# How to deal with invasive species that have high economic value?

Gustavo F de Carvalho-Souza, Melina Kourantidou, Irene Laiz, Martín Andrés Nuñez, Enrique González-Ortegón

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Gustavo F de Carvalho-Souza, Melina Kourantidou, Irene Laiz, Martín Andrés Nuñez, Enrique González-Ortegón. How to deal with invasive species that have high economic value?. Biological Conservation, 2024, 292, pp.110548. 10.1016/j.biocon.2024.110548. hal-05242561

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Policy analysis

# How to deal with invasive species that have high economic value?

Gustavo F. de Carvalho-Souza<sup>a, b, *</sup>, Melina Kourantidou<sup>c, d</sup>, Irene Laiz<sup>b</sup>, Martín Andrés Nuñez<sup>e</sup>, Enrique González-Ortegón<sup>a</sup>

<figure><img src="image_2.png" /></figure>

## ARTICLE INFO

**Keywords:**

- Non-indigenous species

- New resource exploitation

- Integrated participatory strategy

- Citizen science

- Blue economy

## ABSTRACT

The ever-accelerating process of introduction and establishment of invasive alien species (IAS) in marine waters requires engaging different actors in the management and planning. To address this challenge, stakeholders need an integrated approach for defining actions of control and management within an ecosystem-based framework: to seek and enhance coordination, collaboration and trust among all stakeholders affected by changes in linked marine social - ecological systems. This study explores the complexities and opportunities in managing economically valuable IAS, demonstrating the need for tailored management strategies that consider key ecological details needed for successful control such as timing of removals and key economic considerations such as appropriate incentive mechanisms and time horizons in favor of long-term conservation goals. We propose a set of actions that can serve as a roadmap for effective IAS control and management, considering their dual role as nuisances and valuable resources. These actions pertain to local, regional and international levels, encouraging meaningful stakeholder engagement through co-management structures that can foster the development of robust management plans, enabling better IAS control. The outcome holds potential for positive contributions to the blue economy— sustainable use of marine resources, including fisheries, tourism, and renewable energy— and for meeting sustainability objectives.

## 1. Introduction

The growing numbers of biological invasions present a mounting global environmental concern due to their substantial ecological and economic impacts (Simberloff et al., 2013; Diagne et al., 2021). The establishment of non-native species outside their natural ranges is increasing due to global trade, human activities, and warming (Katsanevakis et al., 2014), resulting in alarmingly increasing numbers of invasive alien species (IAS) and severe impacts on ecosystems and human wellbeing (Seebens et al., 2017). Biological invasions pose multifaceted risks to multiple sectors of the economy, threatening global and regional economies. Different countries, interconnected through trade routes, face the peril of invasive species disrupting native ecosystems, leading to biodiversity loss, agricultural yield declines, habitat degradation, damages to human infrastructure and threats to human health, among others (Hudgins et al., 2023). The increasing severity of

such impacts highlight the need for coordinated international action to mitigate these pervasive threats and safeguard ecological, social, and economic wellbeing. The cost of biological invasions worldwide has recently been estimated at a total of $1.288 trillion (in 2017 $US) for the interval between 1970 and 2017, averaging $26.8 billion annually (Diagne et al., 2021). The costs of invasions for Europe have been estimated at $140.20 billion between 1960 and 2020 (Haubrock et al., 2021), while more recent works have provided evidence for even larger hidden costs of biological invasions, with a concerningly increasing future trajectory (Henry et al., 2023). While these estimates may entail uncertainties, the economic toll and risks to biodiversity and human wellbeing are clear and require coordinated management actions, alongside careful policy design.

Given the escalating global concern over the mounting impact of biological invasions, particularly in light of their ecological and economic consequences, the European Union (EU) has positioned itself as a

<footnote><sup>a</sup> Instituto de Ciencias Marinas de Andalucía (ICMAN-CSIC), Campus Universitario Río San Pedro, 11519 Puerto Real, Cádiz, Spain</footnote>

<footnote><sup>b</sup> Departamento de Física Aplicada, Instituto Universitario de Investigación Marina (INMAR), Universidad de Cádiz, Campus de Excelencia Internacional/Global del Mar (CEI-MAR), Puerto Real 11519, Cádiz, Spain</footnote>

