Coasts, Volume 4, Issue 1 (March 2024) – 12 articles

This investigation evaluated two fundamental assumptions of wetland inundation models designed to emulate landscape evolution and resiliency under conditions of sea level rise: that they can (1) migrate landward at the same rate as the transgressing shoreline and (2) immediately replace the plant community into which they are onlapping. Rates of wetland (e.g., marsh, mangrove) migration were culled from 11 study areas located in five regions of focus: Delaware Bay, Chesapeake Bay, Pamlico Sound, South Florida, and Northwest Florida. The average rate of marsh migration (n = 14) was 3.7 m yr⁻¹. The average rate of South Florida mangrove migration (n = 4) was 38.0 m yr⁻¹. The average rate of upland forest retreat (n = 4) was 3.4 m yr⁻¹. Theoretical rates of shoreline transgression were calculated using site-specific landscape slope and scenario-based NOAA sea level rise elevations in 2050. Rates of shoreline transgression over the marsh landscape averaged 94 m yr⁻¹. The average rate of shoreline transgression in the mangrove-dominated areas of South Florida was 153.2 m yr⁻¹. The calculated rates of shoreline transgression were much faster than the observed horizontal marsh migration, and by 2050, the offset or gap between them averaged 2700 m and ranged between 292 and 5531 m. In South Florida, the gap average was 3516 m and ranged between 2766 m and 4563 m. At sites where both horizontal marsh migration and forest retreat rates were available, the distance or gap between them in 2050 averaged 47 m. Therefore, the results of this study are inconsistent with the two fundamental assumptions of many wetland inundation models and suggest that they may overestimate their resilience under conditions of 21st century accelerating sea level rise. Full article

Challenges associated with cubozoan jellyfish detection and the limitations of current detection techniques limit the ability of scientists to fill critical knowledge gaps surrounding their ecology. Environmental DNA (eDNA), however, has proven useful as an ecological survey tool to detect and study these deadly jellyfish. This study aimed to leverage the power of eDNA to detect and explore the distribution of the Australian box jellyfish (Chironex fleckeri), encompassing both its medusae and polyp life history stages, within an open coastal bay (Horseshoe Bay) of Magnetic Island, Queensland, Australia. Our investigation focused on a hypothesis concerning the source locations of the jellyfish within Horseshoe Bay and, through a comparison of both life history stage distributions, aimed to determine potential population stock boundaries. eDNA results aligned with the predicted nearshore distribution of medusae. Further, the elusive benthic polyp stage was also detected. These findings confirmed Horseshoe Bay as a source location of the jellyfish. Moreover, our evidence supported a model that the area likely represents a population stock of the species. This adds to growing evidence suggesting some cubozoan jellyfish have population stocks of small spatial scales in both open and relatively closed ecosystems such as estuaries. In conclusion, this study serves as a notable example of eDNA’s ability to resolve critical knowledge gaps surrounding cubozoan ecology and to enhance the management ability of these deadly jellyfish to reduce envenomations. Full article

The goal of this project is to assess the state of marine biodiversity in the Natura 2000 marine network in Spain and analyze the impact of fishing policies on it. The study focuses on three marine demarcations in Spain: North Atlantic, South Atlantic, and the Strait of Gibraltar and Alborán Sea. The research uses the DPSIR (Drivers of Change-Pressure-State-Impact-Response) framework, a multi-criteria analysis approach to understand the relationships between biodiversity loss, fishing, marine ecosystem integrity, and the provision of ecosystem services. Our results revealed a significant decline in biodiversity since 1985 in the four marine areas studied; this loss was more pronounced in the Gulf of Cadiz (in Andalusia) and less intense in the northern regions of Spain (Galicia and Asturias). This trend aligns with the global degradation of marine ecosystems and loss of biodiversity caused by human activities. The main drivers behind this decline are economic factors promoting industrial fishing and overexploitation. However, there has been a reduction in the industrial fishing fleet since the 2000s, supported by the European Maritime and Fisheries Fund for transitioning toward sustainable fishing methods. Despite the increase in regulations and the establishment of marine protected areas, these measures have not been effective enough to stop the loss of marine biodiversity. The results highlight the importance of combining administrative measures such as creating marine protected areas and implementing fisheries management regulations with the preservation of cultural services provided by these ecosystems. Successful governance models that involve collaboration between fishermen and decision-makers have been observed in northern Galicia and the Gulf of Cádiz. Full article

