Salinity Fluctuations Research Articles

Responses of soil respiration to simulated groundwater table and salinity fluctuations in tidal freshwater, brackish and salt marshes

Hydrological and salinity fluctuations in coastal wetlands induced by climatic change (e.g., drought) and anthropogenic activities can significantly affect the blue carbon sink via soil respiration (CO2 emissions). However, little information is available on the interactive effects of the groundwater table and salinity on soil respiration in coastal wetlands. Here, in situ soil columns were collected from tidal freshwater wetlands, brackish wetlands, and salt marshes to conduct a simulated assessment of the effects of fluctuations in the groundwater table (−30 cm, −20 cm and −10 cm) and salinity (0 ppt, 12ppt, and 26 ppt) on soil respiration in the field. The results showed that soil respiration in tidal freshwater wetlands (0.56–2.1 μmol/m2/s) and salt marshes (0.19–2.02 μmol/m2/s) was higher than that in brackish wetlands (0.17–0.9 μmol/m2/s) in all groundwater table and salinity treatments. The diurnal variation in soil respiration in the three simulated wetlands showed a unimodal curve, while the peak time was influenced by the groundwater table and salinity, with the maximum occurring at 11 a.m.-2 p.m. Soil respiration in tidal freshwater wetlands and brackish wetlands was significantly higher in the deep (−30 cm) and medium (−20 cm) groundwater table treatments than in the shallow (−10 cm) groundwater table treatment (p < 0.05) and significantly higher in the low (0 ppt) and medium (12ppt) salinity treatments than in the high (26 ppt) salinity treatment (p < 0.05). However, soil respiration in salt marshes decreased significantly as the groundwater table and salinity increased (p < 0.05). The groundwater table and salinity exhibited significant interactive effects on soil respiration in brackish wetlands (p < 0.05) and salt marshes (p < 0.01). Additionally, significantly negative correlations were observed between soil respiration and groundwater table and salinity in three wetlands (p < 0.05). Soil respiration in the three wetlands was significantly and positively correlated with microbial biomass carbon (p < 0.05) and significantly and positively correlated with soil organic carbon and total nitrogen (p < 0.01). The findings of this work can help reduce the uncertainty of model to accurately estimate carbon cycling of coastal wetlands at local, regional and global scales, and improve the blue carbon sink of coastal wetlands by regulating the groundwater table and salinity levels in wetland restoration projects.

Effects of Salinity on the Growth, Physiological Characteristics, and Intestinal Microbiota of the Echiura Worm (Urechis unicinctus)

Intertidal biota is subjected to significant fluctuations in salinity. Urechis unicinctus, a typical species thriving in intertidal sediments, have relatively simple anatomy structure and therefore could be considered as an ideal species for salinity acclimation. Moreover, due to the high nutrients, U. unicinctus has become an emerging aquaculture species in China. In this study, we investigated the effects of salinity on the growth performance, coelomic fluid biochemical indices, antioxidant enzyme system, Na+/K+-ATPase, and non-specific immune enzyme activities, as well as intestinal microbiota composition of this species in an 8-week experiment. The results indicated U. unicinctus is a euryhaline species that can tolerate salinities from 15‰ to 40‰ and demonstrated the highest growth performance at 30‰. Physiological characteristic analyses of coelomic fluid and intestines indicated that the salinity range of 15‰ to 30‰ is more suitable, while 10‰ and 40‰ salinity ranges seem unsuitable for juvenile U. unicinctus. Furthermore, intestinal microbiota analysis indicated salinity had a significant effect on the composition structure. KEGG pathway analysis indicated that antioxidant related metabolic pathways and amino acid metabolic pathways may play important roles in gut microbiota under salinity stress. Comprehensive analysis of intestinal bacteria and enzyme activities indicated Unidentified Rhodobacteraceae, Vibrio, and Shimia may play important roles in high salinity acclimation, while Legionellaceae may act as important microbiota in low salinity acclimation. Moreover, Ruminococcus, Oscillospira, Lachnospiraceae, Clostridiales, and S24-7 showed negative correlations with the antioxidant and nonspecific immune enzymes, indicating that these bacteria can be considered as important candidates of probiotics for U. unicinctus aquaculture industry. The findings of this study will extend our understanding of the effects of salinity on the growth and health of U. unicinctus and contribute to a better understanding of the salinity acclimation strategies of organisms in intertidal zones.

