https://orcid.org/0000-0002-2199-6711
Figures
Abstract
The environmental drivers that effect the pelagic amphipod communities in the neritic province have received little attention worldwide. This study analyzed the influence of fluvial discharges and wind regime on the pelagic amphipods in neritic waters of the southern Gulf of Mexico during two contrasting seasons: May (dry, lower discharges and wind speeds) and November (nortes, higher discharges and wind speeds). Zooplankton samples were collected at five depth levels of the water column (0–6, 6–12, 12–18, 45–55, and 95–105 m) using a stratified opening-closing net system. Environmental gradients were assessed by defining three horizontal assemblages (‘coastal’, ‘neritic’, ‘slope’) and two vertical assemblages (‘surface’: 0–18 m; ‘deep’: 45–105 m). Seasonally, the greater volume of nutrient-rich discharges during nortes resulted in a higher amphipod density. Spatially, low salinity waters off river mouths corresponded to the lowest amphipod density and diversity. The horizontal and vertical assemblages showed significant differences during the dry (ANOSIM test, p < 0.05); during nortes, the structure of horizontal and vertical assemblages showed a lower heterogeneity, probably due to wind strength. Differences within the assemblages defined in the horizontal and vertical planes were only evident when Lestrigonus bengalensis was considered in the analysis; however, without this species, the amphipod community showed more homogeneity across the two seasons. Anchylomera blossevillei, Tetrathyrus forcipatus, and the juveniles of Eupronoidae were ecologically relevant in the characterization of the assemblages due to their specific environmental requirements. Diversity, evaluated using the completeness method, increased from the coast to the ocean in both seasons; vertically, diversity was highest in the ‘deep’ assemblage during the dry, but no differences were observed between assemblages in nortes. The greater similarity of the assemblages during nortes was associated with a higher homogeneity in hydrological conditions due to the strong winds that dominate this season. These findings contribute to a deeper ecological understanding of the effects of hydro-meteorological conditions on the structure of pelagic amphipod communities.
Citation: Violante-Huerta M, Sanvicente-Añorve L, Alatorre-Mendieta M, Guerra-Castro E (2025) Cross-shelf and vertical structure of pelagic amphipods (Crustacea) related to hydro-meteorological conditions in the neritic zone, southern Gulf of Mexico. PLoS One 20(12): e0336930. https://doi.org/10.1371/journal.pone.0336930
Editor: Luisa Borges, L3 Scientific Solutions, GERMANY
Received: May 28, 2025; Accepted: October 31, 2025; Published: December 4, 2025
Copyright: © 2025 Violante-Huerta et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: All relevant data are within the manuscript, the Supplemental Documents and the public repository Zenodo: available at https://doi.org/10.5281/zenodo.17298974.
Funding: This research was funded by the Universidad Nacional Autónoma de México. The first author thanks the scholarship (CVU #862851) granted by the CONAHCYT in Mexico during his doctoral studies. However, the funders were not involved in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
Introduction
Pelagic amphipods generally have a cosmopolitan or circumtropical distribution [1,2]. Most species have a clear preference for inhabiting the oceanic province, where the highest diversity was recorded [1]. Instead, the highest abundance of amphipods is found in the neritic province [3]. Among the pelagic amphipods, the suborder Hyperiidea stands out for its dominance and species diversity, since it is an exclusively holoplanktonic group, of which 292 species have currently been recognized [1,2,4,5]. Furthermore, some species from suborders Amphilochidea and Senticaudata are found in the holoplankton of epi-, meso-, and abyssopelagic waters [6–9].
Globally, the ecology of pelagic amphipods has been studied mainly in the oceanic province, and their community structure has been related to temperature and productivity gradients, as a result of diverse mesoscale and coarse-scale oceanographic processes [4,9–12]. However, in the neritic province, the pelagic amphipod community has been poorly studied. Some studies highlight the high abundance of this zooplankton group in neritic waters, but do not provide further ecological data on the community structure [1,3,13]. Only a few studies address the influence of the hydrological processes on the pelagic amphipod community structure in the horizontal plane [14–17]. Among the oceanographic processes that influence the distribution of zooplankton in the neritic zone are the marine currents [18–21], the thermocline depth [22], upwelling processes [23], and continental water discharges [21,24,25] that vary throughout the annual cycle.
Mexico, which has an extensive coastline, has many rivers and lagoons that discharge freshwater, sediments, and organic and inorganic matter into the marine system. Particularly, the greatest hydrological contributions to the Gulf of Mexico are the Mississippi River to the north and the Grijalva-Usumacinta River to the south [26–27]. In the southern Gulf, previous studies have emphasized the importance of the continental water discharges over the distribution and structure of some zooplankton organisms, such as holoplanktonic mollusks [28–31], fish larvae [32], and siphonophores [33]. An additional factor to consider in this region is the seasonal variation in wind patterns, with stronger winds occurring from October to March during the nortes season [34–36], whose effect on zooplankton is scarcely explored. Currently, the implications of the wind regime and the continental discharges on the pelagic amphipod community in the region are unknown, so two main questions need to be answered to better understand the mechanisms that structure this community in the neritic province of the Gulf:
- 1) what is the effect of the continental water discharges on the amphipod community?
- 2) how does the stronger wind regime that occurs during the nortes influence the community structure in both the horizontal and the vertical planes?
This study explores the horizontal and vertical variations in the structure of the pelagic amphipod community in the neritic waters of the southern Gulf of Mexico, during two contrasting seasons in terms of rain and wind regimes: May (dry season) and November (nortes season).
Materials and methods
Seasonality
In the southern Gulf of Mexico, three main meteorological periods have been recognized considering rainfall intensity and wind regime: dry, rainy, and nortes seasons. The dry, lasting from February to May, is characterized by moderate wind speed (4–6 m/s), and the lowest pluviosity in the year (< 300 mm). The rainy, from June to September, the wind speed is similar to the dry period, but the rainfall is the highest throughout the year (800–1200 mm). Finally, the nortes, from October to March, is characterized by sporadic rainfalls and strong cold winds coming from the north that reach speeds of up to 8 m/s, which diminish the surface water temperature [34–36]. It is worth noting that interannual variability in the seasons’ periods exists [37].
