Hyposaline Conditions Research Articles

Lethal and Sublethal Effects of Altered Sand Salinity on Embryos of Beach-Spawning California Grunion

Abstract Embryos of beach-spawning California Grunion incubate terrestrially buried in sand above the tide line. Out of water, these marine teleosts may encounter osmotic challenges including dilution by rainfall or freshwater runoff, or hypersalinity from evaporation or human activities. To test the physiological tolerance of California Grunion embryos, we incubated them in sand at different, ecologically relevant salinities, bracketing their physiological tolerance between 16 and 48 ppt. Fertilization percentage, embryo survival, hatching success, and larval length all decreased when salinity was higher or lower than control seawater, 32 ppt. Some embryos developed deformities that prevented hatching when incubated at high salinities. Mortality at each life stage resulted in significantly lower total survival in hyposaline or hypersaline incubation conditions. Effects of altered salinity include significantly reduced fertilization of eggs, greater mortality of zygotes, smaller hatchlings, and significan...

The distribution and behaviour of Patiriella mortenseni and P. regularis in the extreme hyposaline conditions of the Southern New Zealand Fiords

Echinoderms are a stenohaline phylum, however some species can tolerate varying degrees of exposure to hyposaline conditions. These exposures typically are limited in duration to a few hours to no more than a day or two, and hyposalinity levels range from ~ 8‰ to < 30‰. The unique climatological and hydrographic conditions in Fiordland of southwest New Zealand produce a near-freshwater layer (Low Salinity Layer = LSL) on top of marine (34‰) water. The relative depth of the LSL varies both tidally and with rainfall. This halo-boundary presents a particularly stressful osmotic challenge to organisms found in shallow water. A series of transects in Doubtful Sound and the more northern Milford Sound quantified differences in density and bathymetric distribution of two species of seastars . The surveys revealed that Patiriella mortenseni occurs primarily below the LSL whereas Patiriella regularis is found well within the range of the LSL. Video observations of P. regularis over a rising tide were correlated with salinity measurements and showed a strong correlation between increased salinity and general vertical displacement upwards of the seastars observed moving. Activity coefficients (AC) were used to estimate the degree of neuro-muscular coordination and stress levels of these seastars in two hyposalinity experiments. Reciprocal transplants showed that P. regularis performed equally well in deeper, marine-salinity waters, as in shallow hyposalinity conditions, whereas P. mortenseni showed significantly impaired performance in the hyposaline conditions. These performance estimates were refined in a second experiment by quantifying AC of both species in a seawater dilution series. To rule out the possibility of heretofore unknown osmoregulatory capacity, we exposed both species to 0‰, 5‰, 15‰, 25‰, and 34‰ and recorded the osmolarity of the body fluid after 24 h. P. mortenseni died at salinities below 25‰. In contrast, P. regularis survived and the body fluid was nearly isotonic with the surrounding water. Two final experiments established the hyposalinity-tolerance limits of P. regularis. In a righting-time (RT) experiment we exposed P. regularis to hyposaline water of 5‰ for: 12, 24, 36, 48, 60, 84, and 133 h and recorded righting times immediately after re-immersing them in sea water. All individuals survived and the mean RT ranged from 18 min to 27 h (control group = 1.6 min). Finally, a lethal-exposure experiment to 0‰ (deionized water) confirmed that P. regularis can withstand far greater levels of extreme hyposalinity than has been reported for any other echinoderm.

Micropalaeontological evidence of brackish water conditions during deposition of the Knorringfjellet Formation, Late Triassic–Early Jurassic, Spitsbergen

The Knorringfjellet Formation is a succession of mudstones and sandstones, ranging in age from Norian to Toarcian in western and west-central Spitsbergen, and contains several unconformities with associated hiatuses. Its foraminiferal succession consists almost exclusively of agglutinated taxa, shows extremely low assemblage diversities and a dominance of small-sized species. These faunal features signalize restricted environmental conditions (in contrast to those of a normal marine shelf). Comparisons with ancient and modern analogues suggest that the main restricting factor was hyposaline conditions, to a lesser extent augmented by hypoxia in near-bottom waters. These conditions were caused by high fluvial influx creating gravity stratified water masses. The depositional area was part of an extensive but shallow shelf embayment, which had an open connection to the north to the polar ocean basin. Discontinuities recognized in the foraminiferal succession indicate depositional unconformities within the formation.

