The Gulf of California extends over 1,200 km, encompassing 40 coastal lagoons and 922 islands, and is part of the unique Cortezian marine ecoregion (Spalding et al., 2007). The regional climate is influenced by the El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO), factors contributing to substantial oceanic changes (Luch-Cota et al., 2013). In recent decades, the Gulf of California has experienced pronounced warming, affecting a multitude of marine species and habitats (Nevárez-Martínez et al., 2001; Velarde et al., 2004; Favoretto et al., 2022; Sánchez-Cabeza et al., 2022). It features distinct latitudinal gradients in sea surface temperature and chlorophyll-a concentrations, which delimit three primary oceanographic regions (Brusca, 2010; Ulate et al., 2016). These regions all experience similar maximum summer sea surface temperatures around 30°C. However, during winter, the northern region records cooler temperatures (16°C), the central region exhibits an intermediate average temperature of around 20°C while the southern region remains warmer (22°C). Also, the northern region has the highest annual average chlorophyll-a concentration at 1.6 mg m^–3, compared to the southern region, which has an average of 0.5 mg m^–3 (Ulate et al., 2016).

Seagrass meadows, found in the Gulf of California’s bays, lagoons, and inlets, are increasingly vulnerable to human activities. The eastern lagoons are heavily exploited for agriculture, aquaculture, settlement, and fishing. In contrast, the western bays and inlets face pressures from coastal development and mining activities (Álvarez-Borrego, 1983; Nevárez-Martínez et al., 2001; Velarde et al., 2004; González-Abraham et al., 2015; Páez-Osuna et al., 2016; Sánchez-Cabeza et al., 2022). These cumulative pressures threaten the most favorable habitats for seagrass meadows, underscoring the urgency to address current and future anthropogenic threats in the Gulf of California.

In conducting this review, we undertook a thorough examination of academic and gray literature, national and international herbarium records, and floristic surveys. Our research employed ‘Google Scholar’ for the English search terms ‘Seagrasses’, ‘Gulf of California’ and the name of the species recorded in the region ‘Zostera marina,’ ‘Ruppia maritima,’ ‘Halodule wrightii,’ ‘Halophila decipiens’. Equivalent Spanish terms were used, replacing ‘Seagrasses’ with ‘Pastos marinos’ and ‘Gulf of California’ with ‘Golfo de California.’ The search was conducted from July 2019 to March 2021. Additionally, we classified the studies according to their primary focus and depicted their temporal progression graphically. While our primary emphasis was on peer-reviewed scientific, we included other sources of information such as technical and governmental reports, theses at the undergraduate, master’s, and doctoral levels due to their significant insights into the distribution and condition of the seagrass meadows.

Subsequently, we evaluated seven online herbarium collections from the following institutions: the University of Arizona (ARIZ), Arizona State University (ASU), Autonomous University of Baja California (CMMEX), National Herbarium of Mexico (MEXU) of the National Autonomous University of Mexico, Smithsonian National Museum of Natural History (SI NMNH), Jesús González Ortega Herbarium at the Autonomous University of Sinaloa (UAS), and the University of Sonora (UNISON-USON). From these archives, we extracted details such as species identification, collection dates, locality, and geographical coordinates. Each entry was then organized by location, facilitating the creation of maps that illustrate the historical distribution of each seagrass species throughout the Gulf of California.

Our research compiled records of seagrass species from 28 locations in the Gulf of California, with 20 on the eastern coast and six on the Baja California Peninsula ( Figure 1 ). We compared our results with the official data from Ocean Data Viewer where only nine seagrass locations have been reported (UNEP-WCMC & Short, 2021). This data does not provide information about the extension or the name of the locality, only provide the coordinates. Additionally, they focus on only two of the four species of seagrass in the Gulf of California (Zostera marina and Halodule wrightii). Particularly in Los Cabos, this database includes a record of Phillospadix torreyi and Phillospadix scouleri, both species that are not recorded within the Gulf of California.

