Planktonic ciliate communities along an environmental gradient in the Nile Delta (Damietta region, Egypt)

The spatial patterns of planktonic ciliate communities were studied from May to June 2019 in the Nile Delta’s Damietta region, southeastern Mediterranean. The ciliate communities were sampled from twenty-five sites of five stressed domains with spatial gradients of environmental status. A total of 32 ciliate taxa with six dominant species were identified, comprising 21 tintinnids and 11 aloricate ciliates. The abundance and richness of each ciliate group varied geographically and were most strongly influenced by salinity variations; tintinnid ciliates attained high abundance and richness at high salinity sites in the harbour and coastal region and decreased within the estuary upstream. Aloricate ciliates were poorly represented at most sites but were a substantial proportion of upstream estuarine sites. Multivariate/univariate analyses demonstrated that spatial patterns of the ciliate communities were significantly correlated with environmental variables, especially salinity, chlorophyll-a, and nutrients, either alone or in combination with one another. These results indicate that the ciliates can be useful bioindicators in stressed environments while also allowing the detection of impacts on short time scales by rapidly responding to environmental variations.


The study area
The current study was carried out in 4 regions at the northeastern Nile Delta between 31°20′ N and 31°34′ E, Damietta Harbour with its Barge Canal, Damietta Nile estuary, and the Damietta coast (Fig. 1).The harbour is a semi-closed basin with an area of 3.1 km 2 and depth range of 5-15 m, connected to the sea through the navigational canal and is linked to the Nile estuary by the Barge Canal that is 4.5 km long and 5-7 m depth.In addition to the direct effects of maritime activities, the harbour water quality could be changed when the shipping materials, such as organic fertilizer and cement, dissolve when they reach the water.The Barge Canal is directly affected by Nile River discharge, sewage, and agricultural effluents.The Damietta Nile estuary's length is about 13 km, and it is completely isolated from the riverine water by the Faraskour dam.Although the dam has six gates, they open randomly and rarely release freshwater into the estuary.Thus, the water properties in the estuary are mainly controlled by the land runoff and the tidal regime 19 .The effluents developed from land runoffs and Manzala Lake canals mostly affect the estuary upstream in contrast to downstream, which is affected more directly by the seawater intrusion from the Mediterranean Sea.Given the limited semidiurnal tidal range (30-60 cm maximum) 20 , typical water movement is sluggish but not completely stagnant.The last sampling region is at the Damietta coast and traverses ~ 15 km with an average depth of 15 m (Fig. 1).The four areas have contrasting anthropogenic impacts.Based on previous studies, the Nile estuary and the Barge Canal were known to be the most heavily stressed areas, with their pollution being mainly in the form of organic pollutants and nutrients from domestic sewage and agricultural and industrial discharges.Damietta Harbour was moderately Figure 1.A Map of the study area showing the positions of the sampling sites in Egypt's Damietta region.This map was generated using Esri ArcMap v. 10.5.

Statistical approaches
Mean abundance (Cells l −1 ) was calculated for each species.Traditional biodiversity indices (Shannon-Wiener species diversity, Pielou's of species evenness, and Margelef species richness) were calculated to explore variations between sampling domains.
Analysis of variance (ANOVA) was used to test for differences in the abiotic and biotic parameters between different domains.The data were tested for normality before analysis and transformed into natural logarithms when necessary to achieve normality.Spearman's correlation was used to describe the relationship between selected parameters.ANOVA and Spearman analysis were performed using SPSS 18.The correlation between the dominant ciliates and environmental factors was analyzed and visualized by the R packages Psych 27 .
Multivariate analyses of spatial variations in planktonic ciliate communities were analyzed using the PRIMER v6.1 package 28 .To explore faunal associations and spatial patterns of communities, we constructed a dendrogram of species using a group-average distribution on Bray-Curtis similarity from square-root-transformed data of each species abundance 29 .The contribution of each species to the average Bray-Curtis similarity among domains was analyzed using the SIMPER (Similarity Percentage Analysis) routine 28 .The spatial differences of ciliate communities among the five sampling domains were summarized using the CAP (canonical analysis of principal coordinates) of PERMANOVA + on Bray-Curtis similarities from the square-root transformed species-abundance data 30 .A vector overlay of Spearman correlations with a coefficient (ρ value) of > 0.2 with the CAP axes was employed to show the influence of the most common species 30 .Differences between groups of samples were tested by the ANOSIM (analysis of similarities) 28 .The relationships among the five sampling domains were also explored using MDS/PCA ordinations.The MDS was constructed based on Bray-Curtis's similarity for square-root transformed species abundance data, while the PCA was based on Euclidean distance from log-transformed environmental data 31 .The biota-environment correlation was tested using the routine RELATE.The submodule BIOENV (biota-environment correlation analysis) explored potential relationships between ciliate community structure and the environmental parameters 28 .