The marine ecosystem’s balance is crucial for sustaining biodiversity and supporting fisheries. Marine protected areas have been increasingly used to enhance marine habitats, yet their impact on fish populations remains a topic of debate. This study focuses on a marine protected area in Kitros, Pieria, in Greece, where an artificial reef was constructed, to understand its influence on coastal fish populations. The objectives were to investigate the changes in fish biomass and abundance, comparing the data from periods before and after the construction of an artificial reef. This research compares the data between 2007 and 2008 with the data between 2016 and 2017, collected with bottom trawl surveys strategically executed prior to and after the artificial reef’s installation. Fish species captured were identified, with their lengths and masses measured. The findings indicate an increase in the biomass and abundance of certain fish species after artificial reef deployment, notably the commercially significant Mullus barbatus and Pagellus erythrinus. The artificial reef in Kitros, Pieria, with its surrounding marine protected area appears to have had a positive impact on the local fish populations over the years, suggesting that it can contribute to marine conservation and fishery enhancement. These results underscore the potential of artificial reefs as tools for marine ecosystem management, offering insights for policymakers and environmentalists into coastal resource management. Full article

Mapping coastal regions is important for environmental assessment and for monitoring spatio-temporal changes. Although traditional cartographic methods using a geographic information system (GIS) are applicable in image classification, machine learning (ML) methods present more advantageous solutions for pattern-finding tasks such as the automated detection of landscape patches in heterogeneous landscapes. This study aimed to discriminate landscape patterns along the eastern coasts of Mozambique using the ML modules of a Geographic Resources Analysis Support System (GRASS) GIS. The random forest (RF) algorithm of the module ‘r.learn.train’ was used to map the coastal landscapes of the eastern shoreline of the Bight of Sofala, using remote sensing (RS) data at multiple temporal scales. The dataset included Landsat 8-9 OLI/TIRS imagery collected in the dry period during 2015, 2018, and 2023, which enabled the evaluation of temporal dynamics. The supervised classification of RS rasters was supported by the Scikit-Learn ML package of Python embedded in the GRASS GIS. The Bight of Sofala is characterized by diverse marine ecosystems dominated by swamp wetlands and mangrove forests located in the mixed saline–fresh waters along the eastern coast of Mozambique. This paper demonstrates the advantages of using ML for RS data classification in the environmental monitoring of coastal areas. The integration of Earth Observation data, processed using a decision tree classifier by ML methods and land cover characteristics enabled the detection of recent changes in the coastal ecosystem of Mozambique, East Africa. Full article

Seiches oscillations may account for an important proportion of sea level variations in nearshore environments, inducing overflow and surges while impacting the safety of marine areas. However, complementary investigations are still required to characterize seiches in coastal basins, including especially estuaries. The present study exhibited seiches characteristics in the intertidal zone of the upper Elorn estuary (western Brittany, France), within the city of Landerneau, which is regularly subjected to river overflow and inundation. This investigation relied on five-year measurements of the free-surface elevation. As recorded time series were highly discontinuous around low tide, an original data analysis technique was implemented to exhibit seiches characteristics during the different tidal cycles. Measurements revealed important seiches oscillations with heights liable to exceed 0.6 m and periods of around 45–70 min. Seiches showed furthermore a fortnightly variability with pronounced heights and an increased number of oscillations during neap tides. These variations appeared, however, to be disturbed by the additional effects of meteorological conditions, including especially the influence of wind. The number of oscillations around high tide was thus found to increase in strong wind conditions. These effects were particularly noticeable at low atmospheric pressure, suggesting a sensitivity of seiches to wind meteorological patterns during cyclonic events. Full article