<footnote><sup>c</sup> Department of Sociology, Environmental and Business Economics, University of Southern Denmark, Degnevej 14, 6705 Esbjerg Ø, Denmark</footnote>

<footnote><sup>d</sup> Université de Bretagne Occidentale, AMURE, Plouzanè, France</footnote>

<footnote><sup>e</sup> Department of Biology and Biochemistry, University of Houston, Houston, TX 77204, USA</footnote>

<footnote>* Corresponding author at: Instituto de Ciencias Marinas de Andalucía (ICMAN-CSIC), Campus Universitario Río San Pedro, 11519 Puerto Real, Cádiz, Spain. E-mail address: gustavo.souza@csic.es (G.F. de Carvalho-Souza).</footnote>
key player, implementing comprehensive strategies to effectively manage and mitigate the impact of invasive species on biodiversity (Katsanevakis et al., 2023). The EU's Biodiversity Strategy for 2030, coupled with the Marine Strategy Framework Directive (MSFD) and the pivotal IAS Regulation 1143/2014, exemplifies its commitment to fostering a model for coordinated management policies at a pan-European level. Close to a decade ago, the EU implemented the IAS Regulation on the "Prevention and management of the introduction and spread of IAS" (EU, 2014). The species of Union concern are those whose damage is so significant that justifies the adoption of dedicated measures applicable across the EU, including in countries not affected (EU, 2014). However, despite the ongoing invasions and associated impacts in aquatic realms and particularly marine systems (Cuthbert et al., 2021), only two marine species, including the striped eel catfish *Plotosus lineatus* and the brown macroalgae *Rugulopteryx okamurae*, have been added to the list (EU, 2019, 2022). Using a horizon scanning tool, Tsiamis et al. (2020) identified 26 top-priority marine IAS in EU waters based on feasibility of management. The list is dynamic and allows for the addition of new species following specific criteria and formal risk assessments.

Controlling marine IAS has been less successful than in terrestrial and aquatic enclosed systems (Simberloff, 2021), and can be more costly, due to the sea's high connectivity, difficulties in early identification and increasing shipping volume which facilitates the transfer and introduction of new organisms, especially if these are highly prolific and dispersive (Giakoumi et al., 2019). The high connectivity of marine environments also means that eradication efforts may be hindered by continuous reinfestations. The inherent difficulties and costs in early detection, coupled with the vastness of the marine ecosystem, make it challenging to implement timely and effective control measures.

Traditional invasive species management strategies can be costly and yield limited success, leading to stakeholder frustration and deterring policy makers from future investments, affecting collaborative initiatives and engagement in resource management. In marine ecosystems, the knowledge gaps and difficulties in successful management are particularly pronounced (Lockwood and Robinson, 2014; Cuthbert et al., 2021). In recognition of these challenges, there is an increasing dialogue about the benefits of involving citizen and stakeholder engagement in harvesting IAS. This approach focuses on control through recreational and commercial utilization of certain IAS, leveraging their potential recreational or commercial value where it exists. In recent years, this idea has become popular among managers who see it as a practical and cost-efficient complementary solution for population control, offering an alternative to traditional management methods. Cost-efficiency considerations are tied to the high labor costs of scientists, environmental technicians, or practitioners particularly in marine and costal settings.

Incorporating IAS into local economies and culinary cultures has been used in various contexts for controlling marine invaders. It is often promoted as a win-win solution providing both ecological and economic benefits, even though in practice, its effectiveness has varied. Although it has potential to contribute to the provision of new resources/commodities, alongside shifts in habitats, ecological functions, and food webs (Katsanevakis et al., 2014), commercial harvesting on its own cannot guarantee success in controlling an invasive population (Nuñez et al., 2012; Kourantidou et al., 2022; Meadows and Sims, 2023). At the same time, policies on newly introduced species supporting recreational activities and associated economies (i.e. recreational fishing activities) could come with conservation risks resulting from new invasions. For instance, for some cases in Spain, the environmental legislation (the Law on Natural Heritage and Biodiversity; BOE, 2007) may paradoxically allow for "favoring" exotic populations, thus legalizing the release of exotic species to be used for fishing and hunting purposes. In fact, when these invasive populations have a value in the market, the legislative approach differs to allow for capturing recreational or even commercial benefits of these species, despite the known economic toll of biological

invasions in the country (Angulo et al., 2021). Such policies have often created conflict among stakeholders.

