Intertidal Environments Research Articles

Comparison of Methods for Determining Erosion Threshold of Cohesive Sediments Using a Microcosm System

Erosion of cohesive sediments is a ubiquitous phenomenon in estuarine and intertidal environments. Several methods have been proposed to determine the surface erosion threshold (τc0), which are still debatable because of the numerous and uncertain definitions. Based on erosion microcosm experiments, we have compared three different methods using (1) eroded mass (EM), (2) erosion rate (ER), and (3) suspended sediment concentration (SSC), and suggested a suitable method for revealing the variation of erodibility in intertidal sediments. Erosion experiments using a microcosm system were carried out in the Muuido tidal flat, west coast of South Korea. The mean values of τc0 for three methods were: 0.20 ± 0.08 Pa (EM); 0.18 ± 0.07 Pa (ER); and (3) 0.17 ± 0.09 Pa (SSC). The SSC method yielded the lowest τc0, due to the outflow of suspended sediment from the erosion chamber of the microcosm. This was because SSC gradually decreased with time after depleting the erodible sediment at a given bed shear stress (τb). Therefore, the regression between SSC and applied τb might skew an x-intercept, resulting in the underestimation (or “not-determined”) of τc0. The EM method yielded robust and accurate (within the range of τb step at which erosion begins) results. The EM method represents how the erodible depth thickens as τb increases and therefore seems better suited than the SSC and ER methods for representing depth-limited erosion of cohesive sediments. Furthermore, this study identified the spatiotemporal variations of τc0 by EM method in an intertidal flat. The τc0 in mud flat was about two times higher than that in mixed flat. Compared to the end of tidal emersion, the sediment was 10–40% more erodible at the beginning stage.

Insights into the Ancient Adaptation to Intertidal Environments by Red Algae Based on a Genomic and Multiomics Investigation of Neoporphyra haitanensis.

Colonization of land from marine environments was a major transition for biological life on Earth, and intertidal adaptation was a key evolutionary event in the transition from marine- to land-based lifestyles. Multicellular intertidal red algae exhibit the earliest, systematic, and successful adaptation to intertidal environments, with Porphyra sensu lato (Bangiales, Rhodophyta) being a typical example. Here, a chromosome-level 49.67 Mb genome for Neoporphyra haitanensis comprising 9,496 gene loci is described based on metagenome-Hi-C-assisted whole-genome assembly, which allowed the isolation of epiphytic bacterial genome sequences from a seaweed genome for the first time. The compact, function-rich N. haitanensis genome revealed that ancestral lineages of red algae share common horizontal gene transfer events and close relationships with epiphytic bacterial populations. Specifically, the ancestor of N. haitanensis obtained unique lipoxygenase family genes from bacteria for complex chemical defense, carbonic anhydrases for survival in shell-borne conchocelis lifestyle stages, and numerous genes involved in stress tolerance. Combined proteomic, transcriptomic, and metabolomic analyses revealed complex regulation of rapid responses to intertidal dehydration/rehydration cycling within N. haitanensis. These adaptations include rapid regulation of its photosynthetic system, a readily available capacity to utilize ribosomal stores, increased methylation activity to rapidly synthesize proteins, and a strong anti-oxidation system to dissipate excess redox energy upon exposure to air. These novel insights into the unique adaptations of red algae to intertidal lifestyles inform our understanding of adaptations to intertidal ecosystems and the unique evolutionary steps required for intertidal colonization by biological life.

Diatom (Bacillariophyceae) assemblages in tidal environments of Vancouver Island, British Columbia, Canada

SUMMARYTo understand distributions of coastal diatoms along Vancouver Island, British Columbia, Canada, this paper describes diatom assemblages observed in 47 surface sediment samples from intertidal environments. One hundred and eighty‐four diatom taxa were identified from five transects crossing tidal flats, salt marshes, and freshwater forests in Tofino, Ucluelet, and Port Alberni. Distributions of the diatom assemblages were consistent with those reported elsewhere in the Pacific Northwest, but a few diatom taxa show different trends in their distributions. For example, one benthic speciesDenticula subtilisshows widespread distributions along the transect in Tofino. An ordination shown by Detrended Correspondence Analysis (DCA) using a combined dataset indicated overlapped scatter plots of diatom assemblages, suggesting that assemblages with similar species compositions are observed in more than one location. Hierarchical and k‐means clustering analyses using Euclidean distance recognized unique small groups along each transect. Rank abundance curves show different trends for richness and evenness of diatom assemblages among the five transects.

