Fluctuating Salinity Conditions Research Articles

Growth Pattern and Survival of Mangrove Seedlings on the Coast of Peunaga Cut Ujong, West Aceh

Mangroves are coastal ecosystems with different abilities to adapt to changing environmental conditions. Habitat characteristics that continue to change cause morphological, anatomical, and physiological adaptations of mangrove species. This study aims to observe the survival and growth rate of Rhizhopora mucronata in Peunaga Cut Ujong, Meurebo, West Aceh. The mangroves were planted in 2022 and observed one year after planting. The observation and data collection of 35 tree samples were conducted every two weeks. The results showed a decrease in the survival rate from the third month of observation until the end, showing a decrease of 78%. In contrast, tree growth increased from months 1 to 5. Salinity conditions and substrates dominated by sand with minimal nutrients indicate adaptation to the growth of some relatively small mangrove species. Fluctuating salinity conditions with the dominance of sand have the potential to support the survival of R. mucronata, although with low growth. Its main influence still needs to be studied over a longer period. Keywords: adaptations, growth, morphometrics, salinity

High Ecophysiological Plasticity of Desmarestia aculeata (Phaeophyceae) Present in an Arctic Fjord under Varying Salinity and Irradiance Conditions.

Simple SummaryThe Arctic region has been affected by rising temperatures, directly affecting the organisms living there. One of the organisms that inhabit this area is the seaweed Desmarestia aculeata (Phaeophyceae), widely distributed in the North Atlantic. It is exposed to the high Arctic light regime and fluctuating salinity conditions from glacial and terrestrial run-off. Despite its abundance, little is known about D. aculeata and how environmental drivers will affect it in a future altered by climate change. During the summer of 2019, D. aculeata was collected in Kongsfjorden, Svalbard (78.9° N, 11.9° E) to investigate its physiological and biochemical responses to salinities of 34, 28, and 18, and daily cycles of irradiance (50–500 μmol photons m−2s−1) at 0 °C over 21 days. Photosynthetic parameters and high pigment concentrations show how this species has an effective acclimation to irradiance changes, being unaffected by low salinity. The high concentration of antioxidant phlorotannins at low salinity show how D. aculeata can regulate its daily cycle despite the hyposaline conditions. Salinity and light are interacting factors in the acclimation process. Our work shows the high plasticity of D. aculeata, such that the species will probably be able to tolerate future changes in the Arctic.The seaweed Desmarestia aculeata (Phaeophyceae) is distributed in the temperate zone of the North Atlantic up to the Arctic, where it is exposed to a high Arctic light regime and fluctuating salinity conditions resulting from glacial and terrestrial run-off. Information on how this species is able to thrive under current and future Arctic conditions is scarce. During the Arctic summer of 2019, D. aculeata was collected in Kongsfjorden, Svalbard (78.9° N, 11.9° E) to investigate its physiological and biochemical responses to variations in salinity (salinities: 34, 28 and 18) and daily cycles of irradiance (50–500 μmol photons m−2s−1) at 0 °C over 21 days. The species revealed effective short-term acclimation to both abiotic drivers. Maximal quantum yield of PSII (Fv/Fm) fluctuated with the light cycle at a salinity of 34, while the maximum relative electron transport rate (rETRmax) significantly differed between salinities of 28 and 18. Chlorophyll a and β-Carotene remained at high concentrations in all treatments showing pronounced acclimation during the experiment. High mannitol concentrations were measured throughout the experiment, while phlorotannins were high at low salinity. Hyposalinity and light are interacting drivers of the physiological and biochemical acclimation process for D. aculeata. Our experiment highlights the high ecophysiological plasticity of D. aculeata, suggesting that the species will likely be capable of withstanding future habitat changes in the Arctic.

Comparative Transcriptome Analysis Provides Insights into Response of Ulva compressa to Fluctuating Salinity Conditions.