Continental water discharges gradually increase from June to September-October, with values ranging from 1,600–3,900 m3/s; after which they decrease [38]. This means that the highest discharges occur from the end of the rainy to the beginning of nortes one, and the lowest discharges happen at the end of nortes and the entire dry.
Sampling and laboratory work
Sampling was performed aboard the R/V “Justo Sierra” during the Project entitled “Monitoreo de Pre-reclutas de Especies Estuarino-Dependientes” (MOPEED), carried out in neritic waters of the southern Gulf of Mexico in 1995. Two oceanographic campaigns were performed during two contrasting seasons: dry in May and nortes in November. In each season, 28 sampling stations were organized into five transects perpendicular to the coastline in front of the main continental water discharges of the region: Coatzacoalcos River (I), Carmen and Machona lagoon system (II), Grijalva-Usumacinta fluvial system (III) and the Terminos lagoon (IV and V). Sampling stations were ploted in horizontal maps (Fig 1) using the Ocean Data View (ODV 5.8.3.) software [39]. Temperature and salinity were recorded before the zooplankton sampling, using a CTD sonde (Sea-Bird SBE 9) deployed from the surface (0 m) up to 250 m depending on the bottom depth. This sonde uses a pomp and a TC (temperature-conductivity) duct to ensure a constant flow, allowing both sensors to measure the same water mass and reduce salinity spikes. Afterward, zooplankton was collected at one or up to five levels of the water column, from the surface up to 105 m depth: level 1 (0–6 m), level 2 (6–12 m), level 3 (12–18 m), level 4 (45–55 m), and level 5 (95–105 m); the number of sampled levels depended on the bathymetry. Circular double oblique tows were conducted using a stratified opening-closing net system (75 cm mouth, 500 µm mesh, 2 m long) during 25 minutes at 3 knots. Additionally, an inclinometer was employed to measure the sampling depth using trigonometry. In total, 187 zooplankton samples (94 in dry and 93 in nortes) were collected because not all sampling stations were suitable for collecting samples at all five levels due to the shallower bottom depths. The biological material was fixed in a 4% formalin solution and preserved in 70% ethanol. These samples form part of a project initially conceived in the 1990s to evaluate the influence of continental water discharges on fish and shrimp larvae in the upper layer of neritic waters of the southern Gulf; the deep levels were taken as a complement, not as a priority.
Republished from Ocean Data View under a CC BY license, with permission from Prof. Dr. Reiner Schlitzer (rights holder), original copyright 2025.
In the laboratory, zooplankton biomass was measured using the displacement volume method [40], and data were expressed as mL/1,000 m3. Then, all amphipods were sorted from the samples and identified according to specialized literature [1,2,8,41–44]. Most of the juvenile organisms were not suitable for identification due to their incomplete development and high similarity to other species, which could lead to errors in the identification of taxa. However, they were considered in the formal analysis (e.g., family Eupronoidae, genus Primno). The amphipod abundance data were standardized and expressed as ind/1,000 m3 (available at https://doi.org/10.5281/zenodo.17298974).
Data analysis
Hydrology.
Temperature and salinity data recorded from CTD were used to estimate the mean integrated value for each sampling level using the following formula:
Where Mx is the integrated mean value of x, x is the parameter (temperature or salinity), Zi is the initial sampling depth, Zf is the final sampling depth, and Z is the depth of the integrated variable.
Mean integrated values were used to plot the horizontal distribution of the surface temperature and salinity to identify the influence of the water discharges and to perform the multivariate analyses. Additionally, temperature and salinity data were plotted in vertical profiles along the five transects to observe the distribution of the parameters with depth using the SURFER v15 software.
Biological data.
To identify the environmental gradient generated by the influence of continental water discharges over the structure of the amphipod community, we defined three horizontal assemblages (named ‘coastal’, ‘neritic’, and ‘slope’) and two assemblages in the vertical plane (‘surface’ and ‘deep’).
In the first step of data analysis, which explored the horizontal structure, the ‘coastal’ assemblage was composed of the stations located closer to the major continental water discharges; the ‘neritic’ assemblage comprised stations on the continental shelf; and the ‘slope’ consisted of stations located over the limit of the shelf (Fig 1). Matrices crossing density of amphipod species and sampling stations of each sampling season were transformed by applying a square root to reduce the bias of the dominant species and to meet the normality assumption. Then, to determine which variables (temperature, salinity, zooplankton biomass, amphipod density, and distance to the shore) were associated with each of the assemblages, a Principal Component Analysis (PCA) was performed on the transformed data; as a complement, the amphipod density (ind/1,000 m3) was represented as bubbles at each data point (sampling station). Afterward, an ANOSIM hypothesis test (9999 permutations) was applied to a station’s Bray-Curtis similarity matrix to prove the differences among the three assemblages. The ANOSIM (Analysis of Similarities) test considers the rank of the data to assess differences among groups. The proof uses the rank permutations to calculate the statistical significance, with a resulting R statistic indicating the degree of similarity: R values near 1 indicate differences between data sets, while values close to 0 indicate resemblance between groups. This non-parametric method has no strict assumptions about the underlying data distribution, such as normality or homoscedasticity [45]. Furthermore, a SIMPER analysis was applied to determine the taxa with the greatest contribution to groups’ discrimination. These analyses were made using the PRIMER v7 software [46]. These multivariate procedures were replicated without the dominant species (Lestrigonus bengalensis) to evaluate the effect of this species on the amphipod community structure.
