Emersion Period Research Articles

Mechanisms of sedimentation in lacustrine environment of Babouri-Figuil and Mayo Oulo-Lere basins deposits (North Cameroon) during the Southern Atlantic opening: sedimentary structures and geochemistry constraints

Sedimentary structures are very useful to characterize sedimentation environments. In this study, sedimentary structures are documented in the Lower Cretaceous Babouri-Figuil and Mayo Oulo-Lere intracontinental Basins whose genesis is linked to the opening of the Southern Atlantic Ocean. Geochemical data is also presented with the aim to discriminate the paleoenvironment. Field investigations and facies analyses revealed synsedimentary and postsedimentary structures related or not to tectonic. Synsedimentary structures not affected by tectonic are lamination or bedding (rhythmic), graded bedding, cross-stratification, loads casts, channels, and ripple marks. Those affected by tectonic are convolute bedding, slump (Slump sensus stricto and olistolith). Desiccation cracks and print marks are postsedimentary structures not related to tectonic; others are stratigraphic unconformity, oblique bedding, clastic injection, and volcanic veins. The bottom of the sequence in the two basins is fluvio-lacustrine deposits with oblique stratification and global positive graded bedding; sometimes there is alternation of positive and negative graded beddings related to progressive variation of energy of sedimentation from high to low and low to high. The intermediate level is lacustrine dominated by lamination or bedding that characterizes a calm sedimentation environment marked by regular seasonal fluctuation. The ripple marks, desiccation cracks, and dinosaur footprints indicate the emersion period, and their fossilization indicates slow phases of sedimentation. Channels and load casts correspond to a rapid sedimentation phase. Seismic shocks at time break the fragile stability of deposited materials causing gravitational flows of the sublacustrine avalanche type and give olistolith and convolute bedding to slumps. The clastic or chemical injections and volcanic veins are related to brittle tectonic that affects consolidated deposits. From the geochemical data, the high accumulation of LREE (average: 142.93 ppm) over HREE (average: 13.10 ppm); La/La* generally 2) and the slight to very slight negative Ce/Ce* (0.87–0.99) suggest the nonmarine deposition, and the Y/Ho ratios (< 45) and ratios indicate river condition or transportation. The Sr/Ba ratios, ranging from 0.55 to 6.41, suggest a freshwater environment with fluctuant salinity and sometimes hypersaline (Hypersaline Lake). Thus the synsedimentary structures were essentially formed in lacustrine milieu, and some structures such as graded bedding and cross-stratification affecting the basal deposit indicate a fluviatile to fluvio-lacustrine environment.

Immersion can trigger detachment of juvenile mussels

The nursery stages of mussel aquaculture are highly inefficient with most juvenile mussels being lost within the first few months after seeding, although the precise timing of losses is largely unknown. One possibility is that many juveniles are lost at seeding because they are either impaired or killed by the process of transporting juveniles from collection sites to coastal nursery farms, or because they detach and move away from aquaculture substrata at, or soon after deployment, via secondary settlement behaviour. Three laboratory experiments were used to assess detachment of juvenile mussels from aquaculture substrates following periods of emersion for two batches of wild juveniles undergoing actual transport and one batch of hatchery-reared juveniles during simulated transport periods. The percentage of juveniles retained on their substrates (i.e., not detaching) after a two-minute immersion in seawater and the percentage of dead juveniles were quantified, as was the size of the mussels that were retained on, or detached from, their substrates. Detachment occurred in all experiments (16.9–53.8%) and was greater when the average size of the mussels was small (0.75 ± 0.01 mm). Across all the experiments, larger juvenile mussels were retained in greater numbers with mussels less than 1.75 mm in shell length having a greater propensity to detach from their substrates upon immersion. Very few mussels were dead at the end of the experiments and large proportions of mussels reattached in the aquaria, when given the opportunity. Together, the results of this study indicate that detachment of juvenile mussels is size-specific and driven by secondary settlement behaviour occurring upon or soon after (< 2 mins) immersion. New nursery techniques are required to grow small juvenile mussels to a size beyond which their migratory secondary settlement behaviour is reduced, so that they are less likely to detach upon or soon after immersion while seeding out to farm sites.