Environmental parameters
Environmental parameters showed strong spatial gradients within the study area.Overall, all domains (CR, DH, BC, DS, and US) were significantly different in terms of environmental variables characteristics throughout the study period (PERMANOVA, p < 0.01).All variables showed significant spatial differences except temperature (Table 1).The relatively high values of transparency, ammonia, nitrate, nitrite, and chlorophyll-a (Table 1) indicated the significant influence of anthropogenic activities on these water quality parameters.Along CR and DH, salinity and transparency had higher values than other regions, with a noticeable decrease in the upstream estuary affected by freshwater flow.In contrast, the pH, ammonia, nitrite, and chlorophyll-a values had marked changes, moving to decrease at CR and DH than those of BC, DS, and US, which were relatively similar.DH and BC showed significantly higher concentrations of silicate and soluble reactive phosphate than other sites.The nutrient-rich habitat at the Nile estuary and BC promoted an intensive growth of phytoplankton that could increase water oxygen levels; dissolved oxygen values were significantly higher in those regions when compared to others.

Species distribution and associations
A total of 32 species comprising 11 aloricate (naked) ciliates (belonging to seven different classes) and 21 tintinnids or loricate ciliates (class Spirotricha) were recorded (Table 2).These taxa showed different spatial patterns in species distribution in all domains.Cluster analysis suggested the 32 species fell into four groups (I-IV) at approximately 55% similarity level (Fig. 2): group I was composed of 6 dominant species with high occurrence and contribution, while the other groups (II-IV) represented the assemblages with low occurrence and/or abundance (Fig. 2, Table 2).Three dominant tintinnid forms (e.g., Favella serrata, Leprotintinnus nordqvistii, and

Spatial patterns of protozoan communities
The ciliate communities at the five sampling domains showed clear spatial differences in both species' composition and abundance (Fig. 3).Species numbers showed a maximum mean value at the DS domain and a minimum at the DH domain.However, the mean abundance was highest at the US domain (mean 1745.7 ± 2109.8 cells l −1 ) and lowest at the DS (mean 776.3 ± 741.4 cells l −1 ) domain.In terms of both relative species number and relative abundance, three structural ciliate communities can be identified: (1) those absolutely dominated by tintinnids (e.g., CR and DH domains), (2) those dominated by tintinnids and aloricate ciliates with tintinnids being the primary contributor (e.g., BC and DS domains), and (3) those dominated by aloricate ciliates and tintinnids with aloricate ciliates the greatest contributor (e.g., US domain) (Fig. 3).It should be noted that these spatial patterns of ciliate communities were consistent with the pattern previously described in the water quality variations between the sampling sites (Table 1, Fig. 3).
Traditional biodiversity indices showed similar dynamics (Fig. 4), i.e., generally increased from the CR to the BC, followed by a decrease in the Nile estuary.Variations in the biodiversity of ciliate fauna may reflect the suitable environmental conditions at the coastal region compared with others.
The CAP ordination showed a spatial pattern of ciliate communities (Fig. 5A).The first canonical axis separated the ciliate communities sampled at domains CR and DH (on the right) from those at the other three domains (mostly on the left), while the second canonical axis discriminated US and CR samples (Upper) from those at other (lower).ANOSIM test revealed that there were significant differences among the five domains (global R = 0.47, P < 0.001) and between each pair of domains (P < 0.01), apart from domains pairwise test, BC-DH and DS-BC were non-significant (R = 0.05, P = 0.193 and R = 0.15, P > 0.05, respectively).
A vector overlay of correlations to common species showed that of the top six ranked contributors at sampling domains, vectors for three tintinnid species, namely Codonellopsis morchella, Leprotintinnus nordqvistii, and Tintinnopsis tocantinensis, pointed toward the sample cloud of CR (upper right), another three tintinnids, Favella serrata, Ormosella acantharus, and Tintinnopsis cylindrica toward that of DH (lower right), two aloricate ciliates, Frontonia atra and Paramecium sp toward that of US (upper left), and the remaining four toward those of the other two domains (Fig. 5b).

