Hyposaline Environments Research Articles

Integrative transcriptomic and metabolomic analysis reveals the effects of a sudden drop in salinity on osmoregulation, metabolism, anti-oxidation, and immunity in Eriocheir sinensis megalopa and juvenile stages

Eriocheir sinensis has a special habit of migrating from marine to freshwater during its larval developmental stage. Salinity is an important environmental factor affecting the survival rate and growth performance of its larvae. Currently, the molecular mechanisms involved in the adaptation of E. sinensis larvae to a hyposaline environment remain unclear. Therefore, in this study, we designed an acute hyposaline stress experiment and sequenced the transcriptome and metabolome of the treated samples. After screening and annotation, 3323 and 2874 differentially expressed genes and 273 and 334 differentially expressed metabolites were identified by analysis of the transcriptomic data and metabolomic data at the megalopa and juvenile stages, respectively. Subsequently, a combined analysis of pathways was performed by co-mapping differentially expressed genes and differentially expressed metabolites into a KEGG database. Furthermore, the analysis results showed that 92 and 115 shared KEGG pathways were identified at the megalopa and juvenile stages, respectively. These shared pathways were mainly related to energy metabolism, osmotic pressure regulation, antioxidants, and immunity. The results showed that megalopa and juvenile had similar response mechanisms for adjusting to extremely hyposaline environments. The sudden drop in salinity may have impaired the osmoregulation ability and disturbed the energy metabolism of E. sinensis larvae. The glucose and TCA cycle processes were inhibited, and the cholesterol and glycine metabolisms were significantly changed. In addition, the sudden drop in salinity may cause oxidative stress in the larvae, accelerate the synthesis and consumption of glutathione, damage mitochondrial function, and induce cell apoptosis. Therefore, this study provides key information for understanding hyposaline tolerance mechanisms in E. sinensis larvae.

Tracing ecological fluctuations during the Middle to Late Jurassic of Jhura, Kutch, India, using foraminifera

The aim of this work is to examine ecological patterns by analyzing the distribution of foraminifera in the Jurassic sediments of the Jhura area, Kutch, India. 87 foraminiferal species were recovered, which were analyzed for paleoecological interpretations. Three techniques were employed: 1) Diversity indices, in which four episodes are identified based on different indices values; 2) Clustering and nMDS ordination approaches identify four assemblages of benthic foraminifera, which differ in biotic and abiotic characteristics; 3) Morphogroup analysis, which divides the studied sequence into four paleoecological units. Four depositional episodes are recognized within the studied interval: Episode I (Bajocian to Bathonian), Spirillina polygyrata assemblage shows the calm environment with a high diversity of foraminiferal species and enough nutrients in the outer shelf zone having normal salinity and high level of dissolved oxygen. Episode II (Lower Callovian), Miliammina cf. M. valdensis assemblage occurred in a stressed condition with low diversity of species in a shallower portion of mid-shelf in a hypo-saline environment and reduced oxygen condition having low to average food influx. Episode III (Middle to Upper Callovian), Lenticulina subalata assemblage indicates that this portion deposited in stress-free environmental conditions having normal salinity and well‑oxygenated waters in the deepest section of the outer shelf region with high nutrient supply. Episode IV (Oxfordian), Lenticulina bulla assemblage thrived in hyposaline conditions with low oxygen levels and enough nutrients in the deeper portion of the mid-shelf region. An unstable oceanic shelf is interpreted during the deposition of the examined section because of the fluctuations in all inferred parameters.

Quaternary Evolutionary Stages of Selinitsa Cave (SW Peloponnese, Greece) Reveal Sea-Level Changes Based on 3D Scanning, Geomorphological, Biological, and Sedimentological Indicators