Research note: Salinity tolerance of Arctic kelps from Spitsbergen

SUMMARYThe effect of hypo‐ and hypersaline treatments on the effective quantum yield of photosystem II was comparatively studied with a pulse amplitude modulated fluorometer (PAM) in the brown algal speciesAlaria esculenta,Fucus distichus, Laminaria digitata,Laminaria solidungula,Saccharina latissima(formerlyLaminaria saccharina) andSaccorhiza dermatodeacollected in the Arctic Kongsfjorden (Spitsbergen). While the euryhalineF. distichuswas not affected at all by salinities ranging from 5 to 60 psu,A. esculenta, S. latissimaandL. solidungulaexhibited under hyposaline conditions strong loss of pigments (bleaching) or even high mortality reflecting stenohaline features. In contrast to the latter species,L. digitataandS. dermatodeasurvived all salinities, but showed reduced photosynthetic activities at the lowest and highest salt treatments and hence, can be characterized as stenohaline‐euryhaline organisms. The data are discussed in terms of vertical zonation (eulittoral versus sublittoral habitat), in terms of interactive effects with other abiotic factors such as temperature and in terms of the species‐specific acclimation potential.

The end of the Messinian salinity crisis: Evidences from the Chelif Basin (Algeria)

How did the Messinian Salinity Crisis end is a matter of intense debate between two opposite concepts i.e., the generalised dilution event, the so-called Lago–Mare, followed by the sudden restoration of the marine conditions at the base of the Zanclean, or the early partial or complete marine refill that would have happened earlier during the upper Messinian. The Chelif Basin of Northwestern Algeria, one of the greatest Messinian marginal basins of the Mediterranean, provides an exceptional opportunity to study in detail how this major paleoenvironmental change occurred through continuous sedimentary records of the Miocene–Pliocene boundary. Five sections representative of both the central and marginal areas of the Chelif basin were analysed in detail for sedimentology, mineralogy, foraminifera and ostracod assemblages, and stable isotope composition of carbonates. The late Messinian deposits exhibit a great lithological variability with predominant clastic deposits (sandstones, siltstones, conglomerates, carbonates) with, in some marginal areas, large slided masses of lower Messinian (Tripoli Unit) that settled just before the base of the Zanclean. Most sediments are either azoic or contain microfossils typical of hyposaline conditions sometimes mixed with benthic foraminifera known to be adapted to stressed environments and even to lacustrine conditions. Fewer types of sediment contain assemblages of planktonic foraminifera, including typical Messinian species, which are thought to be reworked. In contrast, diversified communities of benthic and planktonic foraminifera returned suddenly at the base of the Zanclean; the Messinian–Pliocene transition was marked by an abrupt change of the δ 18O values of carbonates from variable but predominantly negative values characteristic of low salinity conditions in the upper Messinian to higher and more stable values in the Zanclean typifying marine conditions. The southern margin continued, however, to be submitted to large inputs of continental waters. The beginning of the marine inundation was a transitional period with poorly diversified assemblages of planktonic foraminifera and benthic communities tolerant to oxygen deficient bottom conditions; more stable marine conditions with better bottom water ventilation were set up after a lag time which would roughly correspond to a precession cycle. Except for the more marginal areas where conglomerates and erosional features are observed, the restoration of marine conditions occurred, without any significant erosion in the more central areas where the contact is well marked by strong burrowing activity by benthic organisms. This indicates the rapid substitution in the basin of brackish waters by marine waters. Both mixing of these two kinds of waters and permanence of freshwater inputs in the initial stage of the Pliocene transgression may explain why the community of marine planktonic foraminifera, introduced by the inflowing Atlantic waters, hardly survived in such unfavourable ecological conditions in the Mediterranean and reached a normal development later when more stable marine conditions settled. This study and the comparison with other sections from both marginal and deep Mediterranean basins confirm that the Lago–Mare was a widespread dilution event that affected the whole Mediterranean at the end of the Messinian which was abruptly interrupted by the sudden marine inundation at the base of the Zanclean.

