustaceans in the muddy and sandy ecosystems; benthic macrophytes, scorpion fish, suprabenthos and lobsters in the coralligenous ecosystem; suprabenthos, salema, seabass and scorpion fish in the rocky ecosystem; and- worse- posidonia itself, salema and crabs in the posidonia ecosystem.
- Fished biomass drops by 36% which is consistent with the high share of FPA in the absence of spatial dynamics and fishing effort relocation.
- Currently appealing diving site will no longer be accessible (-98%) which is expected to support habitats and species biomass regeneration but would mark the end of an attractive activity.
Hence, scenario 1 proposed an extension of FPA up to 30% and located it on the richest areas in terms of biodiversity, which leads to a sharp drop in potential fished biomass indicator. This strong protection may not be sufficient to trigger the system recovery as a whole but greatly change the trophic chain structure improving the biomass of some very important fishing targeted species (see SM6 a-e). This improvement could be seen as a co-benefit aligned with Sala & al., analysis [10]. It opens avenues to move forward searching for “win-win” strategies and opens a perspective of occurring co-benefits for local fisheries in case of spillovers would occur and adequate fisheries management rules were to be defined.
Moreover, if coupled with the same kind of measures allowing to cancel the negative effect of climate change on primary production as in scenario 2, this scenario would exhibit the best results in terms of total and undersea biomass variation- although these indicators alone are insufficient to assess the quality of the ecosystem.
Hence, two hypotheses could be tested: the time horizon may not be sufficient, and/or the intensity of the reintroduction of the keystone species, grouper, is insufficient given the low reproduction rate and longevity of the species. Whatever, it would be interesting to review this scenario searching co-benefits strategies. A new version of the model could test pairing spatial uses rights and different level of protection within a strategic zoning and a connected MPAs network. It would also consider the spillover of marine organisms and the relocation of human activities due to FPA. In this case, would the spillover of marine species be enough so that the relocation of the fishing effort wouldn’t affect too much ecosystem functioning of unprotected areas? In a timely manner, additional measures regulating the fishing effort in a strategic planning/zoning perspective would complement the framework.
Scenario 2 aimed at increasing food provisioning. Simulation results show that:
- Total fished biomass increases by 2% with or without taking into account the climate change impact on primary production, which matches the guideline of the narrative. However, fished biomass increases only in the muddy habitat, by more than 3%, while it decreases by between -3 and -32% in the other habitats, as a result of the counterbalancing effect of keeping the 2% share of FPA. Interestingly, the total biomass in the rocky habitat decreases less (with climate change) or even increases (without climate change) in scenario 2 compared to scenario 1.
- Undersea biomass seems stable when climate change is not included (-0.03%) but will decrease with primary production (-0.89%), in contrast with scenario 1. Compared with scenario 1, few species show significant downward variation, except crabs in the posidonia ecosystem.
- Even with the smallest FPA’s share, currently appealing diving sites are reduced by 63%, which confirms that most existing diving spots are concentrated on areas of high natural value in or around the existing marine reserve of the MPA.
Scenario 2 favors fishing by increasing fishing effort (5%) and limiting FPA (2%). It also supports fishing with the reintroduction of target species and the densification of these species’ habitats. This scenario notably avoids the negative effect of climate change on primary production thanks to ecological measures taken at the watershed level. However comparative simulation results illustrate that the marine park management measures alone would not generate such an effect. In view of the results, the fishing effort may have been increased too early, thereby cancelling out the efforts made elsewhere. Moreover, catches might have been higher if the model had considered a shift of fishing activities from FPA to areas where fishing is allowed. Here, FPA are located on rocky, posidonia, and coralligenous habitats, that are areas of greatest natural value. Even if the share of FPA is the lowest in this scenario, almost all of the rocky habitat (excluding artificial reefs) is concerned, which is one reason explaining the biomass increase in this habitat. This shows the importance of a precise and strategic zoning in determining access rules in MPAs. This is also due to the densification of existing villages and the creation of new villages in the rocky habitat.
Two new hypotheses could then be tested: maintaining the fishing effort at its 2018 level and increasing the introduction of target species? Working more on the dynamics of the trophic chain by reintroducing keystone species rather than target species?
Scenario 3 aimed at increasing eco-tourism. Simulation results illustrate that:
- The main objective of the scenario is not achieved since diving access is restricted by 100 and 91% in the coralligenous and rocky habitats, that host most currently appealing diving sites.
- Undersea biomass (and total biomass) declines more than in scenario 1 (-0.6%), but less than in scenario 2 in the same climatic context of primary production reduction, reflecting the difference in FPA cover of the different scenarios. Interestingly, despite taking for granted the loss of historical ecosystems and traditional economic activities and including primary production reduction, the total biomass increases by 0.12% in the rocky habitat, which is again a better score than what scenario 1 reached.
- Fished biomass lowers by 14%, due to a 10% FPA’s share, and in accordance with a narrative that promotes the creation of alternative economic activities.
Scenario 3 is the scenario that produces the most spectacular results since diving sites access is in sharp decrease whereas it is supposed to favor cultural services.
These results’ explanation lies in a contradiction between the assumptions of the narrative. In fact, by placing 10% of the territory under full protection and locating these areas on sites of high biodiversity, FPA are located on the very sites favored by divers. This contradiction between the goal of this narrative and the restricted access to FPA proves to be a determining factor in the success of the policy. Retrospectively, this may seem obvious but the exact delimitation of access rules to protected areas remains a hot topic. After all, this scenario is interesting because it illustrates an actual dilemma and confirms scenario 2 analysis that access rules need to be aligned and defined with a precise and strategic zoning.
We could then try another hypothesis allowing recreational diving access to FPA while extractive activities remain prohibited.