Salinity Fluctuation on the Genetic Regulatory Mechanisms of the Crustacean, Charybdis japonica

The intertidal salinity fluctuations provide pose a significant physical challenge for the crustaceans that live here. In the present study, Charybdis japonica was selected as the research species to explore the genetic regulatory mechanisms of intertidal crustaceans responding to salinity fluctuations. We cultured C. japonica s with three salinity gradients (the salinity of 15‰, 25‰, and 35‰) and 68.90 Gb clean transcriptome reads were obtained by RNA-seq. All clean reads were then de novo assembled to 41,058 unigene with a mean length of 1,179.39 bp and an N50 length of 2,033 bp. Furthermore, a total of 18,100 (24.74%) unigenes were successfully matched with the sequences from at least one database. We further analyzed the transcriptome structure of C. japonica and a total of 26,853 CDSs and 12,190 SSRs were predicted. The gene expression levels of C. japonica at 25‰ were used as control, and 204 and 5,392 DEGs were found at the salinity of 35‰ and 15‰, respectively. Based on the annotated information of DEGs, we speculated that C. japonicas were subjected to greater stress under the salinity of 35‰ and isotonic intracellular regulation was activated. Furthermore, neuronal activity, oxidation response, intracellular regulatory activity and osmotic regulation-related genes were speculated to be critical genes for C. japonica to cope with salinity fluctuations. The present results will provide fundamental information for revealing the salinity fluctuation-related genetic regulatory mechanisms of C. japonica and other intertidal crustaceans, and then help us predict how future salinity changes will affect the survival of crustaceans.

Antioxidant response of the oyster Crassostrea hongkongensis exposed to diel-cycling hypoxia under different salinities

Intertidal and estuarine bivalves are adapted to fluctuating environmental conditions but the cellular adaptive mechanisms under combined stress scenarios are not well understood. The Hong Kong oysters Crassostrea hongkongensis experience periodic hypoxia/reoxygenation and salinity fluctuations during tidal cycles and extreme weather, which can negatively affect the respiratory organs (gills) involved in oxygen uptake and transport. We determined the effects of periodic hypoxia under different salinities on the oxidative stress response in Hong Kong oysters. Oxidative stress parameters (activities of superoxide dismutase (SOD), and catalase (CAT), tissue levels of malondialdehyde (MDA) and protein carbonyl content (PCC)) were determined in the gills of oysters exposed to diel-cycling hypoxia (hypoxia at night: 12h at 2 mg/L, reoxygenation: 12h at 6 mg/L) and normal dissolved oxygen (DO) (6 mg/L) under three salinities (10, 25, and 35‰) for 28 days. Oxygen regime in combination with salinity changes had significant interactive effects on all studied parameters except SOD. Salinity, DO and their interactions increased PCC after 14 and 28 days of exposure, and the combination of hypoxia/reoxygenation and decreased salinity showed the most severe effect. MDA content of the gills increased only after the long-term (28 days) exposure in decreased or increased salinity under normal DO treatments, showing PCC was more sensitive than MDA as biomarker of oxidative stress. Low salinity suppressed SOD activity regardless of the DO, whereas hypoxia induced SOD responses. CAT activities decreased significantly under high salinity with hypoxia/reoxygenation conditions. Our findings highlighted that periodic hypoxia/reoxygenation with salinity change induced antioxidant responses, which can impact the health of Hong Kong oyster C. hongkongensis and prolonged salinity stress may be one reason for the mortality during its aquaculture process.

