Salinity tolerance of the copepod Apocyclops dengizicus (Lepeschkin, 1900), a key food chain organism in the Salton Sea,California

The copepod Apocyclops dengizicus is a key item in the food chain of the Salton Sea where the salinity is currently 45 g 1^–1. The salinity of the Salton Sea may reach 90 g 1 ^–1 within the next 20 years. This study examined the salinity tolerance of this copepod.Large copepodite and adult A. dengizicus were introduced into various salinities with and without acclimation. The 96 h LC₅₀ without acclimation was 101 g 1^–1. Mortality (at 96 h) without acclimation was low at salinities of 90 g 1 ^–1 or less.Copepod cultures were maintained, with successful reproduction of at least one new generation, at salinities of from 0.5 to 68 g 1 ^–1 for at least 120 days. Copepods maintained at higher salinities, up to 79 g 1 ^–1, remained alive up to 90 days, but a new generation was not produced. In laboratory studies of larval production and survivorship, few nauplii were released at salinities of 68 g 1 ^–1 or higher, and none survived to the copepodite stage.     

Naked amoebae (Protozoa) of the Salton Sea, California

The Salton Sea is an inland lake in California with an average salinity of ca. 44 g l^–1. This productive water body, which supports substantial fish and migratory bird populations, is under threat because of increasing salinity levels. The present study was the first to examine the naked amoeboid protozoa of the Salton Sea and provide a first estimate of their numerical importance. Over a six-month sampling period (June–December, 1999), 45 different morphospecies (considered to be species) of amoebae were isolated. Wherever possible, isolates were identified to species or genus using diagnostic features recognizable by light microscopy. For each isolate, illustrations and brief notes on the diagnostic characters used in the identifications are given. These will allow this paper to be used as an identification guide to amoebae of the Salton Sea in future studies. Of the 45 taxa, around 18 of the isolates (i.e. 40%) are probably new to Science. Preliminary counts, based on enrichment cultivation methods, showed that amoebae in shoreline waters ranged from 14560 to 237120 cells l^–1 (mean 117312 ± 86075 S.D.). The ecological importance of high numbers and high diversity of amoebae is unknown. But it should be noted that several of the amoebae were actively grazing cyanobacterial and algal filaments and filaments of the bacterium Beggiatoa. Others were predominately associated with suspended particulates. As such, amoebae may be important in the cycling of carbon and nutrients in the Salton Sea.     

Platyamoeba pseudovannellida n. sp., a naked amoeba with wide salt tolerance isolated from the Salton Sea, California

A new species of naked amoeba, Platyamoeba pseudovannellida n.sp., is described on the basis of light microscopic and fine structural features. The amoeba was isolated from the Salton Sea, California, from water at a salinity of ca. 44%. Locomotive amoebae occasionally had a spatulate outline and floating cells had radiating pseudopodia, sometimes with pointed tips. Both these features are reminiscent of the genus Vannella. However, the surface coat (glycocalyx) as revealed by TEM indicates that this is a species of Platyamoeba. Although salinity was not used as a diagnostic feature, this species was found to have remarkable tolerance to fluctuating salinity levels, even when changes were rapid. Amoebae survived over the range 0 per thousand to 150 per thousand salt and grew within the range 0 per thousand to 138 per thousand salt. The generation time of cells averaged 29 h and was not markedly affected by salt concentration. This is longer than expected for an amoeba of this size and suggests a high energetic cost of coping with salinity changes. The morphology of cells changed with increasing salinity: at 0 per thousand cells were flattened and active and at the other extreme (138 per thousand) amoebae were wrinkled and domed and cell movement was very slow. At the ultrastructural level, the cytoplasm of cells grown at high salinity (98 per thousand was considerably denser than that of cells reared at 0 per thousand.     

Effects of water salinity on melatonin levels in plasma and peripheral tissues and on melatonin binding sites in European sea bass (Dicentrarchus labrax)

