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Article

Benthic Macrofauna in the Loukkos Estuary, Morocco: Patterns and Environmental Drivers

by
Feirouz Touhami
Laboratory of Biodiversity Ecology and Genome, Faculty of Science, Mohammed V University in Rabat, 4 Avenue Ibn Battouta, B.P. 1014 RP, Rabat 10000, Morocco
Ecologies 2025, 6(3), 53; https://doi.org/10.3390/ecologies6030053
Submission received: 14 June 2025 / Revised: 24 July 2025 / Accepted: 26 July 2025 / Published: 1 August 2025
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Abstract

This study provides the first comprehensive characterization of benthic macrofaunal communities in the Loukkos estuary, highlighting their spatial and seasonal variability and the environmental factors shaping their structure. A total of 47 species were identified across 12 site–season combinations, dominated by molluscs (47%), polychaetes (23%), and crustaceans (21%). Species richness varied considerably along the estuarine gradient, ranging from fewer than five species in the upstream sector to up to 30 species downstream. Overall, higher diversity was observed in the downstream areas and during the dry season. Macrofaunal density also exhibited substantial variability, ranging from 95 ind.m−2 to 14,852 ind.m−2, with a mean density of 2535 ± 4058 ind.m−2. Multivariate analyses identified four distinct benthic assemblages structured primarily by spatial factors (ANOSIM R = 0.86, p = 0.002), with negligible seasonal effect (R = −0.03, p = 0.6). Assemblages ranged from marine-influenced communities at the estuary mouth dominated by Cerastoderma edule, through rich and diverse seagrass-associated communities in the lower estuary dominated by Bittium reticulatum, and moderately enriched mid-estuary communities characterized by Scrobicularia plana and Hediste diversicolor, to species-poor upstream communities dominated by the tolerant species H. diversicolor. Canonical analysis showed that salinity and vegetation explain nearly 40% of the variation in benthic assemblages, highlighting the key role of Zostera seagrass beds as structuring habitats. Moreover, upstream anthropogenic pressures alter environmental conditions, reducing benthic diversity and favoring tolerant species.

1. Introduction

Benthic macrofauna are vital components of aquatic ecosystems, contributing to nutrient recycling by breaking down organic matter and enhancing sediment quality through bioturbation. They serve as key links in food webs, supporting fish and bird populations by transferring energy across trophic levels [1,2,3,4]. Their communities exhibit high sensitivity to environmental gradients, notably variations in salinity and dissolved oxygen, as well as to anthropogenic pressures such as pollution and habitat degradation [5,6]. This sensitivity makes benthic macrofauna effective bioindicators for monitoring estuarine health and guiding management decisions [7,8].
The Loukkos estuary, located on the Atlantic coast of northwestern Morocco near the city of Larache, occupies a strategic position in North Africa, where Mediterranean and Atlantic biogeographic influences converge. It forms the core of the Lower Loukkos complex, a unique hydrological and ecological unit that includes the estuarine zone, adjacent wetlands, and floodplains. The estuary is recognized for its high ecological value and biodiversity and is designated as a Ramsar site, reflecting its international importance as a wetland habitat that supports a wide array of aquatic and terrestrial species. Compared to other estuaries along the Mediterranean–Atlantic African coast, the Loukkos estuary plays a crucial role in sustaining regional biodiversity by providing essential habitats for migratory bird species, serving as nursery grounds for commercially important fish and crustacean species, and maintaining ecological connectivity between marine and freshwater ecosystems. Its complex mosaic of habitats, including extensive seagrass beds, mudflats, and salt marshes, supports a high level of biological productivity and resilience against environmental pressures. These ecological functions emphasize the Loukkos estuary’s importance as a conservation priority within the regional network of Ramsar sites and coastal wetlands [9,10,11].
Despite its recognized ecological significance and protected status, the Loukkos estuary remains relatively understudied, particularly regarding benthic macrofaunal assemblages. Previous research in this estuary has focused mainly on water quality, sediment characteristics, and some aspects of fish and bird ecology [9,10,11,12,13], but detailed investigations of benthic communities are scarce. Such data are critical for understanding ecosystem functioning, detecting environmental changes, and developing effective conservation strategies.
This study presents the first detailed investigation of benthic macrofaunal communities in the Loukkos estuary, aiming to (i) characterize species diversity and abundance patterns across spatial and seasonal gradients, (ii) identify key environmental factors structuring these communities, and (iii) provide a baseline for future monitoring and management efforts. By filling this critical knowledge gap, this research contributes to the broader understanding of estuarine biodiversity in the Mediterranean–Atlantic interface and supports evidence-based conservation policies.