Significant evolutionary stages of Selinitsa Cave (SW Peloponnese, Greece) were revealed by 3D mapping, as well as geomorphological study of the cave and the nearby landscape. Four marine terraces were identified in the area of the coastal cave at 6, 10.7, 16.6, and 30–32 m above sea level (asl), with the terrace at 16.6 m representing Marine Isotope Stage (MIS) 5. The widest karstified space of Selinitsa Cave clusters between 15.73 and 18.05 m above sea level (asl), with the peak lying at 16.4 m asl, corresponding to the level where the phreatic/epiphreatic zone was stable for a sufficient period of time. A tidal notch at 16.4 m asl at the cave entrance is correlated to the marine terrace at 16.6 m. Both features correspond to the sea-level stand at which intense karstification occurred. The tidal notch bears a horizontal arrangement of Lithophaga borings at the vertex. Sedimentological investigation of the Selinitsa fine-grained deposit revealed the paleohydrologic regime of the cave. It is characterized by “slack-water” facies, indicating very low water flow speeds, whereas the thickness of the deposit points to stable hydrological conditions for prolonged periods. The cave sediment height of 18.8 m asl indicates a flooding level higher than sea level. The overlying Plattenkalk flysch is most probably the major source of detritus, and the predominance of authigenic dolomite (>98% modal in the carbonate fraction) indicates a hyposaline environment related to mixing of sea water with percolating fresh water. The approach of this study shows the significance of 3D mapping, bio-geo-Relative Sea Level (RSL) indicators, and sedimentology in deciphering the paleogeographic evolution of coastal karstic systems and subsequently defining the paleoclimate regime of coastal areas in Greece and the eastern Mediterranean during the Late Quaternary.

Effect of low pH and salinity conditions on the antioxidant response and hepatocyte damage in juvenile olive flounder Paralichthys olivaceus

Climate change due to increasing CO2 emissions results in the increase in water temperatures, which is accompanied by the decrease in pH and salinity levels of the ocean. Ocean acidification reflects the gradual pH reduction due to changes in the carbon chemistry, which is caused by the increase in anthropogenic CO2 emissions. The subsequent changes in the water temperatures and carbon chemistry of the oceans affect the survival and distribution of aquatic animals. In this study, we analyzed the levels of cortisol, superoxide dismutase, catalase, and caspase-3 in the plasma of juvenile olive flounder Paralichthys olivaceus under combined hyposalinity and acidification. To evaluate the physiological response to these changes, the superoxide dismutase activity and apoptosis were analyzed in the liver cells. Hyposalinity caused oxidative stress and cell damage, while also activating the antioxidant system. Environmental acidification affected the stress response and antioxidant mechanism of P. olivaceus in the early stage of acclimation but did not appear to exceed hyposalinity stress. These findings suggest that a hyposaline environment may be a stronger environmental stressor than an acidifying environment for P. olivaceus, and will help understand the capacity of P. olivaceus to cope with expected future ocean acidification.

The effectiveness of hyposaline treatments against host-attached salmon lice

Understanding how salinity affects marine parasites is vital to understanding their ecology and treatment, particularly for host-parasite systems that traverse marine and freshwater realms such as the globally important Atlantic salmon (Salmo salar), salmon louse (Lepeophtheirus salmonis) system. Growing concerns for wild fish populations, and decreased efficiencies and burgeoning costs of lice treatments for farmed fish has necessitated more environmentally and socially acceptable delousing procedures, such as hyposaline treatments. The effect of brackish water on L. salmonis following primary attachment is largely unknown, with experimental evidence derived mostly from unattached or newly attached copepodids, or adult stages. We aimed to understand how attached lice respond to hyposaline environments to assess effectiveness as a parasite management strategy and to help better define delousing areas used by wild fish. Louse development at 4, 12, 19 and 26 ppt, and survival at 4 ppt, decreased as exposure times increased, but survival was otherwise unaffected. Subjecting salmon to fluctuating, repeat exposures did not influence efficacy. We confirm that free-swimming stages are susceptible, and show that attached copepodids were more tolerant than previously predicted based on experiments on alternate development stages. These results improve our understanding of the utility of hyposaline treatments in aquaculture and self-treating in wild fish, and could apply to other fish-lice parasite systems. Further, these data are important for models predicting host-parasite interactions and can contribute to predictive models on the transmission dynamics of sea lice from farm to wild fish.

