Coasts

The coastline is a constantly evolving boundary between land and sea, shaped by natural forces and human activities. Given its significant ecological and economic value, this zone faces increasing pressures, highlighting the need for continuous monitoring and improved understanding to support sustainable management. This study analyses the spatial and temporal changes along the Al Qunfudhah coastline from 1984 to 2020. Using a combination of multi-temporal Landsat satellite images and geographic information system tools—specifically the digital shoreline analysis system—the research tracks changes over time. Shoreline positions were accurately extracted using automated methods, particularly the Canny edge detection algorithm. Over the 36-year period, analysis using the linear regression rate (LRR) and end point rate (EPR) methods revealed a general pattern of slight shoreline advancement. The highest rates of accretion were recorded at 12.43 m/year (LRR) and 13.36 m/year (EPR), with average rates of 3.63 m/year and 4.17 m/year, especially in the northern region where a corniche road was developed along the coast. Conversely, the most significant erosion occurred near the boat port, with maximum rates reaching −24.4 m/year (LRR) and −20.9 m/year (EPR) and average rates of −1.23 m/year and −1.08 m/year. These results offer valuable insights into the factors driving coastal changes and provide a scientific foundation for making informed, sustainable decisions about the future of the Al Qunfudhah coastline. Full article

When designing spatial planning programs for processes in coastal zones, it is essential to consider the connections between marine and terrestrial environments and to coordinate institutional work in their implementation. This study examines the environmental policies of two planning processes in the coastal zone, one terrestrial and one marine, which were formally developed and adopted through decrees in the State of Sonora (NW Mexico). The Gulf of California Marine Spatial Planning (MSP-GC) was decreed in 2006, and the Sonora Coast Land Spatial Planning (LSP-SC) was decreed in 2009 and updated in 2015. This study reviewed, compared, and spatially analyzed the environmental policies established by both planning processes. The results show that both planning processes contain environmental policies with limited links between the marine and terrestrial environments in practice. Both planning processes were enacted with effort, resources, and stakeholder participation, but have not been implemented effectively. It is essential to review the mandates of the decrees, conduct an integrated assessment of environmental policies, and seek ways for federal and State institutional structures to drive the implementation of these planning processes. Considering the dates of the MSP (2006) and LSP-SC (2015) decrees, now it is the right time to evaluate them. Full article

This study explored the occurrence, density, and distribution of Fucales along the island of Lampedusa, almost 30 years after the latest studies conducted on the marine vegetation of this island. To carry out this study, we conducted a monitoring activity in 18 sites through both scuba dives and snorkeling. During this study, a total of 13 species (three belonging to Cystoseira sensu strictu (s.s.), five to Ericaria, two to Gongolaria, and finally three to Sargassum) were observed. Nine species were previously reported, four taxa (E. brachycarpa, E. funkii, E. giacconei, and S. cf furcatum) were reported here for the first time in Lampedusa, and six species have not been found anymore. Ericaria giacconei may have always been present on Lampedusa Island, but it might have been misidentified in the past. The record on the island of Lampedusa extends the known distribution range of this species. The presence of S. cf furcatum, a non-indigenous species that is recently expanding in the Mediterranean Sea, could be considered further proof of ongoing seawater warming. In conclusion, we found that the predominant species’ association described in the past for the island of Lampedusa has remained unchanged in terms of species and biodiversity found in the studied sites. Nevertheless, we observed some changes in the Fucalean species, in particular a reduction in the canopy density values of some deep species. Therefore, we believe that the zonation pattern of the MPA should be revised, paying more attention to the conservation of fucalean species. Moreover, it will be important to manage and control the populations of the rabbitfishes, mitigating their impacts on the fucalean stands of the island. Full article

The Mediterranean coast is known for its great tourist attractions, concentration of population, and economic activities. Specifically, in the autonomous regions like Catalonia and Valencia, more than half of the population lives in coastal counties, and the population during the summer months increases due to the influx of tourists. Furthermore, in this stretch of coast, there are some areas of natural interest such as the Delta del Ebro or the Albufera, which are two of the most important wetland areas in the Mediterranean. However, according to studies by Day Today, the retreat of the coastline has increased in recent years, and this influences management of coastal territory both directly and indirectly, mostly harming all sectors with low levels, creating spaces with significant problems. It is for this reason that reporting on climate change and the impact on the coasts is assuming an important role in society, because they are essential tools for planning and management costs. In this thesis, the ground that would be affected by a +1 m, +2 m, and +3 m increase in average sea level, as simulated by the existing flood simulator, has been quantified. And a methodology has been developed for determining the vulnerability of the land based on flooding provided by terrain elevations, and each area studied was evaluated with different degrees of vulnerability: very high, high, moderate, or low. Finally, a first estimate has been made of economic loss that could involve a meter rise in the average sea level for Catalan beaches, and major damage to natural parks, urban areas, and major infrastructure has been identified. This study shows that there are nine areas with high vulnerability due to the low heights of their territory, and the majority of the flooded land is concentrated in the Ebro Delta and the Albufera, which jointly dominate the totals across scenarios. Full article