Regulation of the Cell Cycle, Apoptosis, and Proline Accumulation Plays an Important Role in the Stress Response of the Eastern Oyster Crassostrea Virginica

BackgroundUnderstanding how organisms respond and adapt to environmental changes is central to evolutionary biology. As a sessile organism that has adapted to life in estuaries and intertidal zones, the eastern oyster Crassostrea virginica can tolerate wide fluctuations in temperature and salinity and survive for weeks out of water. To understand the molecular mechanisms underlying the remarkable stress tolerance of the eastern oyster, we studied the transcriptomic changes induced by exposure to air and cold stress. Eastern oysters were maintained for 7 days under four conditions, namely, in seawater (normal) at 22°C, in air at 22°C, in seawater at 5°C and in air at 5°C, and then sampled for RNA sequencing.ResultsTranscriptomic analysis revealed that many genes involved in cell cycle progression and DNA replication were downregulated in oysters exposed to air and cold, which indicates that stress inhibits cell division. Exposure to air at 22°C induced a concerted inhibition of apoptosis through the upregulation of expanded inhibitors of apoptosis and the downregulation of caspases. Interactions between TNF and NF-κB signalling implied a reduction in the inflammatory response and immune functions. Key genes for proline production, fatty acid synthesis and chromosomal proteins were upregulated during exposure to low temperatures, which suggested that proline accumulation, energy conservation, and epigenetic modification of chromosomes are important for coping with cold stress. The upregulation of melatonin, FMRFamide, and neural acetylcholine receptors indicate the significance of the neurohormonal regulation of homeostasis.ConclusionThese results show that air exposure and cold stress alter the expression of key genes for cell division, apoptosis, proline accumulation, fatty acid metabolism, neurohormonal signalling, and epigenetic modifications, suggesting regulation of these processes plays an important role in the stress response of the eastern oyster and possibly other marine molluscs. This study provides new insights into molecular mechanisms of stress response that are essential for understanding the adaptive potential of marine organisms under climate change.

Macrobenthic Assemblages, Distribution and Functional Guilds from a Freshwater-Dominated Tropical Estuary

Assessment of benthic diversity and estuarine ecological quality is becoming increasingly important. Estuaries are not only highly productive and variable environments, but they are also areas of high anthropogenic perturbations. In this study, benthic macrofauna were sorted, identified and analyzed from a freshwater-dominated tropical estuary along the Bay of Bengal to assess their community structure, distribution and functional guilds, and to uncover the environmental drivers influencing their distributional patterns. Results revealed that the studied physio-chemical variables (DO, pH, alkalinity and temperature) were significantly varied (p &lt; 0.05) among the sites. Capitella sp. was dominant (18%) of the forty morphospecies recorded, indicating organic richness of the area. The ANOVA results revealed that macrobenthic density differed significantly (p &lt; 0.01) between the study locations, and diversity indices (Shannon diversity index, H′) also differed significantly (F4,12 = 5.89; p = 0.02). The benthic density decreased from the head to the mouth, which could be related to salinity fluctuations and large freshwater discharges. Upstream sites were completely segregated from downstream and mid-estuarine sites, according to cluster analysis (CA). The SIMPER results clarified the site grouping pattern, showing that Mysis-1 spp., Capitella spp. and Nephtys-1 were the most significant contributors. From the communities, five functional trophic groups were identified where deposit feeders were the most dominant (66.44%). Most of the macrobenthos had strong positive correlations with DO (r = 0.92) and water temperature (r = 0.86) and a negative correlation with soil pH (r = −0.28), per correlation and CCA analyses. Individually, soil pH (r = 0.88) and alkalinity (r = 0.898) showed strong positive correlation with Capitella sp. and Chironomus sp.2. The above results indicate that macrobenthos of this estuary do not follow the usual pattern of spatial distribution, and they are structured by DO, alkalinity and soil pH. In addition, dominance of some pollution indicator species (Capitella sp. and Chironomus sp.) and deposit feeders indicates a poor ecological condition of the estuary.

Molecular mechanism of protein dynamic change in Pacific oyster (Crassostrea gigas) during depuration at different salinities uncovered by mass spectrometry-based proteomics combined with bioinformatics

Salinity stress during depuration of Pacific oysters (Crassostrea gigas) leads to degradation in quality; therefore, an understanding of the molecular mechanisms regulating dynamic changes during depuration is needed. Here, C. gigas was depurated for 72 h at salinities ranging from 26 to 38 g/L, a ± 10–20% fluctuation from that in the production area, and the gill proteomes were analyzed by sequential window acquisition of all theoretical fragment ion mass spectra (SWATH-MS). Of the 1218 proteins analyzed, 241 were differentiating proteins (DPs). Salinity stress led to increased levels of DPs associated with glycolysis and the extracellular matrix–receptor interaction pathway, and decreased levels of DPs associated with the citric acid cycle, lipid metabolism, genetic information processing, and cell transformation, especially in oysters exposed to 38 g/L salinity (+20%). Controlling salinity fluctuation within ± 10% of the production area during depuration was conducive to maintaining quality in C. gigas.