Laboratory data on wave propagation through vegetation with following and opposing currents

Abstract. Coastal vegetation has been increasingly recognized as an effective buffer against wind waves. Recent laboratory studies have considered realistic vegetation traits and hydrodynamic conditions, which advanced our understanding of the wave dissipation process in vegetation (WDV) in field conditions. In intertidal environments, waves commonly propagate into vegetation fields with underlying tidal currents, which may alter the WDV process. A number of experiments addressed WDV with following currents, but relatively few experiments have been conducted to assess WDV with opposing currents. Additionally, while the vegetation drag coefficient is a key factor influencing WDV, it is rarely reported for combined wave–current flows. Relevant WDV and drag coefficient data are not openly available for theory or model development. This paper reports a unique dataset of two flume experiments. Both experiments use stiff rods to mimic mangrove canopies. The first experiment assessed WDV and drag coefficients with and without following currents, whereas the second experiment included complementary tests with opposing currents. These two experiments included 668 tests covering various settings of water depth, wave height, wave period, current velocity and vegetation density. A variety of data, including wave height, drag coefficient, in-canopy velocity and acting force on mimic vegetation stem, are recorded. This dataset is expected to assist future theoretical advancement on WDV, which may ultimately lead to a more accurate prediction of wave dissipation capacity of natural coastal wetlands. The dataset is available from figshare with clear instructions for reuse (https://doi.org/10.6084/m9.figshare.13026530.v2, Hu et al., 2020). The current dataset will expand with additional WDV data from ongoing and planned observation in natural mangrove wetlands.

Drivers and limits of phenotypic responses in vulnerable seagrass populations:Zostera marinain the intertidal

AbstractIntertidal seagrass meadows are exposed to both marine and terrestrial environmental constraints. Seagrass vulnerability to climate changes in these highly dynamic and thermally stressful environments is concerning.Using broadscale monitoring data covering contrasted intertidal environments, this study aims to provide a comprehensive view of the extent, drivers and potential limits ofZostera marinaphenotypic responses. The links between phenotypic and reproductive strategies are also explored.Across 500 km of coastline,Z. marinaexhibited extensive variations of density, morphology, above‐ and below‐ground biomass and rates of clonality. Variance partitioning of phenotypic traits confirmed the strong link between intertidal seagrass populations and broadscale climate variability. However, it also highlighted a non‐negligible role of local factors such as exposure regime, substrate and tidal cycles. In its response to the environment,Z. marinadisplayed a trade‐off between the density and size of shoots, leading to two distinct phenotypic types: high densities and low above‐ to below‐ground biomass ratios (Type 1) in response to both high hydrodynamic and temperature stress, and low densities, high above‐ground biomass per shoot and developed leaves and sheaths (Type 2) in the most stable and less stressful intertidal environments. We argue that Type 1 maximizes self‐facilitation whereas Type 2 minimizes intraspecific competition, and that their occurrence matches predictions from the stress‐gradient hypothesis (SGH). Building on the SGH, we propose a generalized response of seagrass to environmental changes and discuss the role of light as a potential limiting resource for intertidal meadows.Synthesis. Here, we show how the SGH can explain seagrass phenotypic responses, drawing on previous experimental results to provide relevant predictions across different stress gradients. We also show thatZostera marinaresponds to strong hydrodynamics and thermal constraints, both likely to increase in the intertidal with climate changes, with a facilitation‐maximizing phenotypic type (Type 1). This strategy appears incompatible with the competition‐minimizing Type 2 found when seagrass face resource limitation, such as light limitation induced by water quality degradation. This potential limit to the resilience of intertidal seagrass populations in the face of cumulative stressors raises concern about their vulnerability regarding future climate scenarios.