Sea bass is an euryhaline fish that lives in a wide range of salinities and migrates seasonally from lagoons to the open sea. However, to date, the influence of water salinity on sea bass melatonin levels has not been reported. Here, we evaluated the differences in plasma and tissue melatonin contents and melatonin binding sites in sea bass under four different salinity levels: seawater (36‰), isotonic water (15‰), brackish water (4‰) and freshwater (0‰). The melatonin content was evaluated in plasma, whole brain, gills, intestine and kidney, while melatonin binding sites were analyzed in different brain regions and in the neural retina. Plasma melatonin levels at mid-dark varied, the lowest value occurring in seawater (102 pg/mL), and the highest in freshwater (151 pg/mL). In gills and intestine, however, the highest melatonin values were found in the seawater group (209 and 627 pg/g tissue, respectively). Melatonin binding sites in the brain also varied with salinity, with the highest density observed at the lower salinities in the optic tectum, cerebellum and hypothalamus (30.3, 13.0, and 8.0 fmol/mg protein, respectively). Melatonin binding sites in the retina showed a similar pattern, with the highest values being observed in freshwater. Taken together, these results reveal that salinity influences melatonin production and modifies the density of binding sites, which suggests that this hormone could play a role in timing seasonal events in sea bass, including those linked to fish migration between waters of different salinities for reproduction and spawning.     

Marinamoeba thermophila, a new marine heterolobosean amoeba growing at 50 °C

Two amoeba strains were isolated from marine sediment taken at the same place with 18 months interval from a region of the sea floor heated by extended submarine hot springs and fumaroles. These thermophilic amoebae grow at temperatures up to 50 °C. Sequences of the internal transcribed spacer demonstrated that the two strains belong to the same species and are different from any genus for which sequences are known. Phylogeny using small subunit ribosomal RNA places the amoeba in the Heterolobosea. Their closest relatives are the hypersaline flagellate Pleurostomum flabellatum and the hypersaline amoeba Tulamoeba peronaphora. The freshwater amoeboflagellate genera Naegleria and Willaertia belong to the same phylogenetic clade in the Vahlkampfiidae. The new marine species does not transform into flagellates. It forms cysts, which are round to ellipsoidal with few pores. Because of their unique place in the molecular phylogenetic tree, and because there is no morphologically identical species found in the literature, these isolates are considered to be a new species and a new genus, Marinamoeba thermophila.     

The use of the neutral red retention assay to examine the effects of temperature and salinity on haemocytes of the European flat oyster Ostrea edulis (L)

The neutral red retention assay was adapted to assess the effects of a matrix of temperature and salinity combinations on haemocytes of the European flat oyster Ostrea edulis (L.). Oysters were collected from a commercially fished site in the western Solent and were acclimated to different temperature and salinity combinations in the laboratory. The results indicate that the haemocytes are most stable at high salinity and intermediate temperature (28‰/15°C). Furthermore it is evident from the data that at low salinities the adaptive capacity of the cellular processes is reduced to such an extent that the haemocytes are unable to respond to favourable temperature regimes. The use of neutral red as a probe to monitor cellular stability is discussed.     

Preliminary studies of cyanobacteria, picoplankton, and virioplankton in the Salton Sea with special attention to phylogenetic diversity among eight strains of filamentous cyanobacteria

Cyanobacterial diversity in the Salton Sea, a high-salinity, eutrophic lake in Southern California, was investigated using a combination of molecular and morphological approaches. Representatives of a total of 10 described genera (Oscillatoria, Spirulina, Arthrospira, Geitlerinema, Lyngbya, Leptolyngbya, Calothrix, Rivularia, Synechococcus, Synechocystis) were identified in the samples; additionally, the morphology of two cultured strains do not conform to any genus recognized at present by the bacteriological system. Genetic analysis, based on partial 16S rRNA sequences suggested considerable cryptic genetic variability among filamentous strains of similar or identical morphology and showed members of the form-genus Geitlerinema to be distributed among three major phylogenetic clades of cyanobacteria. Cyanobacterial mats, previously described from the Sea were, in fact, composed of both filamentous cyanobacteria and a roughly equivalent biomass of the sulfur-oxidizing bacterium Beggiatoa, indicating their formation in sulfide rich regions of the lake. Flow cytometric analysis of the water samples showed three striking differences between samples from the Salton Sea and representative marine waters: (1) phycoerythrin-containing unicells, while abundant, were much less abundant in the Salton Sea than they were in typical continental shelf waters, (2) Prochlorococcus appears to be completely absent, and (3) small (3–5 m) eukaryotic algae were more abundant in the Salton Sea than in typical neritic waters by one-to-two orders-of-magnitude. Based on flow cytometric analysis, heterotrophic bacteria were more than an order of magnitude more abundant in the Salton Sea than in seawater collected from continental shelf environments. Virus particles were more abundant in the Salton Sea than in typical neritic waters, but did not show increases proportionate with the increase in bacteria, picocyanobacteria, or eukaryotic algae.     

