Seagrass are marine flowering plants that form extensive meadows from intertidal to subtidal and can extend down to 60 m worldwide, except Antarctica. Seagrass habitats are a critical component of coastal systems that deliver a broad range of ecosystem services and functions, playing a significant role in supporting human well-being (De la Torre-Castro, 2006; Nordlund et al., 2016; Ruiz-Frau et al., 2017; De los Santos et al., 2019). In particular, seagrass meadows contribute to coastal protection of shorelines (Boudouresque et al., 2016) by reducing wave energy and trapping sediments (Ondiviela et al., 2014). They also improve water quality by filtering excess of nutrients and contaminants (Serrano et al., 2013), control diseases by removing pathogens from the water (Lamb et al., 2017), play a significant role in food security, supporting economies and livelihoods through fisheries (Unsworth et al., 2018), and sequester and store carbon thus mitigating impacts of climate change (Duarte et al., 2013). In fact, the reduction of seagrass capacity to sequester and store carbon because of its decline is also of high international concern, since seagrass loss can lead to significant increase of CO₂ into the atmosphere (Arias-Ortiz et al., 2018). Seagrass meadows also provide non-material benefits to human societies, such as recreation, aesthetic, cultural heritage and education (Cullen-Unsworth et al., 2014; Garcia Rodrigues et al., 2017).

They are also of fundamental importance to world fisheries production in different ways since seagrasses are nursery and foraging habitats for commercially important invertebrates and fish (e.g. Unsworth and Cullen, 2010; Lilley and Unsworth, 2014; Nordlund et al., 2016; rev. Unsworth et al., 2018). Seagrass meadows are estimated to provide nursery habitat for at least 20% of the world’s 25 larger-scale fisheries (LSF), including the Alaska (walleye) pollock, the most landed species on the planet (Lilley and Unsworth, 2014; Unsworth et al., 2018). In addition, almost 80% of the 10 most caught species by small-scale fisheries (SSF) are associated with seagrass in tropical and subtropical regions (Unsworth et al., 2018). Seagrasses also support fisheries by providing trophic subsidy to contiguous habitats with adjacent fisheries, and, in the case of SSF, they also provide fishing grounds (Unsworth et al., 2018).

In spite of the critical role of seagrasses, they have shown a worldwide declining trend throughout the 20^th century due to cumulative pressures on coastal areas (Waycott et al., 2009; Pendleton et al., 2012; Ruiz-Frau et al., 2017; McKenzie et al., 2020), such as commercial fisheries (trawling), shellfishing (dredging), building of coastal structures, and sewage and nutrient inputs, among others (Cullen-Unsworth and Unsworth, 2013; De los Santos et al., 2019). Nevertheless, encouragingly, increasing awareness about conserving and restoring seagrass meadows have led to a reversal trend involving seagrass recovery across many Australian, Asian, European and North American coastal ecosystems, particularly fast-growing species after restoration programs (De los Santos et al., 2019; Orth et al., 2020; Sinclair et al., 2021).

Although it is evident that fishery activities, including shellfish harvesting, interact with seagrass meadows (Cabaço et al., 2005; Park et al., 2011; Pitanga et al., 2012; Garmendia et al., 2017), the magnitude and impact (positive or negative) of such interactions remain unclear, as some studies report significant decline in seagrass population performance due to shellfishing (e.g. Cabaço et al., 2005), while others not (e.g. Park et al., 2011); even more, results are not always comparable as they might report different species performances. Nonetheless, Nordlund et al. (2018) used experts’ knowledge on 36 global study cases and found that seagrass-based fisheries are of high importance, concluding that wherever seagrass are present, there is most certainly fishing, with recreational, subsistence and commercial value. In addition, (Gagnon et al. 2020) investigated plant-bivalve interactions in coastal habitats (salt marshes, mangroves and seagrass), and reported that most interactions were positive and reciprocal, since plants promoted bivalve survival and abundance by providing substrate and shelter, while bivalves promoted plant growth and survival by stabilizing and fertilizing the sediment and reducing water turbidity. At the same time, (Fales et al. 2020) also carried out a global meta-analysis on ecological variables (e.g. density, size, growth, survival), reporting reciprocal interactions between seagrass and bivalve molluscs, and suggested a variety of outcomes for these interactions, as there are multiple specific mechanisms and spatiotemporal scales enabling the seagrass-bivalves coexistence. However, there is still limited information regarding the interactions between seagrass ecosystems and fisheries as a coupled socio-ecological system.