The impact of wind‐waves and sea level rise on the morphodynamics of a sandy estuarine shoal

SummaryIntertidal shoals are pronounced morphological features found in many estuaries worldwide. Apart from maintaining an ecologically unique intertidal environment, shoals also protect adjacent dyke systems by attenuating waves. The fate of sandy shoals under anticipated sea level rise (SLR) scenarios is underexplored.The current research investigates the long‐term morphodynamic evolution of estuarine sandy shoals under forcing by short fetch, locally generated wind‐waves, tides, and SLR by means of a numerical, process‐based model (Delft3D). The focus lies on a sheltered shoal complex in the Western Scheldt, the Netherlands. Starting from the initial, 1963 bathymetry, we model 50‐year morphodynamic development with schematized wind‐wave forcing. We analyze in detail the impact of locally generated wind‐waves on shoal formation. Finally, we impose regional SLR of 1.10 m and 1.95 m for 100 years.Model results show that, on the spatial scale of intertidal flats, small, locally generated wind‐waves lower and widen the shoals while the adjacent channels deepen. However, on the estuarine system scale, wind‐waves do not lead to fundamentally different channel–shoal patterns and morphodynamic evolution trends. This suggests that channel–shoal formation is mainly due to tide residual sediment transports, with wind‐waves playing a secondary role. SLR leads to a notable intertidal area loss, despite a continuous heightening of the shoals, implying that morphodynamic adaptation lags behind SLR. The inclusion of wind‐waves does not fundamentally change the reaction of the estuarine shoal to SLR. Future research may focus on exploring the impact of including multiple sediment classes.

Gene Body Methylation Confers Transcription Robustness in Mangroves During Long-Term Stress Adaptation.

Whether induced epigenetic changes contribute to long-term adaptation remains controversial. Recent studies indicate that environmentally cued changes in gene body methylation (gbM) can facilitate acclimatization. However, such changes are often associated with genetic variation and their contribution to long-term stress adaptation remains unclear. Using whole-genome bisulfite sequencing, we examined evolutionary gains and losses of gbM in mangroves that adapted to extreme intertidal environments. We treated mangrove seedlings with salt stress, and investigated expression changes in relation with stress-induced or evolutionarily-acquired gbM changes. Evolution and function of gbM was compared with that of genetic variation. Mangroves gained much more gbM than their terrestrial relatives, mainly through convergent evolution. Genes that convergently gained gbM during evolution are more likely to become methylated in response to salt stress in species where they are normally not marked. Stress-induced and evolutionarily convergent gains of gbM both correlate with reduction in expression variation, conferring genome-wide expression robustness under salt stress. Moreover, convergent gbM evolution is uncoupled with convergent sequence evolution. Our findings suggest that transgenerational inheritance of acquired gbM helps environmental canalization of gene expression, facilitating long-term stress adaptation of mangroves in the face of a severe reduction in genetic diversity.

Satellite-Derived Barrier Response and Recovery Following Natural and Anthropogenic Perturbations, Northern Chandeleur Islands, Louisiana

The magnitude and frequency of storm events, relative sea-level rise (RSLR), sediment supply, and anthropogenic alterations drive the morphologic evolution of barrier island systems, although the relative importance of any one driver will vary with the spatial and temporal scales considered. To explore the relative contributions of storms and human alterations to sediment supply on decadal changes in barrier landscapes, we applied Otsu’s thresholding method to multiple satellite-derived spectral indices for coastal land-cover classification and analyzed Landsat satellite imagery to quantify changes to the northern Chandeleur Islands barrier system since 1984. This high temporal-resolution dataset shows decadal-scale land-cover oscillations related to storm–recovery cycles, suggesting that shorter and (or) less resolved time series are biased toward storm impacts and may significantly overpredict land-loss rates and the timing of barrier morphologic state changes. We demonstrate that, historically, vegetation extent and persistence were the dominant controls on alongshore-variable landscape response and recovery following storms, and are even more important than human-mediated sediment input. As a result of extensive vegetation losses over the past few decades, however, the northern Chandeleur Islands are transitioning to a new morphologic state in which the landscape is dominated by intertidal environments, indicating reduced resilience to future storms and possibly rapid transitions in morphologic state with increasing rates of RSLR.

Selection on genes associated with the evolution of divergent life histories: Gamete recognition or something else?