Morphological, Ecological and Molecular Studies of Vannella simplex Wohlfarth-Bottermann 1960 (Lobosea, Gymnamoebia), with a new Diagnosis of this Species

Vannella simplex (Gymnamoebia, Vannellidae) is one of the most common amoebae species, recorded from a variety of regions. It was originally described as a freshwater species, but has also been reported from shallow-water regions of the Baltic Sea. In the present work, we investigated the morphology and biology of three V. simplex isolates, originating from geographically distant regions. Among them is one brackish water strain, isolated from artificial cyanobacterial mats, which were originally sampled in Nivå Bay (Baltic Sea, The Sound). The strain is cyst-forming and can thrive at salinity ranges from 0–50 ppt. Phylogenetic relationships were investigated by sequencing partial SSU rDNA of the cultured V. simplex isolates. Additional sequences were obtained from four environmental DNA extractions of sediment samples collected from different localities in Switzerland. Analysis of all obtained sequences revealed a monophyletic group. Based on the analysis and comparison of morphological, ecological and molecular data sets we compiled a distribution map of V. simplex and propose an emendation of this species.     

Responses of four isolates of marine naked amoebae to reductions in salinity

The salinity tolerances of four species of naked amoebae, isolated from a temperate sandy beach, to gradual and rapid reductions in environmental salinity were tested. The greatest resilience to both forms of salinity change was displayed by a small Platyamoeba sp. Following gradual acclimation, this isolate was able to show normal growth in salinities as low as 17‰ and altered growth rates down to 7‰ and was able to survive and grow normally in media after a rapid drop in salinity from 32‰ to 17‰. A non-eruptive limax isolate was as resilient and showed normal growth after gradual acclimation in 17‰ salinity media, in salinities lower than this generation times increased and cell yields decreased. The maximum rapid drop in salinity that this species could tolerate and still show normal growth was from 32‰ to 17‰. The poorest tolerance to reduced salinity was shown by populations of Mayorella sp. The lowest salinity this species showed growth in was 12‰ but populations in this salinity displayed very long generation times and very poor cell yields. The response of a Vahlkampfia sp. was intermediate between the responses of the other three isolates. All four of these species were able to survive as floating forms for 2 days or longer in 2‰ salinity media which was unable to support their growth and attachment. Viable cells were present after 48 h (Mayorella sp.) to 1 week and more (Platyamoeba sp. and limax amoebae). These results are potentially important in relation to the structuring of natural amoebae communities. In temperate marine habitats, amoebae which have a greater ability to attach (and remain attached) and display normal generation times under conditions of reduced salinity may be able to colonise a wider range of marine habitats and out-compete, other less resilient species.     

Possible importance of algal toxins in the Salton Sea, California

In response to wildlife mortality including unexplained eared grebe (Podiceps nigricollis) die-off events in 1992 and 1994 and other mortality events including large fish kills, a survey was conducted for the presence of algal toxins in the Salton Sea. Goals of this survey were to determine if and when algal toxins are present in the Salton Sea and to describe the phytoplankton composition during those times. A total of 29 samples was collected for toxicity analysis from both nearshore and midlake sites visited biweekly from January to December 1999. Dinoflagellates and diatoms dominated most samples, but some were dominated by a prymnesiophyte (Pleurochrysis pseudoroscoffensis) or a raphidophyte (Chattonella marina). Several types of blooms were observed and sampled. The dinoflagellate Gyrodinium uncatenum formed an extensive, dense (up to 310000 cells ml^–1) and long-lasting bloom during the winter in 1999. A coccolithophorid, Pleurochrysis pseudoroscoffensis, occurred at high densities in surface films and nearshore areas during the spring and summer of 1999. These surface films also contained high densities of one or two other species (an unidentified scrippsielloid, Heterocapsa niei, Chattonella marina). Localized blooms were also observed in the Salton Sea. An unknown small dinoflagellate reached high densities (110000 cells ml^–1) inside Varner Harbor, and an unidentified species of Gymnodinium formed a dense (270000 cells ml^–1) band along part of the southern shoreline during the summer. Three species known to produce toxins in other systems were found. Protoceratium reticulatum (=Gonyaulax grindleyi) and Chattonella marina were found in several samples taken during summer months, and Prorocentrum minimum was found in low densities in several samples. Extracts of most samples, including those containing known toxic species, showed a low level (<10% mortality across all concentrations) of activity in the brine shrimp lethality assay and were not considered toxic. All sample extracts tested in the mouse bioassay showed no activity. One sample extract taken from the bloom of the small dinoflagellate was highly active (100% mortality across all concentrations) in the brine shrimp lethality assay, but the active material could not be isolated. While dense algal blooms are common at the Salton Sea, no evidence gathered in this study suggests that algal toxins are present within phytoplankton cells; however, toxins actively excreted by cells may have been missed. Blooms of phytoplankton likely contribute to wildlife mortality at the Salton Sea. Possible mechanisms including intoxication due to ingestion of feathers in grebes and waterlogging caused by changes in surface tension are discussed.     