INTRASPECIFIC VARIATION IN STRESS‐INDUCED HYDROGEN PEROXIDE SCAVENGING BY THE ULVOID MACROALGA ULVA LACTUCA1

We investigated the presence and kinetics of the oxidative stress response in intertidal and subtidal individuals of the ulvoid macroalga Ulva lactuca L. Stress responses, as measured with both enzymatic and fluorescent‐based antioxidant assays, differed between individuals collected from a subtidal and an intertidal habitat. Subtidal individuals secreted significantly more hydrogen peroxide (H2O2) than intertidal individuals when subjected to osmotic stress or desiccation. The activity of reactive‐oxygen‐scavenging enzymes and the ability to scavenge exogenous H2O2 were lower in subtidal than in intertidal individuals, suggesting that subtidal individuals are less stress tolerant. In vitro experimentation demonstrated that millimolar concentrations of dimethylsulfoniopropionate (DMSP) and its breakdown products could efficiently scavenge H2O2, with DMSP being a less‐effective scavenger than dimethyl sulfide (DMS), acrylic acid, and acrylate. The addition of H2O2 at concentrations of 2.5 mM or greater induced the cleavage of DMSP into DMS and acrylic acid in subtidal individuals. Intertidal individuals were affected in the same manner with the addition of 5 mM H2O2. There were no differences in the amounts of DMSP cleavage in subtidal and intertidal algae when the algae were subjected to hyposaline conditions. Our data suggest that the oxidative‐stress‐induced cleavage of DMSP affords products with efficient H2O2‐scavenging abilities. In addition, U. lactuca individuals growing in intertidal habitats are better acclimatized to changing environments and thus have a higher threshold for oxidative stress than conspecifics in subtidal habitats.

No major deglaciation across the Miocene‐Pliocene boundary: Integrated stratigraphy and astronomical tuning of the Loulja sections (Bou Regreg area, NW Morocco)

An integrated high‐resolution stratigraphy and orbital tuning is presented for the Loulja sections located in the Bou Regreg area on the Atlantic side of Morocco. The sections constitute the upward continuation of the upper Messinian Ain el Beida section and contain a well‐exposed, continuous record of the interval straddling the Miocene‐Pliocene (M‐P) boundary. The older Loulja‐A section, which covers the interval from ~5.59 to 5.12 Ma, reveals a dominantly precession‐controlled color cyclicity that allows for a straightforward orbital tuning of the boundary interval and for detailed cyclostratigraphic correlations to the Mediterranean; the high‐resolution and high‐quality benthic isotope record allows us to trace the dominantly obliquity‐controlled glacial history. Our results reveal that the M‐P boundary coincides with a minor, partly precession‐related shift to lighter “interglacial” values in d18O. This shift and hence the M‐P boundary may not correlate with isotope stage TG5, as previously thought, but with an extra (weak) obliquity‐controlled cycle between TG7 and TG5. Consequently, the M‐P boundary and basal Pliocene flooding of the Mediterranean following the Messinian salinity crisis are not associated with a major deglaciation and glacio‐eustatic sea level rise, indicating that other factors, such as tectonics, must have played a fundamental role. On the other hand, the onset of the Upper Evaporites in the Mediterranean marked by hyposaline conditions coincides with the major deglaciation step between marine isotope stage TG12 and TG11, suggesting that the associated sea level rise is at least partly responsible for the apparent onset of intermittently restricted marine conditions following the main desiccation phase. Finally, the Loulja‐A section would represent an excellent auxiliary boundary stratotype for the M‐P boundary as formally defined at the base of the Trubi marls in the Eraclea Minoa section on Sicily.