Coordination and cooperation among stakeholders impacted by changes in marine ecosystems is instrumental to successfully addressing biological invasions (Giakoumi et al., 2019; Novoa et al., 2018; Shackleton et al., 2019) and is also key to successful ecosystem-based management (EBM) approaches (Long et al., 2015). The EBM framework aims to enhance natural assets, promoting ecosystem resilience against IAS. In marine environments, this involves implementing multiannual plans, robust monitoring and habitat assessment programs, and measures to ensure that exploitation for any non-indigenous species happens with sustainability, conservation and social wellbeing criteria in mind (Kleitou et al., 2021; Levin et al., 2009; Ojaveer et al., 2014).

The aim of this study is to (i) showcase key elements of an integrated approach for stakeholder involvement in IAS control and management and (ii) identify key actions for stakeholders. We assess those dimensions through case studies in the Gulf of Cadiz (GoC), a marine transboundary ecoregion recognized as a biodiversity hotspot and of special conservation importance, both regionally and internationally. The analysis leverages fishery data obtained from official, publicly available sources, provided by the General Directorate of Fisheries and Aquaculture of the Junta de Andalucía (IDAPES, 2023), examining the socio-economic impacts of native and invasive species' fisheries and human activities. The proposed framework provides insights into the role of recreational and commercial harvesting of IAS as an engaging policy tool that simultaneously aims to foster co-management practices and empower regional stakeholders in designing and implementing effective management strategies. The case studies offer valuable policy insights and contribute to the advancement of policy design for effective and engaging management of IAS in aquatic systems. These lessons emphasize bottom-up, stakeholder-driven approaches, ensuring that management strategies are not only effective but also participatory. Such methodologies are key for aligning with broader global sustainability initiatives like the Ocean Decade, Blue Economy, and EU regulatory frameworks and sustainability goals.

## 2. Case study of IAS in SW Europe: The Gulf of Cadiz ecosystem

The accelerated introduction and establishment of invasive species, over recent decades, have had a significant impact on the ecological balance of the GoC ecosystem (González-Ortegón et al., 2020). A prominent example is the American red swamp crayfish *Procambarus clarkii* (Girard, 1852), which was intentionally introduced in southern Spain in the 1970s (in Badajoz and later Seville) for its high economic value and in light of the declines of the European crayfish (*Acevedo-Limón et al., 2020*). The species established successfully and quickly spread throughout the Iberian Peninsula, triggering serious ecological impacts and losses to ecosystem services (Gil-Sanchez and Albercedor, 2002).

Recently, two new non-native species of commercial importance in their native zones have been established in the GoC: the weakfish *Cynoscion regalis* (Bloch & Schneider, 1801) and the Atlantic blue crab *Callinectes sapidus* Rathbun, 1896 (Table 1). It is hypothesized that both species were introduced via ship ballast water with subsequent successful establishment and dispersal (Morais and Teodósio, 2016; González-Ortegón et al., 2022).

The weakfish, native to the northwest Atlantic, has been established in the GoC since 2011 and is targeted by artisanal fishermen in the region (Bañón et al., 2017). The known negative impacts of this invasion include direct predation (e.g. European anchovy; González et al., 2022) or competition for resources with other similar native sciaenid fishes, such as the meagre *Argyrosomus regius* (Asso, 1801).

The Atlantic blue crab has a wide natural range throughout the American eastern shores. It has been reported on European and Mediterranean coasts since the 1930s, and its rate of expansion has accelerated since 2010 to the western Atlantic Ocean (Mancinelli et al., 2017;
<table><caption>**Table 1**
Native and non-native range of two native (green crab and meagre) and two non-native (blue crab and weakfish) species in the Spanish Gulf of Cadiz.</caption><thead><tr><th>Species</th><th>Native distribution</th><th>Non-native distribution</th></tr></thead><tbody><tr><td>Callinectes sapidus</td><td>Atlantic American coasts from Nova Scotia in Canada to northern Argentina, including Bermuda and the Antilles</td><td>Asia, Northern Europe, the Mediterranean Sea and the Black Sea<br/>Northwest Atlantic (from Maryland-Newfoundland), the Southwest Atlantic (Patagonia), the Southeast Atlantic (South Africa), the Northeast Pacific (from California-Alaska), the Northwest Pacific (Japan), and the Southwest Pacific (Australia)</td></tr><tr><td>Carcinus maenas</td><td>European coasts from Iceland and Norway to Mauritania, West Africa</td><td>Europe; Schelde estuary (Belgium/The Netherlands) and Iberian Peninsula</td></tr><tr><td>Cynoscion regalis</td><td>East coast of North America</td><td></td></tr><tr><td>Argyrosomus regius</td><td>Eastern Atlantic: Norway to Gibraltar and Congo, including the Mediterranean and the Black Sea</td><td>Red Sea through the Suez Canal</td></tr></tbody></table>