2. Materials and Methods

2.1. Study Area

This study was conducted within the Lower Loukkos Wetland Complex, located near the Atlantic coastal town of Larache, northwestern Morocco. Covering approximately 6630 ha, the complex encompasses a mosaic of estuarine and floodplain habitats including tidal channels, intertidal sandflats, saltmarshes, seagrass meadows, freshwater marshes, and abandoned and active saltpans [11,12]. It has been designated a Ramsar site since 2005, recognizing its ecological importance. This designation promotes the conservation and sustainable use of the wetland by safeguarding biodiversity, critical habitats for migratory birds and aquatic species, preserving key ecological functions like water purification and flood regulation, and encouraging continuous monitoring and management to address human impacts [11].
The estuary receives freshwater input from the Loukkos River, and is influenced by both seasonal precipitation and tidal inflows, generating pronounced hydrological gradients [10,11]. The estuarine system is characterized by a subhumid thermomediterranean climate, with oceanic influence. Average monthly temperatures range from 10.5–12.5 °C in winter to 22.5–26.0 °C in summer, and annual precipitation averages around 700 mm, concentrated between November and February [11].
Geologically, the area is composed of Holocene alluvial deposits overlying Pliocene marls and shell-rich sandstones. The hydro-ecological functioning of the system is regulated by surface freshwater flows, tidal inputs, irrigation and drainage networks, and a regulating dam upstream that mitigates saltwater intrusion and flood risk [9,11,13].
This ecosystem holds high conservation value at both national and international scales. Its exceptional ornithological importance stems from its position along one of the main Palearctic–African migratory flyways. It hosts a number of vulnerable or near-threatened species at the international scale, such as the Marmaronetta angustirostris and the Aythya nyroca, as well as nationally significant species including the Ardeola ralloides, Ardea purpurea, Netta rufina, and Asio capensis [11,12].
In addition to its high biodiversity value, the Loukkos complex provides vital ecosystem services including groundwater recharge, water purification, flood mitigation, and resources for local livelihoods (traditional agriculture, aquaculture, salt extraction). The site also holds exceptional cultural and historical significance, notably due to the nearby Lixus archaeological site, an ancient urban center that stands as a testament to millennia of human civilization and interaction with the Loukkos landscape [14].
However, the Loukkos estuary is increasingly exposed to multiple anthropogenic pressures that significantly affect its ecological integrity [10,13]. The surrounding basin is a major agricultural zone that supports a diverse, intensive array of activities, including rice cultivation, cereal crops, fruit and vegetable production, industrial crops, arboriculture, and livestock farming. These activities, characterized by extensive irrigation and the widespread use of fertilizers and pesticides, contribute significantly to nutrient enrichment and chemical contamination of estuarine waters through surface runoff and drainage, particularly in the upstream sectors of the estuary. Industrial activities, such as food processing, textile production, and small-scale manufacturing, further exacerbate pollution by discharging untreated or insufficiently treated effluents into the watercourse. In the downstream sectors, port-related activities, including fishing and shipping, impose additional pressures through the release of pollutants such as hydrocarbons, heavy metals, and antifouling agents. Moreover, the expansion of tourism and increasing traffic, especially during the summer season, intensify wastewater discharge and urban runoff, further degrading water quality and posing risks to both aquatic life and human health in the estuary [10,11,13].

2.2. Sampling of Benthic Macrofauna

Six sampling stations were strategically selected along the Loukkos estuary (Figure 1) to represent the full range of ecological conditions along the estuarine gradient. The selection criteria included habitat diversity, encompassing upstream freshwater zones, brackish transitional areas, and downstream saline environments. The presence of seagrass beds was also an important factor in station selection. Notably, station ST2 was chosen within a seagrass meadow area to assess the influence of this habitat on benthic community structure. Accessibility for fieldwork and logistical considerations were also taken into account. Additionally, the proximity of stations to potential pollution sources such as agricultural runoff (ST6 and ST5), urban discharges (ST4, ST3 and ST2), and port-related activities (ST1) was considered to capture anthropogenic influences on benthic assemblages.
Sampling was conducted at low tide during two contrasting seasonal periods, the wet season (January 2023) and the dry season (July 2023), to capture seasonal variability. At each of the six selected stations, three replicate samples were collected using a PVC corer with a diameter of 12.5 cm, sampling sediment to a depth of 20 cm. Each replicate corresponded to a composite sample made by pooling 10 cores, covering a total surface area of 0.12 m2 per replicate and 0.36 m2 per station. Samples were sieved in situ through a 1 mm mesh to retain macrofauna, which were then fixed and preserved in 4% formalin for laboratory analysis.
In the laboratory, macroinvertebrates were carefully separated, identified to the finest taxonomic level possible, and counted. Numerous identification guides and taxonomic keys applied in coastal benthic studies were consulted, including those referenced in [15]. To ensure taxonomic accuracy and update scientific names, the World Register of Marine Species (WoRMS) database was systematically used.