Karst feature in Mishrif Reservoir and effect on drilling and production in Zubair oil field, Southern Iraq

Karst features in the upper part of Mishrif carbonate reservoir can commonly create substantial vugs, pores and fissures and, thus, increasing the porosity and enhancing reservoir connectivity and permeability, this features were formed normally as a result of the carbonate rocks dissolution under the action of meteoric waters during very long periods of emersion spanning from Late Cenomanian to Turonian (about 4.5 Million years). This study deals with the presence of the karst features in Zubair oil field, southern Iraq, where Karst features were observed in the center and northern parts of the field close to the top of Mishrif Formation in most of the cored wells. Characterization of that feature can be achieved from static data at wellbore scale from core, and logs (conventional and non-conventional), and dynamic data such as mud losses, well tests combined with production logs (PLT) in addition to Seismic data. Beside the positive and economic effect of Karst, there is negative effect which includes causing mud losses during drilling in Mishrif Formation because of low reservoir pore pressure, Therefore, acid soluble cement plugs were used to heal that losses to continue drilling.

Effects of seawater acclimation on two Na+/K+-ATPase α-subunit isoforms in the gills of the marble goby, Oxyeleotris marmorata

The marble goby, Oxyeleotris marmorata, is a freshwater teleost, but can acclimate progressively to survive in seawater (salinity 30). As an obligatory air-breather, it can also survive long periods of emersion. Two isoforms of Na+/K+-ATPase (nka) α-subunit, nkaα1 and nkaα3, but not nkaα2, had been cloned from the gills of O. marmorata. The cDNA sequence of nkaα1 consisted of 3069 nucleotides, coding for 1023 amino acids (112.5 kDa), whereas nkaα3 consisted of 2976 nucleotides, coding for 992 amino acids (109.5 kDa). As only one form of branchial Nkaα1 was identified using molecular cloning in this study, O. marmorata lacks specific freshwater- and seawater-type Nkaα isoforms as demonstrated by some other euryhaline fish species. The nkaα1 transcript level was about 2.5-fold higher than that of nkaα3 in the gills of freshwater O. marmorata. During exposure to seawater, the branchial transcript level of nkaα1 increased significantly on day 1 (~3.3-fold) and day 6 (~2.6-fold). By contrast, the branchial transcript level of nkaα3 increased significantly on day 1 (~2.6-fold), but not on day 6, of seawater exposure. Six days of exposure to seawater also led to significant increases in protein abundances of Nkaα1 (~6.9-fold) and Nkaα3 (~2.8-fold) in the gills of O. marmorata. Hence, the mRNA and protein expressions of both nkaα1/Nkaα1 and nkaα3/Nkaα3 were up-regulated in O. marmorata during seawater acclimation. This could explain why Vmax increases but Km for Na+ and K+ remain unchanged in Nka extracted from the gills of O. marmorata acclimated to seawater as reported previously.

Physiological response of the giant acorn barnacle, Balanus nubilus, to oxygen-limiting environments

