Intertidal Environments Research Articles

Mangrove species maintains constant nutrient resorption efficiency under eutrophic conditions

AbstractMangrove species have developed nutrient conservation mechanisms to adapt to oligotrophic intertidal environments. However, nutrient enrichment occurs worldwide, particularly in estuarine and coastal regions. Mangrove species may change their adaptive strategies if nutrient availability increases substantially. To understand how nutrient resorption (a major nutrient conservation strategy) responds to nutrient enrichment, a common mangrove species in China, Aegiceras corniculatum (black mangrove), was selected, and saplings were cultivated in nutrient-enriched soils. After one year, neither N nor P resorption efficiency showed significant variations with nutrient availability and there was no difference between N and P resorption efficiency. Overall, nutrient resorption efficiency of A. corniculatum remained at ∼40%, lower than the global average levels of evergreen plants (∼50%), indicating incomplete resorption of nutrients. Incomplete resorption was also evidenced by the nutrient concentrations, resorption proficiency and N: P ratio of plant leaves. Collectively, these results indicate that black mangrove can maintain constant nutrient resorption efficiency under eutrophic conditions.

Species composition of foraging birds in association with benthic fauna in four intertidal habitats of the Wadden Sea

About 10 to 12 million birds per year use the intertidal flats of the Wadden Sea in north-eastern Europe as a food source during their moulting, wintering or breeding season and as a stop-over site along the East Atlantic Flyway. The tidal flats are inhabited by a highly productive benthic fauna representing an important link between the marine microflora and -fauna and higher trophic levels such as birds. Due to differences in the food preference, bird species might distribute on different habitat types formed in the Wadden Sea. In the present study, the diversity of foraging birds was studied in four intertidal habitats (seagrass meadow, sand flat, mud flat, Elbe tidal flat) and their macrozoobenthic food sources were analysed. Samples of benthic macrofauna were taken seasonally while foraging birds were counted monthly at the studied sites.Results revealed different benthic communities in each of the studied sites with large variation in abundance and diversity of foraging birds. Peak numbers of birds during spring and autumn reflected migration through the region. While the majority of bird species shows an opportunistic habitat choice, some species (e.g. Bucephala clangula, Philomachus pugnax) were observed foraging at one site only. However, results revealed only a weak link between bird assemblages and benthic communities within the tidal flats. As indicated by clear relationships between bird species abundance and tidal stage, avian distribution patterns are probably also strongly dependent on abiotic factors such as distance to roosting sites, inundation time and anthropogenic influences. Therefore, it is not sufficient to study the distribution of favoured prey items in the tidal flats alone but additional information needs to be taken into account to understand the complex distribution patterns of birds in the intertidal environment.

Wave height vs. elevation effect on macroalgal dominated shores: an intercommunity study

Sheltered intertidal environments are characterized by highly diversified macroalgal communities which vary over short spatial scales depending on various environmental pressures. In this study, relations between wave heights and vertical elevation were analyzed in order to identify the respective roles of these factors on the structure of macroalgal communities. We measured both wave heights and elevation on six macroalgal communities of three Northeast Atlantic rocky shores. The effects of these structuring factors on seaweed communities were seasonally evaluated in early summer and late autumn using pressure recorders and digital terrain model data. Results reveal that waves were higher during late autumn than in early summer. At shore-scale, elevation was the main factor determining both the structure and the species composition of the macroalgal communities (13.7% of total variance explained), while hydrodynamics played a lower, although significant role (< 1% of the total variance). Based on the cover of canopy-forming species, intertidal macroalgal communities can be grouped into three clusters, corresponding to three height levels on the shore (higher, middle, and lower shore). Canopy composition and structure were mainly explained by the effect of elevation (45%) in the higher level of the shore and by both elevation (42%) and wave height (2.5%) in the middle shore. On the contrary, low shore communities were affected by a more balanced effect of elevation (explaining 14% of the total variance and wave height associated with site effect explaining 15% of such effect). This study gave new insights of how hydrodynamics and elevation condition the extension of macroalgal communities.