Gamete compatibility, and fertilization success, is mediated by gamete-recognition genes (GRGs) that are expected to show genetic evidence of a response to sexual selection associated with mating system traits. Changes in the strength of sexual selection can arise from the resolution of sperm competition among males, sexual conflicts of interest between males and females, or other mechanisms of sexual selection. To assess these expectations, we compared patterns of episodic diversifying selection among genes expressed in the gonads of Cryptasterina pentagona and C. hystera, which recently speciated and have evolved different mating systems (gonochoric or hermaphroditic), modes of fertilization (outcrossing or selfing), and dispersal (planktonic larvae or internal brooding). Cryptasterina spp. inhabit the upper intertidal of the coast of Queensland and coral islands of the Great Barrier Reef. We found some evidence for positive selection on a GRG in the outcrossing C. pentagona, and we found evidence of loss of gene function in a GRG of the self-fertilizing C. hystera. The modification or loss of gene functionality may be evidence of relaxed selection on some aspects of gamete interaction in C. hystera. In addition to these genes involved in gamete interactions, we also found genes under selection linked to abiotic stress, chromosomal regulation, polyspermy, and egg-laying. We interpret those results as possible evidence that Cryptasterina spp. with different mating systems may have been adapting in divergent ways to oxidative stress or other factors associated with reproduction in the physiologically challenging environment of the high intertidal. RESEARCH HIGHLIGHTS: Recent speciation between two sea stars was unlikely the result of selection on gamete-recognition genes annotated in this study. Instead, our results point to selection on genes linked to the intertidal environment and reproduction.

Recent Sedimentary Deposit and Dynamics Sedimentation Analysis at Teluk Betung Using GPR Interpretation and Core Data

Lampung Bay is an area with a busy shipping traffic from port of Panjang and port of Teluk Betung. There are several river contain sediments and sedimented in Teluk Betung area. By conducting a research in this area, we can determine the sediment depositional system. The research method that will be used is the analysis of sediment deposition profiles from core data and interpretation from Ground Penetrating Radar (GPR). From sedimentary analysis, older sediments have a clay to coarse sand with relatively firm contact with coarsening upward patterns. In the top, they have a medium to clay with a fining upward pattern. The existence of a relatively thick clay layer indicates a relatively marginal depositional environment. These clay layers may form in the lower subtidal environment and gradually change to the upper intertidal environment until supratidal. This can be seen from the GPR result which show the sediment boundary. The GPR profiles confirm that the upper part mostly contains the sand or clay sand with sea water intrusion which has high conductivity and dielectric permittivity . The deeper zone could not well interpreted due to lack of the sediment information, but they show the contact of the sediment layers with different amplitude.

Near-daily reconstruction of tropical intertidal limpet life-history using secondary-ion mass spectrometry

Measurements of life-history traits can reflect an organism’s response to environment. In wave-dominated rocky intertidal ecosystems, obtaining in-situ measurements of key grazing invertebrates are constrained by extreme conditions. Recent research demonstrates mollusc shells to be high-resolution sea-surface temperature proxies, as well as archival growth records. However, no prior molluscan climate proxy or life-history reconstruction has been demonstrated for the tropical rocky intertidal environment—a zone influenced by warmer waters, mixed tides, trade-wind patterns, and wave-action. Here, we show near-daily, spatiotemporal oxygen isotope signatures from the tropical rocky intertidal environment by coupling secondary ion mass spectrometry analysis of oxygen isotopes with the sclerochronology of an endemic Hawaiian intertidal limpet Cellana sandwicensis, that is a significant biocultural resource harvested for consumption. We also develop a method for reliable interpretation of seasonal growth patterns and longevity in limpets. This study provides a robust approach to explore tropical intertidal climatology and molluscan life-history.

Environmental Controls on the Distribution of Modern Benthic Foraminifera in the Florida Everglades and Their Use as Paleoenvironmental Indicators

