The unevenness of the profile varied in topography and length. The most uniform profile was in the winter, with a variation of 1.53m of unevenness and a total length of 60 meters (Fig. 2A). In the summer the topographic variation was greater, with 1.27m of unevenness and a total length of 42 meters (Fig. 2B).
Component 1 (PC1) (Fig. 3, SI. 1) contributed 18% of the variance, which related the lower points of the profile (P1, P2, P3) in the summer to the increase in CaCO3 concentration (10.6 to 14.85%), asymmetry (-0.079 to -0.155), kurtosis (0.910 to 1.023) and mean diameter of the grains (ɸ 2.726 to ɸ 2.918) and a reduction in these variables values in the middle and high points of the profile in the winter and summer. Component 2 (PC2) (Fig. 3, SI. 1) contributed 12.48% of the variance and related P1, P2 and P3 to sediment moisture percentage and selection, which decreased in P9 and P10. There was an inverse pattern for the unevenness of the profile and groundwater depth, which increased in P9 and P10 and decreased in P1, P2 and P3. For the remaining profile points, the values for these variables were intermediate. The granulometric composition of Enseada Beach was well selected and had a very positive asymmetry. In both seasons, the mean diameters of the grains were composed of fine sand in all the profile points and there was an extremely leptokurtic distribution (Fig. 3, SI. 1).
In the comparisons between seasons of the year, the temperature of the percolation water, ammonia, nitrite, nitrate and phosphorous were significantly higher in the summer (p-value < 0.05). For groundwater depth, pH and salinity, the differences between the seasons were not different (Tab. 1). The mean values for groundwater depth were significantly higher in P10 (1.13m), P9 (0.62m) and P5 (0.53m) (Tab. 2). Salinity (P1: 36.67 PSU; P2: 35.83 PSU and P3: 35.33 PSU) and pH (P1: 8.45; P2: 8.45 and P3: 8.30) in P1, P2 and P3 were significantly higher (Tab. 2). The mean values for ammonia were significantly greater in P5 (2.52 mg/L) and P8 (2.30 mg/L) compared to P1 (1.11 mg/L) and P2 (1.02 mg/L). The mean concentrations for nitrite were greater in P7 (0.14 mg/L), P5 (0.09 mg/L), P3 (0.03 mg/L), P8 (0.02 mg/L) and P6 (0.026 mg/L). The mean values for phosphate were greater in P7 (1.93 mg/L), P6 (1.15 mg/L), P2 (1.08 mg/L), P10 (1.06 mg/L), P9 (1.08 mg/L), P8 (0.98 mg/L) and P3 (0.95 mg/L). The differences in the mean values for temperature and nitrate in the profile points were not significant (Tab. 2). In the results of the PCA, component 1 (PC1) contributed 17.88% of the variance and related the increase in temperature, ammonia, nitrite, nitrate and phosphate values to the profile points in the summer, with a tendency for an increase in P7 and P5. In the cluster of winter points, the values of these variables tended to decrease (Fig. 4, SI. 2). PC2 contributed 9.69% of the variance and related the increase in salinity and pH to the lower profile points, which decreased in the direction of the higher points of the beach profile (Fig. 4, SI. 2).
The total density and richness of the infauna taxa were the same in the winter (13.12 ind./0.05m² and 1.8 taxa/0.05m², respectively) and summer (10.9 ind./0.05m² and 1.57 taxa/0.05m², respectively). However, the densities of Donax hanleyanus (1.32 ind./0.05m²) and Hastula cinerea (0.200 ind./0.05m²) were significantly higher in the winter (Tab. 3). In the summer, the densities of a species of Diptera (0.17 ind./0.05m²) and Thoracophelia furcifera (5.20 ind./0.05m²) were higher (Tab. 3). The densities of Hemipodia olivieri, Albunea paretii, a species of Coleoptera, Excirolana braziliensis, Emerita brasiliensis, Haploscoplos sp., Scolelelpis goodbodyi and Orchestia sp. were the same (Tab. 3).
The results of the comparisons of mean densities among the profile points had significantly high density (P1: 18.75 ind./0.05m², P2: 32.87 ind./0.05m² and P3: 20.25 ind./0.05m²) and richness (P1: 2.75 ind./0.05m², P2: 2.75ind./0.05m² and P3: 2.35 ind./0.05m²) values in the lower mesolittoral (Tab. 4). In this part of the profile, Scolelepis goodbodyi (P1: 14.0 ind./0.05m², P2: 32.50 ind./0.05m² and P3: 17.0 ind./0.05m²), Haploscoplos sp. (P1: 1.38 ind./0.05m², P2: 0.50 ind./0.05m² and P3: 1.38 ind./0.05m²) and Emerita brasiliensis (P1: 1.0 ind./0.05m² and P2: 1.0 ind./0.05m²) were dominant. Donax hanleyanus was dominant in the lower and intermediary parts of the profile (P1: 2.25 ind./0.05m², P2: 0.75 ind./0.05m², P3: 1.5 ind./0.05m², P4: 1.5 ind./0.05m², P5: 1.12 ind./0.05m² and P6: 0.62 ind./0.05m²) and the density of Thoracophelia furcifera (P5: 5.12 ind./0.05m², P6: 6.25 ind./0.05m², P7: 7.35 ind./0.05m² and P8: 7.25 ind./0.05m²) was significantly greater in the intermediary part and initial part of the upper portion of the beach profile. The differences in the densities of the remaining benthic infauna taxa were not significant among the profile points (Tab. 4).
The correspondence analysis (CA) produced clusters of benthic infauna by profile point and season, with H. cinerea, Haploscoplos sp., D. hanleyanus, H. olivieri and S. goodbodyi corresponding to the lower part (P1 and P3) and initial portion of the intermediary part of the profile (P4 and P5) in both seasons of the year and predominating in the intermediary points (P6, P7 and P8) in the winter (Fig. 5). E. braziliensis, Orchestia sp. and Coleoptera formed a cluster in the upper points (P9 and P10) in the two seasons and only T. furcifera occupied the upper intermediary portion in the summer (P7 and P8) (Fig. 5).
In the results of the canonical correspondence analysis (CCA), the increase in groundwater depth (axis I: related to 76.4%) in the upper part of the profile in the summer and winter significantly influenced the cluster with the highest densities of Coleoptera, E. braziliensis and Orchestia sp. Further, the decrease of groundwater depth influenced the increase in the density of the cluster of H. olivieri, D. hanleyanus, Haploscoloplos sp., S. goodbodyi and H. cinerea in the summer and winter, when the pH and moisture values of the sediment increased. In axis II (related to 14%), the increase in the concentration of nitrate significantly influenced the increase in the density of T. furcifera at the border between the intermediary (P5) and upper (P7 and P8) parts of the profile in the summer; the concentrations of the remaining nutrients increased with the percolation water temperature. In the opposite direction of the axis, the reduction in the concentration of nitrate significantly influenced the increase in the densities of H. olivieri, D. hanleyanus, E. braziliensis, H. cinerea and Orchestia sp. in the upper points of the profile in the winter; the remaining nutrients and the temperature of the sediment also decreased (Fig. 6, Tab. 5).