2.3. Environmental Data

Hydrological and sedimentary parameters were sampled and analyzed in parallel with benthic macrofauna sampling to characterize the environmental gradients shaping community structure.
Surface water was collected in pre-rinsed 1 L polyethylene bottles, stored at 4 °C, and transported to the laboratory for analysis. Nitrate (NO3−) and ammonium (NH4+) were analyzed using UV-visible spectrophotometry. pH was measured by potentiometric method, salinity was inferred from electrical conductivity (EC) measured via electrometry, and total hardness was calculated from calcium and magnesium concentrations determined by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). Phosphate (PO42−) concentrations were also measured using ICP-AES.
Superficial sediments were sampled at low tide using a manual PVC corer (~300 g from the upper layer), placed in polyethylene bags, and stored in coolers before analysis. Sedimentary parameters included clay content determined by sedimentation method and organic matter content (OM) measured by UV-visible spectrophotometry.
This integrated environmental dataset provides the foundation for interpreting patterns in benthic community composition along the estuarine gradient.

2.4. Statistical Analyses

To assess spatial and seasonal variations in macrofaunal communities, species abundance and richness were used as primary indicators of density and diversity. The normality of these variables was verified using the Shapiro–Wilk test prior to statistical analyses. Additionally, three ecological indices (Shannon diversity (H′), Simpson dominance (D), and Pielou’s evenness (J′)) were calculated to characterize community structure in terms of complexity, dominance, and uniformity of species distribution. The indices were calculated as follows:
H ′ = − ∑ i = 1 S p i   l n ( p i )
D = ∑ i = 1 S p i 2
J ′ =   H ′ ln S
where S = total number of species; pi = proportion of individuals of species i (pi = ni/N); ni = number of individuals of species i; N = total number of individuals of all species.
To analyze macrofaunal community structure, hierarchical cluster analysis (HCA) based on log-transformed species abundances and Bray–Curtis similarity was used to group ecologically similar stations. The significance of these groupings was tested using ANOSIM (global and by factor: season and stations). SIMPER analysis identified key species contributing to group similarities and differences, while IndVal analysis highlighted indicator species for each cluster.
Canonical Analysis of Principal Coordinates (CAP) was performed to investigate the influence of environmental variables on macrofaunal composition. The overall significance of the model and the individual contributions of each variable were assessed using a permutation-based ANOVA from the vegan package. All analyses were conducted using R (v4.4.0) [16].

3. Results

3.1. Structure and Diversity Patterns of Benthic Communities

A total of 47 macrobenthic species were identified across the six sampled stations in the Loukkos estuary during both wet (WS) and dry (DS) seasons (Table 1). These species belonged predominantly to three major taxonomic groups (Table 1 and Figure 2). Molluscs were the most diverse group, with 22 taxa (47%), followed by polychaetes, with 11 taxa (23%), and crustaceans, with 10 taxa (21%). Molluscs also dominated in terms of abundance, accounting for 63% of total individuals, followed by polychaetes, at 25%.
However, the species richness estimator indicates that this observed diversity may underestimate the actual species pool in the system. Notably, the Chao2 index (63.6) suggests that the actual species richness in the Loukkos estuary is likely underestimated, indicating the presence of 16 additional, potentially rare or cryptic species that were not detected during sampling. This underlines the importance of continued and expanded sampling efforts, especially in less covered periods or habitats, to obtain a more comprehensive understanding of the benthic biodiversity in the estuary.
The macrofaunal community in the Loukkos estuary was dominated by six species, which together accounted for approximately 90% of the total abundance (Figure 3). The gastropod B. reticulatum was by far the most abundant species, representing about 50% of total individuals, with particularly high densities at ST2 during DS. This was followed by S. plana, contributing 18% of the total abundance, showing a marked preference for ST4, especially in the WS. H. diversicolor, representing 13%, was mainly concentrated at ST4 and ST5, exhibiting variable seasonal fluctuations between stations. C. carinata, accounting for 3%, showed a peak at ST4 and higher abundances during WS.
Mean benthic densities varied significantly among stations, ranging from 95 ind.m−2 at ST1 during WS to 14,851 ind.m−2 at ST2 during DS, with an overall average of 2535 ind.m−2. Stations ST2 and ST4 exhibited the highest densities, particularly in DS, whereas ST1 and ST6 consistently recorded the lowest values (Figure 4). This pattern suggests more favorable environmental conditions for benthic communities during the DS.
Ecological indices revealed clear spatial and seasonal variations in community structure (Figure 4). Species richness peaked at ST2 during the DS, reaching up to 30 species, while the lowest richness (<5 species) was consistently observed at ST5 and ST6 regardless of season. Overall, species richness tended to be higher during the DS, especially in downstream stations. The Shannon diversity index (H′) was highest at ST3, particularly during the DS, with values approaching 2, indicating a high level of taxonomic diversity. In contrast, ST5 during the DS displayed extremely low Shannon values (close to zero), reflecting strong species dominance and low heterogeneity. This pattern was supported by the Simpson index (D), which showed elevated values at ST3 (up to 0.8) and markedly low values at ST5-DS (<0.1). Evenness (Pielou’s J′) was generally high (>0.8) across most stations, indicating relatively balanced communities. Notably, ST6-DS and ST3-DS exhibited high evenness, suggesting an equal distribution of individuals among the present taxa. Conversely, ST5-DS had the lowest evenness (J′ ≈ 0), confirming the strong dominance pattern revealed by the Shannon and Simpson indices.