PRESENT CONDITION OF MANGROVE ENVIRONMENT AND COMMUNITY STRUCTURE IN TOMINI GULF, SULAWESI, INDONESIA

The mangroves in Tomini Gulf have been exploited for chiefly conversion of mangrove areas into shrimp cultivation and extraction of mangrove wood for various purposes. In this study, interpretation to available map and satellite images and ground check were conducted to describe intertidal environment conditions and general processes of coastal dynamic. At local scale, physiographic factors were used to classify mangrove sub-habitats. A total of 159 sample points were selected to observe structure of vegetation, and the revised two ways classification of Specht was applied to classify structural classification of vegetation. The criterion of mangrove disturbance was developed to classify disturbance level. Interview and field check were conducted to assess the successfulness of implemented rehabilitation programs. Results indicated that there were obvious changes in mangrove vegetation over much the intertidal environments, and these might influence the future development and regeneration of the mangroves. While most rehabilitation programs were unsuccessful, mangrove exploitations still continued. If a sustainable management plan is not developed, the degradation will continue and spread, and the mangrove will lose its ecological functions.

A comparative study of the 2013 typhoon Haiyan overwash sediments from a coastal cave and beach system at Salcedo, Eastern Samar, central Philippines

Typhoon Haiyan crossed the central Philippines on 8 November 2013 and generated storm surge up to 7 m with runup reaching 12 m which deposited overwash sediments inland in many different locations and environments. Collectively, these overwash sediments serve as key modern analogs to compare with geological records of storm events in the region. To date, comparatively few studies have been conducted on sandy storm deposits in carbonate coasts with none to date on storm sediments in coastal caves. Here, we report the grain size and microfossil assemblages of the Typhoon Haiyan overwash sediments from a coastal cave and carbonate beach system in Eastern Samar, central Philippines and infer the source of the Haiyan overwash sediments. We show that overwash sediments inside and immediately outside the cave (beach system) are similar but they can be discriminated from the underlying pre-Haiyan soil through field evidence, grain size, organic matter, and microfossil content. To investigate the source of both the cave and non-cave overwash sediments and in the absence of pre-storm beach sediment samples, we collected post-Haiyan beach sediments in February 2018 when the beach has indicated recovery to its pre-storm condition. We assume that these post-Haiyan beach sediments are representative of pre-storm sediments. The underlying pre-Haiyan soil comprises poorly-sorted, coarse to very coarse sands with higher organic matter content, and a lower microfossil concentration. Also, the pre-Haiyan soil contains foraminifera species similar to those identified in the Haiyan overwash sediments, but rarely containing subtidal foraminifera species. In comparison, the Haiyan overwash sediments share similar attributes with the post-Haiyan coastal sediments, consisting of moderately-sorted gravelly sands predominantly carbonate grains with low organic matter content. The Typhoon Haiyan overwash sediments contain foraminifera species dominated by Amphistegina radiata, Baculogypsina sphaerulata, Calcarina gaudichaudii, Calcarina splengeri suggesting an intertidal environment. Although, lower abundances of benthic species Peneroplis planatus and Quinqueloculina parkeri imply contributions from the subtidal environment. Notably, the Haiyan overwash sediments dominantly contain intertidal foraminifera species with abraded tests similar to foraminifera found in the post-Haiyan beach sediments. The similarity of foraminiferal assemblage and taphonomic condition strongly indicates that the overwash sediments found on the coastal cave were most likely sourced from the beach and reef flat. Our results show overwash sediments in coastal caves are indistinct from those in the nearby beach system indicating the potential of coastal caves to harbor well preserved archives of paleo storm deposits.

An uncommon intertidal record of Halophila decipiens Ostenfeld in the vicinity of mangroves

In this paper, we report the occurrence of Halophila decipiens Ostenfeld found growing in an intertidal environment. At the study site of Sungai Bahan estuary located along the Straits of Johor (Malaysia), the seagrass grew sparsely in the lower littoral zone of the mangrove coastline. Forming discontinuous patches, the seagrass was fully exposed on the mudflats during the lowest spring tides. Predictable times of exposure during low tides coincide with specific diel periods of lower light availability, which enabled avoidance of exposure to excessive irradiance. Hand-collected specimens of H. decipiens were initially defined through morphological and inflorescence characteristics. The identity of the species was confirmed based on analysis of the internal transcribed spacer sequence of its ribosomal DNA. Further analysis of this sequence demonstrated that among global populations, H. decipiens formed a sub-clade with populations from Malaysia and Australia. The colonisation by H. decipiens at the study site demonstrates its opportunistic acclimation to local environmental conditions. This discovery opens opportunities to further explore its ecology, as an instance of a less commonly studied seagrass within the region and to further investigate the unusual intertidal niche associated with the species.