Horizontal assemblages were also compared in terms of diversity, evaluated through the number of species. In both seasons, species accumulation curves of the alpha diversity were performed with the interpolation-extrapolation of the Hill numbers and the incidence-based estimator Chao2 [47]. Moreover, sample completeness was estimated for each assemblage to infer the representativeness of the sampling effort [47] in both seasons, considering a common sample coverage value of 0.75 to compare the interpolated alpha diversity. “Completeness” represents the probability of obtaining the species already recorded in the next sample. In traditional methods to estimate species richness, all species are treated as equal, but their abundances are completely ignored. By contrast, if individuals are equally considered, in a manner that each species is weighted by its abundance, it is possible to estimate the coverage or completeness of a sample [48]. Then, the method allows for comparing species richness of several communities based on samples of equal completeness instead of equal size. The method yields less biased comparisons of species richness between datasets that result from different sampling efforts, allows communities to be ranked according to their true richness, and meets the principle of replicability without loosing any sampling effort, which is essential when discussing diversity [47]. The diversity analysis was performed with the R free software and the iNEXT package [49].
In the second step of data analysis, the vertical structure of the community was explored, considering levels 1–3 (0–6, 6–12, and 12–18 m) as the ‘surface’ assemblage, and levels 4–5 (45–55, and 95–105 m) as the ‘deep’ assemblage. In this second approach, the methods used in the horizontal analysis were applied to verify the differences in the community structure in the water column during both seasons. The common sample coverage value used in this second analysis was 0.95.
Results
Hydrology
Seasonally, the highest temperature values (~28°C), evident in surface waters (0–6 m depth), were recorded during the dry; in nortes, temperatures were below 28°C. In the horizontal plane, temperatures increased from the coast toward the ocean in both seasons; in the vertical plane, the thickness of the warm water layer (>24.5°C) reaches 40 m in dry, and 80 m in nortes (Fig 2).
Horizontal representation corresponds to the 0-6 mean integrated value.
In the horizontal plane, surface salinity (0–6 m depth) increases from the coast toward the ocean during dry, while in nortes, the lowest values (around 32 psu) were observed in the intermediate zone of the study area, indicating the greater effect of the continental water discharges during nortes. In the vertical plane, lower salinity (30–32 psu) was recorded between 0 and 40 m depth in the transects III and IV, evidencing the higher continental water discharge during nortes (Fig 3).
Horizontal representation corresponds to the 0-6 mean integrated value.
Community structure in horizontal and vertical planes
Seasonality.
A total of 39,329 pelagic amphipods were sorted and identified across the seasons surveyed. 86 taxa were identified (72 during dry, and 74 in nortes) and most of them occur in both seasons (S1 Table). The mean (± SD) density of amphipods was slightly higher in nortes (1,170.8 ± 2,098.9 ind/1,000 m3) than in dry (1,059.5 ± 1,538.5 ind/1,000 m3). ANOSIM test (R = 0.016, p = 0.024) confirmed that seasons have significant differences in the density of amphipods.
Cross-shelf assemblages.
During the dry, differences in the community structure among assemblages were significant (ANOSIM test, p < 0.05). The first two axes of the PCA accounted for 60% of the total variation; on axis 1, the zooplankton biomass was the variable with the highest correlation (Table 1) and was associated with the ‘neritic’ assemblage, characterized by a high amphipod density (Fig 4). During nortes, ‘neritic’ and ‘coastal’ assemblages did not show significant differences (ANOSIM test, p = 0.563). In the PCA ordination plot, axes I and II accounted for 67.2% of the total variance, and the salinity was the variable with the greatest correlation on axis 1 (Table 1), which showed a negative correlation with the ‘coastal’ and much of the ‘neritic’ assemblage (Fig 4). Results of a supplementary analysis excluding the most abundant species, L. bengalensis, indicated that the ‘coastal’ and ‘neritic’ assemblages showed no significant differences regardless of the season (S1 Text: ANOSIM test, p > 0.05).
Size of bubbles corresponds to the total amphipod density transformed into square root.
Overall, the highest density of amphipods was registered in the ‘neritic’ assemblage, while the lowest was found on the ‘slope’ (S1 Table). In particular, the highest density values (~1,000 ind/1,000 m3) were found in the transect located in front of the Carmen and Machona lagoon system in both seasons (Fig 5, Transect II). The lowest density values ( = 30.7 ind/1,000 m3) were recorded in the ‘coastal’ assemblage, particularly in the stations located in front of the Grijalva-Usumacinta system and the Terminos lagoon in both seasons (Fig 5, Transects III to V).
Republished from Ocean Data View under a CC BY license, with permission from Prof. Dr. Reiner Schlitzer (rights holder), original copyright 2025.
Species composition varied among assemblages, and the highest number of exclusive species occurred on the ‘slope’ assemblage in both seasons (dry = 28 species; nortes = 27). Among these species, those from the infraorder Physosomata showed the greatest affinity to oceanic conditions, with all species occurring on the ‘slope’ (S1 Table).
Lestrigonus bengalensis was the dominant species during both dry (78.4% of the total abundance) and nortes (86.4%). The species was more abundant in the ‘neritic’ and ‘coastal’ assemblages, and the difference with the ‘slope’ assemblage was more evident during the dry (S1 Table). The SIMPER analysis confirmed that L. bengalensis recorded the greatest contribution to the assemblages’ discrimination in both seasons. Tetrathyrus forcipatus, the juveniles of Eupronoidae, and Anchylomera blossevillei were also key players in the assemblages’ differentiation (Table 2), and coincided with the supplementary analysis excluding L. bengalensis (Table D in S1 Text).
Diversity showed an increasing pattern in a coastal-oceanic direction when comparing assemblages using the common completeness value of 0.75. During both seasons, 15 species were recorded in the ‘coastal’ assemblage, 23 in the ‘neritic’, and 35 in the ‘slope’ (Fig 6).
Vertical assemblages.