3.2. Spatio-Temporal Organization of Benthic Communities

The hierarchical cluster analysis (Figure 5) identified four distinct benthic assemblages, which were confirmed by a global ANOSIM test (R = 0.68; p = 0.001 ***). Separate ANOSIM analyses for season and station factors revealed no significant seasonal effect on benthic community composition (R = −0.03, p = 0.6 ns), whereas spatial differences among stations were highly significant (R = 0.86, p = 0.002 **), highlighting spatial heterogeneity as the dominant factor shaping community patterns.
The composition and characteristic species of the four identified benthic assemblages were further investigated using SIMPER and IndVal analyses (Table 2). Bray–Curtis dissimilarities highlighted clear differentiation among the assemblages. Group 1 exhibited the highest dissimilarity (100%) with Group 4, and values exceeding 94% with Groups 2 and 3, reflecting a highly distinct species composition. Group 2 and Group 3 showed a dissimilarity of 88.45%, while Group 3 and Group 4 were more similar, with a lower dissimilarity of 65.15%, suggesting a relatively close community structure between these two groups. The four benthic assemblages, distributed along the estuarine gradient from downstream to upstream, are characterized as follows:
Group 1: Corresponding to samples from ST1 during both wet and dry seasons (ST1-WS, ST1-DS), this group showed a moderate within-group similarity of 18.6% (Table 2). This was mainly driven by C. edule (49.6%), S. marginatus (32.1%), and N. hombergii (6.1%). IndVal analysis identified D. trunculus and S. armiger as exclusive indicator species for this group.
Group 2: Formed by samples from ST2, sampled in both seasons (ST2-WS, ST2-DS), this group showed a high within-group similarity of 48%, mainly due to the dominance of B. Reticulatum (77.2%). IndVal revealed ten indicator species exclusive to this group, including A. alba, L. koreni, D. neapolitana, P. ulvae, T. reticulata, B. reticulatum, I. chelipes, D. neapolitana, R. decussatus, and H. navicula, in addition to N. hombergii and S. marginatus, which were shared species with Group 1.
Group 3: Including stations ST3 and ST4, sampled in WS and DS, and ST6 sampled in WS (ST3-WS, ST3-DS, ST4-WS, ST4-DS, ST6-WS), this group had a moderate within-group similarity of 20.7%. The dominant species contributing to this similarity included S. plana (60.7%), H. diversicolor (22.8%), and C. carinata (8.9%). IndVal identified C. carinata and C. capitata as indicator species, shared with Group 2.
Group 4: Comprising stations ST5, sampled in WS and DS, and ST6 sampled in DS (ST5- WS, ST5-DS, ST6-DS), this group presented an intermediate within-group similarity of 34.5%. This similarity was primarily attributed to H. diversicolor (85.9%) and Dolichopodidae larvae (9.9%). No exclusive indicator species were found for this group.