Transglutaminase activity decrease during acclimation to hyposaline conditions in marine seaweed Grateloupia doryphora (Rhodophyta, Halymeniaceae)

Polyamines (PAs), such as diamine putrescine (PUT), triamine spermidine (SPD) and tetraamine spermine (SPM) have been related to environmental stress, including salt stress. A marine red macrophyte alga Grateloupia doryphora (Montagne) Howe was used to investigate the role of PAs during acclimation to moderate hyposaline conditions (incubation 24h in 18 psu seawater as compared to 36 psu of natural seawater). The results obtained showed that a moderate hyposaline shock caused an increase in the free fraction of PUT, SPD and SPM, mainly due to a decrease in TGase activity, together with an apparent increase in the l-arginine dependent PAs synthesis (ODC and arginase decreased, and ADC slightly increased). The photosynthetic rate increased in thalli when exposed to free SPD at 18 psu, but it did not increase at 36 psu.

Thalassia testudinum seedling responses to changes in salinity and nitrogen levels

The dominant seagrass in Florida Bay, Thalassia testudinum Banks ex König, is a stenohaline species with optimum growth around marine salinity (30–40 PSU). Previous studies have examined the responses of mature short shoots of T. testudinum to environmental stresses. Our goal was to assess responses of seedlings to changes in water chemistry in Florida Bay that might occur as part of the Comprehensive Everglades Restoration Plan (CERP). Specifically, we examined seedling survival, growth, photosynthesis, respiration and osmolality in response to hypo- and hyper-salinity conditions, as well as possible synergistic effects of depleted and elevated ammonium concentrations. The study was conducted in mesocosms on T. testudinum seedlings collected during August 2003 near Florida Bay. Hyper- and hypo-saline conditions were detrimental to the fitness of T. testudinum seedlings. Plants at 0 and 70 PSU exhibited 100% mortality and a significant decrease in survival was observed in the 10, 50 and 60 PSU treatments. Increased levels of ammonium further decreased growth in the lower salinity treatments. Seedlings in 30 and 40 PSU had the greatest growth. Quantum yield and relative electron transport rate, measured using PAM fluorometry, showed a decrease in photosynthetic performance on either side of the 30–40 PSU optimum. Tissue osmolality decreased significantly with decreased salinity but tissue remained consistently hyperosmotic to the media across all salinity treatments. Maintaining negative water potential and allocating more energy to osmoregulation may decrease the productivity of this species in salinity–stress conditions. Our results suggest that the salinity-tolerance limits of this seagrass at the seedling stage are not as broad as those reported for mature plants. Increased fresh water inflow, especially if co-occurring with an increase in water-column ammonium, could negatively affect successful recruitment of T. testudinum seedlings in northern regions of Florida Bay.

Late Cretaceous dysoxia in a southern high latitude siliciclastic succession, the Otway Basin, southeastern Australia

The warm greenhouse world of the Late Cretaceous created oceans that were poorly stratified latitudinally and vertically. Periodically these oceans experienced globally significant events where oxygen minimum zones enveloped the continental margins. Evidence of the effect of one of these Ocean Anoxic Events (OAEs) is preserved in the southern high latitude strata of the offshore Otway Basin in southeast Australia. During the Late Cretaceous, thick successions (up to 6 km) of mudstone-dominated deltaic to upper bathyal sediments (the Otway Delta) were deposited in an elongate inlet (ca. 500 km wide) between Antarctica and Australia located at least 70° S. The initial Turonian strata of this succession (the Waarre Formation) were deposited in upper delta plain to delta front conditions. The overlying late Turonian Flaxman Formation and basal Belfast Mudstone Formation preserve evidence of transgressive lower delta plain to prodelta conditions at inner to middle shelf depths. These units were subject to periodic dysoxia during deposition caused by intermittent freshwater input and deepening seas resulting in periods of thermohaline stratification and reduced bottom waters. Rapid subsidence from 89.3 Ma to 85.7 Ma created significant accommodation space leading to the seaward progradation of normal marine prodelta to upper bathyal mudstone-dominated facies at middle shelf to upper slope depths. After a period when the oxygen minimum zone contracted near the base of the Coniacian, upward-increasing dysoxia in the Belfast Mudstone Formation heralds the onset of Coniacian to Santonian dysoxic conditions. This event in the Otway Basin correlates to OAE 3, the last Ocean Anoxic Event of the warm Cretaceous before the onset of cooler conditions in the uppermost Cretaceous. The evidence suggests that, rather than confined to low latitude tropical areas, the effects of OAE 3 reached southern high latitude regions during the warm Late Cretaceous. The cessation of growth faulting after 85.7 Ma reduced accommodation space and delta front to prodelta facies prograded rapidly seaward. Hyposaline conditions and higher sedimentation rates due to delta front progradation and shallowing during this time caused the local extinction and dissolution of many of the calcareous benthic foraminiferal taxa of the Belfast Mudstone Formation.

