In response to the need for seaweed biomass, efforts to develop restocking strategies in Chile have focused on red (Rhodophyta) and brown (Phaophyceae) seaweeds, as these two groups are the most commercialized in the country. More publications refer to red (54%; 14 reports) than to brown seaweeds (46%, 12 reports), and most of this research has been financed through government funds. These reports suggest that more restocking studies have been done in the northern region (41%), followed by the central (37%) and southern (22%) regions ( Table 1 ).

The reproduction and propagation strategies employed for restocking natural populations vary among and within species. Most of the evaluated strategies use asexual propagation, except for D. incurvata and M. pyrifera, for which the sexual production of juveniles has been used. The juveniles of these species are produced in laboratory conditions and then seeded in intertidal or subtidal environments ( Table 2 ). For species in which restocking has been attempted through asexual propagation (i.e., C. chamissoi and G. lingulatum), the most common strategy has been the seeding of multicellular propagules obtained through thallus fragmentation ( Table 2 ). The studies have, on occasions, used more than one propagation strategy for the same species; for example, both the seeding of spores on natural substrates and seeding by spore dispersion have been used with S. skottsbergii and both transplantation and disk fragmentation have been used for L. berteroana (Westermeier et al., 2016; Ávila et al., 2017) ( Table 2 ).

Between 2017 and 2019, a Chilean government initiative implemented through SUBPESCA aimed to provide economic support to small aquaculture farmers, fishers, and/or artisanal fisher's organizations by funding up to 70% of the total costs for projects linked to the restocking and cultivation of seaweeds. The program financed 426 projects involving a total of 199 individuals or groups who applied, with an approximate value of USD 2 million ( Table 3 ). Regrettably, only three restocking projects were approved, representing only 1% of this program’s budget. The main reason for the rejection of restocking projects was failure to comply with the monitoring program necessary to apply for this benefit (SUBPESCA, n. d. b). The total area used for this state-funded restocking project is uncertain. However, numerous investigations have been carried out in pursuit of seaweed restocking. A recent systematic study by Eger et al. (2022) analyzes the global efforts of kelp forest restoration. In the study they gathered data from different countries, Chile among them, with a total of 18 journal manuscripts reporting a total of 329.6 m² of kelp restocking. This number does not include efforts made privately by fishing communities.

In Chile, benthic fisheries management is based on Territorial Users Rights for Fisheries (TURF). These are spatial user rights that grant exclusive access to fishers to manage benthic resources in a sustainable manner within a given geographic area (González et al., 2006; San Martín et al., 2010). This system assumes that the success or failure of management depends on users taking care of the management area and its resources, avoiding overexploitation.

A series of restocking experiments on benthic resources have been undertaken within TURF, although mostly without assessing reliable indicators of success (Cárcamo et al., 2021). The implementation of restocking efforts in management areas over large scales remains very low. For example, in the 803 active TURF along the Chilean coast, 109 restocking actions in 82 TURF were officially reported between 2010 and 2018. Of these, 41 corresponded to seaweed restocking, most frequently involving the two red species S. crispata and G. chilensis and the brown seaweed L. berteroana. Seaweed-restocking efforts within TURF respond directly to the importance that each specific organization gives to the species in their management plan ( Figure 6 ).

In northern Chile (i.e., Tarapacá, Atacama, and Coquimbo, see Figure 6 ), activities have focused mainly on the restocking of brown seaweeds (Lessonia spp. and M. pyrifera), which support the constantly growing fisheries in the area, with effects that are socially and ecologically relevant. On the other hand, in the central and southern regions of Chile, red seaweeds are more relevant in terms of exploitation due to an increase in their biomass ( Figure 6 ). No restocking efforts have been reported for Patagonian ecosystems ( Figure 6 ), which represent a relevant research gap for kelps distributed along the southern Chile region. It should be noted that the Magallanes benthic management committee recently agreed to implement an extractive ban on brown seaweeds (i.e., M. pyrifera) that focusses on conserving the ecosystem services that kelp forests provide in Patagonia (Vega et al., 2021).

Restocking activities have focused mainly on seedling transplantation using two techniques: direct seeding and the installation of seedlings with anchoring systems. The most common techniques, widely used with red seaweeds, are direct seeding using net bags with boulders ( Figure 7A ) or the use of a line or rope system ( Figure 7B ). For brown seaweeds, restocking systems have focused on the installation of seedlings with anchoring systems ( Figure 7C ) and the experimental use of cyanoacrylate as a glue ( Figure 7D ). In both cases, the seedlings are protected from herbivores such as the sea urchins Tetrapygus niger and Tegula atra (Cárcamo et al., 2021).