3.3. Environmental Drivers of Benthic Community Structure

The Canonical Analysis of Principal Coordinates (CAP) clearly distinguished the four benthic assemblages (G1 to G4) along environmental gradients (Figure 6). This spatial segregation aligns with patterns previously identified by ANOSIM and hierarchical clustering, thereby confirming the existence of distinct faunal assemblages structured along the estuarine environmental continuum.
The stations clustered distinctly in the ordination space, reflecting a structured response of benthic communities to environmental variability. This pattern is statistically supported by the global permutation test (F = 2.23, p = 0.042), indicating that the selected environmental variables significantly explain the variation in benthic community composition, accounting for approximately 83.35% of the total variance (Table 3).
Among the tested variables, salinity (p = 0.004, 20.85% of variance) and vegetation cover (p = 0.005, 17.59%) emerged as the most influential, jointly explaining nearly 39% of the variation. The pH explained 9.28% of the variance and showed a near-significant trend (p = 0.074), suggesting a possible physiological constraint on species composition. Other variables (total hardness, phosphate, nitrate, ammonium, clay rate, and organic matter) were not statistically significant (all p > 0.05) but contributed minor percentages (2.57–9.28%) to the overall variance, indicating potential secondary or localized effects.
The spatial configuration in the CAP biplot aligns with the longitudinal estuarine gradient, as follows:
Group 1 corresponds to samples from ST1, the most downstream station, strongly associated with high salinity, coarse sediments, and high hydrodynamics, reflecting a marked marine influence.
Group 2 includes samples from ST2 samples, where the presence of vegetation exerts a strong local structuring effect, combined with significant marine influence.
Group 3 mainly includes samples from ST3 and ST4, located in the middle section of the estuary. These stations are characterized by intermediate salinity and sediment features, positioning them centrally in the CAP ordination space. NH4+ concentrations were particularly elevated in this group, especially at ST4.
Group 4 includes samples from ST5 and ST6-DS, representing upstream habitats. This group is spatially associated with higher clay and organic matter contents, suggesting that fine sediments and nutrient enrichment, particularly nitrate likely originating from the Loukkos watershed, may influence community composition, even though these variables were not statistically significant.

