Urbanization Compromises the Sustainability of Coastal Ecosystems: Insights from the Reproductive Traits of the Bioindicator Clam Donax trunculus

Abstract

The sustainability of coastal ecosystems, associated fisheries, and environmental quality is increasingly threatened by anthropogenic activities and rapidly expanding urbanization. This study investigated the ecological impacts of increased coastal urbanization on intertidal sediment quality and the biological parameters of the wedge clam Donax trunculus along the central Moroccan Atlantic coast. Between 2018 and 2022, a period characterized by intensified urban activity, total organic matter (TOM) in sediment significantly increased, whereas temperature and pH remained stable. Concurrently, D. trunculus populations experienced notable declines in abundance and biomass, along with marked disruptions in reproductive dynamics. The proportion of sexually mature individuals decreased, while spent individuals and male-biased sex ratios became more prominent. These findings suggest that urbanization-related pressures such as sediment enrichment, pollution, and physical disturbance are exerting measurable stress on this key bioindicator species. The results highlight the need for improved coastal management to mitigate the ecological consequences of rapid urban expansion on coastal sustainability.

1. Introduction

Coastal ecosystems represent one of the most dynamic and ecologically valuable interfaces between terrestrial and marine environments [1]. Characterized by constantly shifting physical and biological conditions, these habitats support diverse assemblages of species and perform vital ecological functions such as nutrient cycling, sediment stabilization, and water filtration [2]. Among the many organisms that inhabit these environments, bivalve mollusks such as Donax trunculus play a central role in ecosystem functioning because of their abundance, filter-feeding behavior, and sensitivity to environmental disturbances [3,4]. This species, which is widely distributed along the Mediterranean and Atlantic coasts, is also of considerable socioeconomic importance, forming the basis of artisanal fisheries and serving as a valuable protein source for coastal communities [5].

However, these ecosystems are increasingly subjected to anthropogenic pressures, particularly in the form of rapid coastal urbanization. This phenomenon has become a global concern, exerting intense pressure on the sustainability of marine and coastal ecosystems [6,7]. As populations are concentrated in littoral zones, the demand for housing, infrastructure, tourism, and industry accelerates, leading to habitat fragmentation, pollution, and increased exploitation of natural resources [8]. The transformation of natural shorelines into artificial environments disrupts ecological processes, alters sediment dynamics, and weakens adaptive responses to climate-induced changes and anthropogenic stressors [9]. This rapid expansion often occurs without adequate environmental planning or regulatory frameworks, resulting in the degradation of critical habitats such as intertidal zones, estuaries, and sandy beaches [10]. These pressures compromise biodiversity, undermine the productivity of coastal fisheries, and challenge the long-term sustainability of ecosystem services that support both local livelihoods and regional economies [11,12]. Hence, these impacts manifest in various ways, including increased sediment contamination, organic enrichment, habitat fragmentation, and disturbance of benthic fauna [13]. In many cases, the biological consequences of such pressures are difficult to detect in the short term, necessitating the use of sensitive bioindicator species to monitor ecological health and detect early signs of stress [13].

The wedge clam Donax trunculus is recognized as a sentinel species in this context. As shallow-burrowing bivalves that inhabit intertidal zones, they are directly exposed to sedimentary changes, pollution, and human disturbance [14]. Its population dynamics, reproductive cycle, and overall health can reflect broader environmental conditions and serve as early warning indicators of ecosystem alterations [15]. Notably, the reproductive biology of bivalves is particularly sensitive to environmental stressors [16]. Parameters such as gametogenesis, spawning frequency, gonadal maturation, and the sex ratio may shift in response to sediment quality, organic matter content, temperature, and contaminant exposure [17,18]. Urban-derived contaminants such as heavy metals, hydrocarbons, and microplastics are known to interfere with reproductive processes in bivalves through multiple physiological disruptions. Rather than causing immediate mortality, these pollutants often induce sublethal stress responses that target the reproductive system [19,20,21]. For instance, contaminants can trigger oxidative stress, leading to cellular damage in gonadal tissues and impairing the normal progression of gametogenesis [22]. They may also act as endocrine disruptors, interfering with hormonal signaling pathways that regulate sex differentiation and reproductive cycles [23]. Furthermore, the energetic cost of detoxification and cellular repair in polluted environments may divert resources away from reproduction, resulting in delayed maturation, reduced gamete production, or skewed sex ratios [24,25]. Although these effects may not be immediately evident at the population level, they can gradually undermine reproductive output and resilience, ultimately threatening population viability in chronically stressed habitats [26]. Therefore, studying the reproductive traits of D. trunculus provides a powerful lens through which to assess the ecological consequences of environmental change [27].

