Worldwide, mangroves are coastal ecosystems that are distributed in tropical and subtropical zones; they provide many ecosystem services such as water filtration, carbon storage, and coastline maintenance as a buffer to the impact of hurricanes and tides (Nagelkerken et al., 2008; Twilley and Day, 2013). Also, a high primary productivity and complex arrangement of submerged and aerial roots (neumatophores) form a refuge and feeding habitat for many species of fish at different life cycle stages (Blaber, 2000; Laegdsgaar and Johnson, 2001). Even when the ecological relevance of mangrove areas is acknowledged, these ecosystems are the most threatened by anthropic activities (Twilley and Day, 2013; Hamilton and Casey, 2016).

The accelerated reduction in mangrove areas has led to the implementation of different conservation and restoration efforts, with the objective of maintaining ecosystem functions at the local, regional, and global scale (FAO, 2007). Mainly, mangrove restoration activities are based on recovering hydrologic processes and substrate retention through reforestation. Therefore, the ecosystem restoration indicators have focused on hydrology and vegetation structure (McAlpine et al., 2016). However, the biotic interactions that include vertebrates (e.g., fish and birds), invertebrates (e.g., crustaceans and insects), primary producers (e.g., algae and plants), and food webs reflect the restoration progress of ecosystem functions in less time (Bosire et al., 2008).

Fishes serve as bioindicators of the mangrove restoration process, as its narrow relationship with the roots in this habitat (used as refuge, feeding, and reproduction areas) and high recovery rate of species after the restoration process (Laegdsgaar and Johnson, 2001; Nagelkerken et al., 2008; Vaslet et al., 2015). It is estimated that the mangrove fish community in restored mangroves is similar to that of conservation zones in nearly 5 years (Bosire et al., 2008). In addition, mangrove ecosystems are an important source of structure food webs due to the connections with adjacent aquatic systems, such as coral reefs (Nagelkerken et al., 2000; Mumby, 2006) and terrestrial ecosystems, which increase the availability of prey for larger vertebrates such as birds and reptiles (Trexler and Goss, 2009; De Dios Arcos et al., 2019).

Different aspects of the ichthyic community have been assessed in relation to restoration processes, primarily those considering the structure and composition of species (e.g., Trexler and Goss, 2009; Arceo-Carranza et al., 2016; Enchelmaier et al., 2020; Soria-Barreto et al., 2021). Nonetheless, these results only reflect the importance of mangrove ecosystems as refuge (Kovalenko et al., 2019; Le Guen et al., 2019). Recently, the importance in including the trophic interactions among fish and its preys has been proposed as an indirect tool useful to assess the conservation and restoration status of mangrove ecosystems, because of its high connectivity to terrestrial and marine environments and process related to the maintenance of biodiversity and functions at different scales (Palmer et al., 1997; Vander Zanden et al., 2016; Hale et al., 2019; Loch et al., 2020).

Classifying species by functional groups or guilds provides a more detailed perspective of the biotic and abiotic responses related to species ecological relationship, organism–environment responses, incorporating characteristics driving interactions and exploitation of available resources in the ecosystem, and how these influence processes and functions (Elliott et al., 2007; Violle et al., 2007). Also, it can reveal other mechanisms that promote diversity such as the response of communities to environmental changes (i.e., predator–prey relationships), prey preferences, and prey abundance (Kovalenko et al., 2019).

Habitat modification promotes changes in the trophic structure of aquatic ecosystem and modifies the prey diversity availability for the ichthyofauna (Bernardino et al., 2018). Therefore, the feeding habits are modified in order to exploit the available resources in the environment (Elliott et al., 2007; Vander Zanden et al., 2016). In relation to the seasonal dynamics, the ecotone that represents the mangrove ecosystems harbors high functional diversity such as opportunistic species related to a large trophic plasticity, others related to changes in environmental conditions, and in most cases high richness of species with specialized diets, which in most cases migrate to higher, richer, prey-conserved zones. Regarding the aforementioned, the study and comparison of changes in fish diets between recovering zones through restoration processes are relevant in order to assess the status and success of restoration plans and techniques. Therefore, the aim of the present study was to compare the trophic dynamics of eight fish species that inhabit a mangrove ecosystem related to karstic wetlands in the Mexican–Caribbean using freshwater, estuarine, and marine fish species as bioindicators of the restoration process in aquatic environments.

Changes in fish diet are highly related to the richness and abundance of the prey species at a spatial and temporal scale (Hinojosa-Garro et al., 2013). This is also related to environmental seasonal changes and by anthropic activities, where a majority of fish present opportunistic behavior in order to take advantage of peaks in prey abundance (Demopoulos and Smith, 2010). Mangrove deforestation may be due to changes in hydrologic patterns that affect the ecosystem, altering the diversity, biotic interactions, and trophic webs (Shinnaka et al., 2007). Trophic webs connect the resources of the ecosystem with the inhabiting organisms, and through its study, which provide a holistic vision on the state of the ecosystem as compared with information that results only from species richness and abundance (Villéger et al., 2010; Thompson et al., 2012; Ellis and Bell, 2013; Vander Zanden et al., 2016). In the species analyzed in this study, there were interspecific differences identified in the diets, and most of these species fed on zoobenthic organisms, a trophic guild largely reported in marine and estuarine fish within mangrove ecosystems and favored because of high secondary productivity (Elliott et al., 2007; Arceo-Carranza et al., 2013; Dolbeth et al., 2013; Palacios-Sánchez et al., 2019).