Hypoxia in mangroves: occurrence and impact on valuable tropical fish habitat

Abstract. Intertidal mangrove forests are harsh environments that can naturally experience hypoxia in association with low tide. However, we know relatively little about dissolved oxygen (DO) fluctuations and DO-induced responses by fish, although DO is a fundamental water quality parameter. This study examines DO as a potential factor regulating the utilisation of intertidal mangrove forests by fish and consequently their widely recognised feeding, refuge and nursery values. We deployed underwater video cameras, coupled with DO and depth loggers, in a mangrove forest to record changes in fish assemblages in response to tidal variations in DO and other associated environmental parameters. Our results indicate that DO underwent extreme tidal fluctuations, reaching levels as low as 14 % saturation. As DO was identified as a significant factor for explaining variability in fish assemblage composition, we further investigated fish responses to DO fluctuations. Higher taxonomic richness and frequencies of occurrence were observed once DO reached 70 %–80 % saturation. More detailed examination revealed species-specific responses. Three distinct patterns of mangrove utilisation in response to DO were identified, driven by apparent taxa's behavioural DO avoidance thresholds. Most taxa did not display any behavioural avoidance, including presence at the lowest DO levels, while other taxa were not observed either below 50 %–60 % saturation or below 70 %–80 % saturation. This implies that tidal migrations, often observed in intertidal environments, could be the result of differential DO tolerances and are not simply initiated by changes in water depth. Taxa remaining in the mangrove forest even at low DO were on average more frequently observed than the other taxa and were mostly species commonly associated with mangrove habitats. This suggests that being adapted to withstand low DO might be an important condition for using mangrove habitats extensively. The need of being tolerant to low DO could constrain fish utilisation and explain the relatively low species richness often observed in other intertidal mangrove forests.

An Assessment of the Tea Bag Index Method as a Proxy for Organic Matter Decomposition in Intertidal Environments

AbstractIntertidal wetlands capture and store carbon (C) for long periods of time, helping to reduce the concentration of CO2 in the atmosphere. Yet the processes, which govern the decomposition and subsequent long‐term storage of organic matter (OM) and C in these habitats, remain poorly understood. The Tea Bag Index (TBI) uses a standardized OM (green and Rooibos tea) and has the potential to shed light on OM decomposition across habitats, including saltmarshes. Here, we apply the TBI method at two saltmarshes within the same estuary with the aim of (i) reducing the influence of climatic variables and (ii) determining the role of the environment, including the soil characteristics, in the decomposition of OM. We extended the standard (3 months) incubation period over a full year in order to investigate the longer‐term decomposition processes at each site. The initial results partially support previous studies that the early stages of decomposition (leaching of the water‐soluble fraction) is governed by climatic conditions, but may be further enhanced by tidal flushing in saltmarshes. By extending the incubation period, we observed the initiation of midstage OM decomposition (cellulose degradation) upon which the soil characteristics appear to be the dominant control. These results highlight the importance of long‐term TBI incubations to understand early‐stage OM decomposition. The relationship between tea mass (OM) loss and C loss in these intertidal environments is not straightforward, and we would caution the use of the TBI as a direct universal proxy for soil C degradation in such intertidal wetlands.

The Caribbean enigma: the presence of unusual cryptic diversity in intertidal mites (Arachnida, Acari, Oribatida)

The definition, as well as the existence of cryptic species, is still a subject of controversial debates. Some scientists claim that cryptic diversity is a real phenomenon that should be extensively studied while others argue that cryptic species do not exist as they are nothing more than an incompatibility of species concepts. We investigated the enigmatic case of two widely distributed Caribbean intertidal oribatid mites, Carinozetes bermudensis and Carinozetes mangrovi, consisting of five distinct genetic lineages. Morphological features allowing to clearly distinguish between these lineages are absent, and despite certain congruence with genetic data, comprehensive morphometric analyses also do not show clear separation. Species delimitation analyses based on COI sequence data, on the other hand, suggest five distinct genetic species. Despite the lack of diagnostic characters for these suggested species, the lineages can be classified at least into two morphological groups, the bermudensis and the mangrovi group which can only be distinguished by the arrangement of cuticular ventral carinae. Specimens within a group show nearly identical phenotypes, impeding morphological identification and hence rendering the found diversity cryptic. Stabilizing selection caused by the extreme conditions of the intertidal environment is suggested to be responsible for the found morphological stasis. The genetic lineages show more or less clear geographic patterns; in C. mangrovi, there is a northern, an Antillean, and a Pacific lineage, whereas in C. bermudensis, there is a Bermudian and a Caribbean lineage. In a few places, e.g., the Bahamas and Panama, distributions may overlap. Neither the found biogeographic pattern nor the observed ecological needs could explain the reason for the genetic diversification of Caribbean Carinozetes.