Ulva compressa, a green tide-forming species, can adapt to hypo-salinity conditions, such as estuaries and brackish lakes. To understand the underlying molecular mechanisms of hypo-salinity stress tolerance, transcriptome-wide gene expression profiles in U. compressa were created using digital gene expression profiles. The RNA-seq data were analyzed based on the comparison of differently expressed genes involved in specific pathways under hypo-salinity and recovery conditions. The up-regulation of genes in photosynthesis and glycolysis pathways may contribute to the recovery of photosynthesis and energy metabolism, which could provide sufficient energy for the tolerance under long-term hyposaline stress. Multiple strategies, such as ion transportation and osmolytes metabolism, were performed to maintain the osmotic homeostasis. Additionally, several long noncoding RNA were differently expressed during the stress, which could play important roles in the osmotolerance. Our work will serve as an essential foundation for the understanding of the tolerance mechanism of U. compressa under the fluctuating salinity conditions.

Cyanobacteria as a Nature-Based Biotechnological Tool for Restoring Salt-Affected Soils

Soil salinization poses an important threat to terrestrial ecosystems and is expected to increase as a consequence of climate change and anthropogenic pressures. Conventional methods such as salt-leaching or application of soil amendments, or nature-based solutions (NBSs) such as phytoremediation, have been widely adopted with contrasting results. The use of cyanobacteria for improving soil conditions has emerged as a novel biotechnological tool for ecosystem restoration due to the unique features of these organisms, e.g., ability to fix carbon and nitrogen and promote soil stabilisation. Cyanobacteria distribute over a wide range of salt concentrations and several species can adapt to fluctuating salinity conditions. Their application in agricultural saline soil remediation has been demonstrated, mostly in laboratory studies, but there is a lack of research regarding their use in natural ecosystems restoration. In this article, we provide an overview of the current knowledge on cyanobacteria in the context of ecosystem restoration. Examples of the application of cyanobacteria in alleviating salt-stress in plants and soils are presented. Furthermore, we acknowledge gaps regarding the extensive application of cyanobacteria in salt-affected soils remediation and discuss the challenges of NBSs in salt-affected soils restoration.

Analysis of a Cretaceous (late Aptian) high-stress ecosystem: The Romualdo Formation of the Araripe Basin, northeastern Brazil

The Cretaceous (upper Aptian) Romualdo Formation of the Araripe Basin, northeastern Brazil, is a marine-influenced, predominantly fine-grained siliciclastic unit. In the eastern part of the basin, it corresponds to a depositional sequence composed of two transgressive-regressive cycles. Low-diversity benthic macrofaunas document high-stress conditions. Their palaeoecological and taphonomic analysis allows for the detailed reconstruction of the palaeoenvironments and of the temporal changes in the palaeoecosystem. The transgressive part of the lower cycle is a black shale with calcareous concretions that contain excellently preserved fishes and other vertebrates (the famous “Santana fossils”), but apart from abundant ostracods and rare decapod crustaceans, benthic faunal elements are very rare due to anoxic to dysoxic conditions. A low-diversity parautochthonous molluscan fauna of small bivalves and gastropods records fluctuating dysoxic conditions during early regression. Towards the top of the measured sections (late regression), thin gastropod shell beds become conspicuous. At the top of the sections decimetre-thick shell concentrations show signs of reworking and a greater marine influence (transgressive part of the upper cycle). The distribution pattern of three benthic associations and two assemblages is almost equally shaped by three environmental parameters: The low overall species diversity, small size of the fauna, and the lack of stenohaline elements suggest lowered and fluctuating salinity conditions. Fluctuating redox conditions with anoxia to dysoxia, identified especially in the lower parts of the succession, and substrate were the other two factors shaping the faunal distribution. The late Aptian sedimentary and faunal history of the eastern part of the basin indicates restricted marine influence, coupled with increasing freshwater input during phases of sea-level lowstand, and low-energy conditions offshore, which led to widespread anoxia, especially in the lower part of the formation. Thus, palaeoecological analyses are an excellent tool to disentangle the various environmental parameters that shaped the palaeoenvironments of the basin, to understand more closely its Fossil-Lagerstätten, and to corroborate and fine-tune the sequence stratigraphic framework.