Distribution Patterns of Reef Fish Larvae in the Dipolog Srait, Philippines

The composition, abundance and distribution of reef fish were strongly influenced by the trends in salinity, temperature and mixing regimes of the water during the three oceanographic cruises conducted in the vicinity of the marine reserve networks of Dipolog Strait. Forty-seven families of reef fish larvae were identified. Carangidae, Labridae, Scaridae, Gobiidae and Apogonidae were the top five most abundant larvae comprising 64.7 % of the total number of reef fish larvae collected. Shifts in the dominance of the top five most abundant reef fish families occurred primarily between the northeast and southwest monsoons coinciding with the changes in the temperature profiles of the water column. Abundance of reef fish larvae showed variability across the three sampling periods due to the succession of the dominant species of reef fish larvae. Fluctuations in salinity brought about by the transition from Northeast to Southwest monsoon period could explain the variation. Density distribution of reef fish larvae significantly increased with the increasing depth of the mixed layer during northeast monsoon period. The downwelling off the coast of southern Negros in February and April cruises contributed to the high abundance of reef fish larvae in this part of the strait, while the uniform mixing of the water column in June 2010 at southwest monsoon resulted in the weakening of density gradient of reef fish larvae.The study demonstrated the variable responses of the reef fish larvae to the gradients of chlorophyll in the Dipolog Strait. A better understanding on the retention mechanism of reef fish larvae along the coast of southern Negros, where the main marine reserve networks exist, is provided by the present study.

Statistical Detection of Spatio-Temporal Patterns in the Salinity Field Within an Inter-Tidal Basin

Salinity is a key factor affecting biological processes and biodiversity in estuarine systems. This study investigates temporal and spatial changes in salinity at a basin-wide scale for 2005–2015 in the Dutch Wadden Sea. Scan statistics is applied to track salinity variations systematically and to detect potential clusters, i.e., estuarine regions marked by anomalous high-salinity (or low-salinity) values in a certain period (i.e., strong deviations from the expected value in a statistical sense). Clusters’ statistical significance has been assessed via Monte Carlo simulations. Particular attention is devoted to event-driven spatial and temporal patterns characterized by extreme salinity values since these episodes dramatically increase stress levels on organisms living in intertidal areas. Periodic components in the modeled salinity time series are identified using wavelet analysis and eventually removed from the signal before performing scan statistics. Wavelet analysis suggests that tides are the chief agent controlling salinity fluctuations in the system at within-day time scales, whereas no dominant periodicities were detected at longer time scales. Scan statistics reveal long-lasting clusters next to the main freshwater outlets and within the areas characterized by low water exchanges. In contrast, active regions of the estuary can efficiently counteract extreme events and quickly recover their pre-perturbation conditions. Finally, by analyzing the freshwater dispersal in the system, it is found that clusters’ occurrence is related to episodic events characterized by extreme conditions in the southwesterly wind and freshwater discharge. This research demonstrates that scan statistics can be used as a powerful tool for spatiotemporal analyses of marine systems and for identifying data-clustering that may be indicative of emerging environmental hazards (e.g., due to climate change).

Spatial Analysis for Mariculture Site Selection: A Case Study of Kukup Aquaculture Zones in the Peninsula of Malaysia