Ninety percent of these activities have been financed through either central or local government subsidies, whereas only 10% have been financed through competitive bidding for private funds. Restocking activities in TURF have ranged from a few units to a maximum of almost 50,000 seedlings (this was reported for L. trabeculata in Torres del Inca in the region of Atacama, ca. 26°S). However, there are exceptions, as was reported for G. chilensis in Playa Changa (ca. 29°S) in the region of Coquimbo (central Chile, Figure 6 ), where up to 90 tons of biological material were used.

These restocking efforts have focused mainly on the recovery of areas where target species have been previously overexploited or that have suffered from environmental/oceanographic changes created by large-scale events such as the El Niño Southern Oscillation (ENSO; Camus, 1994; Martínez et al., 2003; Vega et al., 2005). It is not yet known whether these activities have been successful, and for most, there are no long-term evaluations to assess their efficacy in terms of population recovery.

Globally, there are still few studies on the impact on coastal communities of the loss of economically important red seaweed biomass due to environmental forcing or overexploitation or the corresponding restoration efforts. Although they are smaller than large Laminaria and Fucus species (Phaeophyceae)), they provide similar ecosystem functions over their spatial scale, such as CO₂ capture, provision of refuge areas for small invertebrates, and substrate stabilization. Several red seaweeds are part of the understory stratum or turf assemblages (Pessarrodona et al., 2021). There are few existing studies that have used transplantation techniques with different devices to evaluate, for example, ecophysiological responses to environmental variability such as solar radiation (e.g., Quintano et al., 2019) or wave exposure (Shaugnessy and DeWreede, 2001) or ecological relationships in seaweed–animal interactions (Enríquez et al., 2009). The effects of wave exposure in relation to the morphology of the red seaweeds Mazzaella splendens and Mazzaella linearis have been evaluated through intertidal transplantation with a device consisting of a base of vinyl-covered metal mesh attached to a rock with screws inserted using a pneumatic hammer drill that supports seaweeds inserted with a polypropylene rope attached to the metal mesh with wire cable ties (Shaughnessy and DeWreede, 2001). The interaction between the red alga Jania pedunculata var. adhaerens (formerly Jania adhaerens) and the sponge Haliclona caerulea was evaluated using artificial substrates tied to heavy concrete blocks (Enríquez et al., 2009). Individuals were induced to reattach to the artificial substrate (10 × 10 × 0.5 cm CaCO₃ squares) by fastening them with cable ties, which allowed the development of their anchoring systems. Experimental transplantation of Gelidium corneum in the subtidal area used several stainless-steel elements, with a frame attached to the rock with rapid-drying concrete, a platform, and screwed cubical containers (Quintano et al., 2019). The devices described in these experiments could be considered prototypes that should be evaluated in future red seaweed repopulation/restoration studies.

Recently Eger et al. (2022) reviewed the history about the kelp restoration projects highlighting the increase in attempts made around the word, using 10 different technologies and 17 kelp genera, becoming the group of brown algae that has received the most attention. The restoration of seaweed forests worldwide has typically followed two general strategies: assisted recovery and active restoration (Wood et al., 2019; Layton et al., 2020). Techniques range from bulk nursery-raised propagules to the cultivation of propagules with more intensive care in individual units. In general, propagules are maintained for several months until they reach the juvenile stage, following which they are transplanted to the sea (Fredriksen et al., 2020; Vanderklift et al., 2020).

A recently described technique is called “green gravel,” in which the general procedure involves collecting fertile Saccharina latissima individuals to obtain spores, which are then inoculated on rocks (2–5 cm in diameter) in a laboratory. The rocks are kept in tanks until seedlings are visible and can be transplanted to the sea, and the substrate is seeded directly onto the seafloor ( Figure 8A ) (Fredriksen et al., 2020). Although this technique can be effective, it is labor-intensive and requires upstream cultivation steps for the maintenance and growth of the seedlings. This methodology also has been evaluated in Ecklonia radiata (Alsuwaiyan et al., 2022) under indoor conditions.

Another evaluated method is the transplantation of adult Ecklonia radiata individuals using concrete cobblestones attached to a steel frame while anchoring the holdfasts with rubber bands ( Figure 8B ) (Layton et al., 2021). The reattachment of individuals to the surface occurs within 3–6 weeks, with survival rates of 75%. According to the authors, this technology is adequate; however, the effort required to transport large cobblestones to the transplantation areas and the use of individuals collected from nature for restocking are inconvenient. It is important to note that the transplantation is based on harvesting individuals from a source/donor population, and thus the technique produces a decrease in the abundance of the source population, at least over the short term. Moreover, the success of the method would also depend on the health of the donor population, its context, its genetic variability, and its capacity to tolerate environmental stressors that could occur at the new sites.