Biological characterization of a clinical and an environmental isolate of <Emphasis Type="Italic">Acanthamoeba polyphaga</Emphasis>: analysis of relevant parameters to decode pathogenicity

Acanthamoeba spp. consists of free-living amoebae, widespread in nature, which occasionally can cause human infections including granulomatous amoebic encephalitis and amoebic keratitis. Acanthamoeba pathogenesis is not entirely known and correlations between pathogenic potential and taxonomy are complex issues. In order to decipher the definition of a pathogenic amoeba, the objective of this work was to decipher the definition of pathogenic amoeba by characterizing two isolates of Acanthamoeba polyphaga obtained from different origins (a keratitis patient and freshwater), looking for differences among them. The clinical isolate grew faster in Peptone-yeast extract-glucose (PYG) medium, transformed more rapidly from a trophozoite to cyst and exhibited increased cytopathic effect on cultured cells. Morphological differences were also noted, since freshwater amoebae presented more acanthopodia than the clinical isolate. Moreover, actin labeling demonstrated that microfilament organization varies between isolates, with the presence of locomotory structures as lobopodia and lamellipodia in the keratitis isolate, which were less adherent on plastic. Zymography demonstrated that the keratitis isolates presented higher proteolytic activity and also were more able to invade collagen matrices. Altogether, we conclude that a group of stable physiological characteristics exist in Acanthamoeba that can be related to pathogenicity.     

Effects of acute temperature or salinity stress on the immune response in sea cucumber, Apostichopus japonicus

Invertebrates are increasingly raised in mariculture, where it is important to monitor immune function and to minimize stresses that could suppress immunity. The activities of phagocytosis, superoxide dismutase (SOD), catalase (CAT), myeloperoxidase (MPO), and lysozyme (LSZ) were measured to evaluate the immune capacities of the sea cucumber, Apostichopus japonicus, to acute temperature changes (from 12 °C to 0 °C, 8 °C, 16 °C, 24 °C, and 32 °C for 72 h) and salinity changes (from 30‰ to 20‰, 25‰, and 35‰ for 72 h) in the laboratory. Phagocytosis was significantly affected by temperature increases in 3 h, and by salinity (25‰ and 35‰) changes in 1 h. SOD activities decreased significantly in 0.5 h to 6 h samples at 24 °C. At 32 °C, SOD activities decreased significantly in 0.5 h and 1 h exposures, and obviously increased for 12 h exposure. CAT activities decreased significantly at 24 °C for 0.5 h exposure, and increased significantly at 32 °C in 3 h to 12 h exposures. Activities of MPO increased significantly at 0 °C in 0.5 h to 6 h exposures and at 8 °C for 1 h. By contrast, activities of MPO decreased significantly in 24 °C and 32 °C treatments. In elevated-temperature treatments, activities of LSZ increased significantly except at 32 °C for 6 h to 12 h exposures. SOD activity was significantly affected by salinity change. CAT activity decreased significantly after only 1 h exposure to salinity of 20‰. Activities of MPO and LSZ showed that A. japonicus tolerates limited salinity stress. High-temperature stress had a much greater effect on the immune capacities of A. japonicus than did low-temperature and salinity stresses.     

Effects of temperature, salinity and irradiance on the growth of the red tide dinoflagellate Gyrodinium instriatum Freudenthal et Lee

The effects of temperature, salinity and irradiance on the growth of the red tide dinoflagellate Gyrodinium instriatum Freudenthal et Lee were examined in the laboratory. Exposed to 45 different combinations of temperature (10–30 °C) and salinity (0–40) under saturating irradiance, G. instriatum exhibited its maximum growth rate of 0.7 divisions/day at a combination of 25 °C and a salinity of 30. Optimum growth rates (>0.5 divisions/day) were observed at temperatures ranging from 20 to 30 °C and at salinities from 10 to 35. The organism could not grow at ≤10 °C. In addition, G. instriatum burst at a salinity of 0 at all temperatures, but grew at a salinity of 5 at temperatures between 20 and 25 °C. It is noteworthy that G. instriatum is a euryhaline organism that can live under extremely low salinity. Factorial analysis revealed that the contributions of temperature and salinity to its growth of the organism were almost equal. The irradiance at the light compensation point (I₀) was 10.6 μmol/(m² s) and the saturated irradiance for growth (I_s) was 70 μmol/(m² s), which was lower than I_s for several other harmful dinoflagellates (90–110 μmol/(m² s)).     