We identified primary seagrass localities through record frequency, occurrence rates, and data on their distribution. First, The Canal del Infiernillo, between the Sonora coast and Tiburon Island, includes all bays and estuaries within, then Bahía Concepción, as a second critical seagrass habitat in the Gulf of California.

In this work, we include new records. Records prior to 2018 are observations by the authors that have not been previously published. While the records obtained during our field validation efforts were collected between 2018 and 2022 ( Datasheet 1 ). In 2020, we identified H. wrightii in Ensenada de la Paz channel. Additionally, H. decipiens was in San Gabriel Bay on Isla Espiritu Santo in 2018, and at the Pichilingue research unit of the Autonomous University of Baja California Sur in 2022.

The analysis of our results shows that several locations are likely facing multiple stress factors. 17 of 28 historical locations are subject to the three main types of human-induced stressors: pollution, coastal modification, and overuse of biological resources ( Figure 2A ). While climate stress occurs in 12 locations. However, this phenomenon is most pronounced at spots like the Colorado River delta, Bahia Concepción, and El Verde coastal lagoon ( Figure 2B ).

We observed that most of the seagrass records are located outside protected areas or in areas with low levels of protection that lack management strategies and plans, such as Ramsar sites. While 13.2% of the records are found within protected areas ( Figure 3 ). However, its presence and relevance are only recognized in the management plan of the Balandra Flora and Fauna Protection Area (DOF, 2012).

Our comprehensive review yielded 77 documents related to seagrasses in the Gulf of California, classified into eight categories. 42 of them were “Peer-reviewed” academic articles. The categories of “Books” and “Book Chapters” followed, with 11 and 6 records respectively. Since 1996, ten theses have been registered spanning bachelor’s, master’s, and doctoral degrees, although only three have been published as peer-reviewed papers. Despite relatively limited, we included two outreach papers and five reports of projects of research in our analysis.

Although research into seagrasses began more than 100 years ago, the rise of peer-reviewed publications occurred at the end of the 20th century, in the 1980s, when the peak of research in a decade was reached, with 12 of them produced between 1980 and 1988. However, from 1990 to 2021, this trend reversed, adding a total of 25 peer-reviewed publications in 31 years, i.e., a rate of 0.80, less than one publication per year. Despite this slowdown, starting in 2010, an important moment stands out in the production of research on seagrasses, with the increase in theses and reports, indicating a resurgence of interest in research and the continued study of seagrasses in the region ( Figure 4A ).

During the first years, there is a trend towards taxonomic and ethnobotanical studies. This period is characterized by no increase in the number of studies until the 1970s when studies focused on the distribution of seagrasses emerge, and the first research mentioning them indirectly (Indirect observations) appears.

Ecology and conservation are the most studied topics, increased almost constantly since the first publication in 1977 and 1992, respectively. Both topics reaching a maximum number of studies in 2021. The last decade of the 20th century was an important time for research, as new lines of research emerged, such as genetics, blue carbon, in which it is necessary to redouble efforts ( Figure 4B ).

The mapping of seagrass habitats remains a significant challenge, despite recent advances in technology that promise to narrow the information gap. Even the wide extent of seagrasses in the Gulf of California, our validation data results only confirmed the presence of seagrasses at 13 out of the 28 historically noted localities ( Datasheet 1 ). This indicates a potential decline of 46.4% from their known historical distribution, a concerning trend also reported by López-Calderón et al. (2016).

The seagrass meadows of the Canal del Infiernillo are the most important within the Gulf of California, due they cover the largest spatial area and appear to be the most consistent in their distribution over time. It extends between the Sonora coast and Tiburon Island, includes all bays and estuaries therein. The Canal del Infiernillo seagrass meadows, estimated at 7,000 hectares in 2010 (López-Calderón et al., 2016). We confirm the presence of seagrasses in the Canal del Infiernillo; however, we cannot know the species composition. Despite this, the meadows have shown remarkable stability and density, possibly due to Comcaac’s conservation efforts. This area is part of the Comcaac (Seri) community’s territory, known for its historical use of seagrasses, and has been under exclusive fishing concession since 1975 (DOF, 1975; Felger et al., 1980; Felger and Moser, 1985).