Several restocking strategies have been employed in Australia, including deploying artificial substrates to which algae recruit naturally, replanting sporophytes (i.e., kelp reproductive fronds), and transplanting ropes seeded with small (5 mm) juvenile seaweed previously cultivated in the laboratory. A repopulation strategy for the kelp Phyllospora comosa was successful. It was based on transport from a distant donor population to the repopulation site to establish a population sufficiently mature and reproductive to create juveniles. Specifically, the seaweeds were harvested carefully, including the holdfast, which was attached to the transplantation site using cable ties on 0.25 m² plastic meshes ( Figure 7C ) (Campbell et al., 2014). The efficacity of this approach was demonstrated by the observation of multiple new generations of this species spreading thousands of meters from the initial repopulation sites. Repopulation also reduces the risks of habitat diversity loss for the epifauna and its consumers (Marzinelli et al., 2016). Although this strategy has been effective, it is not always viable for all kelp due to the differences in their growth rates and types of natural substrate. There is also a genetic risk when translocating seaweeds from one place to another, in addition to the risk of the transportation of their associated epibionts with a genetic risk to the epibionts’ populations (Bonthond et al., 2020). This strategy also uses plastic material, and thus more sustainable technologies would be preferred. For example, biodegradable mesh drilled into the ocean floor is currently being used (http://www.operationcrayweed.com).

Chilean official fisheries statistics indicate that commercial landings have involved more than ten seaweed resource species (some of which may include two or three related biological species) in the last 20 years (SERNAPESCA, 2022). A few of these species have been landed only occasionally, but for the remaining crops the harvesting pressure on natural populations has been persistent over time and along most of their Chilean geographic distribution. Although farming methods for commercially important seaweed species have been developed at the experimental or pilot stage, only one red seaweed, Gracilaria chilensis, is commercially cultivated in Chile. For other red seaweed resources, attempts have only recently been made to design techniques that can increase their abundance or replenish areas affected by natural disasters or anthropogenic activities ( Table 2 ), but more extensive and longer-term restocking trials are needed. In the case of brown seaweeds, experimental restocking has been carried out for few species due to the difficulties of working over a large scale in environments that are highly impacted by wave action.

Some basic studies have been carried out on the biological features of most of these species, which have been successfully cultivated in laboratory conditions at an experimental scale (reviewed in Saavedra et al., 2019). Nonetheless, there are few reports of attempts to apply this knowledge to install new individuals in the field in restocking efforts. Increased awareness of increasing seaweed harvests in Chile, together with the recognition of the environmental services that they provide, have motivated research aimed at exploring seeding techniques that can be integrated into the management practices of six Rhodophyta and three Phaeophyceae) species ( Table 2 ).

In other parts of the world, the situation for restocking activities is similar, although a great effort is being made to address the impact of climate change (e.g., heat waves) on populations of kelp forests due to their ecosystem value. For economically important seaweeds that are constantly harvested without an adequate management program, a lack of appropriate restocking practices may lead to over-extraction, affecting the seaweed populations and the products obtained from them (e.g., Callaway, 2005). Reports of the installation of new individuals in the field mainly involve the transplantation of individuals for experimental purposes (e.g., Enríquez et al., 2009; Quintano et al., 2019), and scale-up for mass implementation would be costly and unfeasible. On the other hand, the attributes of the seaweed resources present on other coasts, together with technological and implementation capabilities and the environmental conditions of those coasts, have allowed for the cultivation of seaweed rather than restocking in some cases (e.g., Eucheuma). Overall, large-scale population restocking techniques for the purpose of biomass production, conservation, and recovery of seaweed ecosystem functions are still lacking.

Essential aspects that must be considered when scaling up restocking techniques include the genetic diversity of the population that is being sampled and its genetic relatedness to the population at the site that is being repopulated. The genetic information is relevant to evaluate the potential impact of introducing new individuals on the genetic diversity of the natural populations (Ottewell et al., 2016). The health of the donor population, its context, its genetic variability, and its capacity to tolerate several environmental stressors that could occur at the new repopulation sites can determine the success of restocking (Reynolds et al., 2012; Wernberg et al., 2018; González et al., 2020; Chemello et al., 2022). Depending on the restocking strategy used, a loss of genetic diversity can lead to situations such as those described for G. chilensis because of domestication through clonal translation to management and cultivation areas (Guillemin et al., 2008; Guillemin et al., 2014).

In addition, an effort should be made to ensure that devices that are permanently deployed in the field are environmentally friendly, e.g., trying to replace plastic pieces with equivalent ones made of biodegradable materials. The chemical stability of plastic materials used in different techniques implies serious environmental problems and human health implications (Li et al., 2020; Gola et al., 2021; Wu et al., 2022), which require evaluation, especially for those practices with potential massive use. Restocking strategies require the use of biodegradable polymers. A possible transformation could involve the use of biopolymers such as polylactic acid (PLA), which has provided an important boost in biomedicine due to its properties such as biocompatibility, water solubility, handling properties, well-established production technologies (Casalini et al., 2019), and 3D printing possibilities (Singh et al., 2019). New techniques exist that could facilitate the anchoring or attachment of kelps to a rocky habitat, such as submersible hammer drills, which have been successfully used for perforation (Wainwright et al., 2020), or the use of organic resins that have strong underwater adhesive capacity (Yan et al., 2022), many of which have been inspired by the adhesion capacity of mollusks (Priemel et al., 2021) and other marine organisms (Fan and Gong, 2022).