Sessile invertebrates in the nearshore coastal and rocky intertidal habitats can experience oxygen limitation during low tide air exposure and environmental hypoxia events. For some organisms, unique morphological characteristics may make these events especially challenging. The giant acorn barnacle, Balanus nubilus, has the largest muscle fibers in the animal kingdom (diameters can exceed 3 mm in adults). At these extreme sizes, muscle cells may already be at the brink of insufficient oxygen delivery owing to low SA:V ratios and long intracellular diffusion distances. We are interested in characterizing the internal oxygen dynamics of B. nubilus during air exposure and seawater anoxia so that we can better understand how they maintain function of their giant muscle fibers during environmentally-induced oxygen limitation. To this end, we examined the following: 1) hemolymph pO2, pCO2, pH and ion (Na+, Cl−, K+, Ca2+) concentrations across 9 h exposure to air emersion, anoxic immersion and normoxic immersion (control), 2) oxygen consumption rates (MO2) of barnacles held in water and air for 6 h (at 10, 15 and 20 °C), and 3) respiratory behaviors (e.g., % time operculum open or cirri extended, cirral beat frequency) of barnacles during acute (6 h) exposure to emersion, anoxic immersion and normoxic immersion. Our data revealed that hemolymph pO2 declined significantly (by 3 h) in the anoxic barnacles, whereas the air-exposed barnacles maintained hemolymph oxygen levels that were intermediate to the control and anoxia barnacles. We also found that MO2 values for B. nubilus were very similar in seawater and air at a common temperature. These results suggest that B. nubilus can effectively acquire oxygen and support aerobic metabolism while in the air. This assumption was corroborated by our behavioral data, which revealed that air exposed (and anoxic) barnacles spent significantly more time engaged in cirral beating than control barnacles. Such a behavioral preference should enhance oxygen delivery to the internal respiratory surfaces inside the shell. Finally, we found significantly higher hemolymph [K+] in the emersed and anoxic barnacles, which - when coupled to the relatively stable pH values we observed in all treatments - may suggest involvement of K+ ions in an effective acid-base buffering system. In sum, we predict that muscle function would be preserved in B. nubilus during periods of low tide emersion, whereas environmental hypoxia events, which are increasing in frequency and duration as global climates change, have the potential to diminish functionality of their giant muscle fibers.

Antioxidant Activity of Dictyotales from Tropical Reefs of Brazil.

Macroalgae produce a large range of primary and secondary metabolites with ecological and economical importance. Studies on antioxidants from marine algae have increased notably, focusing on searching new sources of natural compounds for different applications, in which tropical species have been shown to have high potential, often improved by stressful environmental conditions during the tide cycle with periods of emersion and submersion. Therefore, in order to characterize the antioxidant activity and relate it to local environmental tide exposure, three species of brown marine algae, Canistrocarpus cervicornis, Dictyopteris delicatula, and Lobophora variegata from two beaches on the northeast coast of Brazil were studied. Dichloromethane:methanol (DCM:M) and aqueous extracts were tested for ferric reducing antioxidant power, 2,2-diphenyl-1-picrylhydrazyl, and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) antioxidant assays and total phenolic compounds. Aqueous extracts of C. cervicornis showed up to 10 times major antioxidant activity and phenolic compounds than DCM:M extracts. Different characteristic of antioxidant activity were identified among the beaches, species, and extracts, in which aqueous extracts from C. cervicornis and L. variegata showed the most promising matrices for future prospection of natural antioxidants.

Interactions between sediment microbial ecology and physical dynamics drive heterogeneity in contextually similar depositional systems

AbstractThis study focuses on the interactions between sediment stability and biological and physical variables that influence the erodibility across different habitats. Sampling at short‐term temporal scales illustrated the persistence of the microphytobenthos (MPB) biomass even during periods of frequent, high physical disturbance. The role of MPB in biological stabilization along the changing sedimentary habitat was also assessed. Key biological and physical properties, such as the MPB biomass, composition, and extracellular polymeric substances, were used to predict the sediment stability (erosion threshold) of muddy and sandy habitats within close proximity to one another over multiple days, and within emersion periods. The effects of dewatering, MPB growth, and productivity were examined as well as the resilience and recovery of the MPB community after disturbance from tidal currents and waves. Canonical analysis of principal components (CAP) ordinations were used to visualize and assess the trends observed in biophysical properties between the sites, and marginal and sequential distance‐based linear models were used to identify the key properties influencing erodibility. While the particle size of the bed was important for differences between sites in the CAP analysis, it contributed less to the variability in sediment erodibility than key biological parameters. Among the biological predictors, MPB diversity explained very little variation in marginal tests but was a significant predictor in sequential tests when MPB biomass was also considered. MPB diversity and biomass were both key predictors of sediment stability, contributing 9% and 10%, respectively, to the final model compared to 2% explained by grain size.