González-Ortegón et al., 2022). This species has a wide ecological tolerance, a migratory lifestyle between estuaries and offshore areas, and is able to lay 2–5 million eggs in a single clutch. Recent high temperature events in the Iberian coast (ICES, 2020) may further favor this high fecundity. In fact, a rapid and massive growth of blue crab has been observed in the GoC, enhanced by climate change. Ovigerous females were detected during the 2022 extensive warming period (early spring and early autumn), something not commonly observed in native crabs. Blue crabs were harvested by coastal fishers around that same period (summer of 2022) in several tourist zones within the GoC. The high reproduction rate, combined with an optimal thermal suitability and the absence or decline of potential predators due to multiple factors (e.g., overfishing, pollution, warming), has created concerns on the difficulties embedded in managing and controlling this invader.

Other newly reported non-native species that are becoming established in the GoC are the brown macroalgae *Rugulopteryx okamurae*, native to the western Pacific, and the snapping shrimp, *Alpheus* cf. *lobidens*, native to the Persian Gulf (Barcellos et al., 2023; de Carvalho-Souza et al., 2024). The establishment of these and future IAS are expected to result in ecological changes and adverse impacts, hence requiring conservation priority actions to be taken. However, contrary to the policy framework we propose, capture and trade for non-native species listed in the catalogue of IAS is not allowed under the Spanish Law 42/2007 on Natural Heritage and Biodiversity (unless a special permit has been granted). This policy could be seen as favoring the presence of these IAS, even though the legislation's objective is to prevent their dispersal, thus possibly resulting in unintended consequences and negative externalities.

### 3. Biological invasions and stakeholder engagement: ecological, cultural, and socio-economic dimensions

Engagement of stakeholders entails the inclusion of diverse actors and allowing them to meaningfully interact with each other in management and planning (Table 2). The first step is to identify the relevant stakeholders and agree on shared goals and important issues that need to be resolved (Cavanagh et al., 2016; Novoa et al., 2018; Shackleton et al., 2019), particularly in the presence of stakeholder conflict. Such inclusive approaches are meant to encompass the needs and differences between stakeholders and ultimately lead to a stronger basis for developing realistic and effective management solutions. That is, for IAS management in marine environments, the relevant stakeholders include

<table><caption>**Table 2**
Actions that can be integrated to maximize the chances of a successful IAS management and control framework.</caption><thead><tr><th>Stakeholders</th><th>Management actions to control invasive species</th></tr></thead><tbody><tr><td>Scientists; Students</td><td>Expand scientific knowledge on IAS and their impact on biodiversity and ecosystem services</td></tr><tr><td>Conservation practitioners; Fishermen; Scientists; Citizen scientists</td><td>Restore populations of native predators that feed on IAS, to help improve the local economy through enhancing local fisheries and reducing the cost of IAS control</td></tr><tr><td>Scientists; Conservation practitioners</td><td>Design management and timing of removal initiatives with most suitable life stages in mind, to maximize potential for successful control</td></tr><tr><td>Blue economy entrepreneurs; Chefs; Seafood wholesalers and retailers; Conservation practitioners; Fishermen; Scientists</td><td>Explore known uses of IAS to promote targeted removal strategies contributing to control and successful management of the invasive population in the long run</td></tr><tr><td>Decision makers; Conservation practitioners; Fishermen</td><td>Incentivize targeted fisheries of IAS with licenses, ensuring that disincentives to maintain or recreate invasive populations are not created in the process, and establish an obligation for reporting catch details, including location, to allow for effective monitoring</td></tr><tr><td>Scientists; Conservation practitioners</td><td>Provide education and training to advance knowledge on how to harvest and contribute to combatting IAS</td></tr><tr><td>Scientists; Conservation practitioners; Students; Divers; Volunteers</td><td>Promote public awareness and academic-cultural events</td></tr><tr><td>Scientists; Students; Divers; Volunteers; Local citizens</td><td>Support large removal actions by trained individuals to reduce the impact of IAS in highly invaded ecosystems</td></tr><tr><td>Scientists; Fishermen; Divers; Seafood wholesalers and retailers; Chefs, Blue economy entrepreneurs; Conservation practitioners; Decision makers; Local citizens</td><td>Create regional networks of active professionals to construct or improve plans for managing IAS and where possible promote co-management structures</td></tr><tr><td>Scientists; Conservation practitioners; Decision makers; Non-governmental organizations</td><td>Ensure support from stakeholders for any policy decisions, and management design along with commitment for sustaining efforts related to the implemented policies in a multilateral way, driving the effective integration of EBM for IAS management, both horizontally and vertically</td></tr><tr><td>Scientists; Conservation practitioners; Decision makers; Non-governmental organizations</td><td>Communicate progress throughout the different stages and highlight the impact of information, products, or plans generated by local stakeholders and policy makers for managing IAS</td></tr></tbody></table>