Delta-influenced foraminiferal facies and sequence stratigraphy of Paleocene deposits in Spitsbergen

The Paleocene Firkanten Formation of the Central Basin of Spitsbergen is a succession of terrigenous clastic sediments, interpreted as a major depositional sequence, formed in deltaic coastal plain, delta front and prodelta environments. The present study combines diagnostic features of foraminiferal facies with sedimentary data to elucidate this sequence stratigraphic development. Deposition was initiated by an early Paleocene transgression which led to the deposition of a delta plain to coastal marine sediment package forming the low stand and transgressive systems tracts; these includes coal swamp, lacustrine, lagoonal and barrier deposits. The lagoonal shales are characterised by an agglutinated foraminiferal assemblage of extremely low diversity indicative of hyposaline conditions. Shoreface sandstones overlying the lagoonal strata are interpreted as sand barriers reworked by the advancing transgression. These sandstones are succeeded by a package of prodelta silty shales, which in the lower part includes the maximum transgressive interval. The foraminiferal assemblage of the prodelta shales is also agglutinated but reveals increased diversities suggesting open marine conditions. The prodelta shales and overlying delta front sandtones form a succession of coarsening upwards parasequences of deltaic progradation, representing the regressive systems tract. The entirely agglutinated low diversity nature of the foraminiferal assemblages is in part attributable to the deltaic impact. The restricted character of the faunas is additionally accentuated by the effects of the Paleogene Boreal province.

Hydrological changes related to the variability of tropical South American climate from the Cabo Frio lagoonal system (Brazil) during the last 5000 years

From west to east, the Fluminense coastline, composed of two series of lagoons, presents an aridity gradient induced by a local upwelling that is controlled by trade winds coming from the south Atlantic. The physico-chemical conditions of the lagoons are controlled by the duration of the dry season. They are characterized by hypersaline conditions with organic-carbonate sedimentation in the upwelling-influenced area, and by hyposaline conditions with organic-detrital sedimentation out of the upwelling-influenced area. On a core collected in the Brejo do Espinho hypersaline lagoon, diatom analysis supported by sedimentological data revealed a varying high water level from 4500 to 2200 14C yr BP induced by successive freshwater inputs in to the lagoon. Two major dry events occurred during this period, probably related to relative sea-level fluctuations. At 2200 14C yr BP, a drastic change occurred, as indicated by a carbonate nodule, carbonate-dominated sediments and polyto hypersaline diatoms, all suggesting arid conditions. The Brejo do Espinho record suggests that before 2200 14C yr BP, the central part of the Brazilian coast was mostly subjected to south to southeasterly winds and weaker trade winds, whereas after 2200 14C yr BP, trade winds dominated, implying drier conditions at the easternmost part of the Fluminense coastline. These results would also suggest a late Holocene increase in El Ninlo activity (after 2200 14C yr BP), consistent with several El Nifio records from western South America.

Effects of reduced salinity on reproduction and germling development in Sargassum muticum (Phaeophyceae, Fucales)