This paper investigates the influence of back-to-back major hurricanes “Helene” and “Milton” which devastated south-eastern regions of the USA in 2024, and the extent to which associated storm surges influenced Extreme Value Analysis (EVA) of the long ocean water level record at Key West, Florida dating back to 1913. The highest recorded storm surge of 890 mm was recorded during a major hurricane event in October 1944, approximately 56 mm higher than the peak of the surge recorded at Key West during hurricane “Wilma” in 2005. Reanalysis of 2023 published EVA results for Key West indicate that despite the devastation of “Helene” and “Milton”, the super-elevation of the ocean water surface above Mean Sea Level (MSL) recorded at the Key West tidal facility during these hurricanes were at or below that which would be expected around once per annum. The timing and location of the peak of the storm surge with high predicted tides is no more than coincidental but remain the governing factors behind realizing record-breaking water levels over the historical record. Full article

Pipelines and power cables are critical infrastructures in coastal areas for transporting energy resources from offshore renewable installations to onshore grids. It is important to investigate the hydrodynamic forces on pipelines and cables and their surrounding flow fields, which are highly related to their on-bottom stability. The time-varying hydrodynamic forces coefficients and unsteady surrounding flows of a near-seabed pipeline subjected to a wave-induced oscillatory boundary layer flow are studied through numerical simulations. The Keulegan–Carpenter numbers of the oscillatory flow are up to 400, which are defined based on the maximum undisturbed near-bed orbital velocity, the pipeline diameter and the period of the oscillatory flow. The investigated Reynolds number is set to $1\times {10}^4$, defined based on $U_w$ and $D$. The influences of different seabed roughness ratios $k_s/D$ (where $k_s$ is the Nikuradse equivalent sand roughness) up to 0.1 on the hydrodynamic forces and the flow fields are considered. Both a wall-mounted pipeline with no gap ratio to the bottom wall and a pipeline with different gap ratios to the wall are investigated. The correlations between the hydrodynamic forces and the surrounding flow patterns at different time steps during one wave cylinder are analyzed by using the force partitioning method and are discussed in detail. It is found that there are influences of the increasing $k_s/D$ on the force coefficients at large $\mathrm{K}\mathrm{C},$ while for the small $\mathrm{K}\mathrm{C}$, the inertial effect from the oscillatory flow dominates the force coefficients with small influences from different $k_s/D$. The FPM analysis shows that the elongated shear layers from the top of the cylinder contribute to the peak values of the drag force coefficients. Full article

Given the high sensitivity of small estuaries to environmental changes, the present study aimed to investigate how climate-induced stressors—particularly rainfall and salinity—affect zooplankton community structure in the Amazonian Taperaçu estuary (northern Brazil), where limited spatial scale amplifies ecological responses. This study evaluated the effects of the extremely dry 2015–2016 El Niño period on hydrological patterns and zooplankton dynamics in this shallow tropical estuary. Eight sampling campaigns were conducted, with water and zooplankton samples analyzed using standard methods. Salinity, dissolved inorganic nutrients, and chlorophyll-a concentrations were affected by the marked decrease in rainfall caused by the El Niño event. These changes significantly impacted zooplankton community dynamics, especially the densities of marine-estuarine species Acartia lilljeborgii, Euterpina acutifrons, and Oikopleura dioica, which peaked during months of highest salinity. High recruitment of copepod larval stages was also observed, with peak densities coinciding with dominant adult forms. In contrast, coastal and estuarine species such as Acartia tonsa, Pseudodiaptomus marshi, Oithona oswaldocruzi, and Oithona hebes were negatively affected by reduced rainfall. Species richness, diversity, and evenness during the El Niño period were relatively high compared to previously reported values under normal conditions in the same ecosystem. Environmental and temporal variables accounted for over half the variance in predominant taxa density, indicating that El Niño–driven changes influenced zooplankton structure over time. This suggests that El Niño may have strong impacts at the secondary trophic level, likely to cascade throughout the estuarine food web, altering its dynamics and the flow of carbon and energy through the system. Full article