4. Discussion

This study represents the first detailed characterization of benthic macrofaunal communities within the Loukkos estuary, a coastal Atlantic system in northwestern Morocco of high ecological and socio-economic importance.
A total of 47 macrofaunal species were identified across the estuary, belonging mainly to three taxonomic groups: molluscs, polychaetes, and crustaceans. The observed community composition and structure aligns closely with findings from previous studies conducted in other Moroccan estuarine and coastal systems, including the Bou Regreg, Oum Er Rbia, and Souss estuaries, as well as the Merja Zerga and Oualidia lagoons [17,18,19,20,21]. Comparative analyses reveal that macrobenthic assemblages in these systems are commonly structured along environmental gradients, notably salinity, sediment characteristics, and the extent of human-induced disturbances. These estuaries share dynamic and variable environmental conditions marked by fluctuations in salinity, oxygen levels, and sediment heterogeneity. Such environmental stressors favor the dominance of stress-tolerant benthic taxa, which possess adaptive strategies to thrive under fluctuating and often harsh conditions. These include physiological tolerance to salinity and hypoxia, as well as behavioral and morphological adaptations that facilitate survival in unstable sediments [22,23,24,25].
The macrofaunal community in the Loukkos estuary was strongly dominated by six species (B. reticulatum, S. plana, H. diversicolor, C. carinata, P. ulvae, and C. edule) which together represented approximately 90% of the total individuals. B. reticulatum, which alone accounted for approximately 50% of the total abundance, exhibited notably high abundance at ST2, an area characterized by dense Z. noltei seagrass beds. These vegetated habitats provide a structurally complex environment, offering ample food and shelter, which enhance the survival and reproduction of species [26,27,28]. During DS, B. reticulatum abundance almost tripled, coinciding with increased primary productivity, elevated water temperatures, and stable saline conditions typical of this period [29,30,31,32]. These environmental conditions are known to favor the proliferation of opportunistic benthic species, particularly those capable of rapid population responses to seasonal changes. The gastropod P. ulvae exhibited a similar spatial and temporal distribution pattern to B. reticulatum, suggesting shared ecological adaptations. Their pronounced abundance peaks during the DS may also reflect a reproductive strategy synchronized with periods of environmental stability, which promotes successful recruitment and survival of juvenile stages [33,34].
These dominant taxa fulfill important ecological roles within the estuarine benthic system. B. reticulatum and P. ulvae are grazing gastropods that contribute to the regulation of algal biofilms and microphytobenthos, while H. diversicolor, a bioturbating polychaete, plays a key role in sediment reworking and nutrient cycling. The bivalves S. plana and C. edule enhance water filtration and benthic–pelagic coupling as suspension feeders and C. carinata, a burrowing isopod, aids in organic matter decomposition and sediment restructuring. Together, these species also form a crucial trophic link by serving as food sources for higher consumers such as fish, decapods, and shorebirds, thereby sustaining the estuarine food web [2,3,4].
The macrofaunal assemblages in the Loukkos estuary were clearly structured along a downstream-to-upstream gradient, reflecting both natural estuarine zonation and local anthropogenic pressures. Four distinct benthic assemblages were identified along the estuarine gradient, shaped by a combination of hydrological conditions, sediment characteristics, and anthropogenic influences:
Group G1 (ST1—estuary mouth): Characterized by sandy sediments, high salinity, strong marine influence, and low organic content, this zone hosted the most marine-like assemblage. Dominant species included suspension feeders C. edule and S. marginatus, both adapted to well-oxygenated and high-energy environments. Such conditions typically favor marine opportunistic taxa adapted to dynamic hydrodynamics and high sediment permeability, as reported in other estuarine systems [35,36,37,38].
Group G2 (ST2—lower estuary): This station hosted the most diverse and abundant macrofaunal community, largely due to the presence of dense Z. noltei seagrass beds. These vegetated habitats provided structural complexity, enhanced oxygenation, stabilized sediments, and increased food availability, thus creating a biodiversity hotspot. Dominant taxa included B. reticulatum and P. ulvae, both closely associated with vegetated substrates, as previously discussed. The ecological functions of Zostera beds in promoting biodiversity and productivity are particularly significant in transitional ecosystems such as estuaries [39,40,41].
Group G3 (ST3–ST4—ST6-WS—transitional zone): Assemblages in this mid-estuarine region were shaped by mixed sediment textures, fluctuating salinity, moderate organic enrichment, and signs of eutrophication. Dominant species such as S. plana, H. diversicolor, and C. carinata are known for their tolerance to low oxygen levels and organically enriched sediments. This group typifies areas subject to intermediate disturbance, where tolerant species persist despite environmental fluctuations [42,43,44,45,46]. According to Touhami et al. [10], this zone is among the most impacted by anthropogenic pollution, with evidence of elevated nutrient loads and metal contamination linked to domestic, industrial, and agricultural discharges. These environmental pressures are likely key drivers shaping the structure and resilience of the benthic community in this part of the estuary.
Group G4 (ST5–ST6—upper estuary): This upstream zone was the most impoverished, with low species richness and strong dominance by a few tolerant taxa, including mostly H. diversicolor. Environmental conditions were characterized by reduced salinity, high clay and organic matter content, and elevated nutrient loads (especially NO3−) associated with agricultural runoff upstream. Such parameters are known to cause hypoxic or anoxic conditions in sediment layers, restricting the macrofauna to a few stress-tolerant species [47].
Multivariate analyses revealed salinity and seagrass cover as the primary environmental drivers, together explaining nearly 40% of the total variation in community composition. This finding underscores the role of salinity as a master variable in estuarine ecosystems [48,49] and highlights the exceptional ecological value of vegetated habitats in supporting benthic diversity. Although the pH, nutrient concentrations, and sediment features did not reach statistical significance, they may contribute to localized stress, particularly in upstream areas affected by watershed runoff and organic enrichment [10,50,51,52]. In addition, unmeasured anthropogenic factors, particularly chemical pollution, could further affect benthic community composition. Estuarine systems are often recipients of complex mixtures of contaminants, including heavy metals, hydrocarbons, pesticides, and other industrial residues, which can accumulate in sediments and exert sublethal or chronic effects on benthic organisms [9,10]. These pollutants may impair physiological functions, reduce reproductive success, and increase mortality, thereby altering community structure even in the absence of acute toxicity.
These results have several important ecological implications for understanding and managing estuarine ecosystems such as the Loukkos. The spatial structuring of macrofaunal assemblages, along with the dominance of stress-tolerant and opportunistic species, underscores the sensitivity of benthic communities to environmental gradients and anthropogenic pressures. Salinity clearly acts as a master ecological driver, regulating species distributions along the estuarine continuum, while vegetated habitats emerge as biodiversity hotspots that support high macrofaunal richness and abundance through their provision of structural complexity, oxygenation, and food resources. Seasonal dynamics further modulate community structure, favoring rapid population responses among opportunistic taxa during periods of environmental stability. In contrast, upstream areas affected by agricultural runoff and organic enrichment exhibit community impoverishment and reduced diversity, reflecting the ecological consequences of nutrient loading, hypoxia, and sedimentation. Collectively, these findings highlight the need to preserve vegetated estuarine habitats and reduce upstream pollution to maintain benthic biodiversity and ecosystem functioning. They also reinforce the value of macrofaunal assemblages as effective bioindicators for monitoring ecological quality and detecting shifts linked to both natural and human-induced changes. In this context, a complementary study focusing on biotic indices and trophic structure is underway, which will provide further insight into ecosystem functioning and ecological status across the Loukkos estuary.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the author upon request.