Changing depositional environments reflected by foraminifera in a transgressive-regressive sequence of the Lower Cretaceous on Spitsbergen

The Boreal Valanginian to Barremian foraminiferal succession of the Rurikfjellet Formation in central Spitsbergen is applied to stratigraphic zonation, analyses of depositional conditions and developing a sequence stratigraphic model. The study is based on the Janusfjellet section where the formation is 204 m thick, and represents a depth range from upper bathyal to prodelta top. It contains a continuous benthic foraminiferal succession permitting distinction of five assemblage zones. The assemblages are almost entirely agglutinated and reflect calcium carbonate depletion, which appears as an overall feature of Mesozoic Boreal seas superimposed on other, but more local restricting factors such as salinity and food supply. Close taxonomic similarities within the Boreal Realm are revealed by comparison of the Janusfjellet foraminiferal faunas to those of other pan-Arctic sites. The lower half of the Janusfjellet section contains a significant faunal component comparable to modern bathyal faunas and Late Cretaceous to Paleogene flysch-type assemblages indicating upper bathyal to offshore shelf depths. In the upper half of the section increased diversities are created by enhanced food supply in middle shelf setting. This is succeeded by increasing deltaic impact leading to hyposaline environments reflected by low species diversities. Changing foraminiferal biofacies trends through the Janusfjellet section are portrayed in the framework of the third order transgressive–regressive Wimanfjellet Sequence. Its transgressive systems tract was deposited mainly at upper bathyal depths with maximum flooding surface in the lower (Valanginian) part of the Rurikfjellet Formation. The regressive systems tract reveals an upward shoaling succession from upper bathyal conditions, through marine shelf to hyposaline prodelta setting.

Abundance and Ecology of EndemicAsterorotalia trispinosafrom the Western Bay of Bengal: Implications for its Application as a Paleomonsoon Proxy

AbstractA total of 97 surface sediment samples were collected from the continental shelf and slope of the western Bay of Bengal to assess the potential application ofAsterorotalia trispinosaas a paleomonsoon proxy. The relative abundance of living as well as total (living and dead)A. trispinosaranges from being absent to a maximum of ∼31%. The highest abundance ofA. trispinosais close to the outfall region of the Ganga‐Brahmaputra Rivers and decreases away from the river mouths. Contrary to that,A. trispinosais rare in front of both the Cauvery and Pennar river outfall regions, in the central part of the western Bay of Bengal. The livingA. trispinosaabundance is the lowest in between two major river systems, viz. Ganga‐Brahmaputra‐Mahanadi and Krishna‐Godavari. The relative abundance of both the total and livingA. trispinosais strongly positively correlated with ambient seawater temperature, and negatively correlated with %Corg and salinity. Based on the spatial distribution, we conclude thatA. trispinosais stenohaline in nature, rather than euryhaline, and further that the increased relative abundance ofA. trispinosaindicates warmer and only marginally hyposaline environment. Even though the ecological preference ofA. trispinosasuggests it as a potential paleomonsoon proxy, the restricted distribution implies limited application.

Calcareous nannoplankton and foraminiferal response to global Oligocene and Miocene climatic oscillations: a case study from the Western Carpathian segment of the Central Paratethys

Abstract The reactions of foraminiferal and calcareous nannoplankton assemblages to global warming and cooling events in the time intervals of ca. 27 to 19 Ma and 13.5 to 15 Ma (Oligocene and Miocene) were studied in subtropical epicontinental seas influenced by local tectonic and palaeogeographic events (the Central Paratethys). Regardless of these local events, global climatic processes significantly influenced the palaeoenvironment within the marine basin. Warm intervals are characterized by a stable, humid climate and a high-nutrient regime, due primarily to increased continental input of phytodetritus and also locally due to seasonal upwelling. Coarse clastics deposited in a hyposaline environment characterize the marginal part of the basin. Aridification events causing decreased riverine input and consequent nutrient decreases, characterized cold intervals. Apparent seasonality, as well as catastrophic climatic events, induced stress conditions and the expansion of opportunistic taxa. Carbonate production and hypersaline facies characterize the marginal part of the basins. Hypersaline surface water triggered downwelling circulation and mixing of water masses. Decreased abundance or extinction of K-specialists during each cold interval accelerated their speciation in the subsequent warm interval. Local tectonic events led to discordances between local and global sea-level changes (tectonically triggered uplift or subsidence) or to local salt formation (in the rain shadows of newly-created mountains).