Cultural eutrophication caused by human activity significantly impacts benthic ecosystems. This study investigated how different phytobenthic components—rhodophyte germlings, mesoalgal and macroalgal assemblages, and Ulva cf. lactuca—respond to nutrient enrichment in a tidal channel system in San Antonio Bay, Argentina. Two experiments were conducted: one in spring examined the interaction between nutrient enrichment (N + P, N + P + Fe) and grazing pressure on early and established algal communities, and the other in autumn assessed nutrient effects on assemblages and Ulva cf. lactuca. Results showed that early successional stages, such as germlings and mesoalgae, responded most strongly to nutrient inputs, while mature macroalgae remained largely unaffected. Significant growth of mesoalgae, with increased pigment concentrations (chlorophyll a, c, and carotenoids), occurred at the eutrophied SAO Channel in spring. Nutrient additions increased rhodophyte germlings but eventually reduced diatom-dominated mesoalgal growth. Mature macroalgae showed site-specific differences but did not respond to fertilization. Grazing effects were evident in treatments with protective cages, suggesting herbivory influences early-stage algal development. Overall, the study emphasizes the importance of the successional stage, grazing pressure, and environmental nutrient history in shaping benthic algal responses to eutrophication, offering key insights into the dynamics of coastal ecosystems under increasing nutrient stress. Full article

The aim of this work was to investigate the evolutionary mechanisms of an artificial sedimentary agglomerate formed by cathodic polarization in natural seawater during its abandonment to a natural environment. Previous studies indicate that the mineralogical evolution of the material is controlled by kinetic factors and/or the local precipitation of aragonite on the brucite surface. However, the observation of the precipitation of metastable phase precipitation during the initial immersion of this material (in powder form) has suggested the possibility of a more complex mechanism. The present study builds upon previous experimental work and includes thermogravimetric analysis and infrared spectrometry. The results are analyzed using numerical experimentation to evaluate the proposed hypotheses. Findings show that the transformation mechanism is characterized by the precipitation of metastable calcium carbonate phases. Under supersaturation conditions, these hydrated phases form on the brucite surface, limiting the mineral’s contact with the solution. The subsequent transformation of these amorphous phases into aragonite further reduces brucite–solution interaction, which explains the persistence of brucite both in the residual powder after 120 h of immersion and in the consolidated material after more than 20 years of exposure to natural seawater. Full article

The real-time forecast estimates of total water levels (TWL) associated with coastal storms by the Boston Office of the National Weather Service (NWS), and the analysis, identification, and field mapping of storm tide pathways (STP) by the Center for Coastal Studies (CCS) within the forecast region, has led to improved model forecasts, enhanced allocation of resources prior to storm impact (e.g., placement of flood control measures, identification of evacuation routes, development of applications to visualize and communicate threats, etc.), and increased public awareness of the practical implications of sea level rise and storm-related coastal flooding. Both NWS modeling and STP mapping are discussed here. The coupling of these methods began in 2016–2017 in Provincetown, MA, and its utility was highlighted during the new storm of record for most of southern New England, a nor’easter in January 2018. The use of this information by managers, stakeholders, and the public has increased since combining the TWL modeling and STP mapping in an online portal in 2021, and it continues to be used by emergency managers and the public to plan for approaching coastal storms. Full article

Eelgrass (Zostera marina) is a native perennial marine angiosperm found in shallow bays and estuaries. Eelgrass beds are considered essential fish habitats and provide an important food source for marine organisms and waterfowl. This study examines changes in extent of the eelgrass beds in the southern portion of the Little Narragansett Bay Estuary, Rhode Island/Connecticut, USA, between 2019 and 2022. The primary dataset used to delineate eelgrass beds was side-scan sonar coupled with underwater video imagery. Previous studies showed a decline in the extent of eelgrass here between 2012 and 2016. Our results show an increase in eelgrass coverage from 0.52 km² in 2019 to 0.75 km² in 2022. This increase in the extent of eelgrass occurred against the trends of declining eelgrass coverage both globally and regionally. Full article

Despite being low-resource environments, sandy beaches can contain diverse bacterial assemblages. In this study we examined the spatial heterogeneity of bacterial communities in sand on a beach on the Mississippi Gulf Coast, USA. 16S ribosomal RNA gene sequencing was used to characterize bacterial communities in surface sand along 10 m transects from dry sand towards the upper beach to fully submerged sand, as well as up to 0.4 m deep into the sand. There were clear gradients in bacterial community structure based on position on the beach and depth, and community richness and diversity was greater in moist sand subject to tidal influence than drier sand. Bacterial communities in sand higher up the beach were characterized by members of the phyla Bacillota and Actinomycetota, whereas there was an increased presence of picocyanobacteria (phylum Cyanobacteriota) in sand closer to the water and greater diversity overall. Along with gradients in community structure, microbial activity also showed spatial patterns, with microbial extracellular enzyme activity being greatest in surface sand at intermediate positions along the beach transects that were subject to tidal influences but not fully submerged. This research supports the idea of beaches containing diverse bacterial communities and demonstrates that the existence of gradients in beach environments means that these communities show clear patterns in their spatial distribution. Full article