ABSTRACT This study examined the environmental factors that control the distribution of modern foraminiferal assemblages in the Everglades in order to provide baseline data for a paleoenvironmental study. Total assemblages from the surface 2 cm of 30 sites across the marsh and mangrove environments of southwest Florida were investigated. Eight environmental variables, including average salinity, salinity range, pH, total phosphorus, temperature, and dissolved oxygen, and total organic carbon and total inorganic carbon measured on bulk sediments, as well as the elevation and distance from the coastline were determined for each of the 30 sampling locations. In total, 82 species were identified, the majority of which were calcareous. Diversity decreases, dominance increases, and agglutinated taxa increase from the coastline inland. Rotaliina are equally abundant across the intertidal environment, whereas Miliolina are common near the coast and in lagoons or inland lakes. The most important factor controlling foraminiferal distribution is total organic carbon, followed by total inorganic carbon, distance from coastline, total phosphorus, and salinity. Jadammina macrescens and Miliammina fusca indicate lower salinities (<15 psu). Good indicators for higher salinities are Haplophragmoides wilberti (10–20 psu) and Arenoparrella mexicana (10–20 psu and 28–30 psu). Ammonia spp. prefer salinities >15 psu and Elphidium spp. >20 psu. Ammonia tepida, Helenina anderseni, Trochammina inflata, and A. mexicana prefer organic-rich sediments. Thus, the benthic foraminifera from Everglades sediments are excellent salinity proxies and can be used to determine the history of habitat change in this area as well as to assess past trends in the rate of sea level rise.

Diatoms of the intertidal environments of Willapa Bay, Washington, USA as a sea-level indicator

An understanding of the modern relationship between diatom species and elevation is a prerequisite for using fossil diatoms to reconstruct relative sea level (RSL). We described modern diatom distributions from seven transects covering unvegetated subtidal environments to forested uplands from four tidal wetland sites (Smith Creek, Bone River, Niawiakum River, and Naselle River) of Willapa Bay, Washington, USA. We compared our diatom dataset (320 species from 104 samples) to a series of environmental variables (elevation, grain-size, total organic carbon (TOCSOM), and porewater salinity) using hierarchical clustering and ordination. While no single variable consistently explains variations in diatom assemblages at every site, elevation, salinity, and substrate (mud fraction and TOCSOM) are variables affecting diatom distribution along our transects. Elevation was the major environmental control of diatom variability (explained 27–39% variance) at four transects (Bone River Transect 1, Niawiakum River Transect 2, Naselle River Transect 1 and 2). Salinity and substrate were the major environmental controls (explained 12–32% variance) of diatom variability at three transects (Niawiakum River Transect 1: salinity; Smith Creek Transect and Bone River Transect 2: TOCSOM). Analyses of a combined regional dataset of all transects suggest that elevation is the driver of regional diatom variability in Willapa Bay, with salinity and substrate co-varying along an elevation gradient. We identify species with narrow elevation tolerances that can serve as indicator species of specific environments. Despite the site-specific variability of our modern diatom distribution, the regional dataset provides an important dataset that can be used to reconstruct RSL in Willapa Bay.

Morphological evolution of a non-engineered managed realignment site following tidal inundation

There is growing evidence that managed realignment (MR) sites have lower biodiversity than natural saltmarshes, which has been associated with differences in the physical function and morphological evolution following site breaching. This evidence has been derived from MR sites previously used for intensive arable agriculture or modified during site construction. Therefore, the development of these sites may not be representative of the sedimentological evolution that would have otherwise occurred. This paper presents analysis of high spatial resolution digital surface models derived from the images collected using a small-unmanned aerial system from a non-engineered MR site at Cwm Ivy Marsh, Gower Peninsula, Wales. These models are examined alongside a novel combination of high frequency measurements of the rate and patterns of sedimentation, suspended sediment concentration (SSC), and the sub-surface structure and geochemical profiles. Results indicated that although the site became topographically less variable over a four year period, the intertidal morphology developed through an increase in the abundance of higher order creek systems and sediment being deposited at a rate of between 3 and 7 cm/year. The SSC followed an inverse pattern to water depth, with bed elevation increasing and then decreasing during both the flood and ebb tidal phases. Analysis of the sediment subsurface geochemical composition indicated redox profiles similar to natural intertidal environments; evidence of a fluctuating water table was found at a saltmarsh site, in comparison to waterlogging identified at an anoxic mudflat site. These findings provide a new insight to the sedimentological processes in a MR site without the influence of landscaping or site engineering prior to site breaching, which can be used to inform the design of future MR sites.