Living on the upper intertidal mudflat: Different behavioral and physiological responses to high temperature between two sympatric cerithidea snails with divergent habitat-use strategies

Temperature plays a major role in controlling species' distributions, and small-scale variation in the thermal environment are potentially an important factor that governs distributions on a local scale. For untangling the roles of behavioral and physiological adaptations on species' distribution at a small-scale level, we carried out a comparative study of two mudflat snails (genus Cerithidea) by determining these congeners' burying behavior, lethal temperature, cardiac performance and heat-shock protein (hsp70) gene expression. These two sympatric snails occupy different microhabitats on the upper intertidal mudflat. During periods of emersion, C. cingulata inhabits the open mudflat and C. largillierti usually aggregates around small rocks on the upper intertidal mudflat. Our results indicate that the two Cerithidea congeners show different behavioral and physiological responses to high temperature. Compared to C. largillierti, C. cingulata prefers to bury into the mud, has a higher thermal limit and a higher level of inducible expression of hsp70 mRNA, implying important roles of behavioral and physiological adaptations to the harsh thermal environment on the open mudflat. Furthermore, results of generalized additive modelling (GAM) analysis of cardiac performance and coefficient of variation (CV) of hsp70 mRNA expression showed high inter-individual variation in C. cingulata. These results highlight the importance of behavioral and physiological adaptions in sympatric species' distributions on the mudflat and help to shed light on the mechanisms of how small-scale differences in the thermal environment shape sympatric species’ distributions.

Assimilation and short‐term processing of microphytobenthos nitrogen in intertidal sediments

AbstractMicrophytobenthos (MPB) are an important nitrogen (N) sink in coastal systems, but little is known about the fate of N assimilated by MPB. We used an in situ 15N pulse‐chase experiment in intertidal, nonpermeable, sandy mud to trace the assimilation, transformation, and loss from the sediment of MPB‐N over 31 d. Following assimilation, 15N was tightly retained in surface sediments, with only up to 8.1% transported to 2–10 cm sediments over 31 d. MPB accounted for a considerable portion of the 15N in surface sediments throughout the study (59% ± 13%). Bacteria rapidly assimilated 15N but accounted for only up to 17% of the 15N within surface sediments. Of the assimilated 15N, 78.9% was lost from the sediment over 31 d. Resuspension was the dominant loss pathway (74.4%) and was primarily associated with minor flooding following a rainfall event at 8 d. Biological pathways for N export were far less important. Denitrification, during both sediment exposure and inundation, was the main biological pathway for 15N loss (2.6% total), whereas there was little loss through ammonification and nitrification (NH4+ or NOx efflux; 1.4% combined) and dissolved organic nitrogen efflux (0.5%). It was estimated that the N incorporated by MPB within one emersion period would take ~ 40 d to be entirely removed from the sediment. This study highlights the potential importance of MPB and intertidal sediments for the uptake and longer‐term storage of coastal N, and the need to better quantify the impact of episodic flooding on coastal N budgets.

Characterizing biogeochemical fluctuations in a world of extremes: A synthesis for temperate intertidal habitats in the face of global change.