Ecosystem indicators: Foraminifera, Thecamoebians and Diatoms from the Ologe Lagoon, Nigeria

The Ologe Lagoon in southwestern Nigeria is a natural habitat located closely to both residential and industrial estates. The lagoon is heavily affected by effluents of agricultural and industrial runoff including organochlorine compounds and heavy metals (chloropesticides, DDT and polychlorinated biphenyls, cadmium, manganese, zinc, copper, lead, iron and nickel). Ologe Lagoon is situated in a semi-isolated position and its brackish waters traverse several creeks and lagoons before it reaches the Atlantic Ocean. The lagoon experiences minor tidal but noticeable salinity and pH variations during the rainy season. During the dry season, however, the waters have a comparatively long resident time where sediments act as sink and aggregate contaminants over time. Investigations on benthic foraminifera, thecamoebian and diatom species were carried out to document the current status, composition, spatial distribution, and response of microfaunal assemblages to environmental stressors within the lagoon. The benthic foraminifer assemblage is composed of four highly specialized agglutinated species of Ammotium salsum, Miliammina fusca, Ammobaculites dilatatus and Ammobaculites aff. A. exiguus. They are present at all sample sites with varying abundances. The high abundance of Ammotium salsum is considered an indication of environmental stress. Thecamoebian species of Difflugia oblonga, Difflugia proteiformis and Pontigulasia compressa were also recorded in varying proportions and generally represent less than one percent of the total foraminifera/thecamoebian assemblage. The presence of marine brackish water larger siliceous diatoms of Actinoptychus and Campylodiscus species indicates an interaction between the lagoon and the marine waters although on the minimal scale with regards to actual salinity ranges. The faunal assemblages recovered are characterized by low species richness and alpha diversity indices and are typical of shallow, marginal-marine hyposaline environments. Numerical abundances and spatial distribution patterns suggest taxon-specific habitat preferences and highlight their potential for environmental monitoring studies.

Effects of short-term hyper- and hypo-osmotic exposure on the osmoregulatory strategy of unfed North Pacific spiny dogfish (Squalus suckleyi)

The North Pacific spiny dogfish (Squalus suckleyi) is a partially euryhaline species of elasmobranch that often enter estuaries where they experience relatively large fluctuations in environmental salinity that can affect plasma osmolality. Previous studies have investigated the effects of altered salinity on elasmobranchs over the long term, but fewer studies have conducted time courses to investigate how rapidly they can adapt to such changes. In this study, we exposed unfed (no exogenous source of nitrogen or TMAO) spiny dogfish to hyper- and hypo-osmotic conditions and measured plasma and tissue osmolytes, nitrogen excretion, and changes in enzyme activity and mRNA levels in the rectal gland over 24h. It was shown that plasma osmolality changes to approximately match the ambient seawater within 18–24h. In the hypersaline environment, significant increases in urea, sodium, and chloride were observed, whereas in the hyposaline environment, only significant decreases in TMAO and sodium were observed. Both urea and ammonia excretion increased at low salinities suggesting a reduction in urea retention and possibly urea production. qPCR and enzyme activity data for Na+/K+-ATPase did not support the idea of rectal gland activation following exposure to increased salinities. Therefore, we suggest that the rectal gland may not be a quantitatively important aspect of the dogfish osmoregulatory strategy during changes in environmental salinity, or it may be active only in the very early stages (i.e., less than 6h) of responses to altered salinity.

Nutritional Status as the Key Modulator of Antioxidant Responses Induced by High Environmental Ammonia and Salinity Stress in European Sea Bass (Dicentrarchus labrax).