Fluctuating salinity effect onSphoeroides annulatus(Jenyns 1842) physiological responses

Euryhaline fish, such as the Bullseye puffer Sphoeroides annulatus (Jenyns 1842), experience sudden salinity changes in their natural environment, which is more common than the exception, so they must adapt to survive and cope with extreme salt conditions. Therefore, Bullseye puffer juveniles were exposed to short-term stress (39 hr) by fluctuating salinity conditions (41, 35, 29, 23, 17, 11, 5, 11, 17, 23, 29, 35, 41 psu) with a 3-hr interval between each point at 26 ± 1ºC in a respirometer chamber and acclimation reservoirs. Responses to oxygen consumption rate (OCR: 23–35 mg O2 h–1 kg–1), ammonium excretion rate (AER: 1–1.85 mg NH4+ h−1 kg−1), oxygen-nitrogen atomic ratio (O:N 17–30), osmoregulatory pattern (blood osmotic pressure from 342.4 to 332.8 mmol/kg) and changes in expression levels of Na+/K+-ATPase in the gills (higher values at higher salinities) were measured. Although some signs of stress were detected below the iso-osmotic point (11.4 psu), the puffer fish is a strong euryhaline fish that survives under these conditions. Nonetheless, it could recover when salinity returned to the initial acclimation point because Sphoeroides annulatus is able to live in a wide range of environments with wide natural salinity fluctuations; thus, a common practice in aquaculture has been to expose fish to low salinity for several reasons discussed in this study. This capacity reveals its high plasticity to saline adaptation from 41 to 5 psu an up from 5 to 41 psu, all in less than 2 days.

Does sustained tolerance of reduced salinity seawater alter phagocytosis efficiency in haemocytes of the blue mussel Mytilus edulis (L.)?

Climate change driven increases in precipitation and extreme weather events bring with them periodic introductions of large volumes of freshwater to coastal waters and the possibility of extended salinity reductions capable of challenging marine organisms living there. Mytilus edulis is an osmoconformer, with no physiological capacity to maintain its haemolymph osmolarity above that of a dilute seawater medium. These mussels can however tolerate reduced seawater salinity to some degree by using intracellular volume control mechanisms to extend the range of seawater salinity they can tolerate, allowing them to continue to feed, respire and maintain general cellular function in fluctuating salinity conditions. When M. edulis are exposed to a falling salinity gradient, a critical salinity is reached that triggers closure of the valves, isolating their internal tissues from the surrounding environment and protecting them from further osmotic stress. This study investigated whether sustained tolerance of M. edulis to seawater with salinity just higher than the threshold level for valve closure affected haemocyte phagocytosis efficiency. Phagocytosis by haemocytes plays a significant role in the immune system of M. edulis by removing foreign bodies such as invading micro-organisms, together with dead and dying cells from the haemolymph. Valve gaping behaviour was recorded continuously in mussels exposed to a reducing seawater salinity gradient to establish the critical level initiating valve closure. M. edulis were then held for 5d within a flow through seawater system at a salinity of 25, close to the trigger value for valve closure in the population of mussels investigated (Namsenfjord, Norway). The exposed mussels continued to hold their valves open and active throughout, though mean valve gape and movement between valves were generally lower than control mussels held at ambient seawater with salinity of 34.3. Post-exposure total haemocyte counts and haemolymph protein concentrations in exposed mussels were similar to the controls, while phagocytosis performance, measured using flow cytometry, improved in the reduced salinity exposed mussels. These findings support a conclusion that M. edulis have the physiological capacity to continue to irrigate their gills for at least 5days when held continuously at seawater salinity close to their valve closure trigger level without detriment to haemocyte phagocytosis efficiency, a key component of their immune-response system. Such a capability will be important in the event of increasing persistent reduced salinity episodes.