Previous studies have demonstrated the vulnerability of D. trunculus populations to pollution, sediment alteration, and eutrophication, with adverse effects on population density, size structure, and reproductive performance [28,29]. Urban runoff and sewage discharge, in particular, introduce excess nutrients and contaminants that alter the physicochemical properties of sediment, potentially reducing oxygen availability and food quality for benthic organisms [30,31]. Additionally, physical disturbances such as trampling, sediment compaction, and vehicle traffic can interfere with the burrowing and feeding behavior of clams, further compromising their survival and reproduction [32]. These localized stressors on D. trunculus populations are emblematic of broader patterns driven by coastal urbanization, which intensifies and multiplies such pressures across entire ecosystems [33].

However, few studies have assessed the biological consequences of such transformations on benthic macrofauna, particularly from reproductive and demographic perspectives. While physicochemical monitoring is essential, it often fails to capture the sublethal, long-term effects of environmental change. Reproductive traits, on the other hand, offer a more nuanced and biologically meaningful metric of ecosystem stress. Disruptions to the reproductive cycle can signal population-level impacts with long-term implications for sustainability and resilience [34]. By examining changes in gonadal development stages, sex ratios, abundance, and biomass over time, researchers can gain insights into how urbanization-induced pressures affect population viability and ecosystem function.

The primary objective of this study was to assess the reproductive traits of Donax trunculus as sensitive biological indicators of environmental change in coastal ecosystems subjected to varying degrees of urbanization. Specifically, we hypothesized that (i) increased urbanization leads to a deterioration of sediment quality (e.g., higher organic matter accumulation, altered pH, and temperature) and that (ii) these changes are associated with measurable impairments in the reproductive performance of D. trunculus, including altered gonadal development, skewed sex ratios, and reduced reproductive maturity.

To test these hypotheses, we compared biological and environmental data collected during two distinct periods—2018 (representing low urbanization) and 2022 (representing high urbanization). Our research aims to answer the following key questions: (1) How do urbanization-induced changes in sediment characteristics affect population structure and biomass of D. trunculus? (2) Do shifts in environmental parameters correlate with disruptions in gametogenesis and reproductive development? (3) Can D. trunculus reliably reflect early warning signals of habitat degradation in intertidal sandy beach ecosystems?

By integrating environmental indicators (total organic matter content, temperature, pH) with biological responses, this study aims to determine whether D. trunculus can serve as a robust sentinel species for coastal habitat monitoring. Ultimately, the findings contribute to a broader understanding of how urban expansion impacts intertidal biodiversity, supporting evidence-based management strategies for preserving the ecological integrity and productivity of sandy beach ecosystems.

2. Materials and Methods

2.1. Study Area

The study was conducted along the central Atlantic coast of Morocco, specifically in the Agadir region, which features a diverse geomorphology shaped by terrestrial and marine interactions. The landscape includes sandy shores, rocky formations, and expansive plains [35]. The area experiences variable wind regimes, including periodic hot and dry “Chergui” winds originating from the Sahara. Oceanographic conditions are dominated by northwesterly swells, particularly during winter, when wave heights typically range between 1.5 and 3.5 m [36]. Tidal dynamics are predominantly microtidal and semidiurnal, facilitating the general southward movement of sediment. Nonetheless, episodic events such as intense rainfall can cause temporary but significant beach erosion [37,38].