Sargassum muticum has expanded rapidly along southern Scandinavian coasts since its introduction in the mid-1980s. Expansion into brackish areas has been limited, and the establishment of the species in such waters will largely depend on its ability to tolerate hyposaline conditions. Culture and field experiments have been used to examine the effects of reduced salinity on various life-history stages of S. muticum. In culture, fertilization was prevented at salinities of 15‰ and below, but not at 20 – 30‰. In a crossed two-factor culture experiment, germlings of various ages (1, 8, 15 days old) were cultured at various salinities (0, 5, 10, 15, 20, 25, 30‰) for one week and re-exposed to 30‰ to test for ability to recover. Germling survival was significantly reduced after exposure to 5‰ during the first, but not the second or third, weeks after fertilization. One week's exposure to 0‰ was lethal to germlings. Growth of germlings was reduced by exposure to salinities below 25‰, and growth at 5‰ was less than 10% of that at 25 – 30‰. Growth recovery of germlings after re-exposure to 30‰ was positively related to their age during exposure to sub-optimal salinities. To further explore the effects of salinity on growth and reproduction in S. muticum, plants were transplanted to three sites along a salinity gradient in a Norwegian fjord. At the low salinity site (9.5 – 17.4‰) growth and reproduction were slower than at the other sites where salinities were 14.7 – 27.1‰. These results demonstrate that salinity tolerance in S. muticum is lowest during fertilization, and increases with germling age. The salinity requirements of the least tolerant initial life stages will probably constitute a physiological barrier to the expansion of this species into brackish waters.

HISTORICAL EVIDENCE FOR HABITAT CONVERSION AND LOCAL POPULATION DECLINE IN A NEW ZEALAND FJORD

Although direct links between habitat conversion and human activities are often apparent, their causal mechanisms may be less obvious. We identified historic salinity change, attributed to freshwater input from a hydroelectric power plant, as a potential mechanism of intertidal habitat conversion and severe local decline of the New Zealand littleneck clam (Austrovenus stutchburyi) in Doubtful Sound, New Zealand. Live clams were abundant at sites distant from the power plant with relatively unaltered salinity regimes, and were absent from the inner fjord near the power plant outflow. Remnant shells indicate past habitation by A. stutchburyi at inner fjord sites. Historic salinity conditions inferred from oxygen isotope ratios in shell carbonates confirm that salinity previously reached higher values in the inner fjord, and that A. stutchburyi probably has not inhabited that area since salinity was at pre‐power‐plant levels. A laboratory experiment showed that A. stutchburyi from Doubtful Sound have a high tolerance for low salinity conditions, but that hyposaline conditions become lethal after extended exposure (37‐day LC50 = 2.5). In situ transplant experiments demonstrated that present salinity conditions in the inner reaches of Doubtful Sound are lethal to this species. Our findings suggest that the increased freshwater input maintained by the power plant has converted the habitat in the inner reaches of Doubtful Sound to one with sustained low salinity unsuitable for the survival of A. stutchburyi.

Interactive effects of ultraviolet radiation and salinity on the ecophysiology of two Arctic red algae from shallow waters

In a comparative ecophysiological study, the abundant red macroalgae Devaleraea ramentacea (L.) Guiry and Palmaria palmata (L.) O. Kuntze from shallow waters of the Arctic Kongsfjord (Spitsbergen) were exposed to hyposaline and hypersaline media, in combination with and without artificial UV radiation, to evaluate the interactive effects of both environmental parameters on optimum quantum yield of photosynthesis, as well as on the physiological capability to synthesise and accumulate photoprotective mycosporine-like amino acids (MAAs). While D. ramentacea exhibited euryhaline features and acclimated well to the UV radiation applied, P. palmata can be characterised as a stenohaline plant because of its high mortality even under mild hyposaline conditions (15 PSU). In addition, the latter species showed a limited ability to acclimate to changing PAR/UV radiation, pointing to a relatively low physiological plasticity. Both species synthesised and accumulated MAAs after UV treatment. However, only in D. ramentacea was a correlation between increasing MAA concentration and decreasing photosynthetic sensitivity under UV observed. All ecophysiological data from the laboratory correlate well with field observations, where both red-algal species co-exist in the same shallow-water habitat of the Kongsfjord. However, while P. palmata becomes more often greenish, sometimes slightly bleached over the summer months, D. ramentacea appears much more healthy under the prevailing environmental conditions.