Linkage between planktonic ciliate biodiversity and abiotic factors
The MDS/PCA multivariate approaches revealed that the spatial patterns of the ciliate communities were consistent with those of the environmental parameters (Fig. 6).In both cases, there were high similarities between the three most stressed domains (DS, US, and BC), and somewhat lower similarity between the moderately and least polluted sites (DH and CR).The RELATE analysis revealed a significant correlation between the spatial patterns of planktonic ciliate communities in abundance and changes in environmental variables (R = 0.369; P = 0.001).For PCA, the two principal components explained 55.4% of the total spatial environmental variability.It should be noted that salinity and chlorophyll-a were strongly associated with PCA 1, which was the primary contributor to the spatial environmental patterns (36.5%).For the five domains, the correlations between ciliate abundances and environmental parameters were established by the BIOENV analysis.The results showed that the spatial variations in ciliate communities correlated with the environmental variables, especially temperature, salinity, transparency and chlorophyll-a, either alone or in combination with one another.It was also noted that salinity and chlorophyll-a were the only variables included in most correlations (Table 3), indicating that these were the key factors related to ciliate distribution in the study area.The previous findings showed that the best matching with the spatial variations in ciliate community structure occurred with salinity variations and food availability.www.nature.com/scientificreports/For the six dominant planktonic ciliates, all dominant tintinnids except Favella serrata showed significant positive correlations with salinity (Fig. 7).The Leprotintinnus nordqvistii, and Tintinnopsis cylindrica were significantly negatively correlated with pH, ammonia, nitrate, and chlorophyll-a.The aloricate Frontonia atra and Paramecium sp. were significantly negatively correlated with salinity and water transparency but positively correlated with pH, nitrogenous nutrients, and chlorophyll-a.Other significant positive correlations included those between Ormosella acantharus and temperature, Favella serrata and ammonia + nitrate, Leprotintinnus nordqvistii and transparency.It should be noted that only chlorophyll-a showed a significant negative correlation with species count (r = − 0.352, P ˂ 0.05), Shannon diversity (r = − 0.438, P ˂ 0.01), and species richness (r = − 0.312, P ˂ 0.05), however, all other environmental variables failed to reveal a significant correlation to biodiversity indices.