Marine aquaculture sites at Kukup Strait in the peninsula of Malaysia are experiencing a decline in water quality in the last five years, resulting in high mortality rates (50 - 80%), seasonal massive fish mortalities and poor profitability. Currently, Kukup farmers are involved in intensive aquaculture within the existing aquaculture zone. This study explores the sustainability of a modern mariculture method, where fish farms are relocated to deeper waters with higher flushing rates, and high-density polyethylene (HDPE) are used to improve water quality. Several site selection criteria are utilised in identifying the proposed aquaculture industrial zone: 1) bathymetry depth (operational requirement: 10 m to 30 m), 2) located within the Kukup Port Limit, 3) does not interfere with the Kukup ferry navigation route, and 4) distance from Kukup mainland. Site feasibility analysis, including hydrodynamics, meteorology, water quality, sediment quality and macrobenthos assessment, was conducted to compare the proposed and existing aquaculture sites. It was found that the water quality at the existing site contained higher concentrations of fecal coliform and nutrients and salinity fluctuations. Tropical finfish can survive under these conditions with poorer fish health and higher fish mortality. Apart from that, the flushing capacity is higher in the proposed site, indicating the capacity to handle moderate-intensity aquaculture. Moderate-intensity aquaculture using HDPE cages could be profitable for the local fish farmers. Therefore, it is suggested that other locations within Kukup Straits with deeper waters (&amp;gt; 25 m) with possibly improved water quality and the ability for intensive aquaculture production should be explored for a larger depth and economics of scale.

Cryptic lineages, cryptic barriers: historical seascapes and oceanic fronts drive genetic diversity in supralittoral rockpool beetles (Coleoptera: Hydraenidae)

Abstract Morphologically cryptic lineages confound many estimates of global biodiversity and are often discovered in ecologically specialized taxa, subject to strong morphological constraint. Such a situation may apply in many extreme environments, including supralittoral rockpools, where dramatic fluctuations in water availability and salinity impose strong selection pressures on the inhabitants. Here we explore the genetic diversity and phylogeography of supralittoral rockpool Ochthebius beetles in the eastern Atlantic and western Mediterranean, using a combination of mitochondrial and nuclear markers and dense geographical sampling of the three recognized widespread species. Our results point to the existence of morphologically cryptic lineages within all currently named taxa and suggest that the distribution of these is linked to both historical and contemporary marine hydrogeography; a combination of ocean currents and winds apparently driving the spatial patterns observed. The main contemporary barrier to dispersal for Ochthebius is located around the Ibiza Channel, whilst the Messinian Salinity Crisis appears to have been the ultimate driver of lineage diversification in these insects. Our results show that oceanographic processes do not just shape the evolution of fully marine species, but also impact significantly on the terrestrially derived inhabitants of the coastal zone.

Hyposalinity induces significant polar lipid remodeling in the marine microalga Dunaliella tertiolecta (Chlorophyceae)

Marine microalgae often live in a fluctuating environment including a decrease in salinity caused by global warming induced sea ice melting and freshwater inflows. Under conditions of fluctuating salinity, microalgae have evolved a variety of survival mechanisms such as lipid accumulation and remodeling. The purpose of this study was to investigated the membrane lipid remodeling of the marine green microalga Dunaliella tertiolecta as a short-term acclimation mechanism in response to hyposalinity (20 and 3 PSU) with respect to growth at optimal salinity (38 PSU). We identified 34 lipid species belonging to seven polar lipid classes. Dunaliella tertiolecta accumulates cell lipids and remodels polar lipid classes and their fatty acids composition as response to hypoosmotic stress at 3 PSU. We found that the unsaturation of most polar lipids decreases overall, indicating decreased membrane fluidity and altered permeability, whereas shortening the length of fatty acids of polar lipids is not one of the strategies of D. tertiolecta to cope with the decrease in salinity. Increase in relative content (%) and unsaturation of monogalactosyldiacylglycerols (MGDG) and decrease in relative content (%) and unsaturation of phosphatidylglycerols (PG), suggesting changes in photosynthetic membranes of thylakoids at 20 and 3 PSU. At a very low salinity of 3 PSU, the relative content (%) of phosphatidylinositols (PI) increases, suggesting increased lipid trafficking and signaling in the cells. These changes are statistically significant and we hypothesize that D. tertiolecta is genetically adapted to withstand large salinity fluctuations through polar lipid composition.