In this study, we carried out a global systematic literature review of peer-reviewed scientific studies on trade-offs and/or synergies between seagrasses and fishing and aquaculture activities. A trade-off is defined as a situation where the use of one ecosystem service by human activities directly decreases the benefits supplied by another service (e.g. the impact of the management of a fishery on the abundance of seagrasses) (Rodríguez et al., 2006; Bennett et al., 2009). A synergy occurs where the use of one ecosystem service directly increases the benefits supplied by another service (e.g. effectively managing seagrasses helps to improve fish nurseries) (Gilby et al., 2018). Thus, the aims of this paper were (a) to analyse the current state of knowledge on these interactions, in the context of increasing climate change impacts, (b) to identify knowledge gaps, and (c) to pinpoint key research priorities and the way forward beyond the current state of the art.

Our systematic review shows a rapid growth of studies evaluating the relationships between seagrass ecosystems and fishing activities over the last decade. Trade-off interactions tripled the synergistic ones, driven by seafood market demand and conflicts of use in most cases. Globally, seagrass ecosystems are mainly affected by commercial fisheries of large and small scale, aquaculture and shellfisheries, and to a lesser extent, by recreational fisheries. These activities are enhanced as a result of the increased abundance and recruitment of commercially important species in this type of habitat.

Our results are consistent with the literature indicating that scientific interest in seagrasses has increased in the last decades (Fulton et al., 2020). It is likely that initiatives such as the Millennium Ecosystem Assessment published in 2005 have contributed to increase in awareness and interest on these habitats, as well as theoretical frameworks to better understand the dynamics of multiple ecosystem services (Bennett et al., 2009). Despite the benefits of seagrass ecosystems for human well-being, they had received less attention, in terms of media and scientific reports, than other coastal ecosystems extensively studied, such as coral reefs, salt marshes and mangrove forests (Duarte et al., 2008b; De la Torre-Castro et al., 2014). Seagrasses provide numerous valuable ecosystem services (Costanza et al., 1997) but, as in many other marine habitats, several studies have indicated high rates of global loss for seagrass ecosystems (Duarte, 2002; Orth et al., 2006; Duarte et al., 2008a; Waycott et al., 2009; Pendleton et al., 2012; De los Santos et al., 2019), exceeding those of tropical forests (Duarte et al., 2008b).

Our research indicates that in a relevant proportion, multiple fisheries activities occur on the same seagrass ecosystem (Figure 5, mixed activities), which is also consistent with Nordlund et al. (2018) results, who observed high similarity in seagrass fishery activity across several locations. Therefore, it seems that seagrass meadows tend to be exposed to several threats derived from fisheries and to other multiple anthropogenic threats, such as deterioration of water quality or coastal development (Duarte et al., 2008a; De los Santos et al., 2019). Overfishing is an important source of impact for seagrass, according to our analysis, which is in line with other studies stating that overfishing is linked to the main changes suffered in the structure of seagrass ecosystems (Baden et al., 2012; Alati et al., 2020). Increasing demand for seafood products supporting much of the 60% increase in per capita consumption of animal protein over the last decades (Béné et al., 2015), likely drives the impacts of overfishing in seagrass ecosystems.

Aquaculture alone represented 16% of the activities carried out in the areas where seagrass and fisheries interact, according to our literature synthesis. This aquaculture proportion does not take into account the cases where aquaculture occurred simultaneously with other activities such as recreational fishing, shellfishing or SSF, which would increase such proportion (Figure 5, mixed activities). From our literature review results, all the studies reported a negative impact of aquaculture practices, mainly emissions from fish cages but also by harvesting practices (e.g. Ruiz et al., 2001; Díaz-Almela et al., 2008; Kletou et al., 2018 Pérez et al., 2008), that ultimately led to degradation of seagrass meadows. Aquaculture has been considered as a potential sustainable solution for feeding the world’s population with products of marine origin. Currently, aquaculture generates around half (52%) of all fishery product production for human consumption (FAO, 2020). Through aquaculture it is possible to reduce not only the dependence of wild fisheries, but also the impacts of overfishing on marine ecosystems, however, aquaculture must be carried out sustainably in order to fulfill these expectations of beneficial effects (FAO, 2018). Suspended animal aquaculture usually generates organic enrichment via biodeposition (Dumbauld et al., 2009), transforming the sedimentary and biological structure of benthic communities into less diverse and poorer environments, a pattern that is shared with diverse anthropogenic sources (Pearson and Rosenberg, 1978). Generally, biodeposition from finfish farms and other anthropogenic sources is greater than those produced by shellfish farms (Pohle et al., 2001; Crawford et al., 2003), although benthic communities response will depend on the species cultured, the environment setting or the stock density (Dumbauld et al., 2009).