During dry, the PCA results indicated a clear separation between the ‘surface’ (levels 1–3: 0–18 m) and ‘deep’ (levels 4 and 5: 45–105 m) assemblages (Fig 7); the highest zooplankton biomass was associated with the levels that compose the ‘surface’ assemblage, which showed a higher amphipod density. During nortes, the ‘deep’ assemblage was more heterogeneous, since level 4 (45–55 m) was environmentally closer to the ‘surface’ assemblage, which was characterized by low salinity (Fig 7). Indeed, R values from the ANOSIM test confirmed the greater affinity of the level 4 (45–55 m depth) with the surface levels (0–18 m depth) during nortes, compared to dry (Table 3). Differences between the vertical assemblages (‘surface’ and ‘deep’) were confirmed by the ANOSIM test (dry: R = 0.411, p = 0.0001; nortes: R = 0.24, p = 0.0003). The complementary analysis excluding L. bengalensis showed no significant differences between the two assemblages in the vertical plane in both seasons (S1 Text: ANOSIM test, p > 0.05). The highest density of individuals (>1,000 ind/1,000 m3) was recorded in the ‘surface’ assemblage in both seasons (Figs 5 and 7).
Size of bubbles corresponds to the total amphipod density transformed into square root.
Again, L. bengalensis contributed the most to the discrimination of the vertical assemblages, as shown in the SIMPER analysis, since it represents more than 20% of the dissimilarity between them during the studied periods (Table 4). In the supplementary analysis excluding L. bengalensis, the rest of the species differentiating the vertical assemblages (e.g., juveniles of Primno, T. forcipatus) (Table E in S1 Text) were the same as in the main analysis (Table 4).
Diversity showed a clear stratification during the dry. When comparing the diversity with a common completeness value of 0.95, the ‘deep’ assemblage (58 species) was more diverse than the ‘surface’ one (50 species). In the nortes, no differences in diversity (55 species) were observed between assemblages (Fig 8).
Discussion
Seasonality
Worldwide, the ecology of pelagic amphipods in neritic waters has been poorly studied. The current study, conducted in the neritic province of the southern Gulf of Mexico, aimed to determine the effects of continental water discharges and wind regimes on the pelagic amphipod community. Seasonally, overall amphipod abundance showed significant differences (ANOSIM test, p < 0.05), with higher values during the nortes ( = 1,170.8 ± 2,098.9 ind/1,000 m3) compared to the dry (
= 1,059.5 ± 1,538.5 ind/1,000 m3). In the Ross River in Australia, nutrient discharges into the marine environment caused an increase in the abundance of hyperiid amphipods [14]. In the Gulf of Mexico, previous studies have indicated that at the beginning of nortes, a significant continental discharge occurs into the neritic province of the southern Gulf of Mexico [32,50,51], primarily due to the influence of the Grijalva-Usumacinta System (approximately 2,678 m3/s) [26]. Runoff greatly affects the amount of nutrients and sediments in the marine environment, leading to variations in the secondary production of surrounding waters that depend on the intensity of discharges throughout the year [51]. In this study, the higher correlation of the runoff (related to salinity) and productivity (related to zooplankton biomass) during nortes was evidenced in the PCA (Table 1). Enriching marine waters by continental discharges could positively affect the primary and secondary production at the beginning of the nortes, which can explain the observed differences in amphipod density.
Cross-shelf assemblages
Results showed that differences among the horizontal assemblages were more evident during the dry (ANOSIM test, p < 0.05); during nortes, no significant differences were found between the ‘neritic’ and the ‘coastal’ assemblages (ANOSIM test, p > 0.05). This could be a consequence of the strong winds (8 m/s) characteristic of the nortes [34–36], which homogenize the hydrological conditions. Generally, the density of cross-shelf assemblages showed the following order: ‘neritic’, ‘coastal’, and ‘slope’ regardless of the season (S1 Table). In the dry, the PCA showed that zooplankton biomass was the variable with the greatest influence on the amphipod density (Table 1), which was higher in the ‘neritic’ assemblage (Fig 4). This is consistent with the previous observations in the oceanic province of the Gulf during the summer, since it is during this season when the zooplankton biomass increases as well as the density of amphipods [9], probably due to their affinity to inhabit the high productivity areas where they find their food [3,9,52]. During nortes, salinity was the most influential factor over the amphipods (Fig 4; Table 1). The lowest salinity zones in both seasons (Fig 3) coincided with the lowest amphipod density in the ‘coastal’ assemblage (Fig 5, Transect III), suggesting that pelagic amphipods avoid low-salinity waters derived from the continental discharges. Certainly, salinity conditions are a critical factor affecting the distribution of species because of the marine origin of amphipods and their low tolerance to low-salinity waters [1,15]. However, in addition to the continental discharges and the wind regime, other oceanographic processes can influence the zooplankton community in this area, such as marine currents [18–21], thermocline depth [22], and upwelling events [23] (among others), which also need further exploration.
Lestrigonus bengalensis was the species with the greatest contribution to the discrimination of assemblages in both seasons (Table 2), due to its high abundance (> 1,000 ind/1,000 m3) (S1 Table). The dominance of this species in the neritic province has been previously recorded in the Gulf of Mexico [3,17], but also in other tropical regions of the world [1,13,53,54]. This species has a broad tolerance to hydrological variability [14,15,53], and this was probably the reason why this species dominated in the horizontal assemblages, even in the lowest salinity zones (~30 psu) located in front of the Grijalva-Usumacinta System during nortes. This species registered the highest density values in the ‘neritic’ assemblage, following by the ‘coastal’, and decreased considerably in the ‘slope’ in both seasons (S1 Table); as stated, this could be a consequence of L. bengalensis’ preference for inhabiting neritic waters [1,13,17]. Due to its carnivorous habits, this species increases its density in high productivity areas where a higher food availability exists [14,52]. The relevance of this species in the neritic province as an indicator of the influence of hydro-meteorological variability on the horizontal plane was evidenced in a supplementary analysis excluding this species, which showed more homogeneity between the ‘coastal’ and the ‘neritic’ assemblages during both seasons (S1 Text). In the oceanic province, the dominance and relevance of this species as an indicator of the environmental variability could vary seasonally, since other taxa (e.g., juveniles of the Primno genus, Anchylomera blossevillei, and Stenopleura atlantica) may exceed the density of L. bengalensis during the summer [9,52].