Effects of environmental salinity on the immune response of the coastal fish Scatophagus argus during bacterial infection

The coastal aquaculture is characterized with environmental salinity fluctuation, and the effects of salinity stress on the immunity of cultured fish are needed to be further explored. Scatophagus argus is an important species in the wild fisheries and aquaculture industry, it would be of great value to reveal the impact of salinity change on the immune response in this species. Understanding the effects of salinity stress on immune response can provide valuable insights into salinity management in the aquacultural process. The head kidney, which is an organ unique for teleost fish, functions not only as a central immune organ but also as a crucial role in the stress response during which the secretion of immunoregulatory molecules i.e. cytokines is facilitated. In the present study, Individuals of S. argus acclimated to 3 different salinities [0‰ (FW), 10‰ (BW), and 25‰ (SW)] were injected intraperitoneally with A. hydrophila, and then monitored throughout one week. The effects of environmental salinity on the immune response in S. argus stimulated by A. hydrophila infection were investigated. mRNA expression profiles of cytokine genes IL-1β, IL-6, IL-10 and TNF-α in different salinity groups was quite different. mRNA expression of cytokine genes in BW group and SW group rose more quickly and significantly higher than FW group (p < 0.05) at early stages (6–24 hpi) after bacterial injection, and before 96 hpi, the highest value of cytokine expression at each time point was recorded in SW group. Immune parameters such as lysozyme level, complement C3 activity and IgM content in BW and FW groups were lower than SW group at each time point from 24 to 144 hpi after bacterial injection. In addition, leukocyte profiles in the head kidney and blood were also investigated. Although hypoosmotic acclimation could temporarily stimulate monocyte and neutrophil proliferation, it was observed that the number of monocytes, neutrophils and lymphocytes of the head kidney and blood in SW group increased more quickly than BW and FW groups after bacterial infection. Our results indicate that hypoosmotic stress due to the decrease of environmental salinity has suppressive immunoregulatory effects on the immune response of S. argus.

SNP Based Trait Characterization Detects Genetically Important and Stable Multiple Stress Tolerance Rice Genotypes in Salt-Stress Environments.

Soil salinity is a major constraint to rice production in coastal areas around the globe, and modern high-yielding rice cultivars are more sensitive to high salt stress, which limits rice productivity. Traditional breeding programs find it challenging to develop stable salt-tolerant rice cultivars with other stress-tolerant for the saline environment in Bangladesh due to large yield variations caused by excessive salinity fluctuations during the dry (boro) season. We examined trait characterization of 18 advanced breeding lines using SNP genotyping and among them, we found line G6 (BR9621-B-1-2-11) (single breeding line with multiple-stress-tolerant QTL/genes) possessed 9 useful QTLs/genes, and two lines (G4:BR9620-2-7-1-1 and G14: IR 103854-8-3-AJY1) carried 7 QTLs/genes that control the desirable traits. To evaluate yield efficiency and stability of 18 rice breeding lines, two years of field experiment data were analyzed using AMMI (additive main effect and multiplicative interaction) and GGE (Genotype, Genotype Environment) biplot analysis. The AMMI analysis of variance demonstrated significant genotype, environment, and their interaction, accounting for 14.48%, 62.38%, and 19.70% of the total variation, respectively, and revealed that among the genotypes G1, G13, G14, G17, and G18 were shown to some extent promising. Genotype G13 (IR 104002-CMU 28-CMU 1-CMU 3) was the most stable yield based on the AMMI stability value. The GGE biplot analysis indicates 76% of the total variation (PC1 48.5% and PC2 27.5%) which is performed for revealing genotype × environment interactions. In the GGE biplot analysis, genotypes were checked thoroughly in two mega-environments (ME). Genotype G14 (IR103854-8-3-AJY1) was the winning genotype in ME I, whereas G1 (BR9627-1-3-1-10) in ME II. Because of the salinity and stability factors, as well as the highest averages of grain yield, the GGE and AMMI biplot model can explain that G1 and G13 are the best genotypes. These (G1, G6, G13, G14, G17, and G18) improved multiple-stress-tolerant breeding lines with stable grain yield could be included in the variety release system in Bangladesh and be used as elite donor parents for the future breeding program as well as for commercial purposes with sustainable production.