Radiolarian fluxes from the southern Bay of Bengal: sediment trap results

A study of radiolarian fluxes collected during 1991–93 from time-series sediment traps deployed at 1071 and 3010 m water depth in the southern Bay of Bengal (SBBT) yielded 40 species/groups of radiolarians. Among the order Polycystina, the species of sub-order Spumellaria were by far the most abundant (∼95%) followed by sub-order Nassellaria (5%). This is contrary to reports from the Atlantic and Pacific Oceans and is attributed to the prevailing hyposaline condition resulting from the monsoonal rainfall. Higher radiolarian fluxes occurred during March–May, when moderate salinity and a high sea surface temperature (SST) regime prevailed at the trap site. R-mode cluster analysis of the radiolarian flux data revealed three assemblages represented by the cooler (A) and warmer (C) surface dwelling fauna (0–50 m) dominated by spumellarians, and a deeper dwelling (B) sub-surface fauna (50–100 m) associated with deep dwelling (>100 m) nassellarian species. Spongaster tetras tetras, a surface water radiolarian species, exhibited its preference for high SST and moderate salinity conditions during the pre-monsoon season (March–May). Radiolarian fluxes responded to seasonal changes in SST and salinity variations due to the monsoonal precipitation, and the freshwater runoff from the Indian rivers causing a hyposaline condition in the Bay of Bengal. Results imply that the radiolarian assemblages in the down core data may reveal the monsoonal history in the geological past.

The effects of stressors on the dynamics of Bonamia exitiosus Hine, Cochennec‐Laureau &amp; Berthe, infections in flat oysters Ostrea chilensis (Philippi)

AbstractOysters, Ostrea chilensis, infected with Bonamia exitiosus were held under stressful conditions for 14 days, and then under normal conditions for 3.5 months, to determine the affects of stress on B.exitiosus infection levels.The stressors used were (1) air exposure for 8 h daily; (2) hot water (25–26 °C), or (3) cold water (7 °C) for 1 h daily; (4) hyposaline (15‰), or (5) hypersaline (39–40‰) water; (6) starvation in filtered sea water; and (7) vigorous stirring four times a day. A control tank held oysters in static sea water, which was changed daily. Oysters were also (8) kept in a trough among heavily infected oysters (trough exposure), or (9) in a trough without other oysters (control), for 4 months. Oysters in hyposaline conditions all died within 3 weeks, but this was apparently unrelated to Bonamia infection. Otherwise, cumulative mortalities were highest in trough exposure, cold, hypersaline and hot treatments. There was a significant difference in prevalence between treatments, and the stir, hot, cold, hypersalinity and trough exposure treatments had significantly higher intensities of infection than controls. The mean intensity of Bonamia infection was significantly higher among female and spent oysters than in male and hermaphrodite oysters.

Induction of phosphorus deficiency and phosphatase activity by salinity (NaCl) stress in Gracilaria tenuistipitata (Gigartinales, Rhodophyta)

The role of phosphorus (P) deficiency in the induction of phosphatase activity by salinity stress has been investigated in a brackish red macroalga Gracilaria tenuistipitata var. liui Zhang et Xia by determining changes in the intracellular concentrations of P and the specific activities of cellular acid (ACP; EC 3.1.3.2) and alkaline (AP; EC 3.1.3.1) phosphatases in response to varying salinity (adjusted by increasing or decreasing NaCI concentration in artificial seawater). After 4 d exposure to salinity ranging from 12 to 75 practical salinity units (psu), the net photosynthetic rate, specific growth rate, and P concentrations were found to be highest at 25 psu and lower as salinity decreased or increased. Unlike the 25 psu treatment, net photosynthetic rate, specific growth rate, and P concentrations in algae grown at 12 or 75 psu was not recovered by NaH2PO4 (60 μM) supplementation, indicating that the availability of P was restricted under both hyposaline and hypersaline conditions. The specific activities of both ACP and AP were higher when exposed to low salinity, especially at 12 psu. The specific activities of both APC (r2 = 0.75, p < 0.05) and AP (r2 = 0.84, p < 0.05) were inversely related to the logarithm of salinity (12–75 psu). Time-course experiments showed that compared to a constant level at 25 psu, the intracellular concentrations of P decreased to a plateau 1 d after exposure to 12 psu, and concomitantly, the specific activities of both ACP and AP increased, the phosphatase activities showing an inverse relationship to P concentrations. When exposed to 55 psu, the specific activities of both ACP and AP showed a transient increase with a peak around 12 h, whereas the concentrations of P decreased rapidly to a plateau after 1 d. The pattern in changes of ACP- and AP-specific activities was different in hyposaline and hypersaline conditions. The present results suggest that the limitation of P may be associated with the induction of cellular phosphatase activities by hyposaline stress in Gracilaria tenuistipitata. The relationships between hypersaline stress and a transient increase of cellular phosphatase activity are discussed.