The economic evaluation of ecosystem services and functions to the coastal environment of the new seaweeds should be considered as a relevant input during the decision-making process when considering implementing a large-scale restocking program (Cuba et al., 2022). The proper implementation of success indicators of restocking activities, from the individual to the ecosystem level, must include local/geographical considerations in relation to abiotic and biotic factors, the demographics of the populations to be impacted, and the timing for achieving changes in coastal ecosystems.

The management of benthic resources takes place in a socio-ecological system with social, political, and cultural characteristics that must be considered (Reyers et al., 2018). To begin the implementation of a large-scale restocking effort, it is necessary to evaluate whether the socio-ecological system presents the necessary enabling conditions for the implementation of such a strategy (Cárcamo et al., 2021). This raises important challenges in the Chilean case. First, artisanal fishers’ organizations must have the organizational maturity and social capacities to successfully implement technological and stocking projects (Abelson et al., 2016; Chen et al., 2020). In this sense, there is a lack of knowledge in Chile that necessitates the prioritization of organizations that have the necessary organizational maturity to implement restocking projects. Secondly, artisanal fishing in Chile and in particular the TURF system is highly vulnerable to illegal fishing (Gelcich et al., 2017; Oyanedel et al., 2018). Recent studies have shown that benthic resources are particularly exposed to poaching and illegal extraction (Romero et al., 2022). Restocking projects may generate a greater abundance of resources, and therefore greater incentives for illegal extraction (Cárcamo et al., 2021). The implementation of monitoring and surveillance systems emerges as a central element for the success of restocking projects in Chile. These systems should consider enforcement efforts by government agencies and the capacity for self-monitoring of artisanal fisher's organizations that manage TURF areas. Self-monitoring has been recognized as a central element in the sustainability of the Chilean TURF system (Estévez and Gelcich, 2020). Thirdly, it is necessary to evaluate the willingness of fisher’s organizations to participate in restocking initiatives that may not represent direct economic benefits in the short term (Blount et al., 2017). Therefore, given the number and size of the restocking initiatives carried out by TURF, it is necessary to consider which management tools could encourage restocking initiatives: possibilities of participation in organizations in the development of projects (Garaway et al., 2006), risk perception of the viability of the resource or the generation of other parallel financing instruments such as blue carbon markets. Although the willingness to participate in restocking programs has not been evaluated in Chile, the TURF system offers an opportunity to develop projects within the framework of a co-management model.

In Chile, restocking activities have been developed through management actions in an annual TURF plan or through the application for a bonus in accordance with Law NO. 20.925. The enactment of Law No. 20.925 “Bonus for the Repopulation and Farming of Seaweeds” in 2016 sought to diversify and increase the coverage of commercially important algae. This bonus is potentially a great opportunity for the artisanal fishing and small-scale aquaculture sector from an ecological and economic point of view. However, an a priori analysis indicates that the law has not achieved its objective of diversifying and protecting resources. On the one hand, administrative procedures and enforcement conditions by artisanal fisher's organizations make it difficult to obtain permits for these activities. On the other hand, this subsidy has concentrated on the cultivation of the red algae G. chilensis without promoting the restocking of a diversity of species (Quiroga, 2018; Carcamo et al., 2021). Thus, the true impact of the law on the resource, the increase in its coverage, the organizations, and the environment is unknown.

To strengthen the system and reduce the failure of restocking experiences, it is necessary to redesign some elements of the subsidy. At present, incentives are assigned at the end of the activity and after positive evidence and productive results are provided. This can be considered a weakness in the law given that it ignores the high variability and instability of the marine environment, in addition to externalities such as pollution, tsunamis, and climate change, which may affect the development of actions aimed at repopulation and/or cultivation. Alternatively, subsidies should be associated with the generation of early incentives that support the implementation of these practices, with a follow-up of their effectiveness over time, as well as assistance regarding the commercialization and innovation needed to create added value (Henríquez-Antipa and Cárcamo, 2019). In addition, some of the additional challenges remaining are: (1) to promote fishery diversification by incorporating other algae into productive activities, (2) to scale up restocking efforts, (3) to generate science-based technological entities that are in charge of supplying seeds and seedlings for seaweed production, (4) to develop appropriate infrastructure in the coastal areas for developing these technologies, and (5) to garner substantial support from the state for small-scale activities.