Conflicts of Interest

The author declares no conflicts of interest.

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Figure 1. Location of the study area in northern Morocco and distribution of the sampling stations along the Loukkos estuary, from the river mouth to the control dam.
Figure 1. Location of the study area in northern Morocco and distribution of the sampling stations along the Loukkos estuary, from the river mouth to the control dam.
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Figure 2. Spatial representation of total macrofaunal abundance per station with proportional distribution of major taxonomic groups (molluscs, polychaetes, crustaceans, and others). Circle size reflects total abundance; larger circles indicate higher abundance.
Figure 2. Spatial representation of total macrofaunal abundance per station with proportional distribution of major taxonomic groups (molluscs, polychaetes, crustaceans, and others). Circle size reflects total abundance; larger circles indicate higher abundance.
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Figure 3. Boxplots of the six dominant benthic species (accounting for over 90% of total abundance) across the six stations (from ST1 to ST6) and two seasons, dry (DS) and wet (WS).
Figure 3. Boxplots of the six dominant benthic species (accounting for over 90% of total abundance) across the six stations (from ST1 to ST6) and two seasons, dry (DS) and wet (WS).
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Figure 4. Boxplots of species richness, abundance, and diversity indices across stations and seasons in the Loukkos estuary. Each boxplot represents values from three replicate samples per station and season.
Figure 4. Boxplots of species richness, abundance, and diversity indices across stations and seasons in the Loukkos estuary. Each boxplot represents values from three replicate samples per station and season.
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Figure 5. Dendrogram resulting from Hierarchical Clustering Analysis (HCA) of sampling stations based on benthic community composition, showing four distinct groups.
Figure 5. Dendrogram resulting from Hierarchical Clustering Analysis (HCA) of sampling stations based on benthic community composition, showing four distinct groups.
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Figure 6. Canonical Analysis of Principal Coordinates (CAP) ordination of benthic macrofaunal communities based on environmental variables.
Figure 6. Canonical Analysis of Principal Coordinates (CAP) ordination of benthic macrofaunal communities based on environmental variables.
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Table 1. List of benthic taxa identified in the Loukkos estuary during the study period.
Table 1. List of benthic taxa identified in the Loukkos estuary during the study period.
MolluscsPolychaetes
BivalvesCapitella capitata (Fabricius, 1780)
Abra alba (W. Wood, 1802)Chaetopterus sp.
Cerastoderma edule (Linnaeus, 1758)Diopatra neapolitana (Delle Chiaje, 1841)
Donax trunculus (Linnaeus, 1758)Glycera tridactyla (Schmarda, 1861)
Mactra stultorum (Linnaeus, 1758)Hediste diversicolor (O.F. Müller, 1776)
Mytilus galloprovincialis (Lamarck, 1819)Heteromastus filiformis (Claparède, 1864)
Ruditapes decussatus (Linnaeus, 1758)Lagis koreni (Malmgren, 1866)
Scrobicularia plana (da Costa, 1778)Nephtys hombergii (Lamarck, 1818)
Solen marginatus (Pulteney, 1799)Perinereis cultrifera (Grube, 1840)
Venus verrucosa (Linnaeus, 1758)Prionospio sp.
Spisula subtruncata (da Costa, 1778)Scoloplos armiger (Müller, 1776)
GastropodsCrustaceans
Aplysia sp. Afruca tangeri (Eydoux, 1835)
Bittium reticulatum (da Costa, 1778)Callinectes sapidus (Rathbun, 1896)
Bulla striata (Bruguière, 1792)Carcinus maenas (Linnaeus, 1758)
Haminoea navicula (da Costa, 1778)Cyathura carinata (Krøyer, 1847)
Littorina obtusata (Linnaeus, 1758)Idotea chelipes (Pallas, 1766)
Neverita sp.Gammarus sp.
Peringia ulvae (Pennant, 1777)Melita palmata (Montagu, 1804)
Phorcus turbinatus (Born, 1778)Palaemon elegans (Rathke, 1836)
Rissoa parva (da Costa, 1778)Sphaeroma sp.