The other three relevant species in the discrimination between assemblages were A. blossevillei, T. forcipatus, and the juveniles of Eupronoidae (Table 2). The ‘coastal’ assemblage was characterized by the higher density of T. forcipatus during both seasons, and the juveniles of Eupronoidae in nortes (S1 Table). The former taxon showed its highest abundance in the ‘coastal’ assemblage in both seasons (S1 Table). Indeed, the distribution pattern of this species shows a rare case among amphipods in which abundance decreases from the coast to the edge of the shelf, and whose hydrological tolerances are worth further study. For the juveniles of Eupronoidae, it seems that the hydrological conditions characterizing this assemblage during nortes represent a favorable environment for the reproduction of some members of the family, whose identity is unknown. In our study, we recorded seven Eupronoidae species –five from Eupronoe and two from Parapronoe– whose reproductive periods are unknown and may differ from one species to another throughout the year.
The ‘neritic’ assemblage was characterized by the high density of A. blossevillei and T. forcipatus (S1 Table) depending on the season. During dry, A. blossevillei was the most abundant species, but its density decreased drastically (approximately 45 times) in nortes (S1 Table). This species prefers to inhabit high-salinity waters [55], and this is probably the reason why the species’ density decreased in nortes and was not found in the ‘coastal’, where low-salinity waters occur (Fig 3). The little-known species T. forcipatus showed a clear preference for inhabiting the neritic waters during both seasons, but reached its highest density during nortes in the ‘neritic’ assemblage (S1 Table), suggesting its affinity to this season.
The ‘slope’ assemblage was characterized by the largest number of species and the high density of Eupronoidae juveniles, and A. blossevillei (S1 Table). In particular, the dominance of Eupronoidae juveniles in this assemblage is very interesting, since they also predominate in the ‘coastal’ assemblage. This could be a consequence of the fact that “Eupronoidae juveniles” may represent a group of different species whose hydrological preferences and tolerances are also different. Therefore, it is likely that the species responsible for the high density in the ‘slope’ assemblage were different from those that dominated in the ‘coastal’. Among the Eupronoidae species recorded in this work, Eupronoe minuta and Eupronoe intermedia showed their highest density in the ‘slope’ assemblage in both seasons (S1 Table), and these are probably the species responsible for this pattern. The preference of E. minuta and E. intermedia for inhabiting the oceanic environment is well known in the Gulf, especially E. intermedia [9,10,16].
Diversity increased from the coast to the ocean in both seasons (Fig 6). The increase in diversity towards the ‘slope’ is due to the oceanic nature of the pelagic amphipods [1]. In this study, some taxa from the infraorders Physocephalata (Phrosinidae, Hyperioides, Tryphana, most species of Oxyscephalus, Phronima, Streetsia, Vibilia, and Paraphronima), all Physosomata species, and the non-hyperiid S. atlantica were only found in the ‘slope’ assemblage (S1 Table), whose preferences for inhabiting the oceanic province have been widely recognized [1,8,9,56]. Seasonally, no differences in diversity were observed when comparing the corresponding horizontal assemblages (Fig 6), which contrasts with previous records in the oceanic province of the Gulf, where higher diversity has been recorded during the warm season compared to the cold one [9,10].
Vertical assemblages
The highest density was observed in the ‘surface’ assemblage in both seasons (Figs 5 and 7), which coincides with other records of amphipods [54,57,58], and other zooplankton groups [28–31,59,60]. The high productivity of surface waters promotes an increase in the concentration of zooplankton organisms and, consequently, their trophic interactions in this area [61]. Lestrigonus bengalensis had the highest contribution in the vertical assemblages’ discrimination in the two seasons (Table 4). This species prefers to inhabit surface waters [1,54], where higher food availability exists. The dissimilarities between the two assemblages were greater during the dry than in nortes, because the environmental conditions of level 4 (45–55 m) during nortes could influence the vertical distribution of amphipods, as observed in other zooplankton groups [62]. Seasonal differences among vertical assemblages were only evident when the dominant species was included; without considering L. bengalensis, the vertical structure of the community was homogeneous regardless of season (S1 Text), highlighting the importance of this species in the neritic province.
Assemblages’ diversity varied seasonally. During the dry, the highest diversity was observed in the ‘deep’ assemblage. In contrast, diversity in both assemblages was more homogeneous during nortes (Fig 8), probably due to the effect of the more intense wind regime [34–36]. The above contrasts with the most recent study of pelagic amphipods in the oceanic province of the northwestern Caribbean Sea, since diversity was higher in the upper 50 m strata during the same season (nortes); this pattern was related to the day-night migration of the species [58]. However, the effect of the day-night vertical migration of species on diversity may vary between the neritic and the oceanic environments because the vertical migration range of pelagic amphipods is generally about 100 m [54], which cannot always be achieved in the neritic province.
Conclusions
This study explored the horizontal and vertical variations in pelagic amphipod community structure in neritic waters of the southern Gulf of Mexico during two contrasting seasons: dry and nortes, differing in the volume of fluvial discharges and wind patterns. Results revealed that the greatest stratification of the cross-shelf and vertical assemblages occurred during the dry. In nortes, the effect of strong winds reduced the stratification: horizontally, there were no significant differences between the ‘neritic’ and ‘coastal’ assemblages; vertically, the assemblages were more homogeneous. The environmental variables with the greatest influence on the amphipod density were zooplankton biomass (proxy of food availability) and salinity, in response to the oceanic nature of these animals and their carnivorous habits. Lestrigonus bengalensis was dominant and represented a key species for detecting hydro-meteorological variation in the neritic province; without this species, the community showed a greater homogeneity regardless of the season. Horizontally, diversity increased from coast to ocean in both seasons, due to the amphipods’ oceanic preferences. Vertically, diversity was clearly different during dry, with higher diversity in the ‘deep’ assemblage; during nortes, diversity was the same in the two assemblages, which was related to the homogenizing effect of strong winds. Our results enrich the knowledge about the pelagic amphipod ecology and provide valuable information on the effects of the variability of wind regime and continental discharges on the amphipods.