Dinamismo, complejidad y especificidad de los litorales estuarinos: análisis de la dinámica litoral en Punta Atalaya, Buenos Aires, Argentina

Los litorales son espacios complejos y dinámicos, producto de la interacción entre las dinámicas naturales y las valoraciones sociales a lo largo del tiempo. Esta interacción desencadena procesos variados que confieren especificidad a sus costas. En los litorales estuarinos se forman ambientes intermareales denominados marismas, intensamente modificadas en las grandes metrópolis urbanas.La dinámica de estos ambientes ha sido extensamente estudiada en el hemisferio norte, encontrándose escasas investigaciones en el hemisferio sur. En el presente trabajo se realiza un estudio multitemporal de una marisma de formación reciente en la costa de Punta Atalaya (partido de Magdalena, Buenos Aires, Argentina), situada en el sector intermedio de la costa argentina del estuario del Río de la Plata, utilizando la línea de costa como indicador del límite exterior de este ambiente. Se partió de su identificación en fotografías aéreas e imágenes de satélites de alta resolución en el periodo 1929-2016. Mediante la utilización de un software especializado en el análisis multitemporal de cambios, inspecciones en el campo y revisión de bibliografía general y específica, se realizó una aproximación explicativa de la dinámica litoral de esta franja territorial.Se determinó que la costa de Punta Atalaya presenta una tendencia progradante en el último siglo, aunque cambios en la microescala temporal y espacial son detectados a lo largo de todo el periodo, respondiendo a dinámicas acrecionales y erosivas que derivan de la interacción de procesos biológicos, sedimentarios, meteorológicos y sociales. Cada proceso puede desencadenar múltiples respuestas y tener impactos diferenciales en tiempo y espacio. En este sentido, se cuestionan las nociones de equilibrio utilizadas en las clásicas investigaciones acerca de los balances sedimentarios costeros. El sector correspondiente al área de estudio no posee categoría de área protegida, por lo que su valoración ambiental en este sentido debe contemplar la dinámica del mismo.

Variation in microplastics composition at small spatial and temporal scales in a tidal flat of the Yangtze Estuary, China

Microplastics are small, degrade slowly, and easily persist in the water column because they are close to neutrally buoyant. Understanding the distribution of microplastics is fundamental to evaluating the ecological risks that they cause and to identifying ways to control microplastics pollution. Most of the existing research on the distribution of microplastics in the coastal zone has focused on large spatial and temporal scales. To build on past work, we investigated variation in microplastics in a tidal flat of the Yangtze Estuary on small spatial (sediment depth, mudflat vs. vegetation zone) and temporal (fortnightly and semidiurnal) scales. Microplastics were more abundant in surface (0–2 cm) sediments during neap versus spring tide cycles, likely indicating increased deposition during periods with calm waters and increased suspension when water was more turbulent, but did not vary at greater depths in the sediment. Individual microplastics particles were also larger during neap versus spring tide periods. In contrast to the variation between spring and neap tide periods, we found no variation in the abundance of microplastics on the semidiurnal scale. Microplastics were also more abundant in the transect in the vegetation than at slightly lower elevations in the adjacent mudflat. Across all samples, the abundance of microplastics was negatively correlated with the strength of hydrological processes such as submergence time and flow velocity. Our results showed that sampling of microplastics in the intertidal environment needs to consider variation among spring and neap tide cycles, and also among different intertidal habitats that may differ only slightly in elevation. We encourage coupling sampling with direct measures of hydrological processes so that variation in microplastics abundance and size can be rigorously linked to hydrological processes.

Impacts of ocean acidification on intertidal benthic foraminiferal growth and calcification.