Short-term fluctuations in salinity and turbidity: effects on the embryonic stage of two abalone species, Haliotis discus discus and Haliotis gigantea

Marine gastropod eggs are often distributed in the intertidal zone, where they are potentially exposed to short-term salinity and turbidity changes due to heavy rains that may adversely affect their embryonic development. In this study, the embryos of two abalone species, disk abalone Haliotis discus discus and giant abalone Haliotis gigantea, were exposed to various salinities (34, 30, 26, 22, 18 and 14 psu) or turbidities (0, 100, 300, 500 and 700 NTU) for a single 3 h period, and subsequently maintained at normal control conditions (34 psu and 0 NTU). The short-term low salinity stress decreased the hatching and survival rates, and increased the abnormality rate for both species. As for turbidity stress, negative effects on hatching and survival rates were observed in both species when their embryos were exposed to increased turbidity. The abnormality rates of both species at turbidities of 500 and 700 NTU were significantly higher than those at turbidities of 0 and 100 NTU. Overall, exposure of embryos to low salinity or high turbidity for even a short period can clearly have substantial impacts on the embryonic development of the two abalone species, and disk abalone was more sensitive to salinity and turbidity stresses compared to giant abalone.

Hypersalinity accompanies tectonic restriction in the eastern Mediterranean prior to the Messinian Salinity Crisis

This study describes the hydroclimate evolution of the eastern Mediterranean Basin during the early Messinian (7.2 to 6.5 Ma) time-interval based on analysis of a succession at Agios Myron (Crete, Greece), prior to the onset of the Messinian Salinity Crisis (5.96–5.33 Ma). Specifically, we report sea surface temperature and salinity reconstructions based on a combined analysis of biomarkers and oxygen isotopes of planktonic foraminifera. Data reveal that a negative water budget and strong hydrologic and climate variability characterized the eastern Mediterranean Basin at this time, and we identify three distinct phases. In Phase 1 (7.2–6.9 Ma), a shift to more positive oxygen isotope values in planktonic foraminifera at ~7.2 Ma is attributed to progressive gateway restriction of Mediterranean–Atlantic corridors and subsequent cooling until 6.9 Ma. In Phase 2 (6.9–6.7 Ma), distinct warm and hypersaline events (at 6.9–6.82 and 6.72 Ma) resulted in stressed marine microfauna during periods of strong evaporation. An important step-change in the Mediterranean restriction at 6.72 Ma may have resulted from shallowing of the Mediterranean gateways and reduced Mediterranean marine outflow. During Phase 3 (6.7–6.5 Ma) this gateway shallowing reduced the oceanic input into the Mediterranean Basin causing significant hydrological changes, reflected in a wide range of temperature and salinity fluctuations accompanied by enhanced water-column stratification. The data presented here counterbalance the general lack of quantitative temperature and especially salinity estimates available for the Mediterranean Messinian, time interval where we still highly rely on modelling for such evaluations. This study highlights the severity of preconditioning stages leading to the Messinian Salinity Crisis in the Mediterranean and sets values for extreme salinity conditions that could still host marine life. • Three restriction phases affected the eastern Mediterranean between 7.2 and 6.5 Ma. • Colder water and normal salinity characterized the Mediterranean during 7.2–6.9 Ma. • Periods of strong evaporation observed for the 6.9–6.7 Ma interval. • Warm-hypersaline events (6.9–6.82 and 6.72 Ma) caused extreme environmental stress. • Restriction at 6.7–6.5 Ma was induced by tectonics and modulated by climate.

The effect of depuration salinity on the survival, nutritional composition, biochemical responses and proteome of Pacific oyster (Crassostrea gigas) during anhydrous living-preservation

Control of depuration salinity is crucial to quality maintenance of live Pacific oyster (Crassostrea gigas) during anhydrous living-preservation. In present study, the survival, nutritional composition, biochemical responses and proteome changes of C. gigas were investigated during preservation in anhydrous conditions at 4 °C for 7 days after depuration (72 h) at salinity of 26–38 g/L, corresponding to −20%, −10%, 0, +10% and +20% fluctuation away from original production salinity in the spring of 2021. The results showed that the mortality, nutritional components and biochemical responses of C. gigas were sensitive to excessive salinity stress, especially at +20% fluctuation. In-depth proteomic analysis by sequential window acquisition of all theoretical fragment ion mass spectra (SWATH-MS) disclosed that proteome of C. gigas was altered widely and some functional proteins were up and down-regulated significantly. In conclusion, slight fluctuation (±10%) of depuration salinity is helpful in quality-maintaining of C. gigas in subsequent anhydrous living-preservation.