marine scientists and coastal users of all sorts, such as fishermen, divers, seafood wholesalers/retailers, chefs, blue economy entrepreneurs, environmental technicians, decision makers, students, and local citizens. Although the perspectives and interests of all these different actors differ, it is important to build a common solid understanding and reconcile views and expectations with respect to management goals before designing policies and actions. Scientists typically care for distribution, establishment, spread, pathways, control measures, future predictions, and impact extent on biodiversity, ecosystems, human health, and society.

For the case of the invasive blue crab, natural scientists are focusing on issues such as: genetic diversity and population connectivity, larval development and habitat preferences, growth and life-history parameters, trophic ecology, and potential impacts on native species (http://invblue.csic.es). Economic and social dimensions that fall within social scientists' interests, such as those of environmental and resource economists, include economic impacts on ecosystems, local industries
and communities alongside benefits of control, management costs, market failures, and distribution of costs of invasions across societal actors. Other social sciences considerations include trade dimensions, cooperation, and incentives for removals as well as risk assessments and efficiency of policy instruments. These interests are closely aligned with those of regional stakeholders such as fishers, retailers and entrepreneurs, a lot of whom seem concerned about the impact of the increase in exotic populations, like the blue crab, on native species of commercial interest, for example, through predation (Ortega-Jiménez et al., 2023).

A notable addition to the stakeholder landscape in aquatic ecosystems is the citizen science programs. These are central to stakeholder engagement and have been used for several years globally to aid with early detection and monitoring of new IAS. These programs go beyond engagement of professionals and regional actors and often encompass members of the general public, such as coastal residents. Numerous global initiatives showcase citizen involvement in tackling invasive species challenges. Notable examples include the 'Seawatchers' project in Spain (http://www.observadoresdelmar.es) and similar programs in Portugal, where citizens contribute geo-referenced observations of marine species, aid in species identification, and monitor the spread of invasive species (Encarnação et al., 2021). Additionally, initiatives like the 'Sun-coral' project in Brazil trains divers, public managers, and local communities to remove invasive corals, generating additional income through the sale of craftwork made from coral skeletons (Creed et al., 2017). Human removal of IAS like the lionfish (*Pterois* spp.) in areas where diving is possible, has been a method employed to engage the public in local spearfishing competitions in the western Atlantic (Chapman et al., 2019). In the Caribbean, several women's organizations manufacture jewelry from lionfish fins, spines, and tails, providing increased household income and empowerment, business skills, and awareness about bioinvasion threats (Chapman et al., 2019). Nevertheless, in the Caribbean, the eradication of lionfish has posed significant challenges attributed to their metapopulation dynamics and the presence of deep refuge populations (Andradi-Brown et al., 2017).

Stakeholder engagement can include informal partnerships, multidisciplinary actions, or public events (e.g., culinary experiences such as IAS tastings or chef cook-offs, academic-cultural fairs/workshops, etc.) to raise awareness on these species, as shown for example in Greece (http://www.4alien.gr) and Portugal (Cerveira et al., 2022). The search for innovative culinary experiences using natural and sustainable ingredients has inspired creative chefs from world-renowned Michelin-acclaimed restaurants to develop new recipes. The platform “Eat The Invaders” (http://eattheinvaders.org), where the concept of “Invasivorism” was coined, shares information about IAS for preparing gourmet meals across the US. These types of initiatives have been shown to successfully raise awareness on invasive species problems and at times contribute to controlling invasive populations.