Bahía Concepción hosts the only population of Z. marina on the east coast of the Gulf of California. Documented on two beaches, El Requeson and Punta Arenas, these meadows cover roughly 33.74 hectares (López-Calderón et al., 2016). However, during our field work in January 2023, no Zostera marina was found, only Ruppia maritima was present. This finding may be due to the increase in temperatures in the region ( Figure 2 ), due to Z. marina declines at temperatures above 25°C and disappears at 28°C, while R. maritima has a wide range of tolerance to temperature changes (Phillips and Meñez, 1988; Lazar and Dawes, 1991; Meling-Lopez and Ibarra-Obando, 1999; Santamaría-Gallegos et al., 2000). The ecological succession between both species had already been previously reported at the this and another sites, mainly in areas of lower environmental quality (Meling-Lopez and Ibarra-Obando, 1999; Cho et al., 2009; López-Calderón et al., 2010).

The status of seagrass meadows on the eastern Gulf of California coast is uncertain. We can confirm the presence of seagrasses in 13 sites. However, we do not know the composition of the seagrass species, since the key meadows are found predominantly within coastal lagoons, with high levels of eutrophication. For example, Bahía de Kino, where significant anthropogenic activities have been recorded, it is too difficult identified species using remote technologies.

Regarding the several new locations for H. wrightii and H. decipiens in La Paz ( Supplementary Table 1 ), we think that changes in seagrass distribution can be attributed to the reproductive strategies and seasonal dynamics, linked to life cycles, which can result in meadows disappearing for years at a time, especially among annual species (Pérez-Estrada et al., 2021). H. wrightii, a perennial species, primarily propagates vegetatively (Santamaría-Gallegos, 2016; Pérez-Estrada et al, 2021). While H. decipiens, an annual species, germinates from seeds and is visible from April to October, declining in winter in most locations (Dawes and Lawrence, 1980; Dawes et al., 1995; Kuo and Kirkman, 1995; Kenworthy, 1999; Deis, 2000; Santamaría-Gallegos, 2016). These species form transient, scattered patches that are often underreported and difficult to detect due to algal overgrowth. Misidentification with macroalgae or other seagrasses is common, which may have contributed to the overestimation of H. decipiens in the Gulf of California’s marine flora records.

While documented changes in Z. marina meadows exist, other species lack comprehensive distribution data. For example, R. maritima was last officially reported in Los Cabos in the late 1990s (Ramírez-García and Lot, 1994; León de la Luz et al., 1997), with no subsequent sightings. Consequently, seagrass mapping and monitoring efforts should account for their dynamic nature. Regular long-term monitoring, as suggested by Valle et al. (2013), including both remote sensing and fieldwork over periods such as four years, could yield more accurate spatial distribution models for these populations (Bremner et al., 2023). It is crucial to conduct detailed fieldwork to revalidate species distributions and understand the ecological dynamics of seagrass meadows in the Gulf of California.

Coastal lagoons and estuaries along the Sonora and Sinaloa coastlines are subject to three major human-induced stressors: pollution, coastal modification, and overuse of biological resources Figure 2A . The environmental stress in these regions is largely attributed to population growth and the indirect effects of agricultural and livestock runoff (Montes et al., 2012; Páez-Osuna et al., 2017).