Discussion
The multivariate analyses applied in the present study have proved their utility in detecting changes in community structures and evaluating relationships between communities' ecological patterns and environmental parameters along environmental stress gradients.These findings are consistent with many previous studies e.g., 6,[32][33][34] .The multivariate approaches collectively demonstrated that spatial patterns of planktonic ciliate communities were significantly associated with the spatial changes in environmental status.Furthermore, BIOENV analysis demonstrated that the variations in ciliate community structures were significantly related to specific www.nature.com/scientificreports/environmental parameters, especially salinity, either alone or in combination with other factors, particularly chlorophyll-a and temperature.Accordingly, the clear spatial distribution of the ciliate community in the study area was primarily driven by natural environmental forces, mainly salinity, temperature, and trophic status.According to Sanders 35 and Xu et al. 36 , the ciliate communities are sensitive to changes in environmental variables such as salinity, temperature, nutrient levels, and food supply.These changes could be more pronounced in sheltered systems like estuarine and harbour waters.The study area is an interconnected ecosystem influenced by multiple anthropogenic disturbances 18 .The distribution of hydrographic parameters showed a noticeable variables gradient, revealing the influence of the Nile Delta runoffs and the tidal regime.During the sampling period, the estuarine water intrusion did not significantly affect the CR and DH sites since the salinity obtained here was around 36 ppt, considerably higher than that of the estuarine waters.The high dissolved inorganic nitrogen concentration gradients inside the estuary were due to the land runoff and low water exchange with the adjacent sea 19 .The saltwater intrusion in estuaries is caused by a complex interaction process mainly related to freshwater flux upstream and tidal currents 37 .In the Damietta estuary, the freshwater flow is obstructed by the Farskour dam and the extremely low tidal range at the Nile Delta coast, with a 30-60 cm variation in daily mean sea level 20 , making the land runoffs the key players controlling the water properties in the estuary, particularly upstream.Our results showed that the abundance of ciliates in the present study was among the highest values ever reported for the Egyptian coastal waters of the Mediterranean Sea (Table 4).Beaver and Crisman 38 observed great variability in ciliate density depending on the trophic status of the environment.As a rule, the abundance of ciliates increased with eutrophication 39 .The Egyptian coasts, mainly the Nile Delta and Alexandria, were reported to be eutrophic due to very high terrestrial inputs 40 .So, the issue of low ciliate abundances in such eutrophic regions needs to be clarified.The use of different fixatives/preservatives and various methods of sample concentrations can influence estimates of ciliate abundance significantly 41,42 .According to Stoecker et al. 41 , fixation with acid Lugol's solution, which was used in the present study, results in significantly higher cell counts than fixation with formaldehyde, such as was used as fixative in most other studies in the Egyptian waters.Also, the filtration process could be another reason for the low abundance of ciliates.Sime-Ngando et al. 43 reported an average loss of 15% of ciliates due to the filtration process, while Lynn et al. 44 , suggest half the community may be smaller than 20 microns in mesotrophic tropical waters.The filtration process with a mesh size bigger than 20 microns applied in other studies (Table 4) could reasonably explain the low ciliate densities reported in Egyptian waters.It's surprising to some extent that abundances are not higher given the eutrophic status of our region; thus, factors such as predation by mesozooplankton may be controlling populations.Several studies of copepods feeding on natural microplankton assemblages have demonstrated copepods' predation on both loricate and aloricate ciliates, suggesting ciliates supply from 1 to 80% of total carbon ingested 45,46 .In tropical and subtropical systems, small copepods are often the dominant zooplankton 47,48 and play a significant role in the cycling of nutrients 49 .The small cyclopoid copepod of the genus Oithona is extremely abundant in neritic areas of the tropics and subtropics [50][51][52] ; and in Egyptian waters, Oithona is the most abundant copepod genera 18,19,53,54 .Feeding studies on Oithona spp.have revealed an omnivorous diet, feeding primarily on ciliates and dinoflagellates 55,56 ; phytoplankton, particularly diatoms, have been occasionally reported to make up a considerable fraction of their natural diet 57 .In a mesocosm experiment, Zöllner et al. 58 reported a drastic decrease in ciliates abundance with increasing copepod abundance and were nearly eliminated with maximal zooplankton densities.So, selective copepod grazing could be responsible for the reduction of ciliates abundance in Egyptian waters.In eutrophic environments, ciliates are thought to be regulated by metazooplankton rather than food supply 59 .Also, coastal hydrodynamics was reported as a limiting factor for the development of ciliates 60 ; however, further investigations are needed to clarify this issue.Nonetheless, our abundances fall within the range observed in other studies within oceanic and coastal regions globally (Table 4) 61 , suggesting any biases in our values are not severe.
The lowest ciliate numbers in the estuary downstream and the highest ciliate numbers in the estuary upstream fall together with the highest values of nutrients and chlorophyll-a.The data correlating trophic state to the ciliate abundance contribute to that hypothesis.For the estuary upstream, a significant increase in ciliate densities with increasing trophic state was found, corresponding to results from several studies e.g., 9,[81][82][83][84] .However, the significant decrease in ciliate abundance downstream may be due to the toxic effects of antifouling paint particles on the survival and growth of protozoa species 85 .Antifouling paints comprise various substances, including pigments, metals, and hydrocarbons, major chemical contaminants in estuaries 86,87 .When present in high concentrations, they are possibly damaging the estuarine organisms.The downstream region hosts about 65% of the Egypti an fisheries fleet 88 ; antifouling paint particles are usually released into waters during in-water cleaning activities to manage ships' hulls for repair, cleaning, and painting.The regulation of ciliates is influenced by the biomass of phytoplankton, bacterioplankton, and heterotrophic nanoflagellates 67 .Many ecological models used phytoplankton biomass as a common denominator for predicting ciliate abundance; they considered it a measurable food source for algivores ciliates 89 .Ciliates can tightly regulate phytoplankton grazing, consuming between 60 and 70% of the sea's total primary productivity 90 .In the Egyptian coastal water, photosynthetic pico-(0.2-2μm) and nanoplankton (2-20 μm) comprise the majority of phytoplankton biomass 91,92 .In the York River estuary, The contribution of large cells (microplankton, > 20 μm) to total phytoplankton biomass increased during winter, whereas that of small cells (pico-and nanoplankton) increased during summer 93 .Unfortunately, we don't have any previous studies about pico-and nanoplankton in the study area; the present study sampling was during summer, which may reflect the effective contribution of small cells to the phytoplankton biomass, particularly in the Nile estuary and BC.According to Rassoulzadegan et al. 94 , a significant biomass of pico and nanoplankton in aquatic systems is believed to be heterotrophic.Inorganic nutrients and light can influence both the autotrophic and heterotrophic states 95 .Globally, coastal zones  www.nature.com/scientificreports/are heterotrophic 96 ; rates of heterotrophic activity can exceed primary production in many aquatic ecosystems 95 .A significant input of nutrients in the study area with sufficient summer light is undoubtedly important in moments of increased autotrophic and heterotrophic growth.In the present study, we found no significant correlation between the total ciliate abundance and chlorophyll-a (r = − 0.233, p = 0.104), although the PCA suggests a negative link in the harbour and coastal region where tintinnids were the dominant and a positive one at the estuary that dominated by aloricate ciliates.Also, correlation analysis suggests a positive association between chlorophyll-a and aloricate ciliates (r = 0.560, p ˂ 0.001) and a negative association with tintinnids (r = − 0.448, p ˂ 0.01).We have to admit here that autotrophic organisms are not the only denominators of ciliate food sources, as indicated by the results of statistical analyses.The positive relationship of aloricate ciliates with phytoplankton biomass indicates possible trophic relationships consistently with the dominance of the autotrophic cells in the Nile estuary and BC, particularly the genera Frontonia and Paramecium, which represented the most numerous www.nature.com/scientificreports/trophic assemblage in the estuary 19 .In contrast, the tintinnid ciliates appeared not to be controlled by the availability of autotrophic prey, as suggested by the absence of a relationship between them and the phytoplankton biomass in the present study.Our data confirmed previous results of Sitran et al. 97 that tintinnid diversity and abundance were negatively correlated to chlorophyll-a in the water column.Tintinnids have been shown to exhibit wide food plasticity (detritus, picoplankton, bacterioplankton, and nanoflagellates) 61,73,97 in different ecosystem conditions, which may explain the lack of a clear link between phytoplankton biomass and tintinnid abundance or diversity.With the decreasing micro phytoplankton biomass, tintinnids are generally unable to feed on colonial diatoms or consume large prey 97 .Tintinnids have shifted their feeding toward bacterioplankton and nanoflagellates during the decline of phytoplankton biomass in the harbour and coastal regions.Din 98 repoted a significant decrease in nanoflagellates biomass in parallel with the tintinnid increased biomass.Species distribution of 32 ciliate species, particularly the six dominant species, represented a clear spatial pattern that contributed to the spatial variations in the ciliate communities within the study area.These dominant taxa belong to spirotrichs (e.g., Tintinnopsis and Favella) and oligohymenophoreans (e.g. the scuticociliates Paramecium), commonly encountered in freshwater and marine habitats.The ciliates can tolerate extreme salinity changes, and some can sustain direct transfer from marine to freshwater 99 .Therefore, ciliate communities in estuarian and coastal marine environments probably include freshwater, brackish, and marine species 100 .To date, the only available detailed studies about the ciliate diversity in the region were from the Damietta Harbour, with 37 species (Dorgham et al. 62 , the Damietta coastal region, with 49 species 10 , and the Nile estuary of Damietta Branch with 22 species, 19 .These differences in ciliate diversity are likely due to the study sites, the climate variability, the sampling period/and or sampling protocols applied in the different studies 74 .The dominance of the tintinnid ciliates during the present investigation is consistent research performed on a cross-wide range of marine trophic levels 70,72 .The strong presence of tintinnid in all domains except the upstream estuary might be coupled with the high salinity values and a better adaptation of many tintinnids to lower nutrient concentrations.Aloricate ciliates usually dominate the ciliate community in the upstream region 19 since they prefer conditions of low salinity and higher nutrient concentrations.According to Martínez-López et al. 101 , the decrease in tintinnid abundance is associated with increased gradients of environmental stress that could be more favourable to aloricate ciliates.www.nature.com/scientificreports/Species diversity, evenness, and richness indices are commonly used to summarize the community biodiversity 102 and are usually utilized as amenable indicators for assessing water quality 5,6,8,32,33 .In general, the higher values of these three indices usually reflect better water conditions 6,8 .In the present study, the three biodiversity indices employed showed relatively higher values in the samples from less stressed domains (e.g. the coastal region) than in the samples from more stressed ones (e.g. the estuary upstream).According to Huston 103 , the changes in diversity can only be assessed when sites are compared along spatial contamination gradients.Wong and Dowd 104 successfully applied diversity indices to assess environmental changes across anthropogenic impacts.The selected regions in our study are usually characterized by natural gradients linked to the sitessea or sites-lake (Manzala) interface that are anthropized by chemical contaminants, potentially affecting the diversity of ciliate communities.Acute and permanent anthropogenic stress in the estuary upstream may hinder adaptation by rare species, and potentially eliminating them from the species pool lowered the diversity of ciliate communities 105,106 .In contrast, according to Xu et al. 107 , planktonic ciliates ecological response to the influence of eutrophication can be complex and non-linear.In the present study, we found that nutrients had no direct impact on ciliate diversity indices; however, chlorophyll-a was inversely correlated, based on the Spearman correlation analysis.It is worth mentioning that the diversity indices are influenced by species dominance, which may be controlled by environmental variables unrelated to pollution, such as salinity and food availability.