Coastal and intertidal habitats are at the forefront of anthropogenic influence and environmental change. The species occupying these habitats are adapted to a world of extremes, which may render them robust to the changing climate or more vulnerable if they are at their physiological limits. We characterized the diurnal, seasonal and interannual patterns of flux in biogeochemistry across an intertidal gradient on a temperate sandstone platform in eastern Australia over 6years (2009-2015) and present a synthesis of our current understanding of this habitat in context with global change. We used rock pools as natural mesocosms to determine biogeochemistry dynamics and patterns of eco-stress experienced by resident biota. In situ measurements and discrete water samples were collected night and day during neap low tide events to capture diurnal biogeochemistry cycles. Calculation of pHT using total alkalinity (TA) and dissolved inorganic carbon (DIC) revealed that the mid-intertidal habitat exhibited the greatest flux over the years (pHT 7.52-8.87), and over a single tidal cycle (1.11 pHT units), while the low-intertidal (pHT 7.82-8.30) and subtidal (pHT 7.87-8.30) were less variable. Temperature flux was also greatest in the mid-intertidal (8.0-34.5°C) and over a single tidal event (14°C range), as typical of temperate rocky shores. Mean TA and DIC increased at night and decreased during the day, with the most extreme conditions measured in the mid-intertidal owing to prolonged emersion periods. Temporal sampling revealed that net ecosystem calcification and production were highest during the day and lowest at night, particularly in the mid-intertidal. Characterization of biogeochemical fluctuations in a world of extremes demonstrates the variable conditions that intertidal biota routinely experience and highlight potential microhabitat-specific vulnerabilities and climate change refugia.

Adaptations to the mudflat: Insights from physiological and transcriptional responses to thermal stress in a burrowing bivalve Sinonovacula constricta

Understanding physiological adaptations of organisms to temperature changes that characterize their habitat is the first step in predicting the putative effects of global climate change on population dynamics. Mudflats are an important part of the intertidal zone and experience extreme and fluctuating temperatures. Therein, species would be potentially susceptible to global warming. The present study explored physiological adaptations of burrowing species to life in an intertidal mudflat by analyzing the potential operative temperatures in the mudflat, and assessing cardiac performance and the transcriptional response to thermal stress by a typical burrowing bivalve, the razor clam Sinonovacula constricta in different thermal environments, mimicking conditions during low tides. Clams showed higher thermal sublethal limits in mud with overlying air than in mud with overlying water, indicating an adaptation to rapidly changing ambient temperatures and thermal environments during emersion. This sublethal limit was far above the maximum operative temperature in the actual habitat site and suggests a potential buffer zone to ensure survival under unexpected high temperatures, that could occur with global warming. In response to high temperature, S. constricta exhibited the common heat stress response by up-regulating expression of the Bcl2-associated athanogene 3 (BAG3) and heat shock proteins to cope with the adverse effects of high temperature on protein homeostasis. Increased expression of key genes, including molybdenum cofactor synthesis 3 (MOCS3), oligoribonuclease (REX2), and NFκappaB inhibitor alpha (NFIA) may further remit the effect of thermal stress during the emersion period and delay a situation where clams reach their thermal sublethal limit, thereby helping to endure high temperature during low tide. These results clearly illustrate significant adaptations of a burrowing bivalve to life in intertidal mudflats at both physiological and molecular levels and can provide insights into potential physiological or evolutionary responses that could aid survival of mudflat species in a changing global climate.

Intra-Annual Variability in Responses of a Canopy Forming Kelp to Cumulative Low Tide Heat Stress: Implications for Populations at the Trailing Range Edge.

Anthropogenic climate change is driving the redistribution of species at a global scale. For marine species, populations at trailing edges often live very close to their upper thermal limits and, as such, poleward range contractions are one of the most pervasive effects of ongoing and predicted warming. However, the mechanics of processes driving such contractions are poorly understood. Here, we examined the response of the habitat forming kelp, Laminaria digitata, to realistic terrestrial heatwave simulations akin to those experienced by intertidal populations persisting at the trailing range edge in the northeast Atlantic (SW England). We conducted experiments in both spring and autumn to determine temporal variability in the effects of heatwaves. In spring, heatwave scenarios caused minimal stress to L.digitata but in autumn all scenarios tested resulted in tissue being nonviable by the end of each assay. The effects of heatwave scenarios were only apparent after consecutive exposures, indicating erosion ofresilience over time. Monthly field surveys corroborated experimental evidence as the prevalence of bleaching (an indication of physiological stress and tissue damage) in natural populations was greatest in autumn and early winter. Overall, our data showed that L.digitata populations in SW England persist close to their upper physiological limits for emersion stress in autumn. As the intensity of extreme warming events is likely to increase with anthropogenic climate change, thermal conditions experienced during periods of emersion will soon exceed physiological thresholds and will likely induce widespread mortality and consequent changes at the population level.