Most of the fish inhabiting these estuarine environments are characterized as having generalist-type diets that are flexible in taking advantage of temporal peaks in prey abundance, such that the diet in these estuarine species reflects the variety and type of available resources in its environment (Livingston, 1984; Elliott et al., 2007). This was found in the fish diets from the Sian Ka’an zone, primarily in F. polyommus, a species registering a shift in its diet and taking advantage of the abundance of microcrustaceans such as amphipods and tanaidaceans. This shift in diet suggests an altered state in the environment caused by anthropic activities, in this case, the road interrupting the hydrologic flow and decreasing the vegetation cover related to mangroves, and microhabitats for fish prey existing in the restored zone.

Many of estuarine and marine species using the estuaries in early phases of development are considered generalist. This is found to be related with the ontogenetic development and change in the morphoanatomical characteristics of fish, which allows them to shift from one food source to another, functioning like opportunistic species that exploit the available resources found in the surroundings, making them capable of responding to biotic and abiotic changes, either in a disturbed zone with less diversity in prey, or in a conserved zone that present higher numbers in potential prey (Wooton, 1990; Bellwood et al., 2006). This trophic flexibility is common in estuarine fish, with species temporally exploiting the peaks in prey abundance that exist, however, when there are disturbances that alter the trophic webs and lower the trophic levels; some fish respond by consuming prey at lower trophic levels, such as F. polyommus that is secondary consumer (Poot Salazar et al., 2005) in the conserved zone (feeding zoobenthos), and primary consumer in the restored zone feeding on detritus and phytobenthos. Contrarily, for a marine fish such as L. griseus, a species associated with mangroves in their juvenile phase, feed on microcrustaceans, and upon migrating to the reef zones, the food source is based on macrocrustaceans and fish, additionally increasing its trophic level (Faunce and Serafy, 2008). Similarly, S. testudineus can change its diet according to the available resources, between microcrustaceans and mollusks (Palacios-Sánchez and Vega-Cendejas, 2010; Chi-Espinola and Vega-Cendejas, 2013), but they remain at the same trophic level and zoobentophagous guild.

Nonetheless, there are species that have one food guild, and one type of prey, better adapted to a specialist strategy, such as the juveniles of A. stipes, with a diet based on the consumption of zoeas larvae, of decapods and copepods (Vaslet et al., 2015). Atherinomorus stipes is related with mangrove areas in the Mexican–Caribbean; notwithstanding, its presence is limited by ecosystem alterations, more so, if there is an increase in turbidity of the water, limiting foraging and hindering its encounter with preferred prey (Nash et al., 2017). This high turbidity in water observed for the restored zone probably explains the low abundance of this specie.

The sharing of food resources reduces competition between fish; however, in estuarine environments, many species share from a pool of prey, more so, in the juvenile phases; thus, in theory, the amount of food available for each individual is affected by the consumption of individuals co-occurring in nursery zones. Saulnier et al. (2020) and Day et al. (2020) reported that marcrobenthos produced in these zones directly affect the density of juvenile organisms, which relates to zones that are better conserved and have mangrove habitats, and submerged grasses that provide feeding zones. Fish, therefore, are important elements that serve in quantifying diversity, abundance, and composition of prey found in conserved and impacted environments, and in this case, those that are found in the process of restoration.

An alteration in hydrology, because of anthropogenic actions in estuarine ecosystems, drives a change in the fish assemblages, whether in its taxonomic composition or in functional aspects such as the food guilds and trophic levels (Baptista et al., 2015; Arceo-Carranza et al., 2016; Soria-Barreto et al., 2021). This was reflected in differences in the diets presented by resident species from the mangrove; for example, in F. polyommus, the altered hydrology affected the vegetation and microhabitats for available prey; thus, it presented a diet based on detritus and macrophytes in the restored zone, resources that are characteristic for ecosystems in secondary succession (Harrington and Harrington, 1982).

This study provides evidence on the impact that is generated in the trophic webs (species richness and prey abundance in diets) due to anthropic activities (Bosire et al., 2008). The interruption of water flow caused by road construction in this area of the Mexican–Caribbean affects not only the mangrove cover, but also the faunal diversity (benthonic and nektonic), including the predator–prey interactions of the fish communities present (Bosire et al., 2008; Chen and Ye, 2011). Shifting to alternative prey provokes changes in the vertical structure of the food web decreasing the number of trophic levels, modifying the structure and function of the biological communities in these coastal wetlands. According to some studies on mangrove restoration, there is a gradual shift to more heterogeneous food sources after several years of the restoration process (Loch et al., 2020).

Finally, the results of this work show that trophic ecology of fish are a useful tool, especially in prey abundance, trophic levels, and trophic guilds, key points to know the ecological functions of the community and thus determining and monitoring restoration processes. This garners relevance when there is an attempt to find ecological indicators that show the advances in restoration projects, and in so doing, establish the functional success of the restoration of coastal wetlands. In this case, F. polyommus, being an opportunistic organism, is ideal to know the food resources in the conserved and restored mangroves.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

LH-M and DA-C contributed in the idea and design of the study. LH-M performed the analysis and writing of the manuscript. DA-C and LE-V contributed in the writing and criticism of the intellectual content. All authors contributed to the discussion, review, and approval of the final manuscript.

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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