In the 1970s, the discovery of much higher mercury (Hg) concentrations in Mediterranean fish than in related species of the same size from the Atlantic Ocean raised serious concerns about the possible health effects of neurotoxic monomethylmercury (MMHg) on end consumers. After 50 years, the cycling and fluxes of the different chemical forms of the metal between air, land, and marine environments are still not well defined. However, current knowledge indicates that the anomalous Hg accumulation in Mediterranean organisms is mainly due to the re-mineralization of organic material, which favors the activity of methylating microorganisms and increases MMHg concentrations in low-oxygen waters. The compound is efficiently bio-concentrated by very small phytoplankton cells, which develop in Mediterranean oligotrophic and phosphorous-limited waters and are then transferred to grazing zooplankton. The enhanced bioavailability of MMHg together with the slow growth of organisms and more complex and longer Mediterranean food webs could be responsible for its anomalous accumulation in tuna and other long-lived predatory species. The Mediterranean Sea is a “hotspot” of climate change and has a rich biodiversity, and the increasing temperature, salinity, acidification, and stratification of seawater will likely reduce primary production and change the composition of plankton communities. These changes will likely affect the accumulation of MMHg at lower trophic levels and the biomagnification of its concentrations along the food web; however, changes are difficult to predict. The increased evasion of gaseous elemental mercury (Hg°) from warming surface waters and lower primary productivity could decrease the Hg availability for biotic (and possibly abiotic) methylation processes, but lower oxygen concentrations in deep waters, more complex food webs, and the reduced growth of top predators could increase their MMHg content. Despite uncertainties, in Mediterranean regions historically affected by Hg inputs from anthropogenic and geogenic sources, such as those in the northwestern Mediterranean and the northern Adriatic Sea, rising seawater levels, river flooding, and storms will likely favor the mobilization of Hg and organic matter and will likely maintain high Hg bioaccumulation rates for a long time. Long-term studies will, therefore, be necessary to evaluate the impact of climate change on continental Hg inputs in the Mediterranean basin, on air–sea exchanges, on possible changes in the composition of biotic communities, and on MMHg formation and its biomagnification along food webs. In this context, to safeguard the health of heavy consumers of local seafood, it appears necessary to develop information campaigns, promote initiatives for the consumption of marine organisms at lower trophic levels, and organize large-scale surveys of Hg accumulation in the hair or urine of the most exposed population groups. Full article

Coastal retreat processes are usually associated with many anthropogenic actions, such as the regulation of river basins, the construction of hydraulic storm defence works in coastal areas and the building of housing on the beach. To all of this, we should also add the increase in sea levels due to the effect of climate change. The chosen area of study corresponds to the coastal area of the municipality of Guardamar del Segura, belonging to the Segura River Basin. The methodology applied in this study comprised the gathering of historical information, the extraction of data using GIS, the compiling of data using official organisations and the analysis of all these data from a geographical perspective. The obtained results show the chronology of the regulation works in the Segura Basin and their relationship with the reduction and negative trend in average ordinary flows (1940–2023) and the extraordinary, swelled flows recorded in the period 1994–2023. Furthermore, the coastlines from 1923 to 2023 were mapped, enabling us to determine the evolution of the coastline retreat processes experienced in the dune ridge of Guardamar del Segura and the increase in the frequency of impacts due to storms on Babilonia Beach. Finally, data on wind, waves and marine currents recorded at a gauging station were incorporated, enabling us to understand their impact on this coastal sector. The results obtained are discussed, and they indicate the need to incorporate data on sediment into the study in order to complete it. The conclusions reveal the existence of a relationship between all these anthropogenic elements in the beach erosion processes experienced in the village of Guardamar del Segura. Full article

Southwestern Peru has an arid climate typical of subtropical west coasts bordering cold ocean currents. Mountain runoff is barely able to sustain urban needs and motivates this research. Using high-resolution satellite reanalysis products, the meso-scale climate and weather variability are explored via point-to-field regression. A time series spanning 1970–2022 of Tacna area (18 S, 70.2 W, 570 m) rainfall, potential evaporation, wind, and weather parameters were evaluated for thermodynamic and kinematic features. Although sea breezes draw marine air inland, they simultaneously generate low-level divergence and subsidence aloft. Potential evaporation in early summer causes water deficits that are rarely offset by late summer runoff from the Andes Mountains. Winter (May–September) showers from passing cold fronts are more frequent during El Niño. Warming of the tropical east Pacific accelerates subtropical westerly winds that lift over the coastal plains. Quasi-stationary Rossby wave patterns amplify transient troughs at 70 W, but the winter showers rarely exceed 4 mm/day due to low-level stability from negative heat fluxes over cool seawater offshore. Two winter wet spells were studied using satellite and surface data (July 2002, July 2009). Light showers were prominent in elevations from 400 to 900 m. An early summer dry spell was considered (November 2020), wherein southeast winds, coastal upwelling, and low dewpoint temperatures coincided with La Niña conditions. A rain-gauge transect showed that summer convection stays east of the Andes escarpment and seldom benefits the coastal plains. Thus, water resources in Tacna are strained beyond the carrying capacity. Full article