Salinity fluctuation is one of the main factors affecting the overall fitness of marine fish. In addition, water borne ammonia may occur simultaneously with salinity stress. Additionally, under such stressful circumstances, fish may encounter food deprivation. The physiological and ion-osmo regulatory adaptive capacities to cope with all these stressors alone or in combination are extensively addressed in fish. To date, studies revealing the modulation of antioxidant potential as compensatory response to multiple stressors are rather lacking. Therefore, the present work evaluated the individual and combined effects of salinity challenge, ammonia toxicity and nutritional status on oxidative stress and antioxidant status in a marine teleost, European sea bass (Dicentrarchus labrax). Fish were acclimated to normal seawater (32 ppt), to brackish water (20 ppt and 10 ppt) and to hypo-saline water (2.5 ppt). Following acclimation to different salinities for two weeks, fish were exposed to high environmental ammonia (HEA, 20 mg/L representing 50% of 96h LC50 value for ammonia) for 12 h, 48 h, 84 h and 180 h, and were either fed (2% body weight) or fasted (unfed for 7 days prior to HEA exposure). Results show that in response to decreasing salinities, oxidative stress indices such as xanthine oxidase activity, levels of hydrogen peroxide (H2O2) and lipid peroxidation (malondialdehyde, MDA) increased in the hepatic tissue of fasted fish but remained unaffected in fed fish. HEA exposure at normal salinity (32 ppt) and at reduced salinities (20 ppt and 10 ppt) increased ammonia accumulation significantly (84 h–180 h) in both feeding regimes which was associated with an increment of H2O2 and MDA contents. Unlike in fasted fish, H2O2 and MDA levels in fed fish were restored to control levels (84 h–180 h); with a concomitant increase in superoxide dismutase (SOD), catalase (CAT), components of the glutathione redox cycle (reduced glutathione, glutathione peroxidase and glutathione reductase), ascorbate peroxidase (APX) activity and reduced ascorbate (ASC) content. On the contrary, fasted fish could not activate many of these protective systems and rely mainly on CAT and ASC dependent pathways as antioxidative sentinels. The present findings exemplify that in fed fish single factors and a combination of HEA exposure and reduced seawater salinities (upto 10 ppt) were insufficient to cause oxidative damage due to the highly competent antioxidant system compared to fasted fish. However, the impact of HEA exposure at a hypo-saline environment (2.5 ppt) also defied antioxidant defence system in fed fish, suggesting this combined factor is beyond the tolerance range for both feeding groups. Overall, our results indicate that the oxidative stress mediated by the experimental conditions were exacerbated during starvation, and also suggest that feed deprivation particularly at reduced seawater salinities can instigate fish more susceptible to ammonia toxicity.

The effect of temporal variability in salinity on the invasive red alga Gracilaria vermiculophylla

Non-native, invasive species are often characterized by being tolerant to environmental stressors, leaving them more fit relative to native species. The red alga Gracilaria vermiculophylla originates from the NW Pacific but has recently spread along the coastlines of Western Europe, where it has become abundant in many shallow, soft-bottom estuaries. Salinity is important for the local and regional distribution of algae. The distribution of G. vermiculophylla in Europe suggests that it thrives well in hyposaline environments and that it may be more fit than some native algae under such conditions. Little, however, is known about the ecophysiology of G. vermiculophylla and it is therefore difficult to predict its spread and future distribution. Laboratory experiments with G. vermiculophylla showed that steady-state salinity above 15 psu was optimal for growth and that the growth rate was reduced at salinities below 15 psu. Variable salinity reduced the growth rate and larger oscillations were more stressful than small ones. Exposure to very low salinity (0–5 psu) was stressful for the alga and algae exposed to these low levels for 2–4 days were unable to recover fully. Gracilaria vermiculophylla did not seem to perform better in hyposaline conditions than many native, estuarine species. The present distribution of G. vermiculophylla in Scandinavia can be explained well by its response to salinity, but this may not explain its present success relative to many naturally occurring algal species.

Salinity-related growth rates in populations of the European clam Macoma balthica and in field transplant experiments along the Baltic Sea salinity gradient

Most benthic invertebrates and plant species that survive in the brackish Baltic Sea are characterized by populations in which growth is reduced and genetic diversity is low, indicating that these species live under marginal conditions. In this study, we tested for a salinity-related growth rate reduction in 21 European Macoma balthica populations. Additionally, we transplanted clams into hyposaline environments, along the Baltic Sea salinity gradient, and compared survival, growth and condition with control groups. All transplants into hypoosmotic environments were successful. Despite the osmotic shock, the results showed no reduced growth rates in transplanted individuals. Only the clams that had been transplanted into the extremely oligohaline Gulf of Bothnia (0.5–3.0 PSU) exhibited reduced growth rates in comparison to the control group. From this study we conclude that M. balthica has an exceptional capacity to acclimatize to extremely brackish conditions, which may explain its abundance and diversity in the Baltic Sea.