The Agadir coastal region lies within the Souss-Massa Basin, bordered by the Anti-Atlas and High Atlas mountain ranges. This area includes the Souss estuary, a critical ecological zone and biodiversity hotspot. The broader Agadir district is a key destination for maritime tourism, offering numerous recreational opportunities such as marinas, surfing, and sailing [39]. The hinterland also draws tourists for outdoor activities such as hiking and exploring oases. The coastline is increasingly valued for its scenic and recreational potential, with multiple beaches contributing significantly to regional tourism. Major infrastructural developments, including the Taghazout Bay resort, the touristic villages of Aghroud and Taghazout, the renovated Agadir marina, and the municipal bay, have further enhanced the area’s attractiveness, blending natural features with modern amenities [27].

This segment of the Moroccan Atlantic coast has undergone intense urban development, driven primarily by the construction of the 615-hectare Taghazout Bay tourist complex. Initially, the area was classified as a “village” with low urban influence, according to the bathing area registration and evaluation (BARE) framework [40]. However, following the full implementation of the tourist infrastructure, the classification shifted to “urban”. The complex now includes various facilities, such as hotels, beach resorts, restaurants, commercial outlets, a beach club, a medina, and sports academies for golf, tennis, surfing, and football [41].

To quantify the extent of urbanization, an index was computed via the following formula [42]:

$$\mathrm{U}\mathrm{I}=\sum {\displaystyle \frac{\left({\mathrm{X}}_{\mathrm{i}}-{\mathrm{X}}_{\mathrm{m}\mathrm{i}\mathrm{n}}\right)}{\left({\mathrm{X}}_{\mathrm{m}\mathrm{a}\mathrm{x}}-{\mathrm{X}}_{\mathrm{m}\mathrm{i}\mathrm{n}}\right)}}$$

where UI (Urbanization Index) is the average urbanization score for a given year, Xi is the individual score per category, and X_max and X_min are the highest and lowest possible values (from 0 to 5). The categories assessed included proximity to urban centers, the presence of buildings on the beach, beach cleaning practices, the quantity of solid waste, the presence of vehicles on the sand, the quality of the night sky, and the frequency of visitors. For each category, we qualitatively attributed a value from 0 to 5 based on specific criteria adapted from González et al. [42], allowing for a standardized and comparative assessment of urbanization pressure. Each value was assigned following a detailed classification table that distinguishes low (0–1), medium (2–3), and high (4–5) levels of urbanization, depending on observable indicators such as distance from urban areas, infrastructure on the beach, the extent and frequency of mechanical cleaning, visible waste, vehicular access, light pollution, and beach usage intensity (Table S1). Monthly data collection for all the studied parameters was conducted across six sampling sites during two time periods “2018 and 2022” (Table S2). This scoring approach provided a qualitative framework for synthesizing qualitative field observations into a unified index, facilitating temporal comparisons between years of contrasting urbanization levels.

2.2. Sampling

Specimens of Donax trunculus were sampled monthly at each of the six sites during 2018 and 2022 (Figure 1). Individuals ranging from 24 to 31 mm within the sexually mature size class [27] were collected by hand at low tide, with 30 individuals obtained per site per month. For sediment analysis (the habitat of D. trunculus), particularly total organic matter (TOM) content, 500 g of intertidal sediment was collected via a small shovel. All the biological and sediment samples were kept on ice at −4 °C and promptly transported to the laboratory for further processing and analysis.

2.3. Gonadal Analysis of Donax trunculus

The reproductive cycle of D. trunculus was examined histologically using specimens collected monthly during both 2018 and 2022. Gonads were fixed in Gendre’s solution and then dehydrated in a graded ethanol series (70%, 80%, 90%, and 95%), followed by immersion in butanol and embedding in paraffin. Serial sections (5 µm) were stained with Harris’ hematoxylin and counterstained with eosin following standard histological protocols [16,27]. The slides were observed under a light microscope to identify gametogenic stages.