Steromphala umbilicalis (da Costa, 1778)Upogebia pusilla (Petagna, 1792)
Tritia reticulata (Linnaeus, 1758)Others
Tritia incrassata (Strøm, 1768)Ophiura ophiura (Linnaeus, 1758)
Dolichopodidae larave
Larvae Pisces
Nemertea ind.
Table 2. Summary of SIMPER and IndVal analyses characterizing the benthic assemblages identified by hierarchical clustering. This table combines the results of two complementary approaches: the SIMPER analysis, which quantifies inter-group dissimilarities, intra-group similarities, and the main species contributing (>5%) to within-group similarity; and the Indicator Value (IndVal) analysis, which identifies species significantly associated with each assemblage (only species with p < 0.05 are reported).
Table 2. Summary of SIMPER and IndVal analyses characterizing the benthic assemblages identified by hierarchical clustering. This table combines the results of two complementary approaches: the SIMPER analysis, which quantifies inter-group dissimilarities, intra-group similarities, and the main species contributing (>5%) to within-group similarity; and the Indicator Value (IndVal) analysis, which identifies species significantly associated with each assemblage (only species with p < 0.05 are reported).
GroupStationsSIMPER AnalysisIndVal Analysis
Dissimilarities Between GroupsSimilarity Within GroupDominant Species (Contribution > 5%)Indicator Species with p-Value and Significance
G1ST1-WS
ST1-DS		100% dissimilarity with G4
>94% with G2 and G3		18.6%C. edule (49.6%)D. trunculus (p = 0.043 *)
S. marginatus (32.1%)S. armiger (p = 0.043 *)
N. hombergii (6.1%)
G2ST2-WS
ST2-DS		88.45% dissimilarity with G3
>94% with G4		48%B. reticulatum (77.2%)A. alba (p = 0.025 *)
L. koreni (p = 0.025 *)
R. parva (p = 0.025 *)
B. reticulatum (p = 0.027 *)
P. ulvae (p = 0.021 *)
T. reticulata (p = 0.015 *)
I. chelipes (p = 0.034 *)
D. neapolitana (p = 0.031 *)
R. decussatus (p = 0.024 *)
H. navicula (p = 0.034 *)
(Shared with G1)
N. hombergii (0.004, **)
S. marginatus (0.020 *)
G3ST3-WS
ST3-DS
ST4-WS
ST4-DS
ST6-WS		65.15% dissimilarity with G420.7%S. plana (60.7%)(Shared with G2)
H. diversicolor (22.8%)C. carinata (p = 0.035 *)
C. carinata (8.9%)C. capitata (p = 0.040 *)
G4ST5-WS
ST5-DS
ST6-DS		100% dissimilarity with G1
>94% with G2		34.5%H. diversicolor (85.9%)No exclusive indicator species detected
D. larvae (9.9%)
Table 3. Results of the permutation-based ANOVA from the Canonical Analysis of Principal Coordinates (CAP) model assessing the influence of environmental variables on benthic community composition.
Table 3. Results of the permutation-based ANOVA from the Canonical Analysis of Principal Coordinates (CAP) model assessing the influence of environmental variables on benthic community composition.
FPr(>F)% Variance Explained% Cumulative Variance
Global Model test2.22540.042 --
Variables
Salinity (Sal)5.01100.00420.8520.85
Vegetation (VEG)4.22680.00517.5938.44
pH2.22980.0749.2847.72
Total hardness (TH)1.80670.1637.5255.24
Phosphate (PO42−)1.76000.1707.3262.56
Nitrate (NO3−)1.53450.2376.3968.95
Clay (%)1.46280.2596.0975.04
Ammonium (NH4+)1.37960.2765.7480.78
Organic matter (MO)0.61720.7562.5783.35
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Touhami, F. Benthic Macrofauna in the Loukkos Estuary, Morocco: Patterns and Environmental Drivers. Ecologies 2025, 6, 53. https://doi.org/10.3390/ecologies6030053

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Touhami F. Benthic Macrofauna in the Loukkos Estuary, Morocco: Patterns and Environmental Drivers. Ecologies. 2025; 6(3):53. https://doi.org/10.3390/ecologies6030053

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Touhami, Feirouz. 2025. "Benthic Macrofauna in the Loukkos Estuary, Morocco: Patterns and Environmental Drivers" Ecologies 6, no. 3: 53. https://doi.org/10.3390/ecologies6030053

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Touhami, F. (2025). Benthic Macrofauna in the Loukkos Estuary, Morocco: Patterns and Environmental Drivers. Ecologies, 6(3), 53. https://doi.org/10.3390/ecologies6030053

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