Mangroves: obligate or facultative halophytes? A review

Salinity plays significant roles in regulating the growth and distribution of mangroves, and the salt tolerance mechanisms of mangroves have been the focus of research for several decades. There are contradictory views regarding the relationship between mangroves and salt: (1) Mangroves are facultative halophytes, i.e. freshwater is a physiological requirement and salt water is an ecological requirement for mangroves because they are capable of growing in freshwater. The former prevents excess respiratory losses while the latter prevents invasion and competition from non-halophytes. (2) Mangroves are obligate halophytes, i.e. salt is necessary for their growth. Mangroves cannot survive in freshwater permanently and salt water is a physiological requirement. Up to now, mangroves are usually considered as facultative halophytes. In this review, we provided five lines of evidence to evaluate these two contradictory views: (1) the results of laboratory culture experiments and field investigations; (2) the viviparous nature of mangroves; (3) the salt accumulation of mangroves under freshwater or low salinity; (4) the effect of salinity on the photosynthetic rate and in vitro enzyme activities, and (5) the effects of salinity fluctuation on mangrove growth and physiology. Contrary to widely accepted view, our evaluations of the aforementioned evidence suggest that mangroves are obligate halophytes. Mangroves can grow in freshwater for a limited time by drawing upon the nutrients and salt reserves in their hypocotyls while prolonged culture in freshwater is fatal to them. Mangroves have the ability to absorb Na+ and Cl− rapidly and preferentially under low-salinity conditions. Not all of the enzymes in mangroves are sensitive to salt. In fact, the activities of some enzymes are even stimulated by low or moderate salinity. Plants grown under constant salinity in a laboratory setting are unlikely to behave in the same way as those in their natural habitat with fluctuating salinity. Thus, studies on the effects of freshwater or low salinity and salinity fluctuation on mangroves, as well as the physiological mechanisms that allow maintenance of function under fluctuating salinity conditions should be strengthened in future research.

Hydrological response of an east-Saharan palaeolake (NW Sudan) to early-Holocene climate

We present a palaeolimnological record in western Nubia (NW Sudan, eastern Sahara) isolated from large-scale artesian systems and thus reflecting hydrological changes resulting from local rainfall. Past changes in lake water chemistry and water depth are interpreted by combining results from biological indicators (diatoms, ostracodes and charophytes) with geochemical and stable oxygen and carbon isotope data. Palaeolake Gureinat existed from ~10.9 cal. ka BP until at least 7.1 cal. ka BP and is devided into five lake phases. For the first two millennia the lake was shallow and fluctuating salinity conditions prevailed (500 to 3000 μS/cm). After ~8.7 cal. ka BP, the lake level rose, waters became fresh to oligosaline, and the lake had a minimum depth of at least 8 m. Both transgressive and stable lake phases were punctuated by at least three drops in lake level with complete desiccation at around 10.9 and 8.9 cal. ka BP. The third of these regressions may be coeval with the 8.2 ka climatic event. Sediments younger than 7.1 cal. ka BP representing the mid-Holocene fading of the wet phase were removed by deflation. This record shows that lakes in the eastern Sahara registered short-term climatic events, as long as they were isolated from large-scale artesian groundwater systems. Consequently, even in this continental region, early-Holocene climatic fluctuations affected water levels and salinities of hydrologically isolated lake systems.