Foraminiferal Distribution in the Central and Western Parts of the Late Pleistocene Champlain Sea Basin, Eastern Canada

Marine sediments from the late-glacial Champlain Sea have been sampled at 20 localities representing the deeper part of the basin, between Ottawa and the Rivière St-François, Québec. Foraminiferal assemblages have been extracted and a sequence of three deep water and two shallow water ecozones recognized. The lowermost zone (A) is characterized by Cassidulina reniforme, Islandiella helenae and I. norcrossi and represents a paleosalinity of 25 to 30%o. The overlying zone B is dominated by Elphidium excavatum. It represents salinities decreasing from 25 to as low as 10%o. The uppermost zone (C) contains only a sparse assemblage of a morphotype of E. excavatum. If suggests a paleosalinity of no more than 10%o. A mostly unfossiliferous silt and clay layer of variable thickness (post-C) occurs above zone C. It is probably lacustrine. Below zone A and above the Late Wisconsinan till there is a pre-A interval whose variable assemblages represent hyposaline environments east of Montréal, predominantly lacustrine conditions west of Montréal and alternating hyposaline/ lacustrine environments near and south of Montréal. Bottom water temperatures were probably "Arctic" (within a few degrees of 0°) from the pre-A interval up to zone B inclusively. The data from zone C are too poor to estimate temperatures. The shallow water zones indicate environments with high (zone EH) or low (zone EA) salinities but of shallower depths than the deep water zones. The existence of two sequences is interpreted as the result of (probably seasonal) water stratification. The data does not allow to determine the depth of the limit between the shallow and deep waters.

The expression of gill Na, K-ATPase in milkfish, Chanos chanos, acclimated to seawater, brackish water and fresh water

Juvenile milkfish Chanos chanos (Forsskål, 1775) were transferred from a local fish farm to fresh water (FW; 0‰), brackish water (BW; 10‰, 20‰) and seawater (SW; 35‰) conditions in the laboratory and reared for at least two weeks. The blood and gill of the fish adapted to various salinities were analyzed to determine the osmoregulatory ability of this euryhaline species. No significant difference was found in plasma osmolality, sodium or chloride concentrations of milkfish adapted to various salinities. In FW, the fish exhibited the highest specific activity of Na, K-ATPase (NKA) in gills, while the SW group was found to have the lowest. Relative abundance of branchial NKA α-subunit revealed similar profiles. However, in contrary to other euryhaline teleosts, i.e. tilapia, salmon and eel, the naturally SW-dwelling milkfish expresses higher activity of NKA in BW and FW. Immunocytochemical staining has shown that most Na, K-ATPase immunoreactive (NKIR) cells in fish adapted to BW and SW were localized to the filaments with very few on the lamellae. Moreover, in FW-adapted milkfish, the number of NKIR cells found on the lamellae increased significantly. Such responses as elevated NKIR cell number and NKA activity are thought to improve the osmoregulatory capacity of the milkfish in hyposaline environments.

Enhanced Superoxide Production by Membrane Vesicles from Halobacterium halobium in a Hyposaline Environment

Membrane vesicles were prepared from the halophilic archaebacterium, Halobacterium halobium, which was grown either in medium containing 4 M NaCl or in a relatively hyposaline medium containing 1.25 M NaCl. Membrane vesicles prepared from bacteria grown in the lower salt environment consumed more oxygen, oxidized more NADH and generated more superoxide than vesicles prepared from cells grown in the normal 4 M NaCl containing medium. The enhanced respiratory activity of the membrane fragments obtained from the halophile which was grown and assayed in a hyposaline environment, along with the concomitant increased flux in superoxide, demonstrate a relation between an environmental perturbation and an altered electron transport activity.