To be successful however, any management campaign using mechanical removal (that would be for example required for supplying such culinary initiatives to secure a steady supply) careful attention must be paid to invasion and population dynamics. For example that could include removing enough individuals of vulnerable life-history stages to cause a decline in population growth and size (Nuñez et al., 2012). For the cases of the blue crab and weakfish populations, fishing pressure at early stages of the invasion have good potential for successful control. These types of initiatives should therefore be informed by ecological knowledge and be designed and timed accordingly to have a meaningful contribution to the control of the invasion problem.

The recently introduced blue crab and weakfish in the GoC are not well-known yet as a food resource among the locals. While both stocks and prices are increasing, the blue crab is gaining culinary value due to its good taste, making it a potential target for future management programs. Despite this potential, it is also important to bear in mind that the economic exploitation of IAS may motivate people to keep these unwanted species (Nuñez et al., 2012), so that any management initiatives involving harvest strategies need to be designed with appropriate

incentive mechanisms and time horizons in mind in favor of long-term conservation goals. Effective strategies to avoid the cultural absorption of these species depend on how these IAS are presented to the local population alongside the design of incentive mechanisms if harvest is used as a means of control (Mancinelli et al., 2017; Meadows and Sims, 2023; Jungers et al., 2023; Xuan et al., 2023). Information campaigns are crucial to share with clarity the management goals behind any implemented initiative for controlling the spread of IAS, to avoid negative knock-on effects.

Transitioning to awareness, education, and engagement initiatives specific to the blue crab, sharpens the focus on the pivotal role of informed public participation. Awareness and public education have been identified as central priorities in determining and understanding the trade-offs present for IAS exploitation (Giakoumi et al., 2019). Furthermore, engaging relevant local stakeholders and the general public in management initiatives, such as removing IAS (by fishing/harvesting) or creating byproducts, enhances their acceptability and participation. Educational initiatives, like the OCEAN Night project (http://oceannight.eu), are developing science communication actions to educate citizens about IAS-related issues and encourage engagement in conservation. The OCEAN Night immerses people of all ages in interactive ludic games to raise awareness about the IAS and help educating younger generations in particular. It is an excellent example for promoting engagement that demonstrates how participants have acquired an active role in disseminating the information and directly engaging in activities such as fishing to control IAS in the GoC. This highlights the important role of such awareness and education initiatives and their potential for impact that aid conservation efforts.

These types of actions aim to generate meaningful engagement to support policies that require societal-level backing. The expectation is that such initiatives, besides their educational role, also help people feel connected with the need and process of developing practical solutions, thus promoting a society that is more interested, aware, and committed to marine citizenship and literacy.

## 4. Cooperation, market dynamics and socio-ecological challenges in fisheries policy for IAS management

Regional cooperation is essential to limit the spread of IAS, conduct accurate risk assessments, and mitigate the impacts on ecosystem and fisheries (Katsanevakis et al., 2014). Co-management processes have been shown to have great potential in managing invasive species and allowing for an inclusive approach that promotes meaningful engagement with regional stakeholders (Moon et al., 2015). In the case of the GoC ecosystem, steps have been taken in this direction and are backed by existing EU base directives (MSFD and Water Framework Directive) that guide decision-making processes for achieving societal and policy goals.

Bringing together various different stakeholder groups such as government, research, fishing, tourism, aquaculture, shipping, and non-governmental organizations (Llope, 2017) and engaging them in participatory processes resulted in the implementation of several fisheries management measures, such as effort regulation and seasonal closures (de Carvalho-Souza et al., 2021), and in the establishment of a fishing reserve (BOJA, 2004). These collaborative efforts have played a crucial role in reverting the progressively degrading ecosystem of the GoC linked to high fishing pressure and the dominance of opportunistic species. The measures adopted in the last 20 years have resulted in a more stable ecosystem, where top-down control is regaining importance (de Carvalho-Souza et al., 2021). The increase of important functional groups, such as hake, cephalopods, rays, and sharks in the GoC may have a positive effect in relation to the invasive blue crab and weakfish IAS. These predator species occupy high trophic levels and are known to predate on these IAS in their native zones (Epifanio, 2019). Recovery of the predators and fishing management plans (quotas and closed seasons) for them can contribute to IAS control. The fishing sector can therefore
play a key role in achieving such goals. Additionally, in a world of depleting fish stocks, including in the GoC (Coll et al., 2014), IAS that have a value in the market are increasingly becoming the target of commercial exploitation for the fishing industry (Glamuzina et al., 2021).