Cold water temperatures define the poleward range limits of south American fiddler crabs

Temperature increase due to climate change has caused shifts in the range distribution of several organisms globally. In coastal intertidal environments most organisms have an amphibious life cycle and their poleward range limits may be delimited by their thermal tolerance during the pelagic larval stages. Fiddler crabs are key species in intertidal environments and their early larval stages occur in coastal waters. We evaluated the mean and monthly minimum sea surface temperature (SST) gradient over the South American coast and compared it to the minimum and maximum critical thermal limits (CTmin and CTmax) of the first larval stage of eight fiddler crab species to assess whether temperature delimits their distributional ranges. We found a clinal decrease in mean SST of 0.28 °C per latitudinal degree along the distribution of fiddler crabs in South America. Cold tolerance differed among the larvae of fiddler crab species, which corresponds to the latitudinal temperature gradient observed in their poleward range limits. Thus, our results suggest that cold water temperature can define the poleward range limits of South American fiddler crabs. The CTmax cannot explain the northern poleward range limits of the fiddler crabs. Fiddler crabs larvae showed a similar tolerance to high temperatures (mean 40.5 °C) regardless of species (except Leptuca uruguayensis) and these are higher than environmental temperatures observed in South America. We also observed an increase in mean SST of 0.9 °C in the last 37 years. This increase in water temperature may explain the recent poleward range expansion of one South American fiddler crab species, Leptuca cumulanta. Therefore, we showed that differential thermal responses at the early larval stage have consequences on the geographic range limits of the fiddler crab species. Our findings allow us to hypothesize that fiddler crabs’ poleward range limits may expand to higher latitudes in the future due to global warming.

Genomic insights into molecular adaptation to intertidal environments in the mangrove Aegiceras corniculatum.

Mangroves have colonised extreme intertidal environments characterised by high salinity, hypoxia and other abiotic stresses. Aegiceras corniculatum, a pioneer mangrove species that has evolved two specialised adaptive traits (salt secretion and crypto-vivipary) is an attractive ecological model to investigate molecular mechanisms underlying adaptation to intertidal environments. We assembled de novo a high-quality reference genome of A. corniculatum and performed comparative genomic and transcriptomic analyses to investigate molecular mechanisms underlying adaptation to intertidal environments. We provide evidence that A. corniculatum experienced a whole-genome duplication (WGD) event c. 35 Ma. We infer that maintenance of cellular environmental homeostasis is an important adaptive process in A. corniculatum. The 14-3-3 and H+ -ATPase protein-coding genes, essential for the salt homeostasis, were preferentially retained after the recent WGD event. Using comparative transcriptomics, we show that genes upregulated under high-salt conditions are involved in salt transport and ROS scavenging. We also found that all homologues of DELAY OF GERMINATION1 (DOG1) had lost their heme-binding ability in A. corniculatum, and that this may contribute to crypto-vivipary. Our study provides insight into the genomic correlates of phenotypic adaptation to intertidal environments. This could contribute not only within the genomics community, but also to the field of plant evolution.

A taxonomist‘s nightmare – Cryptic diversity in Caribbean intertidal arthropods (Arachnida, Acari, Oribatida)

There has been a long controversy about what defines a species and how to delimitate them which resulted in the existence of more than two dozen different species concepts. Recent research on so-called “cryptic species” heated up this debate as some scientists argue that these cryptic species are only a result of incompatible species concepts. While this may be true, we should keep in mind that all concepts are nothing more than human constructs and that the phenomenon of high phenotypic similarity despite reproductive isolation is real. To investigate and understand this phenomenon it is important to classify and name cryptic species as it allows to communicate them with other fields of science that use Linnaean binomials. To provide a common framework for the description of cryptic species, we propose a possible protocol of how to formally name and describe these taxa in practice. The most important point of this protocol is to explain which species concept was used to delimitate the cryptic taxon. As a model, we present the case of the allegedly widespread Caribbean intertidal mite Thalassozetes barbara, which in fact consists of seven phenotypically very similar but genetically distinct species. All species are island or short-range endemics with poor dispersal abilities that have evolved in geographic isolation. Stabilizing selection caused by the extreme conditions of the intertidal environment is suggested to be responsible for the morphological stasis of this cryptic species complex.