Remote sensing offers an effective alternative for estimating mangrove carbon stocks by analyzing the relationship between satellite pixel values and field-based carbon measurements. This research was carried out in the mangrove forests of western Bali, Indonesia, encompassing three areas situated in a non-conservation mangrove forest area. This study assessed 32 remote sensing vegetation indices derived from Sentinel-2 satellite imagery to identify the optimal model for quantifying the above-ground carbon (Cag) content in mangrove ecosystems. Field data were collected using stratified random sampling and were used to develop regression models linking the Cag with vegetation indices. The Simple Ratio (SR) index exhibited the highest correlation (r = 0.847, R² = 0.707), while the Three Index Vegetation Above-Ground Carbon (TrIVCag) model, combining the SR, Specific Leaf Area Vegetation Index (SLAVI), and Transformed Ratio Vegetation Index (TRVI) indices, achieved the best performance (r = 0.870, R² = 0.728). The model validation results confirmed the reliability of the TrIVCag model, as indicated by a correlation of 0.852 between the model estimates and measured Cag values from independent field data. In 2023, the mangrove area in western Bali (excluding West Bali National Park) was estimated at 376.85 ha, with a total above-ground carbon stock of 34,994.55 tonC/ha. Region A had the highest average Cag at 98.97 tonC/ha, followed by Regions B (66.58 tonC/ha) and C (86.98 tonC/ha). This model offers a practical and scalable approach to carbon monitoring and is expected to play a valuable role in supporting blue carbon conservation efforts and contributing to climate change mitigation. Full article

This study analyses the impacts of winter storms on beach response, as well as the subsequent recovery during spring and summer, at a dissipative sandy beach in Brandon Bay, Ireland. Shoreline dynamics were assessed through the integration of field data from five survey campaigns conducted between October 2021 and November 2022 with a 1D Xbeach (version 1.23) numerical model. Cross-sectional profiles were measured at seven locations, revealing pronounced erosion during winter, followed by recovery in calmer seasons, especially in the lower beach zone. The model effectively simulated short-term storm-induced morphological changes, demonstrating that rates of shoreline retreat and profile alteration are higher in the eastern bay, where wave energy is greater. Most morphological changes occurred between the low and high astronomical tide marks, characterized by upper beach erosion and lower beach accretion. Models were subsequently employed to examine future climate scenarios, including sea level rise and increased storm intensity. The projections indicated an exponential increase in erosion rates, correlated with higher storm wave heights and frequencies. These results highlight the dynamic response of dissipative beaches to extreme events and reinforce the necessity for adaptive coastal management strategies to address the escalating risks posed by climate change. Full article

The symbiotic microbiome constitutes a consortium that has been persistently domesticated by a specific algal species, fostering a close and enduring association with the host. The majority of microbial taxa remain uncharacterized. These unknown microbes, often referred to as “microbial dark matter (MDM)”, have important ecological contributions. Given the challenges in discerning symbiotic microbes in natural environments, herein, ecological characteristics of MDM and known taxa within symbiotic communities were investigated in a simulated bloom process using Alexandrium pacificum without antibiotic treatment. Specifically, increased diversification was observed in MDM along the bloom process. Higher trophic interaction and less vulnerability of the molecular network were found in MDM taxa. The “bridge” role of MDM species was better than that of known taxa, as shown by higher betweenness centralization. Deterministic processes dominated in MDM taxa, which promote phylogenic diversity of such groups to some extent. The findings highlight that MDM taxa play an important role in sustaining community stability and functioning. This study broadens our understanding of the ecological contribution of MDM under disturbances from dinoflagellate blooms, providing essential theoretical insights and empirical data to inform the management of coastal toxic blooms. Full article