Dynamic measurements of black oystercatcher (Haematopus bachmani) predation on mussels (Mytilus californianus)

AbstractIntertidal zone mussels can face threats from a variety of predatory species during high and low tides, and they must balance the threat of predation against other needs such as feeding and aerobic respiration. Black oystercatchers (Haematopus bachmani) on the Pacific coast of North America can depend on the mussel Mytilus californianus for a substantial portion of their diet. Observations suggest that oystercatchers tend to focus on mussels beginning to gape their valves during rising tides, following periods of aerial emersion. We present detailed, autonomous field measurements of the dynamics of three such predation events in the rocky intertidal zone. We measured accelerations of up to 4 g imposed on mussels, with handling times of 115–290 s required to open the shell and remove the majority of tissue. In each case a single oystercatcher attacked a mussel that had gaped the shell valves slightly wider than its neighbors as the rising tide began to splash the mussel bed, but no other obvious characteristic of the mussels, such as body temperature or orientation, could be linked to the oystercatcher's individual prey choice.

Acid-base physiology over tidal periods in the mussel Mytilus edulis: size and temperature are more influential than seawater pH.

Ocean acidification (OA) studies to date have typically used stable open-ocean pH and CO2 values to predict the physiological responses of intertidal species to future climate scenarios, with few studies accounting for natural fluctuations of abiotic conditions or the alternating periods of emersion and immersion routinely experienced during tidal cycles. Here, we determine seawater carbonate chemistry and the corresponding in situ haemolymph acid–base responses over real time for two populations of mussel (Mytilus edulis) during tidal cycles, demonstrating that intertidal mussels experience daily acidosis during emersion. Using these field data to parameterize experimental work we demonstrate that air temperature and mussel size strongly influence this acidosis, with larger mussels at higher temperatures experiencing greater acidosis. There was a small interactive effect of prior immersion in OA conditions (pHNBS 7.7/pCO2 930 µatm) such that the haemolymph pH measured at the start of emersion was lower in large mussels exposed to OA. Critically, the acidosis induced in mussels during emersion in situ was greater (ΔpH approximately 0.8 units) than that induced by experimental OA (ΔpH approximately 0.1 units). Understanding how environmental fluctuations influence physiology under current scenarios is critical to our ability to predict the responses of key marine biota to future environmental changes.

High-frequency depositional cycles in the Muschelkalk (Middle Triassic) of southern Poland: Origin and implications for Germanic Basin astrochronological scales

High-frequency depositional cycles are often used for long-distance correlations within sedimentary basins and constructing high-resolution chronostratigraphic scales calibrated to the orbital clock. Such an approach has been used for the tropical, epicontinental Muschelkalk Sea covering most of Europe in the Middle Triassic. This paper aims at establishing the spatial extent and internal architecture of shallow-marine Muschelkalk cycles within a small (120 by 50 km) area of the Germanic Basin, to identify their local vs. regional distribution and cycle-forming mechanisms. Three groups of cycles are distinguished: 1) peritidal cycles representing a tidal flat-lagoon system which experienced longer periods of emersion; 2) shallow subtidal cycles formed around the fair-weather wave base; and 3) deep subtidal cycles developed around the storm wave base. The three cycle types differ markedly in the composition, facies homogeneity, sedimentary trends, hierarchical organization, continuity, and degree of lateral changeability and complexity, which collectively translates into the ease of cycle recognition. Despite the differences, the defined cycles do not extend laterally beyond the studied area and have laterally variable facies heterogeneities, sedimentary trends, and thicknesses. This variability resulted from more or less mosaic infilling of accommodation space, reflecting local bathymetry, physicochemical conditions, and carbonate production and accumulation rates on the platform. Accommodation space evolved by the interplay of eustatic sea-level fluctuations regional subsidence, and synsedimentary tectonic-block movements, but the contribution of these factors changed over time and was to varying degrees masked for each of the three cycle types by intrinsic sedimentary processes. The study shows that Middle Triassic cycles of the Germanic Basin have a local to sub-regional distribution and thereby are inappropriate for basin-wide correlations and chronostratigraphic inferences. It also strengthens the opinion of several workers that correlation of idealized cycles is unrealistic without checking the horizontal continuity of facies and key surfaces directly in the field.