The primary environmental threat comes from agricultural pollutants like fertilizers and pesticides. These substances accumulate in sediments and water, posing risks to the health of ecosystems and leading to significant marine pollution (Carvalho et al., 1996; Galindo-Reyes et al., 1999; Páez-Osuna et al., 2017; Ruíz-Fernández et al., 2002). In Sonora and Sinaloa, the expansion of aquaculture has also been problematic. Related coastal alterations have substantially affected local hydrology and altered coastal processes. Organic discharges and nutrient outflow from aquaculture operations diminish water quality, which in turn adversely affects vegetation cover (Alonso-Pérez et al., 2003; González-Abraham et al., 2015), and may lead to succession events in vegetation, such as those observed between R. maritima and Z. marina (López-Calderón et al., 2010).

In Baja California Peninsula, coastal alterations and tourism are the primary threats to seagrass meadows ( Figure 2A ). In Los Cabos, tourism infrastructure has led to significant ecological strain, with the San José estuary’s geomorphology reduced by over 40% in 20 years, affecting its ecosystem services (Arizpe et al., 2018; Wurl, 2019). While, tourism development, combined with natural events like hurricanes and climate phenomena, has been detrimental, particularly to H. wrightii in La Paz Bay’s Balandra MPA (Pérez-Estrada et al., 2021).

Environmental stressors, such as pronounced warming and heatwave events, are higher in Loreto and Concepcion Bay ( Figure 2B ). The seagrass meadows of Bahía Concepción face a challenging environment due to their small size, human threats, nutrient discharges leading to eutrophication, and climate change impacts. Studies indicate a significant decrease in seed banks from 1995 to 2010 (Santamaría-Gallegos et al., 2000; López-Calderón et al., 2016).

The Midriff Islands Region, including Bahía de los Ángeles, Tiburon, and Ángel de la Guarda islands, faces less environmental pressure, making these sites potential climate refugia ( Figure 2B ). The cooler temperatures and upwelling events here present a research opportunity for understanding future climate impacts on seagrasses (López et al., 2006).

Despite some seagrasses being located within protected areas, their conservation is not guaranteed due to the highly disturbed and fragmented coastal landscape. As shown in Figure 3 , few seagrass records fall within fully protected zones with restrictions on extractive activities. Most are in minimally protected or unprotected areas. If current pressures like habitat degradation and population reduction continue, some seagrass populations may risk extinction in the short to medium term. Immediate and proactive conservation measures are critical for seagrass recovery and preservation.

Despite increased recognition of the importance of seagrass conservation, often linked with the protection of mangroves and reefs, a significant gap persists between scientific understanding and its integration into effective policy and conservation action (Duarte et al., 2008; López-Calderón et al., 2014; Fortes et al., 2018). For example, despite its recognition as a Priority Marine Area, granted in 1998 by CONABIO, USAID, WWF, FMCN and Packard Foundation (López-Calderón et al., 2016), Bahía Concepción lacks formal protection and a dedicated conservation strategy.

The complex interaction among resource management, public policy, and economic objectives in coastal regions creates a barrier to implementing laws that protect seagrass ecosystems. Developing management plans that safeguard key ecosystems while accommodating local economic interests is a delicate balance, often met with opposition to restrictions (Bennett and Dearden, 2014). Standard conservation strategies may not always be suitable for seagrass habitats due to their unique dynamics and fragility. For instance, the establishment of the Balandra Flora and Fauna Protection Area in November 2012 (DOF, 2012), which aimed to limit certain activities, paradoxically intensified tourism pressure, thereby potentially impacting the local H. wrightii population (Pérez-Estrada et al., 2021). This development highlights the insufficient consideration given to seagrass meadows within management plans. Consequently, despite numerous seagrass locations falling within designated protection areas (refer to Figure 3 ), there is no assurance that these habitats are effectively safeguarded.

Community engagement is crucial in conserving seagrass ecosystems, which are frequently undervalued and misunderstood. Successful conservation models have leveraged environmental education and citizen science to involve coastal communities in monitoring seagrass populations (Cunha et al., 2013; Yaakub et al., 2014). Identifying and safeguarding potential threat zones, creating micro-protected areas, and conducting water quality assessments could provide vital sanctuaries for seagrass recovery and scientific study. A multidisciplinary approach is essential for seagrass conservation, one that addresses the ecological, societal, and economic facets of these critical habitats.