Our results suggest that after commercial fisheries and aquaculture, shellfisheries alone represent around 15% of the activities interacting with seagrass ecosystems. Several authors have described negative effects of clam harvesting (and its associated trampling) on seagrass mostly by changes in the species population structure through the reduction of shoot density and total seagrass biomass (Cabaço et al., 2005; Dumbauld et al., 2009; Barañano et al., 2017; Garmendia et al., 2017; De los Santos et al., 2019; Ferris et al., 2019). Mechanical damages by bivalves harvesting (namely clams) and other fisheries were among the main causes of trade-off interaction in our analysis. Other studies have also observed the same pattern regarding mechanical practices and stated that the harvest method and intensity cannot only influence the initial impact but also the recovery time of the meadow (Ferris et al., 2019). Manual methods of harvest are suggested as a source of lower disturbances, since they usually imply smaller harvested areas and result in faster recovery times (e.g. Cabaço et al., 2005).

The global research efforts of seagrass-fishery studies is biased toward temperate zones of the Northern hemisphere, mainly USA and Europe, despite the largest abundance and diversity of seagrass species found in tropical zones, especially in the Indo-Pacific region (Short et al., 2007). We found a mismatch between the research efforts and the hot-spot habitat distribution that most likely can be explained by the socioeconomic differences among regions (Nordlund et al., 2018). This is also supported by the fact that species of tropical distribution (Figure 4) were underrepresented in the analysed publications, where species from more developed temperate regions predominated (Short et al., 2007). Such an imbalance of research efforts usually translates into reduced funding priorities, conservation awareness, capacity building and management support in developing regions, where seagrass-based fisheries are likely to be of most importance. For example, we found that most of the synergies described in the scientific literature belong to studies developed through the coasts of Australia and the USA, where governments adopted spatial management strategies aimed at the protection of seagrass habitats. In fact, seagrass ecosystems are considered a priority for conservation in the USA and Europe and their protection is enforced (De los Santos et al., 2019; Muething et al., 2020).

Conservation of seagrass ecosystems should be a priority worldwide, as the multiple ecosystem services they offer are threatened under the increasing impacts and threats from climate change (Duarte et al., 2018), most likely through the loss of suitable habitats (Dolch and Reise, 2010; Dolch et al., 2013; Short et al., 2016; Ondiviela et al., 2020). Seagrasses are valuable ecosystems for mitigation of climate change given their capacity for carbon sequestration. In fact, their organic carbon stored per unit area is similar to that of forests (Fourqurean et al., 2012), and their ability to serve as carbon sinks has been estimated to account for up to $250 million USD in large seagrass ecosystems like the ones in Southeast Asia (Stankovic et al., 2021). However, the evidence suggests that such capacity diminishes with anthropogenic impacts (Duarte et al., 2013), which was a concern observed in our literature search when the terms “climate change” or “global warming” were included, as the vast majority of publications were related to the carbon sink function delivered by seagrasses. Even more, climate change will likely affect the magnitude and character of the interactions between seagrasses and anthropogenic activities like fisheries. For instance, in the West Coast of Australia, the heatwave caused by El Niño during the 2010-2011 summer, resulted in a massive collapse of a ~1300 km² seagrass ecosystem. This caused not only the increase of carbon stock emissions during the six consecutive years, but also had a large impact on marine food webs, including fish communities, invertebrates, birds and marine mammals (Serrano et al., 2021). Additional anthropogenic pressure with physical disturbance on the sedimentary carbon stocks of seagrasses (like the one caused by fishery-related activities) can cause a decrease of up to 85% in the seagrass carbon stocks (Román et al., 2022). Therefore, the precautionary approach should be considered when designing management plans aimed at the use of the space where seagrasses and human activities overlap.