Evaluating physiological responses of a kelp to environmental changes at its vulnerable equatorward range limit

A recommendation of: Aline Migne, Gaspard Delebecq, Dominique Davoult, Nicolas Spilmont, Dominique Menu, Marie-Andree Janquin and Francois Gevaert Photosynthesis of Laminaria digitata during the immersion and emersion periods of spring tidal cycles during hot, sunny weather https://hal.sorbonne-universite.fr/hal-01827565v4

Testing the relative importance of intertidal seaweeds as ecosystem engineers across tidal heights

The persistence of seaweeds as community-structuring organisms is critical for the maintenance of many ecosystem functions on rocky intertidal shores. We measured the relative importance of seaweeds in structuring the abundance, richness, and distribution of macroinvertebrates at three tidal levels on a rocky shore. Through manipulative experiments, we characterized temperature, irradiance, and desiccation underneath seaweed canopy plots made up of either Silvetia compressa or Stephanocystis dioica, assembled at three biomasses. We assessed differences in the abundance, richness, and the distribution of macroinvertebrates underneath the canopy as a function of seaweed species and biomass and evaluated differences due to the tidal height of the installed experimental seaweeds. We found that manipulated seaweed biomass significantly affected the community structure of associated macroinvertebrates at all tidal levels, especially at higher biomass treatments. Although contrary to other studies, we found no effect on richness underneath the canopies at any tidal height. Our results show that intertidal seaweeds provide protection from water loss, heat, and irradiance when compared to manipulative controls with no canopy cover. We also found that the relative importance of the experimental seaweed canopies in their ability to mitigate stressful abiotic conditions increased with prolonged emersion periods, such as at higher levels in the intertidal zone. At the higher tidal level tested, a greater abundance of macroinvertebrates was associated with the experimental canopies in comparison to the manipulation-control plots and the natural substrate. These results emphasize the role of intertidal seaweeds as bioengineers and highlight the importance of preserving and restoring high densities of leathery seaweeds on degraded shores in order to preserve the dynamics of the intertidal ecosystem overall.

The Madenli (Central Taurides) Upper Cretaceous platform carbonate succession: Benthic foraminiferal biostratigraphy and platform evolution