Influence of constant and fluctuating salinity on responses of Mysidopsis bahia exposed to cadmium in a life-cycle test

Two 28-day, life-cycle tests were conducted to evaluate effects of constant and fluctuating salinities on chronic toxicity of cadmium to Mysidopsis bahia at 27°C. Salinities of 10 to 32%. and cadmium concentrations of 1 to 9 μg l were examined. Estimated median tolerance concentrations at day 28 ranged from 4.8 to 6.3 μg Cd l over the salinity range of 13 to 29%.. Size and fecundity of exposed and unexposed females were predicted to be comparable when cadmium was ⩽5.0 μg Cd l and salinities ⩾ 20%. and at concentrations of less than 5 μg l at lower salinities. At higher cadmium levels both responses were impaired regardless of salinity. Reproduction in control treatments was an order of magnitude lower in low (10 and 13%.) as compared to high (21, 29, 32%.) salinity treatments. This effect of salinity on reproduction was not moderated by periodic exposure to higher, more suitable salinities. Survival, growth and reproduction were not impacted by addition of 5 μg Cd l under fluctuating salinity conditions. The no-effect concentration is 4–5 μg Cd l regardless of salinity. Changes in survival, growth and reproduction observed are consistent with the principal distribution of M. bahia in estuaries relative to salinity. Comparison of these data with previously reported acute responses suggests that the acute water quality criterion for cadmium should be salinity-dependent whereas the chronic criterion need not be.

Osmoregulation of the Estuarine PrawnPalaemon Longirostris(Caridea: Palaemonidae)

The caridean prawnPalaemon longirostris(Milne-Edwards) (Palaemonidae) occurs predominantly in the upper regions of large river estuaries in Europe, and reaches its northern limit of geographical distribution along southern parts of Britain (Smaldon, 1979). All post-larval stages are thought to live under dilute and fluctuating salinity conditions, although there are conflicting reports as to whether ovigerous females need to migrate to the sea at times of egg hatching (Gurney, 1923; Fincham & Furlong, 1984). The species has been known to be extremely euryhaline for some considerable time (Gurney, 1923), yet the salinity tolerance limits of larval (Antonopoulou & Emson, 1989) and post-larval stages (Campbell & Jones, 1989) have been established only recently. Apart from studies on salinity tolerances, and some preliminary measurements of blood and urine osmolality (Parry, 1957), the osmoregulatory adaptations ofP.longirostristo its dynamic habitat have not been investigated previously. The present paper describes the osmoregulatory responses ofP.longirostrisacclimated to a wide range of salinities, and also reports on the ability of individuals to compensate for sudden acute salinity change.

Sedimentology of part of the Lower Oil-Shale Group (Dinantian) sequence at Granton, Edinburgh, including the Granton “shrimp-bed”

ABSTRACTThe Dinantian Lower Oil-Shale Group of the Edinburgh area records the evolution of a SW–NE trending basin within an area of fluvial-dominated deltaic sedimentation, with rare marine incursions from the E. The sequence at Granton records the abandonment of a delta lobe, with deltaic sandstones overlain by lagoonal mud-shales. These thinly-laminated non-bioturbated mud-shales record low-energy, stagnant conditions. Fish, ostracodes and conchostracans inhabited the lagoon at this time.Within the mud-shale sequence is the dolomitic Granton “shrimp-bed” which contains fenestrae, possible gypsum pseudomorphs andin situshrinkage breccias suggesting periods of emergence. The “shrimp-bed” contains a number of laminae packed with soft-bodied fossils including marine forms, which resulted from brief marine incursions into the stagnant lagoon. The fluctuating salinity conditions seem to have favoured the development of an unusual fauna of shrimp-like crustaceans, fish, conchostracans, ostracodes and bellerophontid gastropods. This fauna appears to have suffered periodic mass mortalities during marine incursions which brought orthocone cephalopods, polychaete worms and conodonts into the lagoon, according to our current knowledge of the distribution of these marine taxa in the sequence.The Granton sequence displays a variety of ductile and brittle deformation features most of which can be attributed to local SW-directed extension related to regional dextral strike-slip across the Midland Valley of Scotland.