Supporting information
S1 Table. Mean density (ind/1,000 m3) of the pelagic amphipods recorded in the neritic province of the southern Gulf of Mexico, during dry and nortes (1995). n = number of samples.
https://doi.org/10.1371/journal.pone.0336930.s001
(DOCX)
S1 Text. Pelagic amphipod community structure without Lestrigonus bengalensis.
https://doi.org/10.1371/journal.pone.0336930.s002
(DOCX)
Acknowledgments
The Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México supported the oceanographic cruises MOPEED, coordinated by Dr. César Flores-Coto. The authors are grateful to F. Zavala-García, M. Martínez-Mayén, and G. Molina-Sandoval for the technical support during the development of this work. Additionally, L. F. Álvarez-Sánchez helps us make the supporting data available in the public repository Zenodo. Finally, we appreciate the comments from the editor and anonymous reviewers who helped improve the manuscript.
References
- 1.
Vinogradov ME, Volkov A, Semenova T. Hyperiid amphipods (Amphipoda, Hyperiidea) of the world oceans. Washington D.C.: Smithsonian Institution Libraries; 1996.
- 2.
Vinogradov G. Amphipoda. In: Boltovskoy D, editor. South Atlantic Zooplankton. Leiden: Backhuys Publishers; 1999. pp. 1141–240.
- 3. Gasca R. Distribution and abundance of hyperiid amphipods in relation to summer mesoscale features in the southern Gulf of Mexico. J Plankton Res. 2004;26(9):993–1003.
- 4. Burridge AK, Tump M, Vonk R, Goetze E, Peijnenburg KTCA. Diversity and distribution of hyperiid amphipods along a latitudinal transect in the Atlantic Ocean. Progr Oceanogr. 2017;158:224–35.
- 5.
Horton T, Lowry J, De Broyer C, Bellan-Santini D, Copilas-Ciocianu D, Corbari L, et al. World Amphipoda Database. Database: World Register of Marine Species [internet]. 2025 [cited 2025 Apr 23]. Available from: https://www.marinespecies.org/aphia.php?p=taxdetails&id=1205
- 6. Lowry JK, Stoddart HE. Amphipoda crustacea IV. Families Aristiidae, Cyphocarididae, Endevoursidae, Lysianassidae, Scopelocheiridae, Uristidae. Mem Hourglass Cruis. 1997;10:1–148.
- 7. Hughes LE, Lowry JK. A review of the world Cyphocarididae with description of three new species (Crustacea, Amphipoda, Lysianassoidea). Zootaxa. 2015;4058(1):1–40. pmid:26701505
- 8. Violante-Huerta M, Sanvicente-Añorve L, Marrón-Becerra A, Lemus-Santana E, Flores-Coto C. First records of non-hyperiid planktonic amphipods (Amphilochidea and Senticaudata) from deep waters of southwestern Gulf of Mexico, with an identification key. Rev Mex Biodivers. 2020;91:e912975.
- 9. Violante-Huerta M, Sanvicente-Añorve L, Alatorre-Mendieta M, Guerra-Castro E. Coarse-scale vertical distribution of pelagic amphipods in two contrasting seasons of the southern Gulf of Mexico. Front Mar Sci. 2025;12.
- 10. Gasca R, Manzanilla H, Suárez-Morales E. Distribution of hyperiid amphipods (Crustacea) of the southern Gulf of Mexico, summer and winter, 1991. J Plankton Res. 2009;31(12):1493–504.
- 11. Lavaniegos BE. Pelagic amphipod assemblage associated with subarctic water off the West Coast of the Baja California peninsula. J Mar Syst. 2014;132:1–12.
- 12. Lavaniegos BE. Hyperiid amphipods from the Gulf of Ulloa and offshore region, Baja California: The possible role of the gelatinous zooplankton as a transport vector into the coastal shelf waters. PLoS One. 2020;15(11):e0233071. pmid:33151968
- 13. Bowman TE. Pelagic amphipods of the genus Hyperia and closely related genera (Hyperiidea: Hyperiidae). Smithson Contrib Zool. 1973;136:1–76.
- 14. Zeidler W. Distribution and abundance of some Hyperiidea (Crustacea : Amphipoda) in Northern Queensland Waters. Mar Freshw Res. 1984;35(3):285–305.
- 15. Valencia B, Lavaniegos B, Giraldo A, Rodríguez-Rubio E. Temporal and spatial variation of hyperiid amphipod assemblages in response to hydrographic processes in the Panama Bight, eastern tropical Pacific. Deep Sea Research Part I: Oceanographic Research Papers. 2013;73:46–61.
- 16. Velázquez-Ramírez B. Estructura de la comunidad de hipéridos (Amphipoda: Peracarida) en el sur del Golfo de México. B.Sc. Thesis, Universidad Nacional Autónoma de México, 2021. Available from: https://tesiunam.dgb.unam.mx/F/MAV1FT5NIRAVHNAPVN3TSBPI2NUKIJY52MKB4SK4381ND2F7NB-16011?func=full-set-set&set_number=107059&set_entry=000010&format=999
- 17. Sanvicente-Añorve L, Velázquez Ramírez B, Hermoso-Salazar M. Pelagic amphipods (Crustacea, Amphipoda, Hyperiidea) from the southern Gulf of Mexico with notes on the distribution of species. Biodivers Data J. 2023;11:e97347. pmid:38327308
- 18. Sanvicente-Añorve L, Zavala-Hidalgo J, Allende-Arandía M, Hermoso-Salazar M. Connectivity patterns among coral reef systems in the southern Gulf of Mexico. Mar Ecol Prog Ser. 2014;498:27–41.