Holocene environmental change on the Atlantic coast of NW Iberia as inferred from the Ponzos wetland sequence

The intertidal environment of the Ponzos beach (NW Iberian Peninsula) hosts a sedimentary sequence (including large wood fragments) deposited during the first half of the Holocene in a hygrophilous continental wetland. Pollen and macrofossil data alongside radiocarbon dating allow reconstruction of the changes that occurred during the Early and Middle Holocene in the landscape of the NW Iberia coastal lowlands, as well as the local wetland plant communities, in response to the climate variations and the eustatic sea‐level oscillations. The sequence represents the evolution of a coastal wetland from its initial phases as a hygrophilous wetland towards the subsequent installation of a freshwater lagoon. Pollen data show the dominant role of Atlantic (mainly deciduous) woody taxa, the scarcity of conifers and the lack of Mediterranean elements in the coastal landscapes around the Ponzos site. The presence and abundance of some taxa such as deciduous Quercus, Castanea, Fagus, Tilia and Ulmus during the Early Holocene provides further support for the occurrence of glacial refuges in the Cantabrian‐Atlantic area during the Last Glaciation. The diverse vegetation that characterizes the modern landscapes in this territory established later, spreading from these glacial reservoirs of biodiversity. In this sense, the notable and early presence of Fagus at the beginning of the Holocene, a tree also previously recorded during several phases of the Last Glacial Cycle on the NW Iberia coasts, is noteworthy. In addition, during the Early and Middle Holocene are recorded other trees that are currently extirpated as natural taxa in the area, such as Pinus, Tilia and Carpinus.

Redox metabolism in mussels (Brachidontes solisianus) under the influence of tides in a rocky beach in Southern Brazil

Aquatic invertebrates use antioxidant systems to endure intertidal environments, where temperature, oxygen availability and radiation incidence vary greatly. The upregulation of antioxidants during oxygen-limiting conditions, such as intertidal aerial exposure (AE), is known as preparation for oxidative stress (POS). Preparation for oxidative stress has been commonly reported for animals exposed to hypoxia in the lab, but few studies have investigated it under ecologically relevant natural settings. Here, we studied metabolic enzymes, antioxidants, and oxidative stress markers in Brachidontes solisianus mussels exposed to a natural tidal cycle in a rocky beach in Southern Brazil. Animals were collected at 6 time-points throughout the tidal cycle: after 2 h of AE; then after 1 h, 3 h, and 7 h of immersion; followed by 0.5 h and 4 h of AE. The activities of malate dehydrogenase, isocitrate dehydrogenase, and pyruvate kinase were unaffected by aerial exposure. Similarly, the acitivities of enzymes of the antioxidant system, catalase, glutathione transferase, glutathione reductase, and glucose 6-phosphate dehydrogenase did not change significantly throughout the tidal cycle. In contrast, total and reduced glutathione levels significantly increased at 4 h AE by 47% and 64%, respectively, compared with those in submerged mussels (1 h, 3 h, and 7 h immersion groups combined). Lipid peroxidation and carbonyl protein levels significantly increased after 4 h of AE compared with those in mussels underwater for 7 h. Our results indicate the occurrence of POS in B. solisianus mussels exposed to air under natural conditions during tidal cycles.

Ocean Acidification Amplifies the Olfactory Response to 2-Phenylethylamine: Altered Cue Reception as a Mechanistic Pathway?

With carbon dioxide (CO2) levels rising dramatically, climate change threatens marine environments. Due to increasing CO2 concentrations in the ocean, pH levels are expected to drop by 0.4 units by the end of the century. There is an urgent need to understand the impact of ocean acidification on chemical-ecological processes. To date, the extent and mechanisms by which the decreasing ocean pH influences chemical communication are unclear. Combining behaviour assays with computational chemistry, we explore the function of the predator related cue 2-phenylethylamine (PEA) for hermit crabs (Pagurus bernhardus) in current and end-of-the-century oceanic pH. Living in intertidal environments, hermit crabs face large pH fluctuations in their current habitat in addition to climate-change related ocean acidification. We demonstrate that the dietary predator cue PEA for mammals and sea lampreys is an attractant for hermit crabs, with the potency of the cue increasing with decreasing pH levels. In order to explain this increased potency, we assess changes to PEA’s conformational and charge-related properties as one potential mechanistic pathway. Using quantum chemical calculations validated by NMR spectroscopy, we characterise the different protonation states of PEA in water. We show how protonation of PEA could affect receptor-ligand binding, using a possible model receptor for PEA (human TAAR1). Investigating potential mechanisms of pH-dependent effects on olfactory perception of PEA and the respective behavioural response, our study advances the understanding of how ocean acidification interferes with the sense of smell and thereby might impact essential ecological interactions in marine ecosystems.