2.4. Sex Ratio Determination

The sex ratio was assessed monthly. Preliminary sex identification was based on gonadal coloration—creamy white for males and orange to purplish hues for females—although this method was often inconclusive. Therefore, microscopic examination of gonadal tissue was used for confirmation. The sex ratio was calculated via the following formula [16]:

$$\mathrm{S}\mathrm{e}\mathrm{x} \mathrm{r}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}={\displaystyle \frac{\mathrm{N}\mathrm{u}\mathrm{m}\mathrm{b}\mathrm{e}\mathrm{r} \mathrm{o}\mathrm{f} \mathrm{m}\mathrm{a}\mathrm{l}\mathrm{e}\mathrm{s}}{\mathrm{N}\mathrm{u}\mathrm{m}\mathrm{b}\mathrm{e}\mathrm{r} \mathrm{o}\mathrm{f} \mathrm{f}\mathrm{e}\mathrm{m}\mathrm{a}\mathrm{l}\mathrm{e}\mathrm{s}}}$$

Histological observations revealed five distinct gametogenic stages: undifferentiated, developing, mature, spawning, and spent. These were classified on the basis of morphological and cytological characteristics [27].

2.5. Abundance and Biomass of Donax trunculus

Species abundance was quantified as the number of individuals per square meter (ind/m²) using methods presented in Ben-Haddad et al. [43]. The fresh weight of all individuals was measured to estimate biomass. The samples were then dried at 50 °C for 48 h to obtain dry weights. To calculate the ash-free dry weight, the samples were combusted at 500 °C for 5 h in a muffle furnace, and the ash weight was subtracted from the dry weight [44]. Biomass values were expressed as grams per square meter (g/m²).

2.6. Physicochemical Analysis of Sediment

The sediment temperature (°C) and pH were measured monthly at each site via a calibrated Thermo Scientific ORION Star A329 multiparameter handheld meter. The total organic matter (TOM) content in the sediment was determined using the loss on ignition (LOI) method, which involves combustion at 500 °C for 24 h [45].

2.7. Data Analysis

After confirming the normality of each dataset via the Shapiro–Wilk test (p > 0.05), two-tailed t-test analysis was conducted to assess differences between the low- and high-urbanization periods. For each site, the mean value across all twelve months of the year was calculated, and these annual averages were used as replicates. Comparisons were thus made between the two periods on the basis of site-level yearly means. All the statistical analyses and graphical outputs were performed via GraphPad Prism 9, ArcMap 10.8.1, OriginPro 2021, and XLSTAT 2025.1.

3. Results and Discussion

The results of this study reveal a significant transformation in the degree of urbanization within the study area between 2018 and 2022. In 2018, the calculated urbanization index was 0.41, reflecting a relatively low level of urban development. However, by 2022, this index sharply increased to 0.91, approaching the maximum theoretical value (UI = 1) that denotes full urbanization. This marked increase represents more than a 120% rise in urbanization intensity over a four-year period, more than doubling the urban footprint. This rapid escalation highlights a critical phase of urban expansion, likely driven by intensified anthropogenic activities and accelerated infrastructure growth. The concentration of total organic matter (TOM) in intertidal sediment markedly increased from the low urbanization period (2018) to the high-urbanization period (2022). Specifically, TOM levels rose from 5.35 ± 0.55 to 8.3 ± 1.50% (Median ± SD), and this increase was statistically significant (p = 0.0008; p < 0.05) (Figure 2). This enrichment in organic matter likely reflects the intensification of anthropogenic inputs associated with urban development, including wastewater discharge, recreational activities, and runoff from impervious surfaces, which contribute to the accumulation of organic detritus in coastal sediments.

In contrast, the temperature and pH remained relatively stable across both periods. The sediment temperature values were comparable between 2018 (Median ± SD: 24.75 ± 0.70 °C) and 2022 (24.9 ± 0.65 °C), indicating no significant variation (p = 0.80; p > 0.05). Similarly, the pH values fluctuated minimally (Median ± SD: 8.50 ± 0.06 in 2018 vs. 8.46 ± 0.14 in 2022), indicating that urbanization did not significantly alter these physicochemical parameters during the study period (p = 0.97; p > 0.05) (Figure 2).