- 19. Sanvicente-Añorve L, Zavala-Hidalgo J, Allende-Arandía E, Hermoso-Salazar M. Larval dispersal in three coral reef decapod species: influence of larval duration on the metapopulation structure. PLoS One. 2018;13(3):e0193457. pmid:29558478
- 20. Sanvicente‐Añorve L, Velázquez‐Villegas E, Sánchez‐Campos M, Allende‐Arandía MaE, Zavala‐Hidalgo J. Haline tolerance of stomatopod (Crustacea) larvae and pelagic dispersal of two common species in the Western Atlantic. J Geoph Res: Biogeosci. 2024;129(7).
- 21. de Santana CS, Lira SM de A, Varona HL, Neumann-Leitão S, Araujo M, Schwamborn R. Amazon river plume influence on planktonic decapods in the tropical Atlantic. J Mar Syst. 2020;212:103428.
- 22. Ge R, Chen H, Liu G, Zhu Y, Jiang Q. Diel vertical migration of mesozooplankton in the northern Yellow Sea. J Ocean Limnol. 2021;39(4):1373–86.
- 23. Medellín-Mora J, Atkinson A, Escribano R. Community structured production of zooplankton in the eastern boundary upwelling system off central/southern Chile (2003–2012). ICES J Mar Sci. 2019.
- 24. Axler K, Sponaugle S, Briseño-Avena C, Hernandez F Jr, Warner S, Dzwonkowski B, et al. Fine-scale larval fish distributions and predator-prey dynamics in a coastal river-dominated ecosystem. Mar Ecol Prog Ser. 2020;650:37–61.
- 25. Tosetto EG, Neumann-Leitão S, Araujo M, Minto Dimoune D, Bertrand A, Nogueira Júnior M. Amazon River plume habitats shape planktonic cnidarian assemblages in the Western Atlantic. PLoS One. 2023;18(8):e0290667. pmid:37624787
- 26.
Hudson PF, Hendrickson DA, Benke AC, Varela-Romero A, Rodiles-Hernández R, Minckley W. Rivers of Mexico. In: Benke A, Colbert C, editors. Rivers of North America. San Diego: Elsevier Academic Press; 2005. pp. 1031–84.
- 27.
Toledo-Ocampo A. Marco conceptual: caracterización ambiental del Golfo de México. In: Vázquez-Botello A, Rendón-von Osten J, Gold-Bouchot G, Agraz-Hernández C, editors. Golfo de México Contaminación e Impacto Ambiental: Diagnóstico y Tendencias. 2da ed. Campeche: Universidad Autónoma de Campeche, Universidad Nacional Autónoma de México, Instituto Nacional de Ecología; 2005. pp. 25–52.
- 28. Sanvicente-Añorve L, Lemus-Santana E, Flores-Coto C, Alatorre-Mendieta M. Vertical segregation of holoplanktonic molluscs in the epipelagic layer, southern Gulf of Mexico. Helgol Mar Res. 2012;67(2):397–405.
- 29. Lemus-Santana E, Sanvicente-Añorve L, Hermoso-Salazar M, Flores-Coto C. The holoplanktonic Mollusca from the southern Gulf of Mexico. Part 1: heteropods. Cahiers Biol Mar. 2014;55:229–39.
- 30. Lemus-Santana E, Sanvicente-Añorve L, Hermoso-Salazar M, Flores-Coto C. The holoplanktonic Mollusca from the southern Gulf of Mexico. Part 2: pteropods. Cahiers Biol Mar. 2014;55:241–58.
- 31. Lemus-Santana E, Sanvicente-Añorve L, Alatorre-Mendieta M, Flores-Coto C. Population structure and mating encounter rates in a marine pelagic invertebrate, Firoloida desmarestia (Mollusca). Sex Early Dev Aquat Org. 2015;1(2):163–73.
- 32. Espinosa-Fuentes ML, Flores-Coto C. Cross-shelf and vertical structure of ichthyoplankton assemblages in continental shelf waters of the Southern Gulf of Mexico. Estuar Coast Shelf Sci. 2004;59(2):333–52.
- 33. Sanvicente-Añorve L, Alba C, Flores-Coto C, Castillo-Rivera M. Siphonophores off a riverine system in the southern Gulf of Mexico: factors affecting their distribution and spatial niche breadth and overlap. Aquat Ecol. 2008;43(2):423–35.
- 34. Yáñez-Arancibia A, Day JW. Ecological characterization of the Términos Lagoon, a tropical lagoon-estuarine system in the Southern Gulf of Mexico. Oceanol Acta. 1982;5(4):431–40.
- 35.
Yáñez-Arancibia A, Day JW, Lara-Domínguez AL, Sánchez-Gil P, Villalobos-Zapata G, Herrera-Silveira JA. Ecosystem functioning, the basis for sustainable management of Terminos Lagoon, Campeche Mexico, Chapter 9. In: Day JW, Yáñez-Arancibia A, editors. The Gulf of Mexico Origin, Water, and Biota. Ecosystem-Based Management. Vol. 4 College Station: Texas A & M University Press; 2013. pp 167–199.
- 36.
CONAGUA. Datos climáticos en Veracruz, Ver., México 1917-1998. Veracruz: Comisión Nacional del Agua - Centro de previsión del Golfo de México; 1999.
- 37. Aké-Castillo JA, Vázquez G. Phytoplankton variation and its relation to nutrients and allochthonous organic matter in a coastal lagoon on the Gulf of Mexico. Estuar Coast Shelf Sci. 2008;78(4):705–14.
- 38. Martínez-López B, Zavala-Hidalgo J. Seasonal and interannual variability of cross-shelf transports of chlorophyll in the Gulf of Mexico. J Mar Syst. 2009;77(1–2):1–20.
- 39.