Effects of Ablation of the Cerebral Organs and Cerebral Ganglia on Volume Regulation in an Intertidal Nemertine Paranemertes peregrina

In the Nemertina, cytological and physiological evidence points to an involvement of the cerebral organs and neurosecretory system (cerebral ganglia) in isoosmotic volume regulation. The solutes involved and the compartmentalization of the response between extra- and intracellular spaces have not been previously investigated. Intact and decerebrated (i.e., lacking cerebral organs and cerebral ganglia) Paranemertes peregrina were subjected to hypoosmotic (100% seawater [SW] → 70% SW for 72 h) as well as fluctuating salinity conditions (100% SW → 70% SW for 3 h → 100% SW for 12 h → 70% SW for 3 h). Replacement therapy experiments were not performed. In hypoosmotic media, intact individuals of P. peregrina regulate volume via putative neuroendocrine (1) stimulation of nephridial or gut elimination of extracellular water, Na, and Cl; (2) reduction in the permeability of the body wall or gut to inorganic ions; or (3) both mechanisms. The experiments performed do not allow for conclusive separation of these effects. There was also evidence for intracellular regulatory volume decrease (RVD) via organic solutes, but no direct effect of decerebration was observed. Under fluctuating salinity conditions, intact individuals of P. peregrina do not undergo regulatory volume increase (RVI) upon return to full-strength SW. However, RVD accomplished by Na and Cl excretion is potentiated by prior exposure to a diluted medium. Decerebration results in inability of the worms to restore their original water content upon return to full-strength SW as well as in the absence of RVD upon reexposure to hypoosmotic conditions. The excess water and inorganic solutes gained by decerebrated worms during initial exposure to diluted SW contribute substantially to the effects observed in these organisms under fluctuating salinity conditions. The relative contributions of the cerebral organs and the cerebral ganglia to volume regulation are not elucidated by the present study.

Effects of fenvalerate on larval development of Palaemonetes pugio (holthuis) and on larval metabolism during osmotic stress

Larvae of the estuarine grass shrimp, Palaemonetes pugio, were reared in the laboratory from hatch through metamorphosis under optimal salinity conditions (20‰) in a range of lethal and sublethal concentrations of the pyrethroid insecticide, fenvalerate. A nominal concentration of 3.2 ng fenvalerate/l significantly reduced the percentage of larvae that completed metamorphosis. Oxygen consumption rates were significantly higher for larvae exposed to this lethal concentration for only 24 h. Exposure to a sublethal concentration of 1.6 ng fenvalerate/l prolonged the duration of complete larval development. Acute osmotic stress modified the metabolism of larval P. pugio reared in sublethal fenvalerate concentrations of 0.1 and 0.2 ng/l and these metabolic responses varied with stage of development. After 8 days of exposure to fenvalerate, oxygen consumption rates were elevated when larvae were exposed acutely to hypoosmotic stress (10‰ S). Metabolic responses of premetamorphic larvae to hypersomotic stress (30‰ S) were also modified by sublethal fenvalerate exposure. Alterations in metabolic-salinity patterns of larval grass shrimp developing under sublethal concentrations of fenvalerate suggest reduction in the ecological fitness of this sensitive life stage by limiting their capacity to adapt to the fluctuating salinity conditions of estuarine waters.

Activity and respiration in the anemone, Metridium senile (L.) exposed to salinity fluctuations

Activity and respiration in the anemone, Metridium senile (L.), were monitored under both constant and fluctuating salinity conditions. During constant exposure to 50% sea water it was found that the animals retracted the tentacles and that the rate of oxygen consumption decreased by ≈50%. The same response was elicited from animals in 100% sea water in a contracted state. Animals exposed to continually fluctuating salinities were found to retract the tentacles, contract the body wall, and produce amounts of mucus during periods of decreasing salinities. These reactions were reversed during exposure to increasing salinity. Oxygen consumption never ceased entirely in animals exposed to dilute sea water and it was found that during declining oxygen tension M. senile regulated its oxygen consumption until the environmental oxygen tension fell to ≈30% saturation.