Foraminifera are expected to be particularly susceptible to future changes in ocean carbonate chemistry as a function of increased atmospheric CO2. Studies in an experimental recirculating seawater system were performed with a dominant benthic foraminiferal species collected from intertidal mudflats. We investigated the experimental impacts of ocean acidification on survival, growth/calcification, morphology and the biometric features of a calcareous species Elphidium williamsoni. Foraminifera were exposed for 6 weeks to four different pH treatments that replicated future scenarios of a high CO2 atmosphere resulting in lower seawater pH. Results revealed that declining seawater pH caused a decline in foraminiferal survival rate and growth/calcification (mainly through test weight reduction). Scanning electron microscopy image analysis of live specimens at the end of the experimental period show changes in foraminiferal morphology with clear signs of corrosion and cracking on the test surface, septal bridges, sutures and feeding structures of specimens exposed to the lowest pH conditions. These findings suggest that the morphological changes observed in shell feeding structures may serve to alter: (1) foraminiferal feeding efficiency and their long-term ecological competitiveness, (2) the energy transferred within the benthic food web with a subsequent shift in benthic community structures and (3) carbon cycling and total CaCO3 production, both highly significant processes in coastal waters. These experimental results open-up the possibility of modelling future impacts of ocean acidification on both calcification and dissolution in benthic foraminifera within mid-latitude intertidal environments, with potential implications for understanding the changing marine carbon cycle.

Reconstruction of nearshore chemical conditions in the Mesoproterozoic: evidence from red and grey beds of the Yangzhuang formation, North China Craton

ABSTRACT Mesoproterozoic red beds near ancient coasts have not aroused extensive interest. A new geochemical study of the alternating red and grey dolostones from the Yangzhuang Formation provides a better understanding of the redox conditions of nearshore sedimentary environments. In this contribution, whole-rock samples are characterized by positive correlations of rare earth elements (REE) vs. Th and FeT vs. Th and flat-type REE distribution patterns, indicating massive terrigenous input, which is considered to be inherited from felsic rocks. Relatively high (Femag+Feox)/FeT and Fe3+/Fe2+ ratios in red beds indicate more oxidized conditions in supratidal environments compared with the lower oxygen contents in intertidal environments. Under these two distinct chemical sedimentary conditions, acetic acid-leached red and grey samples both have HREE-depleted distributions, suggesting significant freshwater invasion. Moreover, limited terrigenous redox-sensitive elements (RSEs) can reach the coast where the red beds are deposited, whereas relatively high RSE enrichment factors originating from shallow oceans are recorded in grey beds. In the Mesoproterozoic, limited oxidative weathering, shallow seawater desalination, and low organic production occurred near the coast. Meanwhile, a prolonged period of low Mo and U availability preserved in carbonate minerals confirmed that marine oxygen levels failed to satisfy the deposition of offshore red beds. During the regression, potentially exposed sediments connected to atmospheric oxygen guaranteed the oxidation of iron and the formation of red beds, and these events were coupled with negative δ13Ccarb shifts in the Yanliao rift zone.

Earliest Carboniferous stromatolites from the Qianheishan Formation, Dashuigou section, northwestern China: Implications for microbial proliferation after the end‐Devonian mass extinction

Earliest Carboniferous stromatolites were found in the Qianheishan (QHS) Formation in the Dashuigou section, Gansu Province, northwestern China. These stromatolites are exposed in a conglomerate‐dominated succession of about 22.5 m in thickness, which can be traced laterally for more than 200 m in outcrop. They consist mainly of micrite, peloids, oncoids, silt‐sized quartz grains, and sparry calcite with rare fine to coarse quartz grains and bioclasts. The occurrence of marine fossils (e.g., bryozoans) and fenestral structures in the stromatolites suggests that they developed in intertidal environments. Three types of stromatolite laminae were distinguished including micritic laminae, grain‐dominated mixed laminae, and micrite‐dominated mixed laminae. These laminae are separated by thin micritic crusts and form two lamination styles of repetitive lamination and alternating lamination. The development of grain‐rich and micrite‐rich laminae in the stromatolites implies that they were formed by the combination of microbial baffling, binding, and calcification. Facies analysis suggests that growth and demise of the stromatolites were controlled by relative sea‐level changes. They grew during a continuous relative sea‐level rise, indicated by variations in their thickness and morphology. Stromatolites change from thin‐bedded laminar forms in the lower part of the studied interval to medium‐bedded wavy‐laminar forms and thick‐bedded domal forms in the middle and upper parts, respectively. Their demise was triggered by dramatic relative sea‐level fall, evidenced from the sandstone facies overlying the stromatolite interval. The occurrence of the QHS stromatolites provides an excellent example for microbial proliferation and profound changes in the marine biosphere after the end‐Devonian Hangenberg extinction event.