Caulerpa cylindracea, Indo-Pacific and thermophilic macroalgal species, have spread in Italian coastal waters, especially in the western Mediterranean Sea. Also, along the Calabria coastline, this Invasive Alien Species (IAS) was able to colonize most of the western and eastern seasides of the region. This research was conducted between 1999 and 2021 through a detailed cost-effective citizen science program. The novelty of this research was to determine the overall distribution of Caulerpa cylindracea along Calabria seawaters from the Tyrrhenian to the Ionian coasts. The results of the monitoring survey highlighted the presence of Caulerpa cylindracea in 45 collecting stations throughout the Calabrian coastline. This regional assessment showed the extensive adaptability of the species to different environmental conditions: from exposed to sheltered sites, in shaded and sunny coastal areas and also throughout pristine and polluted waters. The rapid and increasing spread of the species could affect the structure of Mediterranean biota or, otherwise, could lead in time to new ecological niches. As highlighted in the most recent literature, it is necessary to update monitoring and mapping plans for the protection of marine biodiversity through close coordination between scientists, citizens and policy makers, all engaged to ensure effective management of invasive processes. Full article

“Red tide” is the popular name for a harmful algal bloom that occurs frequently in Florida waters and has significant impacts on the environment, the economy, and human and animal health. This paper addresses the limited understanding of public attitudes surrounding red tide and the potential for message framing to increase support for mitigation action. A sample of Florida residents (n = 498) was randomly shown a digital article framed around different red tide impacts (economic loss, human health risks, ecosystem damage, or harm to charismatic species) or a control article not framed around a specific red tide impact. Participants were then queried about their emotional responses, support for red tide mitigation policies, and intentions to change their behavior to mitigate impacts. Participants reported higher levels of negative emotions after viewing the harm to charismatic megafauna framing, indicating that messaging may play a significant role in eliciting environmental emotions. Message frames did not significantly impact other policy attitudes. Results demonstrate barriers to shifting support for mitigation where public support for action is already high. Full article

Synthesis of geologic and chronologic data generated from Holocene sedimentary sequences recovered along the inner continental shelf, shoreface, and modern coastal zone of the Georgia Bight reveal a synchronous sequence of paleoenvironmental events that occurred in response to rate of sea level rise tipping points. During the early Holocene (11.7–8.2 cal kyr BP), the paleoshoreline was overstepped and submerged by rapidly rising seas that averaged ~5 mm yr⁻¹. Rates of rise during the middle Holocene (8.2–4.2 cal kyr BP) averaged ~2 mm yr⁻¹ and this deceleration resulted in the formation of coastal environments and sedimentary sequences that were subsequently reworked as the shoreface continued its landward and upward migration. The modern coastal zone emerged commensurate with the late Holocene (4.2–0 cal kyr BP), when the rate of sea level rise averaged <1 mm yr⁻¹. Analysis of water level data collected at six NOAA tide gauge stations located along the Georgia Bight coast indicates the rate of relative sea level rise has increased from a historical average of 3.6 ± 0.2 mm yr⁻¹ (<1972 to 2022) to 6.6 ± 0.8 (1993 to 2022) and during the 21st century it has averaged 9.8 ± 0.3 mm yr⁻¹ (2003 to 2022). The current rate of sea level rise is nearly double the early Holocene rate of rise. Based upon a novel application of the principle of uniformitarianism (i.e., the past is the key to the future), the likely geomorphic trajectory of the Georgia Bight coastal zone under conditions of 21st century accelerating sea level rise will be one of increasing instability (e.g., coastal erosion) and flooding (e.g., overwash, breaching). Evidence of an emerging instability within the coastal zone has been previously reported throughout the region and supports the trajectory of geomorphic change proposed herein. This will ultimately result in the submergence of existing landscapes and replacement by estuarine and marine environments, which may hasten in pace and scale given the current rate of sea level rise is expected to continue accelerating throughout this century. These findings have not been previously reported and should be considered by coastal practitioners responsible for conceptualizing risk, as well as the formulation and implementation of adaptation action plans designed to mitigate threats to the built and natural environment induced by climate change. Full article