Conclusion
The planktonic ciliate community structures represented significant differences among the sampling domains.The spatial variations in the community structural parameters were significantly related to the spatial changes of environmental variables, especially salinity, either alone or in combination with other parameters.The distribution patterns of tintinnid and aloricate ciliates between the sampling precisely reflect the gradients of ecological parameters and are a significant part of assessing the environmental status.Six species dominated the 32 ciliate taxa recorded over the study period, significantly related to salinity and/or nutrients or chlorophyll-a.Our results suggest that the spatial pattern of planktonic ciliate communities and taxonomic biodiversity could be used as favourable bioindicators for monitoring water quality status for the management of this region.With their short life cycle, delicate pellicle, and easy sampling and identifying features, these planktonic ciliates have specific advantages to be used to assess environmental changes in aquatic ecosystems compared to metazoans.However, further studies over long-term periods are needed to verify this conclusion.

Figure 2 .
Figure 2. A dendrogram of 32 planktonic ciliates at five domains in Egypt's Damietta region, plotted using group-average clustering on Bray-Curtis similarities from square root-transformed species abundance data.I-V = groups I-V.

Figure 3 .
Figure 3. Spatial variations in species number (A), abundance (B), relative species number (C), and relative abundance (D) of planktonic ciliates from the five domains in Egypt's Damietta region.The letters indicate significant differences based on one-way ANOVA with the Tuckey's test.

Figure 4 .
Figure 4. Traditional biodiversity measures species richness, species evenness, and species diversity of planktonic ciliate communities demonstrating variable patterns among five sampling domains in the Damietta region.

Figure 5 .
Figure 5. Canonical analysis of principal coordinates (CAP) on Bray-Curtis similarities from square root -transformed species-abundance data of five sampling domains in the Damietta region during the period from May to June 2019 (A) and correlations of 12 common species that showed the highest correlations with the two CAP axes (b).

Figure 6 .
Figure 6.Multidimensional scaling (MDS) for spatial patterns of planktonic ciliate communities (A) on Bray-Curtis similarities for square root abundance data, and principal component analysis (PCA) ordination (B) based on log-transformed abiotic data of five sampling domains in Damietta region.Tem, temperature; Sal, salinity; WT, water transparency; SRP, soluble reactive phosphate; Chl-a, chlorophyll-a.

Table 1 .
Environmental variables monitored at the five sampling domains in Egypt's Damietta region.The letters indicate significant differences based on one ANOVA analysis with Tukey's-b post hoc test.Wt, water transparency; DO, dissolved oxygen; SRP, soluble reactive phosphate; Chl-a, chlorophyll-a.

Table 3 .
Summary of Biota-environment (BIOENV) analysis results, with the 10 best correlations corresponding to different variables in the Damietta region.R-value: Spearman correlation coefficient.

Figure 7 .
Spearman correlations between environmental parameters and dominant species in the Damietta region.T, temperature; Sal, salinity; WT, water transparency; SRP, soluble reactive phosphate; Chl-a, chlorophyll-a.