Since 1980, the number of peer-reviewed publications and the increase in theses and reports indicate a resurgence of interest in seagrass research, led mainly by local researchers ( Figure 4A ). However, there are still notable gaps in knowledge.

Seagrasses have been documented since 1645, documenting the cultural and ethnobotanical uses of these plants (Felger and Moser, 1973; Felger, 1976; Felger and Lowe, 1976; Sheridan and Felger, 1977; Valencia et al., 1985; Felger et al., 2013). This type of research has been published as ethnobotanical studies and floristic lists that also provide information on distribution (Den Hartog, 1970; McMillan and Phillips, 1979b; Wilder et al., 2007). On the other hand, in the 1960s emerged biological and ecological studies ( Figure 4B ). The first topic describes mainly phenological and reproductive aspects of seagrasses (Dawson, 1944; Setchell, 1946; Dawson, 1960; Edwards, 1978; McMillan and Phillips, 1979a; McMillan, 1983; Phillips and Backman, 1983; Phillips et al., 1983).

Meanwhile the ecological issues explore interactions with other species, including algae, fishes, invertebrates (Phillips and McRoy, 1980; Paul & Bowers, 1982; Oliva-Martinez and Ortega, 1983; Phillips, 1984; Ortega et al., 1986; Ezcurra et al., 1988; Flores-Verdugo et al., 1988; Ibarra-Obando and Ríos, 1993). Other aspects addressed in ecological studies include biomass quantification, population changes, and energy flow models (Sánchez-Lizaso and Riosmena Rodríguez, 1997; Torre-Cosio, 2002; López-Calderón et al., 2010, López-Calderón et al., 2014; Pérez-Estrada et al., 2021; Van Dam et al., 2021).

New critical research themes, as conservation and genetics, emerged from the 1990s, providing assessment of biodiversity threats and conservation status of the ecosystem (Glenn et al., 1992; Brusca et al., 2005; Basurto, 2008; Morzaira-Luna and Daneman, 2018; Riosmena-Rodríguez et al., 2013; López-Calderón et al., 2016). Including the evaluation of variability, resilience, and connectivity of Z. marina populations on the Gulf of California and the Pacific coast (Backman, 1991; Muñíz-Salazar et al., 2005; Talbot et al., 2016) ( Figure 4B ).

Despite this broad spectrum of research, there exist certain areas of study that remain under-researched, representing significant knowledge gaps. For instance, seagrass distribution has been examined since the initial records on the coasts of the Gulf of California (Den Hartog, 1970; McMillan and Phillips, 1979a; Aguilar-Rosas and López-Ruelas, 1985; Ibarra-Obando and Ríos, 1993; Riosmena-Rodríguez and Sánchez-Lizaso, 1996; Santamaría-Gallegos et al., 2006). However, the depth of information varies greatly: some reports merely document species presence, while others include meadow sizes. Estimations of meadow extent are seldom reported, with the only data originating from Canal del Infiernillo, Bahía Concepción and Bahía Balandra (Torre-Cosio, 2002; Hinojosa-Arango et al., 2014; López-Calderón et al., 2014, López-Calderón et al., 2016; Pérez-Estrada et al., 2021).

The subject of blue carbon in seagrass, though well-studied globally (Lavery et al., 2013; Oreska et al., 2017; Friess, 2023), is lacking in the Gulf of California, with only two studies providing information (Flores-Verdugo et al., 1995; Herrera-Silveira et al., 2018). Lastly, fishing and aquaculture research indirectly offer information on seagrass distribution (Paul and Bowers, 1982; Santamaría-Gallegos et al., 1999; Zetina-Rejón, 1999; Bourillón-Moreno, 2002).