Bivalves such as oysters rely on aragonite and calcite for shell formation via the biomineralization of calcium carbonate. Ocean acidification reduces carbonate ion availability, compromising shell growth and inducing dissolution under undersaturated conditions ($\Omega$ < 1). This study assessed the aragonite and calcite saturation state ($\Omega$) as a proxy for evaluating habitat suitability for oyster aquaculture and restoration. Temperature, salinity, pH, and total alkalinity were monitored across multiple sites and used to calculate the aragonite and calcite saturation state via the Seacarb package. Calcium hardness and dissolved oxygen were also measured to evaluate compliance with hatchery water quality standards. Results indicated temporal and spatial fluctuations in saturation states, with frequent undersaturation during cooler months. Spearman correlation analyses demonstrated significant positive relationships between temperature and salinity (p = 0.46), between pH and aragonite saturation state (p = 0.72), and between alkalinity and aragonite saturation state (p = 0.51). These findings highlight the importance of carbonate chemistry variability and seasonal drivers in determining the suitability of sites for oyster cultivation and restoration under changing environmental conditions. Full article

This study aimed to evaluate how tidal modulation influences breaking waves on a macrotidal beach along the Amazonian coast under varying climatic conditions. The study utilized medium-term data (2006–2018) from national and international institutions and short-term data (2012–2014) from in situ measurements at Ajuruteua Beach. Offshore winds and waves, predominantly from the northeast, were influenced by severe storms associated with La Niña and El Niño events. During these periods, wave heights exceeded 5 m, with wave periods ranging from 12 to 20 s. Tidal fluctuations (typically 5.0–6.0 m) modulated nearshore wave heights and periods, with variations determined by offshore conditions and climatic influences. Wave heights decreased from 2–5 m offshore to 1–2 m nearshore. At low tide, sandbanks dissipated wave energy, resulting in significantly smaller breaking waves (0.1–0.5 m) compared with high tide (1–1.8 m). The northern part of Ajuruteua Beach experienced a progressive retreat, with a total area loss of 0.15 km² and a shoreline retreat of 0.360 km between 2007 and 2021. The combination of high hydrodynamic energy and unregulated development led to the destruction of 43 buildings between 2007 and 2013 and an additional 44 houses between 2013 and 2021 within the intertidal zone. Moreover, the absence of coastal management strategies has exacerbated erosion, underscoring the urgent need for planning and regulatory frameworks. Based on the findings of this study, it is recommended that land use be regulated and both short- and long-term physical processes be systematically integrated into future coastal protection planning. Full article

The city of Acapulco was impacted by two near-consecutive hurricanes. On 25 October 2023, Hurricane Otis made landfall, reaching the highest Category 5 storm on the Saffir–Simpson scale, causing extensive coastal destruction due to extreme winds and waves. Nearly one year later (23 September 2024), Hurricane John—a Category 2 storm—caused severe flooding despite its lower intensity, primarily due to its unusual trajectory and prolonged rainfall. Digital shoreline analysis of PlanetScope images (captured one month before and after Hurricane Otis) revealed that the southern coast of Acapulco, specifically Zona Diamante—where the major seafront hotels are located—experienced substantial shoreline erosion (94 ha) and damage. In the northwestern section of the study area, the Coyuca Bar experienced the most dramatic geomorphological change in surface area. This was primarily due to the complete disappearance of the bar on October 26, which resulted in a shoreline retreat of 85 m immediately after the passage of Hurricane Otis. Sentinel-1 Synthetic Aperture Radar (SAR) showed that Hurricane John inundated 2385 ha, four times greater than Hurricane Otis’s flooding (567 ha). The retrofitted QGIS methodology demonstrated high reliability when compared to limited in situ local reports. Given the increased frequency of intense hurricanes, these methods and findings will be relevant in other coastal areas for monitoring and managing local communities affected by severe climate events. Full article

Heavy metal pollution from human activities is an increasing environmental concern. This study investigates the concentrations of Cu, Pb, Zn, Cd, Hg, and As in the coastal seawater offshore of Beihai, Guangxi, in April 2021, and explores their relationships with dissolved inorganic nitrogen, phosphate, and salinity. Our results reveal higher heavy metal concentrations in the northern nearshore waters and lower levels in southern offshore areas, with surface waters generally exhibiting greater enrichment than bottom waters. Surface concentrations show a decreasing trend from the northeast to the southwest, likely influenced by prevailing northeast monsoon winds. While bottom water concentrations decline from the northwest to the southeast, which indicates the influence of riverine runoff, particularly from the Qinzhou Bay estuary. Heavy metal levels in southern Beihai waters are comparable to those in the Beibu Gulf, except for Hg and Zn, which are significantly higher in the water of the Beibu Gulf. Notably, heavy metal concentrations in both Beihai and Beibu Gulf remain considerably lower than those observed in the coastal waters of Guangdong. Overall, Beihai’s coastal seawater meets China’s Class I quality standards. Nonetheless, continued monitoring is essential, especially of the potential ecological impacts of Hg and Zn on marine life. Full article