Blue crab and weakfish have been listed as commercial species in Spain since 2019 (BOE, 2019). In late 2021, the regional government of Andalusia allowed the shellfishing of blue crabs by issuing its first licenses. Owing to great local interest for shellfishing, these measures had an immediate effect on the catches of these species (Fig. 1). The average prices for blue crab (2021–2022) in the GoC fish markets range from €5.70 to €6.60 per kg, which are comparable to other high-quality native species. However, weakfish has a lower average price of €2–2.30 (2021–2022), compared to the meagre which is the native equivalent and has a depleted stock (€9.43–10.59, 2021–2022). While the factors determining the price difference have not been studied, the general perception is that unfamiliarity with a new fish product such as that of the weakfish may be driving a low market interest and therefore price.

Public awareness activities to inform about the quality of IAS seafood products and their food safety can help improve consumer and retailers' perceptions while information on their ecological role and harvesting conditions could make the product more attractive, which can all be expected to contribute to a better market price. Such initiatives that shift market perceptions can help shift attention away from overfished native stocks and contribute to the conservation of the latter and the viability of the local fishing sector.

An additional dimension that hasn't been assessed as much thus far in the IAS and fisheries literature is how the markets for invasive species in one location (invaded range) interact with market and resource dynamics in their native locations (Kaiser et al., 2021). Such interactions may include economic demand and supply dynamics, where for example the demand for the species in its new range can impact demand and harvesting in its native range. Prices may also be affected; for example, the influx of a new perhaps cheaper source of the species from the invaded range may lower global prices. Economic implications in both ranges can influence resource management policies. For example, overfishing in the native range due to increased demand might lead to stricter conservation measures and a shift to increased supply from the market in the invaded range. The US market, where the blue crab is native, has generated around $240 million in 2021 (Fig. 2), but its abundance has shown severe fluctuations from year-to-year and many

regions have seen decreases in landings in recent years (NOAA, 2023). Likewise, weakfish is classified by the IUCN Red List as endangered in its native zone since, according to their most recently available assessment (ASMFC, 2022), as there has been a large increase in natural mortality and the stock has been severely depleted to a degree that hasn't allowed for recovery (Barbieri and Barbieri, 2020).

The commercial harvest of these species in non-native areas of distribution can temporarily help reduce pressure on stocks in native areas of distribution while simultaneously supporting fishers and associated businesses in coastal regions where the invasion is present. Such actions that complement markets for the same product require communication and integration across scientists, managers and stakeholders to ensure that shared goals are in place that can facilitate efficiency (i.e. through quality controls, traceability procedures, standardization in marketing and export strategies (Mancinelli et al., 2017), as well as adherence to sustainability and conservation principles with respect to the invasion, in pursuing these market pathways (Kaiser et al., 2021; Kourantidou and Kaiser, 2019a).

The invasive blue crab and weakfish in the GoC are two examples that highlight the many challenges in IAS control due to complexities in life cycles. The high economic value of the blue crab and its ability to reproduce in coastal areas, particularly by spreading females with eggs (Epifanio, 2019), make it attractive for local fishermen who may wish to maintain a viable population of the invasive crab. The control of blue crab populations, therefore, may rely on the willingness of fishermen and compliance with any management regulations in place. Both the blue crab and the weakfish share a complex life cycle that depends on both the open sea and coastal zones for juvenile development. Understanding the intricacies of their life cycles is crucial for effective fishery management and control. In those cases where fisher incentives are inadequate, policy makers can resort to either targeted removal efforts or the use of bounties to further incentivize fishers. These options need to be weighed upon cost and efficiency considerations, and conservation goals in mind to avoid development of incentives to maintain the invasive populations in the long run. Such considerations are critical, especially in the light of past experiences where valuable invasions have shifted research agendas and management goals in favor of conservation, have led to pressure for sustaining exploitation of the invasion over time, and have even resulted in “sustainability” seafood certifications (Spiridonov, 2018; Kourantidou and Kaiser, 2019a, 2019b; Kourantidou and Kaiser, 2021; Nuñez et al., 2012; Demirel et al., 2021; Katsanevakis