Robonerite: A low-cost biomimetic temperature logger to monitor operative temperatures of a common gastropod (Nerita spp.) in tropical urban seascapes

Abstract Temperature is a major stressor in the intertidal environment. During emersion, the interaction between physicochemical factors and the external morphology of intertidal organisms results in significant differences between organismal body temperatures and ambient temperatures. Standard temperature loggers do not consider the morphology of the target species and may not serve as effective proxies for body temperatures. Methods such as thermocouples also present their own set of issues, being invasive and potentially damaging. Biomimetic temperature loggers that mimic the organisms of interest are, however, easily deployed in the field and can be used to investigate biological impacts of field temperatures. Due to their high abundance on tropical seawalls and the key ecological roles they play, nerite gastropods (Nerita spp.) were selected as the model organism for the basis of biomimetic “Robonerites”. Here, we discuss the development of Robonerites and present results from field and laboratory tests on their effectiveness and accuracy in measuring the in situ body temperatures of nerites on tropical seawalls.

Shallow-marine ironstones formed by microaerophilic iron-oxidizing bacteria in terminal Paleoproterozoic

The microbial origin of Precambrian iron formations is debated due to the lack of direct fossil evidence. In order to reveal the genesis of ironstones under low-oxygen levels, integrative studies of sedimentology, petrography, mineralogy, and geochemistry were conducted on the intertidal to shallow subtidal ooidal and stromatolitic ironstones from the terminal Paleoproterozoic Chuanlinggou Formation (ca. 1.65–1.64 Ga) of North China, using microscopy, SEM, EDS, ICP-OES, ICP-MS and MC-ICP-MS techniques. Mineralogical study shows that the Fe-rich mineral is predominantly hematite that resulted from dehydration of amorphous Fe-oxyhydroxide during diagenesis. Petrographic observation indicates that the iron was oxidized and precipitated from seawater rather than sourced from terrestrial detritus. Basinward increases of the ironstone abundance, Eu anomalies (from 1.39 to 1.56) and δ56Fe values of the ironstones (from +0.5‰ to +1.0‰) suggest that the iron was mainly sourced from seafloor hydrothermal fluids, and partially oxidized and precipitated in shallow subtidal to intertidal environments. The common existence of Fe-oxide coated sheaths, spiral stalks, residual extracellular polymer substances (EPS) and other biogenic fabrics indicates that microaerophilic iron-oxidizing bacteria (FeOB) may have played an important role in precipitating the Chuanlinggou ironstones. The extremely low oxygen concentrations implied by the proliferation of microaerophilic FeOB in the shallow waters, the weak positive Ce anomalies (0.94–1.12) and low Mn concentrations in the ironstones are broadly consistent with the previous result of a Cr isotope study. Thus the establishment of a microaerophilic FeOB genetic model for the widespread Chuanlinggou ironstones in North China provides new insight into the origin of Precambrian iron formations and the redox evolution of ocean-atmosphere systems during the “Boring Billion”.

Transformation of arsenic lipids in decomposing Ecklonia radiata

To investigate the release and degradation of arsenolipids present in the marine brown macroalga Ecklonia radiata, tissues were collected in various stages of decomposition from intertidal environments, while tissues were also decomposed in laboratory-based microcosms prepared using combinations of autoclaved and natural (non-autoclaved) seawater and sand. Field collected macroalgae samples contained 20–120 μg g−1 total As of which 1–10% were arsenolipids comprising mainly an arsenic hydrocarbon (AsHC; 3–13% of total arsenolipids) and four di-acyl arsenic phospholipids (AsPLs; 86–95%). Additionally, a mono-acyl AsPL was found in all water-column decomposing samples. Arsenolipid concentrations in live tissues were similar to those in tissues decomposing in the water-column (1.3–2.9 μg g−1 dry mass), which were both up to four times higher than those in decomposing tissues collected from intertidal environments (0.7–1.3 μg g−1 dry mass). In the microcosm experiments, the arsenolipid content of E. radiata decreased substantially as decomposition proceeded. In the majority of microcosms, more than 75% of the arsenolipids present initially disappeared within 5 days with only the AsHC persisting until day 60 (the length of the experiment). This study demonstrates that the habitat in which decomposition occurs influences the release and degradation of arsenolipids with the greatest losses occurring when tissues decompose in intertidal environments. Microbial diversity, biomass, and overall activity are thus likely to play important roles in the persistence of arsenolipids in decomposing algae.