The Upper Cretaceous succession in the Madenli area (western Central Taurides, Southern Turkey) consists of platform carbonate rocks deposited in entirely peritidal environments, which are sensitive to sea level changes driven by global eustasy, but also strongly affected by local and regional tectonics. It includes economically important bauxite deposits. Previous works suggest different ages for bauxite formation ranging from the Albian to the Santonian. Benthic foraminiferal biostratigraphy and facies analysis of the Madenli and Doğankuzu outcrop sections allow for a more precise dating of the platform emersion periods. The footwall limestones of the bauxite deposits consist of well-bedded limestones (Unit-1), which contain a benthic foraminiferal assemblage (BFA) including mainly Biconcava bentori and Pastrikella biplana, Chrysalidina gradata (BFA I), assigned to the middle-upper Cenomanian. In the Madenli section, the first bauxite deposit occurs in the upper part of Unit-1 as a layer interbedded with pinkish sparitic and dolomitic beds (subunit-1a) deposited in supratidal environment. Subunit-1a is stratigraphically equivalent to the Doğankuzu and Mortaş bauxite deposits considered as karst-related, unconformity-type deposits. The hanging-wall limestones of the bauxite are represented by the massive limestones (Unit-2) starting locally with either the upper Cenomanian characterized mainly by the presence of Pseudolituonella reicheli or upper Campanian comprising mainly Murciella cuvillieri and Moncharmontia apenninica (BFA II). There is no field evidence of a discontinuity surface at the contact between the lower part of Unit-2, including BFA I, and the upper part of Unit-2, including BFA II. This contact is defined as a paraconformity indicating a stratigraphic gap from the Turonian to the early Campanian. The top of Unit-2 is truncated by another discontinuity surface associated with a minor bauxite deposit. The overlying Unit-3 is characterized by well-bedded, rudist-bearing limestones topped by laminated and dolomitized limestones organized in shallowing upward cycles. It is assigned to the upper Maastrichtian based on the presence of Rhapydionina liburnica (BFA III) and rudist assemblage. A third emersion period of the platform corresponds to the early Maastrichtian.

Ecophysiology of photosynthesis of Vaucheria sp. mats in a Svalbard tidal flat

The photosynthetic performance of a Vaucheria sp. community in the Adventfjorden tidal flats near Longyearbyen, Svalbard, the Arctic was evaluated in a series of in situ and ex situ measurements based on variable chlorophyll fluorescence and gasometric approaches. The in situ measurement did not indicate any possible drivers from the selected environmental parameters (temperature, PAR, UVR, emersion period duration) of photosynthetic activity. Two ecotypes, spikes or loose filaments, observed in the field were related to emersion and immersion periods during the tidal cycle. Ex situ long-term monitoring identified PAR as the main controlling factor of photosynthesis. No limitation of photosynthetic activity due to temperatures or light was detected. The detailed ex situ photosynthesis measurements of Vaucheria sp. samples pre-acclimated to different irradiances did not reveal any decrease of photosynthesis in high light. Irradiance affected only the photosynthesis rate, but not the photosynthesis efficiency. The Vaucheria sp. was acclimated to the prevailing low-light conditions but was able to tolerate high-light conditions on sunny days of the late Artic summer.

Metabolomics based on UHPLC-QToF- and APGC-QToF-MS reveals metabolic pathways reprogramming in response to tidal cycles in the sub-littoral species Mimachlamys varia exposed to aerial emergence

Mimachlamys varia is a sub-littoral bivalve encountered from Norway to the Mediterranean Sea, which lives mostly byssally attached to rocks. During the low tide period, M. varia individuals, located highest on the shore, may experience short time of aerial exposure and face a low availability of oxygen. Here we report a comparative metabolomic profiling of gill samples of M. varia obtained by both LC-QToF and APGC-QToF mass spectrometry, to analyze metabolic changes occurring during emersion in comparison with immersion. Scallops were grown in aquaria with a simulated intertidal environment mimicking short-duration air exposure that they might experience during extreme tides: alternating 2 h emersion and 10 h immersion. Our results show a switch from aerobic to anaerobic metabolism after only 2 h of emersion, with the resort to different pathways: glucose-lactate, glucose-succinate and aspartate-succinate pathways. Furthermore, carnitine-conjugated metabolites were found to accumulate during emersion, as well as urate. The level of tyrosine on the contrary was found to decrease. These findings indicate a complex metabolic reprogramming that occurs after a two hour emersion period and upon re-immersion. Furthermore, M. varia is used as sentinel species in pollution biomonitoring, through the assay of biomarkers to evaluate the effects of pollutants. Here we show that emersion induces a significant decrease of superoxide dismutase activity, an enzyme developed by bivalves to face oxidative stress and used as biomarker. These findings have to be taken into account to normalize sampling during campaigns of environmental monitoring, by taking in situ, as far as possible only immersed individuals.