Environmental Change at Deep-Sea Sponge Habitats Over the Last Half Century: A Model Hindcast Study for the Age of Anthropogenic Climate Change

Deep-sea sponges inhabit multiple areas of the deep North Atlantic at depths below 250 m. Living in the deep ocean, where environmental properties below the permanent thermocline generally change slowly, they may not easily acclimatize to abrupt changes in the environment. Until now consistent monitoring timeseries of the environment at deep sea sponge habitats are missing. Therefore, long-term simulation with coupled bio-physical models can shed light on the changes in environmental conditions sponges are exposed to. To investigate the variability of North Atlantic sponge habitats for the past half century, the deep-sea conditions have been simulated with a 67-year model hindcast from 1948 to 2014. The hindcast was generated using the ocean general circulation model HYCOM, coupled to the biogeochemical model ECOSMO. The model was validated at known sponge habitats with available observations of hydrography and nutrients from the deep ocean to evaluate the biases, errors, and drift in the model. Knowing the biases and uncertainties we proceed to study the longer-term (monthly to multi-decadal) environmental variability at selected sponge habitats in the North Atlantic and Arctic Ocean. On these timescales, these deep sponge habitats generally exhibit small variability in the water-mass properties. Three of the sponge habitats, the Flemish Cap, East Greenland Shelf and North Norwegian Shelf, had fluctuations of temperature and salinity in 4–6 year periods that indicate the dominance of different water masses during these periods. The fourth sponge habitat, the Reykjanes Ridge, showed a gradual warming of about 0.4°C over the simulation period. The flux of organic matter to the sea floor had a large interannual variability, that, compared to the 67-year mean, was larger than the variability of primary production in the surface waters. Lateral circulation is therefore likely an important control mechanism for the influx of organic material to the sponge habitats. Simulated oxygen varies interannually by less than 1.5 ml/l and none of the sponge habitats studied had oxygen concentrations below hypoxic levels. The present study establishes a baseline for the recent past deep conditions that future changes in deep sea conditions from observations and climate models can be evaluated against.

The Effect of Feeding on Briareum violacea Growth, Survival and Larval Development under Temperature and Salinity Stress.

In recent years, climate change has often caused fluctuations in seawater salinity and temperature, which threaten the survival and growth of corals. Effectively improving the stress response to temperature and salinity changes in corals to prevent bleaching is one of the important issues. This study initially explored the use of artificial polyunsaturated fatty acids to assess the ability of Briareum violacea to slow bleaching, enhance growth, stabilize larval development and reduce antistress factors (superoxide dismutase and catalase) when they were exposed to temperature and salinity stress. The salinities used in the experiment were 25, 30, 35 and 40 psu, and the temperatures were 20, 25 and 30 °C. It was divided into two parts: Experiment 1-Effects of temperature and salinity and feeding on digestive enzymes, reproduction and stress response of B. violacea; Experiment 2-Effects of temperature and salinity and feeding on the settlement and survival of larvae. The results showed that the feeding treatment group reduced the superoxide dismutase, catalase and mortality of corals under stress and significantly improved larval development and larval settlement.

An Integrated Approach for Evaluating the Restoration of the Salinity Gradient in Transitional Waters: Monitoring and Numerical Modeling in the Life Lagoon Refresh Case Study

Large lagoons usually show a salinity gradient due to fresh water tributaries with inner areas characterized by lower mean values and higher fluctuation of salinity than seawater-dominated areas. In the Venice Lagoon, this ecotonal environment, characterized in the past by oligo-mesohaline waters and large intertidal areas vegetated by reedbeds, was greatly reduced by historical human environmental modifications, including the diversion of main rivers outside the Venice Lagoon. The reduction of the fresh water inputs caused a marinization of the lagoon, with an increase in salinity and the loss of the related habitats, biodiversity, and ecosystem services. To counteract this issue, conservation actions, such as the construction of hydraulic infrastructures for the introduction and the regulation of a fresh water flow, can be implemented. The effectiveness of these actions can be preliminarily investigated and then verified through the combined implementation of environmental monitoring and numerical modeling. Through the results of the monitoring activity carried out in Venice Lagoon in the framework of the Life Lagoon Refresh (LIFE16NAT/IT/000663) project, the study of salinity is shown to be a successful and robust combination of different types of monitoring techniques. In particular, the characterization of salinity is obtained by the acquisition of continuous data, field campaigns, and numerical modeling.