Schlitzer R. Ocean Data View. 2025. Available from: https://odv.awi.de
- 40.
Postel L, Fock H, Hagen W. Biomass and abundance. In: Harris R, Wiebe P, Lenz J, Skjoldal HR, Huntley M, editors. ICES zooplankton methodology manual. London: Academic Press; 2000. pp. 83–192.
- 41. Zeidler W. A review of the hyperiidean amphipod superfamily Vibilioidea Bowman and Gruner, 1973 (Crustacea: Amphipoda: Hyperiidea). Zootaxa. 2003;280(1).
- 42. Zeidler W. A review of the families and genera of the hyperiidean amphipod superfamily Phronimoidea Bowman & Gruner, 1973 (Crustacea: Amphipoda: Hyperiidea). Zootaxa. 2004;567(1).
- 43. Zeidler W. A review of the hyperiidean amphipod superfamily Lycaeopsoidea Bowman & Gruner, 1973 (Crustacea: Amphipoda: Hyperiidea). Zootaxa. 2004;520(1).
- 44. Zeidler W. A review of the families and genera of the superfamily Platysceloidea Bowman & Gruner, 1973 (Crustacea: Amphipoda: Hyperiidea), together with keys to the families, genera and species. Zootaxa. 2016;4192(1):zootaxa.4192.1.1. pmid:27988727
- 45.
Clarke KR, Gorley RN. Primer V7: User Manual/Tutorial. Plymouth: PRIMER-E Ltd.; 2015.
- 46.
Clarke KR, Gorley RN, Somerfield PJ, Warwick RM. Change in marine communities: an approach to statistical analysis and interpretation. Plymouth: PRIMER-E Ltd.; 2014.
- 47. Chao A, Jost L. Coverage-based rarefaction and extrapolation: standardizing samples by completeness rather than size. Ecology. 2012;93(12):2533–47. pmid:23431585
- 48. Chao A, Kubota Y, Zelený D, Chiu C, Li C, Kusumoto B, et al. Quantifying sample completeness and comparing diversities among assemblages. Ecol Res. 2020;35(2):292–314.
- 49. Hsieh TC, Ma KH, Chao A. iNEXT: an R package for rarefaction and extrapolation of species diversity (Hill numbers). Methods Ecol Evol. 2016;7(12):1451–6.
- 50.
Czitrom SPR, Ruiz F, Alatorre MA, Padilla AR. Preliminary study of a front in the Bay of Campeche, Mexico. In: Nihoul JCJ, editor. Marine interfaces ecohydrodynamics. Amsterdam: Elsevier Science; 1986. pp. 301–11.
- 51. Zavala-García F, Flores-Coto C, Espinosa-Fuentes M de la L. Relationship between zooplankton biomass and continental water discharges in the southern Gulf of Mexico (1984-2001). Rev Biol Mar Oceanogr. 2016;51(1):21–31.
- 52. Hereu CM, Arteaga MC, Galindo-Sánchez CE, Herzka SZ, Batta-Lona PG, Jiménez-Rosenberg SPA. Zooplankton summer composition in the southern Gulf of Mexico with emphasis on salp and hyperiid amphipod assemblages. J Mar Biol Ass. 2020;100(5):665–80.
- 53. Siegel-Causey D. Factors determining the distribution of hyperiid Amphipoda in the Gulf of California. Ph.D. Thesis, University of Arizona. 1982. Available from: https://www.proquest.com/docview/303060859?fromopenview=true&pq-origsite=gscholar&sourcetype=Dissertations%20&%20Theses
- 54. Thurston MH. The Vertical Distribution and Diurnal Migration of the Crustacea Amphipoda Collected during the SOND Cruise, 1965 II. The Hyperiidea and General Discussion. J Mar Biol Ass. 1976;56(2):383–470.
- 55. Dick RI. Hyperiidea (Crustacea: Amphipoda) key to South African genera and species, and a distribution list. Ann South Afr Mus. 1970;57(3):25–86.
- 56. Violante-Huerta M, Sanvicente-Aorve L, Hermoso-Salazar M, Marrn-Becerra A. Morphological variations of Phrosina semilunata Risso, 1822 juveniles (Crustacea: Amphipoda: Hyperiidea), new evidence from the Gulf of Mexico. Zootaxa. 2021;4995(3):594–600. pmid:34810547
- 57. Cornet C, Gili J-M. Vertical distribution and daily migrations of hyperiid amphipods in the northern Benguela in relation to water column stratification. Deep Sea Res Part I: Oceanogr Res Pap. 1993;40(11–12):2295–306.
- 58. Domínguez-Nava A, Gasca R, Carrillo L, Vásquez-Yeomans L, Suárez-Morales E. Hyperiid amphipod vertical distribution and community structure in the upper 100 m of the northwestern Caribbean Sea. Bull Mar Sci. 2021.
- 59. Sanvicente-Añorve L, Alatorre MA, Flores-Coto C, Alba C. Relationships between fish larvae and siphonophores in the water column: effect of wind-induced turbulence and thermocline depth. ICES J Mar Sci. 2007;64(5):878–88.
- 60. Castillo-Estrada G, De Silva-Dávila R, Carrillo L, Vásquez-Yeomans L, Silva-Segundo CA, Avilés-Díaz L, et al. Horizontal and vertical distribution of cephalopod paralarvae in the Mesoamerican Barrier Reef System. J Mar Biol Ass. 2020;100(6):927–37.
- 61. Gray C, Kingsford M. Variability in thermocline depth and strength, and relationships with vertical distributions of fish larvae and mesozooplankton in dynamic coastal waters. Mar Ecol Prog Ser. 2003;247:211–24.
- 62. Espinosa-Fuentes ML, Flores-Coto C, Sanvicente-Añorve L, Zavala-García F. Vertical distribution of zooplankton biomass and ichthyoplankton density during an annual cycle on the continental shelf of the southern Gulf of Mexico. Rev Biol Mar Oceanogr. 2009;44(2):477–88.