<figure><img src="image_3.png" /><figcaption>**Fig. 1.** Monthly data of total catch weight (black solid lines) and total market price (native, green; invasive, red) during the first sale in fish market, at auction or wholesale market of two native (green crab and meagre; upper panels) and two non-indigenous (blue crab and weakfish; lower panels) species in the Spanish Gulf of Cadiz (between 2000 and 2023). Note that scales are adjusted to each variable's range of values. The inset shows the margin economic profit trend (€/kg) from the market prices for each species (black points and dashed lines). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>
<figure><img src="image_4.png" /><figcaption>Fig. 2. Annual data of total landings (black solid lines) and total market price (blue solid lines) of blue crab and weakfish from US landings (between 1950 and 2021). Note that scales are adjusted to each variable's range of values (NOAA, 2023). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

et al., 2023; Kourantidou et al., 2022).

## 5. Call for action: stakeholder engagement, policies and management for marine IAS

The accessibility and widespread availability of information can bring together different groups interested and competent to contribute to IAS management. Multiple groups of stakeholders across the world are already working on ways to understand, mitigate, and exploit IAS, providing unique opportunities for a meaningful involvement in their control and conservation. Here we have provided two examples from the GoC that highlight the possibilities and complexities associated to commercially harvestable invasive populations. Drawing from these cases as well as the international literature on such species, markets and affected communities, we call for action suggesting eleven action items that can be integrated to maximize the chances of a successful IAS management and control framework (Table 2).

The GoC ecosystem highlights the opportunities and challenges of managing valuable IAS in a biodiversity hotspot area. The presence of a potential market for these species adds complexity, but it also offers a unique opportunity to develop new ways of mitigating the invasion impacts by designing suitable management actions and encouraging stakeholder engagement. Importantly, a key lesson emerging from this experience, that has previously not attracted as much attention when communicating to the general public, is the importance of the timing of removals considering life stages and popular dynamics. These considerations need to feed into fisheries management and the design of any relevant policies around fisheries ensuring that local stakeholders are on board with such targeted management approaches from early on. Thus far, invasive species have been managed in a predominantly reactive manner, seeking to address impacts post- occurrence or in response to social pressure. This results in policy measures with only partial or limited effectiveness in terms of control, primarily owing to their insufficient enforcement delayed or uncoordinated implementation, with various disparities in time and context. Drawing upon insights from the assessment of the IAS in the GoC and the broader literature on these types of invasions, our approach alongside the proposed actions aim to pave the way for more meaningful stakeholder engagement and coordinated efforts as part of a robust set of policies, and management practices in tackling IAS.

### CRediT authorship contribution statement

**Gustavo F. de Carvalho-Souza:** Writing – review & editing, Writing – original draft, Investigation, Formal analysis, Data curation, Conceptualization.
**Melina Kourantidou:** Writing – review & editing, Writing – original draft, Conceptualization.
**Irene Laiz:** Writing – review & editing, Writing – original draft, Supervision.
**Martín Andrés Nuñez:** Writing – review & editing, Writing – original draft, Supervision.

Enrique González-Ortegón: Writing – review & editing, Writing – original draft, Supervision, Conceptualization.

### Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

### Data availability

Data will be made available on request.

### Acknowledgments

This work is a contribution of the EcoInvadiz project (P18-RT-5010) from the Regional government of Andalusia and the InvBlue project (PID2019-105978RA-100) from the Spanish Ministry of Economy and Competitiveness (MINECO), "Plan Nacional I + D". We would also like to thank the anonymous reviewers and the handling editor Dra. Vanessa Adams for their comments on the manuscript. Their suggestions greatly improved its clarity and overall presentation. GF de C—S conducted this work under a postdoctoral contract of the Margarita Salas Programme, Spanish Government's Ministry of Universities, funded by NextGeneration EU funds (UCA/R155REC/2021), and the Spanish State Research Agency (PTA2022-021378-I). MK has received funding from the European Union's Horizon 2020 research and programme under the H2020 Marie Skłodowska-Curie Actions grant agreement No 899546.

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