Interplay between biotic and environmental conditions in pre-salt Messinian microbialites of the western Mediterranean (Upper Miocene, Mallorca, Spain)

Microbial buildups that predate the Messinian salinity crisis, including one of the few Phanerozoic examples of ‘giant’ microbialites, crop out upon the island of Mallorca (W Mediterranean). Sedimentological and geochemical data from microbialites and associated deposits, both essentially dolomitic, indicate that they grew in shallow marine conditions but relatively restricted from the open marine realm. Two microbialite-bearing sequences occur, both consisting of subtidal to supratidal deposits. Periods of restriction led to evaporative and hypersaline conditions that favored the development of microbialites and local precipitation of sulfates. By contrast, ephemeral periods marked by more open conditions were devoid of microbialites and allowed production of bioclastic deposits. Microbialites range from decameter- to decimeter-scale, reflecting differences in accommodation space. Despite contrasting sizes, all microbialite bodies record similar mesostructure evolution through time, from thrombolites to stromatolites, with a sharp transition between these endmembers. The change from subtidal to shallower, more restricted and saline intertidal environments triggered biotic substitution of thrombolite-generating microbial communities to stromatolite-generating ones. Furthermore, a wide variety of microstructures, from agglutinated to micritic with fossilized microbes, indicates that two main accretion processes occurred: microbially-influenced primary dolomite precipitation and grain trapping and binding, which were controlled by the interaction between microbes and changes in environmental conditions (e.g. grain supply, hydrodynamics and hydrochemistry). Therefore, the diversity of macro-, meso- and microstructures of these microbialites was caused by a complex interplay between depositional, biotic and hydrological parameters, which offers useful insights for the palaeoecological interpretation of other examples, at any scale and throughout geological time.

Adaptive Evolution Patterns in the Pacific Oyster Crassostrea gigas

Estimation of adaptive evolution rates at the molecular level is important in evolutionary genomics. However, knowledge of adaptive evolutionary patterns in Mollusca is very scarce, especially for oysters. Such information would help clarify how oysters adapt to pathogen-rich and dynamically changing intertidal environments. In this study, we characterized the patterns of adaptive evolution in the Crassostrea gigas genome, using population diversity analysis and congeneric comparison. Our analysis revealed that gene expression patterns were positively associated with adaptive evolution rates, which suggested that positive selection played an important role in gene evolution. The genes with more exons and alternative splicing events had higher adaptive evolution rates. The rates of adaptive evolution in immune-related and stress-response genes were higher than those in other genes, suggesting that these groups of genes experienced strong positive selection. This study represents the first analysis of adaptive evolution rates in oysters and the first comprehensive study of a Mollusca species. These results provide a system-level investigation of association between adaptive evolution rates with some intrinsic genetic factors. They also suggest that adaptation to pathogens and environmental stressors are important forces driving the adaptive evolution of genes.

Dynamics of salt marsh margins are related to their three‐dimensional functional form

AbstractThe three‐dimensional configuration of sedimentary landforms in intertidal environments represents a major control on regional hydrodynamics. It modulates the location and magnitude of forces exerted by tidal currents and waves on the landform itself and on engineered infrastructure such as sea walls or coastal defences. Furthermore, the effect is reflexive, with the landforms representing an integrated, long‐term response to the forces exerted on them. There is a strong reciprocal linkage between form and process (morphodynamics) in the coastal zone which is significantly lagged and poorly understood in the case of cohesive, vegetated sediments in the intertidal zone. A method is presented that links the geometric properties of the tidal flat–salt marsh interface to the history and potential future evolution of that interface. A novel quantitative classification scheme that is capable of separating marsh margins based on their functional form is developed and is applied to demonstrate that relationships exist between landform configuration and morphological evolution across a regional extent. This provides evidence of a spatially variable balance between self‐organized and external controls on morphodynamic evolution and the first quantitative basis for a quick assessment procedure for likely future dynamism. © 2019 John Wiley &amp; Sons, Ltd.