Glendonites as a paleoenvironmental tool: implications for early Cretaceous high latitude climates in Australia

Glendonites, calcite pseudomorphs after the metastable mineral ikaite (CaCO 3 · 6H 2O), occur in the Late Aptian interval of the Bulldog Shale in the Eromanga Basin, Australia and in other Early Cretaceous basins at high paleolatitudes. Ikaite precipitation in the marine environment requires near-freezing temperatures (not higher than 4°C), high alkalinity, increased levels of orthophosphate, and high P CO2. The rapid and complete transformation of ikaite to calcite at temperatures between 5 and 8°C provides an upper limit on the oxygen isotopic composition of the pore waters: −2.6 <δ w <−3.4‰SMOW. If it is assumed that these pore waters are representative of the shallow Eromanga Basin, the calculated δ w can be used to reassess belemnite fossil oxygen isotopic paleotemperatures—temperature recorded by fauna living in the basin at the time of ikaite precipitation. Data previously reported as 11 to 16°C (assuming δ w = 0.0‰SMOW) yield paleotemperatures ranging from −1 to 5°C, squarely in the range of ikaite stability. The low δ w indicates hyposaline conditions, most likely caused by mixing high latitude meteoric waters with seawater. The 18O depleted, low temperature waters suggest that the region was at least seasonally colder than previously accepted.

Investigations of some intertidal green macroalgae to hyposaline stress: Detrimental role of putrescine under extreme hyposaline conditions

We found recently that putrescine and spermidine accumulated in a marine green macroalga Ulva fasciata Delile exposed to hyposaline stress (5‰) (T.M. Lee, M.H. Chen, Hyosaline effect on polyamine accumulation in Ulva fasciata (Uvales, Chlorpphyta). Bot. Bull. Acad. Sci. (1998) in press). Changes of polyamine levels in relation to hyposaline (5‰) tolerance were determined in some marine green macroalgae including Chaetomorpha crassa, Chlorodesmis caespitosa L. Agardh, Ulva fasciata Delile, Ulva reticulata Foreek., Ulva lactuca L., Boodlea composita (Harv.) Brand and Valoniopsis pachynema (Mart.) Boergs, which as evaluated by specific growth rate and chlorophyll levels C. crassa and C. caespitosa were highly tolerant and V. pachynema was less tolerant. On exposure to 5‰, free putrescine accumulated in algae except C. caespitosa and C. crassa, soluble conjugated putrescine in C. crassa, C. caespitosa and U. lactuca, and insoluble conjugated putrescine in algae except B. composita. Free spermidine accumulated in algae except C. caespitosa, U. lactuca and B. composita, soluble conjugated spermidine in V. pachynema and C. caespitosa, and insoluble conjugated spermidine in V. pachynema, C. caespitosa, B. composita and U. lactuca. Spermine only accumulated in B. composita as the free form. The relative changes in 5‰-induced free putrescine accumulation are negatively correlated with specific growth rate ( r 2=0.90) and chlorophyll levels ( r 2=0.70). The 5‰-induced free putrescine accumulation, chlorophyll loss and growth reduction in axenically cultured U. fasciata were inhibited by both α-difluoromethylarginine (0.2 mM) and α-difluoromethylornithine (0.2 mM), the specific inhibitor of arginine decarboxylase and ornithine decarboxylase, respectively, and their effects were reversed by 0.5 mM putrescine. Application of 0.5 mM putrescine decreased both chlorophyll levels and growth rate in U. fasciata axenically cultured at 30‰, but 0.5 mM spermidine and 0.5 mM spermine had less effect. Overall, polyamines, especially putrescine and spermidine, accumulated in some marine green macroalgae under extreme hyposaline conditions, and free putrescine synthesized from ADC or ODC may be a causal factor of hyposaline injury.