Seagrass ecosystems can remain functional as providers of fundamental ecosystem services in spite of a changing climate if other cumulative impacts do not interfere with their resilience capacity, which can only be achieved by effective fisheries management and conservation measures (Unsworth et al., 2015; Wallner-Hahn et al., 2016). However, the provision of some services may require determining a minimum threshold of habitat area below which the ecosystem fails to effectively deliver the service (De Groot et al., 2012). Effective communication from the scientific community is also essential to increase the awareness of the society and public administrations in order to ensure seagrass conservation (Duarte et al., 2008b).

It is important to highlight that socioeconomic studies were a minority in our literature review, which represents a critical knowledge gap in this research field. However, the scientific literature suggests that it is crucial to understand the relevance of seagrass in supporting the well-being of people, as impacts on seagrass ecosystems go beyond a resource decline, they can affect directly or indirectly human communities depending on coastal systems. Beyond the more obvious loss of fisheries support if a seagrass meadow is lost, a clear example of this connection can be made with tourism. For instance, in Green Island, Australia, tourists are attracted by the high density of turtles, which depend on seagrass for feeding; however, tourists do not necessarily establish the connection between healthy seagrass meadows and the presence of turtles (Cullen-Unsworth et al., 2014).

Insufficient reporting in some of the reviewed literature (ca. 10% of the studies), made it impossible to gather information on some of the variables we considered, such as the cause of the interaction and the type of fishery or the species involved; most likely because those aspects were not within the scope of the analysed studies. Nevertheless, based on the results of our literature review, we advocate for developing studies on this field to improve their reporting on the interactions between seagrass meadows and fisheries. More detailed information about the activities carried out in these habitats will improve our understanding to sustainably manage these interactions (De la Torre-Castro and Lindström, 2010; Wallner-Hahn et al., 2016; Ferris et al., 2019; Riera et al., 2020). In contrast to the well documented significance of coral reefs for fisheries, that of seagrass remains poorly understood. However, we document a fast increase in studies reporting fishery-seagrass interactions, which, if accompanied by improved reporting of the nature of the interactions and the socio-economic context of the fishery, would help improve the sustainable management of seagrass-associated fisheries.

The interest and awareness regarding the importance of seagrass ecosystems for human well-being appears to have rapidly increased in the past two decades. However, seagrasses are globally subjected to multiple threats and pressures from fisheries worldwide, as the studies reporting trade-off interactions almost tripled those reporting synergies between seagrass ecosystems and fisheries. The seafood market demand and the conflicts of use generated in coastal areas are the main drivers for such trade-offs. Results indicate that seagrass ecosystems are mainly affected by industrial and small-scale fisheries, but also by aquaculture and shellfisheries, and to a lesser extent, by recreational fisheries. In most cases, these activities have negative effects on seagrass ecosystems as they cause mechanical damage by their fishing gears or boat propellers, by overfishing itself, or by aquaculture cages’ emissions. Nonetheless, the scientific knowledge on synergistic interactions is improving, as most studies focused on this subject reported a larger abundance or recruitment of species with commercial interest mediated by seagrass habitat provision.

Most of the research effort has been allocated to ecological studies in developed countries with an underrepresentation of studies in tropical regions, which represents a mismatch and a knowledge gap precisely in the regions where seagrass ecosystems are more abundant. Similarly, another relevant gap identified in our review is the lack of studies with an in-depth socioeconomic scope, since even when socioeconomic variables were considered in a study, the ecological approach was dominant. A third gap was identified as the fisheries management system was not specified in many of the reviewed publications, which represents a key knowledge gap with implications for sustainable management. Therefore, we advocate for an improvement in the reporting of future studies regarding fishery-seagrass interactions, as key interdisciplinary studies would help improve the sustainable management of both seagrasses and fisheries.

The original contributions presented in the study are included in the article/Supplementary Material. Further inquiries can be directed to the corresponding author.

All authors equally contributed to the manuscript.

This research was supported by the Spanish Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación (10.13039/501100011033) for the ZEUS project (grant RTI2018-095583-B-I00) and by the Autonomous government Xunta de Galicia-FEDER (project ED431C 2021/42): “ERDF A way of making Europe”. SV thanks the Consellería de Educación da Xunta de Galicia (Galicia, Spain) for funding support Grupo de Referencia Competitiva GI-2060 AEMI, under grant ED431C2019/11.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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