Transgression et paleoenvironnement à l'Oligocène en Bretagne (France). Sédimentologie, micropaléontologie, palynologie et palynofaciès du Rupélien du Bassin de Rennes

The main Oligocene basins on the Armorican Massif are tectonic in origin and generally orientated in a NNW-SSE direction. One of them, the Rennes basin, was drilled to a depth of 140 m and provides the most complete section so far obtained through the Oligocene. Micropalaeontological analyses (spores, pollen, foraminifera and ostracods) give a Rupelian (Stampian) age for the entire sequence. Sedimentological and mineralogical investigations show the absence of coarse-grained detritics among the different deposits. Kaolinite is present throughout the section; smectites and illites are also present and reveal environmental changes. The anoxic confinement of the waters, shown by the presence of pyrite, alternates with more oxygenated periods. Carbonate-rich sediments dominate in the upper part of the section. The lower two-thirds of the sequence have a very high organic matter content and are rich in pollen and spores, but devoid of mineralized fossils. Variations of the different palyno-ecological groups and analyses of the organic matter (palynofacies) are used to differentiate paludal and marine environments and to recognize water level fluctuations with high- and low-stand episodes. The upper part of the section contains foraminifera and ostracod-rich levels. Their studies delineate four ecozones indicating fresh water influences and the degree of confinement of the basin. The environmental succession of the microfaunal association and the morphologies of the taxa are related to changes in water salinity and water depth. These results reveal that there were repeated episodes of early marine influences in the paludal environment under predominantly anoxic conditions. With the appearance of a characteristics fauna, open marine conditions were gradually established in a hyposaline environment that was still subject to sporadic continental influences. At the peak of the transgression, platform-type sedimentation was developed close to the coast. The succession was terminated by a sudden return to lagoonal facies that corresponds to the end-Rupelian regression. A comparison of the Oligocene basins of Brittany and of the British Isles reveals similar structural features and basin orientations on both sides of the Channel. This suggests that the basins experienced a similar geodynamic evolution, in a distensive context. The Rupelian deposits of the Armorican Massif are situated in the Oligocene palaeogeographical scheme of Northwest Europe. Thus, the obvious Aquitanian affinities of the foraminifera and ostracod fauna demonstrate easy southwestward marine communications of the basins with the Atlantic Ocean.

Comparative Physiological Ecology of Centrarchids in Hyposaline Environments

Empirical evidence and data from this study suggests that there are intrafamilial differences in salinity tolerance that apparently change longitudinally along salinity gradients. Lepomis punctatus and Micropterus punctulatus require a significantly longer time to acclimate to increased salinity than L. microlophus, which apparently acclimates within 1 h. Both increased salinity (0–8 ppt) and the time (1–72 h) exposed to a particular salinity impact osmotic and hematocrit regulation. Observed intrafamilial differences in osmotic and hematocrit regulation underlay the distribution and relative abundance of centrarchids and could explain their seasonal use o low salinity marshes. Furthermore, the > 12-h acclimation times of L. punctatus and M. punctulatus suggest that these two species may never become fully acclimated to a salinity during a diurnal tidal cycle.

Messinian salinity crisis and its paleogeographical implications

During the Late Messinian (uppermost Miocene) the region that is now Italy was occupied by a lake or system of lakes similar to those of the Paratethys existing to the east. Lacustrine deposits are known, not only in Italy, but extending southward through Sicily into the northern part of Tunisia. These strata contain faunas tyoical of a hyposaline environment. The lakes generally exhibit shallow-water characteristics and follow the structural trends of the “geosynclinal” development of Italy during the Late Miocene. We conclude that the water level ofthe hyposaline lake system was conspicuously lower than the general level of the World Ocean system. We support the point of view that the western Mediterranean was in a state of partial desiccation. In the area studied, the sharp contact between Miocene and Pliocene deposits points to a sudden change from a region of shallow lakes or subaerial erosion to the deposition of deep-water sediments. The sudden appearance of d deep-water environment is explained if the Pliocene transgression is considered to be a consequence of the re-establishment of communications with the open sea.

Geographic Variation for Salt Water Tolerance in the Frog Rana sphenocephala

Adult Rana sphenocephala from hypersaline environments in Florida are more tolerant of dilute sea water than are individuals of the same species from hyposaline environments. This increased tolerance to brackish water appears to be a result of a decrease in the rate of water loss for frogs from hypersaline environments. The decrease in the rate of water loss appears to be a result of a more concentrated plasma, which has the effect of reducing the osmotic gradient between the frog and its environment, and an increased body size, which has the dual effect of reducing the surface area relative to the internal volume of water and increasing skin thickness, probably reducing permeability. A decreased rate of water loss appears to be adaptive for frogs living in the constantly fluctuating salinity typical of a Florida salt marsh.