The population dynamics of Donax trunculus clearly responded to the shift in urbanization intensity. A significant decline in the abundance was observed (p = 0.0086; p < 0.05), with values (Median ± SD) decreasing from 41.85 ± 12.73 ind./m² under low urbanization to 23 ± 5.60 ind./m² under high urbanization (Figure 3). This reduction may be attributed to habitat degradation, increased human disturbance, and deteriorated sediment quality, all of which can adversely affect bivalve recruitment, survivability, and spatial distribution. Biomass followed a similar downward trend, declining from 25 ± 12.67 g/m² in 2018 to 20.50 ± 5.83 g/m² in 2022 (Median ± SD). However, this change was not statistically significant (p = 0.09; p > 0.05). The nonsignificant difference in biomass, despite lower abundance, could suggest a compensatory increase in the size or condition of surviving individuals, although further size-class analysis is needed to confirm this hypothesis.

The distribution of gonadal development stages in Donax trunculus populations notably shifted between the low urbanization (2018) and high-urbanization (2022) periods, suggesting significant impacts of urban development on reproductive dynamics (Figure 4). Under low urbanization, the population was dominated by individuals in the mature (35%) and developing (26%) stages, with spent individuals constituting only 12% of the total population. This pattern is typical of a healthy, actively reproducing bivalve population [27,46]. In contrast, during the high-urbanization phase, there was a marked increase in the proportion of spent individuals (45%), accompanied by a sharp decline in the percentages of developing (10%) and mature (21%) individuals. The stability of the spawning stage (approximately 11–12%) between both periods suggests that spawning events continue to occur but are likely less successful, as indicated by the reduction in post-spawning recovery and gametogenesis.

This shift in gonadal stages indicates a disturbance in the reproductive cycle, potentially driven by environmental stressors associated with urbanization. Increased sediment organic matter, as previously observed, can alter oxygen availability and food quality, affecting energy allocation toward reproduction [30,47]. Excessive organic matter accumulation may also create hypoxic microenvironments within the sediment, leading to oxidative stress and impaired gonadal function. Under such conditions, individuals may reallocate energy toward stress response and detoxification pathways, at the expense of gametogenesis and reproductive output [24,25]. Additionally, anthropogenic disturbances such as sediment compaction, pollution, and human trampling can disrupt gamete development and lead to reproductive exhaustion [18,48].

The percentage of sexually mature individuals (in the developing, mature, and spawning stages) decreased from 73% under low urbanization to 42% under high urbanization, indicating a potential decline in the reproductive capacity of the population. This reduction in maturity suggests either delayed gonadal development or reproductive inhibition, possibly as a physiological response to degraded environmental conditions.

The sex ratio also exhibited a noticeable shift toward male dominance, changing from 1.18:1 (male:female) under low urbanization to 1.40:1 during high urbanization. A Chi-square test confirmed a significant deviation from a 50:50 sex ratio (χ² (1) = 10.00, p = 0.001 < 0.05), as the observed value exceeded the critical value (3.84) (Figure 5). Such male-biased sex ratios have been documented in bivalve populations exposed to stress, including pollution and habitat disturbance [17]. This skew may reflect endocrine-disrupting effects that alter sex differentiation, or sex-specific sensitivities to environmental stressors [23]. For example, males may exhibit greater metabolic resilience under polluted or hypoxic conditions, resulting in higher survival rates compared to females [24,29]. This skewed sex ratio could thus represent a demographic response to long-term contamination and habitat degradation [49].

The observed alterations in gonadal development stages and sex ratios of Donax trunculus reflect reproductive stress likely induced by increased anthropogenic pressure on benthic populations. The sharp increase in the number of spent individuals may also be interpreted as a sign of reproductive exhaustion or premature spawning events, possibly triggered by environmental stressors such as hypoxia, energy deficiency, or fluctuations in food availability [13]. The concurrent decline in the number of mature individuals suggests disruption in the reproductive cycle, possibly due to environmental degradation and habitat alteration. These reproductive impairments may contribute to the observed population decline and could have long-term consequences for population resilience and sustainability. Furthermore, the male-biased sex ratio indicates additional reproductive instability, further exacerbating the vulnerability of this bioindicator species in urbanizing coastal environments [16,50] (Figure 6).

Before translating urbanization metrics into biological indicators, it is important to understand how physical habitat conditions are altered. Urban expansion modifies sediment composition, increases compaction, reduces interstitial oxygen, and elevates contaminant loads—collectively creating a hostile environment for sediment-dwelling species like D. trunculus. These physical alterations underpin the biological responses observed in this study. The results of this study revealed clear evidence of how increasing coastal urbanization can alter the structure and reproductive dynamics of Donax trunculus populations. While temperature and pH remained relatively stable between the low- and high-urbanization periods, significant changes in sediment composition and biological indicators were observed.

One of the most notable findings was the increase in total organic matter (TOM) in sediment samples from highly urbanized sites. Organic enrichment is often associated with inputs from untreated or poorly managed urban runoff, beachgoer waste, and sewage leakage [43]. While moderate TOM may support detritivorous species, excessive enrichment can reduce oxygen levels in the sediment, shift microbial communities, and create stressful conditions for benthic fauna [51,52]. This change in sediment quality likely contributed to the decline in D. trunculus abundance and biomass observed during the high-urbanization phase (Figure 6).

The decline in population density and biomass suggests that D. trunculus is sensitive to even moderate urban pressure. Disturbances such as trampling by beach users, sediment compaction, and pollution may disrupt burrowing behavior and reduce food availability [32]. Combined, these factors translate physical changes in the environment into measurable biological effects, reinforcing the value of bioindicators in tracking the ecological consequences of urban growth [41]. This finding has direct implications for the sustainability of local fisheries that depend on this species. Reduced populations may not only affect harvest yields but also compromise the role of this bivalve in maintaining ecosystem functions, such as sediment aeration and water filtration [53].

Reproductive data further highlight the biological stress experienced by D. trunculus under urban influence. The sharp increase in the proportion of spent individuals and the decrease in mature stages during the urbanized period point to reproductive disruption. Spawning stress or premature gamete release can result from elevated organic matter or altered sediment dynamics (Figure 6). The observed shift in the sex ratio toward male dominance may reflect an environmental stress response or altered survival of females, although further investigation is needed to confirm the underlying mechanisms [31].

Indeed, previous studies have shown that the study area has undergone rapid coastal urbanization since the 1960 earthquake, which prompted a modern reconstruction plan. Over the past three decades, its population has increased from 403,000 in 1990 to nearly one million in 2023, driven by growth in tourism, fisheries, agriculture, and port-related activities [35]. This transformation has positioned the region as a strategic economic and tourist hub. However, the resulting urban expansion has resulted in significant environmental trade-offs, particularly along coastlines, where increasing anthropogenic pressures are undermining the natural assets that initially fuel a city’s development [43].

The environmental consequences include widespread plastic pollution, primarily from tourist activity and poor waste management, which degrades the visual quality of beaches and causes economic losses by deterring visitors and increasing cleanup costs [54]. Microplastic contamination originating from untreated wastewater and direct discharges from industrial and touristic activities further exacerbates environmental stress [55]. This has notably impacted species such as Donax trunculus, which have been found to ingest significant quantities of microplastics that increased in parallel with urbanization [5], as well as to bioaccumulate trace metals such as cadmium (Cd) and copper (Cu), further reflecting environmental contamination [41]. Such exposure may induce physiological stress, disrupt reproductive processes, and potentially contribute to increased mortality rates [56]. In addition, unregulated off-road vehicles further threaten beach habitats by compacting sediments, destroying vegetation, and disturbing wildlife [57]. Otherwise, the accumulation of animal waste on beaches, such as that from camels and horses used for tourism, contributes to the enrichment of organic matter and the proliferation of fecal bacteria, posing risks to public health and the integrity of coastal ecosystems [58].

Overall, the observed alterations in the sediment quality and reproductive parameters of D. trunculus highlight a pressing ecological concern. In addition to the direct implications for this commercially and ecologically important species, the results suggest potential cascading effects on the structure and functioning of sandy beach ecosystems under increasing urban pressure. Sustained environmental degradation may compromise the resilience of D. trunculus populations, ultimately threatening the stability of associated benthic communities. These findings emphasize the need for targeted conservation measures and informed coastal management strategies to mitigate anthropogenic impacts and ensure the long-term sustainability of vulnerable intertidal habitats. Furthermore, additional scientific studies are essential to better understand the impact of environmental stressors on the reproductive traits of species inhabiting coastal zones. In-depth laboratory investigations will help clarify the mechanisms underlying reproductive impairment and support the development of effective monitoring and mitigation approaches.

4. Conclusions and Recommendations

The sustainability of coastal ecosystems and associated fisheries is under increasing pressure from anthropogenic activities and the rapid pace of urbanization along shorelines. This study provides clear evidence that increased coastal urbanization between 2018 and 2022 led to significant ecological changes in intertidal environments. While physicochemical parameters such as temperature and pH remained relatively stable, a marked rise in total organic matter points to greater organic loading, likely stemming from urban runoff, untreated sewage discharge, and intensified recreational and infrastructural development. These changes coincided with a significant decline in the abundance of Donax trunculus and a disruption of its reproductive cycle, including a sharp increase in the number of spent individuals and a skewed sex ratio favoring males. These biological responses indicate that D. trunculus is highly sensitive to anthropogenic stressors and serves as a reliable bioindicator of coastal habitat degradation. The reproductive impairment observed may also reflect early signs of broader ecological shifts, such as altered recruitment, population declines in higher trophic levels, and disruption of benthic-pelagic energy transfer. Such cascading effects could ultimately compromise the functional integrity of intertidal food webs. If these trends persist, local populations may face long-term demographic decline, undermining the ecological integrity of intertidal zones and compromising the sustainability of small-scale fisheries that rely on this species. The degradation of benthic habitats not only diminishes biodiversity and ecological function but also jeopardizes traditional harvesting activities, food security, and the socioeconomic value derived from healthy, resilient coastal systems.

While we cannot halt urbanization, an inevitable outcome of growing economic development that benefits the population, we must strive for a balanced approach that equally prioritizes environmental health. Sustainable progress demands compromise, where human advancement goes hand in hand with the protection of our natural ecosystems. To preserve the sustainability of coastal ecosystems and the viability of related fisheries, several targeted measures are recommended. First, improving wastewater management is essential, with priority given to treating and regulating discharges into coastal zones to limit organic enrichment and the accumulation of micro-pollutants in intertidal sediments. This can be achieved by upgrading decentralized wastewater treatment plants near coastal hotels and urban outfalls through the implementation of advanced tertiary treatment technologies, such as membrane filtration and UV disinfection. Second, controlling beach access and use through designated pathways and restrictions on vehicle traffic can help mitigate trampling and sediment compaction, thereby preserving benthic habitats. Enforcing vehicle-free zones and installing raised boardwalks in sensitive dune and intertidal zones are practical measures that can be rapidly deployed. Establishing long-term monitoring programs is also crucial for tracking changes in sediment quality and bivalve health, enabling early detection of ecological stress and facilitating adaptive coastal management strategies. Such programs should include seasonal sampling campaigns, real-time data collection through automated sensors, and the integration of bioindicators like bivalves to assess pollution levels.

These actions should be embedded within a broader Integrated Coastal Zone Management (ICZM) framework, promoting cross-sectoral coordination and evidence-based policymaking to balance development and conservation goals. Municipalities of the study region should establish interagency working groups involving urban planners, environmental authorities, and tourism stakeholders to align urban growth with coastal resilience targets. Additionally, raising public awareness through environmental education initiatives aimed at tourists and local communities can help reduce littering and promote more responsible, sustainable use of beach resources. This includes installing multilingual educational signage, launching “clean beach” campaigns, and involving local schools in beach stewardship programs. Finally, given its demonstrated sensitivity to anthropogenic pressures, Donax trunculus should be systematically integrated into biomonitoring protocols to assess and evaluate the ecological status of sandy beach environments affected by urbanization. When linked to early warning systems, such efforts can support rapid decision-making and timely interventions, helping prevent long-term degradation and loss of ecosystem services.