An autecological study of the potentially toxic dinoflagellate Alexandrium affine isolated from Vietnamese waters

The potentially toxic dinoflagellate species Alexandrium affine isolated from Ha Long Bay (Tonkin Gulf), Vietnam was cultured and maintained for morphological, physiological and toxicological studies. Classical morphological examinations including plate pattern were in good agreement with the international nomenclature of the species. The fine structure of A. affine, including morphology of its developmental stages during vegetative and sexual reproduction was found to be typical of other species in the genus. Two general trends in growth of A. Affine from Vietnamese waters were apparent: (1) growth rates were low at low salinities (10 and 15 psu) in all experimental temperatures (21–27 °C); (2) growth rates were high at salinities 25, 30, and 35 psu in all temperatures. There were no significant differences in growth rates at different salinities at low temperature (21 °C), and the most significant difference in growth rate was between high temperature–high salinity and high temperature–low salinity. The optimum temperature and salinity for growth were 24 °C and 30 psu. Maximum division rates per day (0.5–0.7) were at salinities 30 and 35 psu and at temperatures 24 and 27 °C. But the best conditions for division rate were 21 and 24 °C at salinities 30 and 35 psu. Toxicity analyses indicated A. affine to be both toxic and non-toxic at certain times. In the former case, toxicity was very low, 2.28 fmol  per cell; the toxicity component of A. affine was compared with that of A. leei and the mussel Perna viridis including neoSTX, STX, and GTX₁–GTX₄.     

Influence of salinity on the rates of oxygen consumption in two species of freshwater fishes,Phoxinus erythrogaster (family Cyprinidae), and Fundulus catenatus (family Fundulidae)

A dye process in a textile plant in southern Kentucky (USA) produces large quantities of saline waste-water which eventually enter Lake Cumberland via a municipal sewage treatment plant on Lily Creek. The impact of hypersaline conditions on two fish species native to the Cumberland River drainage system, redbelly dace (Phoxinus erythrogaster) and northern studfish (Fundulus catenatus), was assessed. These species were subjected to salinities of 0, 4, and 10 after which routine oxygen consumtpion values were determined. Significant correlations of salinity with oxygen consumption were demonstrated for both species with P. erythrogaster showing greater overall impact of salinity on metabolic rate.     

Abundance and growth response of microalgae at Megalon Embolon solar saltworks in northern Greece: An aquaculture prospect

There is continuous interest in many countries in maintaining and manipulating the rich ecological value of hypersaline ecosystems for aquaculture. The Megalon Embolon solar saltworks (northern Greece) were studied in sites of increasing salinity of 60–144 ppt to evaluate Dunaliella salina abundance and microalgal composition, in relation to physical and chemical parameters. Cluster and ordination analyses were performed based on the biotic and abiotic data matrices. Using fresh aliquots from 60 and 140 ppt salinity waters, phytoplankton performance was appraised with flask cultures in the laboratory by varying the inorganic PO₄-P concentration at 23 °C and 30 °C. At the saltworks, among the most abundant microalgae identified were species of the genera Dunaliella, Chlamydomonas, Amphora, Navicula, and Nitzschia. Dunaliella salina populations were predominant comprising 5–22% of the total microalgal assemblages during spring, but only 0.3–1.0% during the summer, when grazing by Artemia parthenogenetica and Fabrea salina was intense. D. salina cell density in April–July was in the range of 0.4–12.5 × 10⁶ L⁻¹ with typical densities of 1.5–4.5 × 10⁶ L⁻¹. Overall, microalgal densities were high in salinities of ≥100 ppt when inorganic-P concentrations were ≥0.20 mg L⁻¹ within saltworks waters. Multivariate analysis of species abundance showed that algal growth responses were primarily related to variation in salinity and inorganic-P concentrations, but also to NO₃-N concentration. In the laboratory, experiments indicated effective fertilization and denser microalgal growth under high inorganic PO₄-P applications (4.0 and 8.0 mg L⁻¹) at 60 ppt salinity and 23 °C. The lower PO₄-P applications (0.6–2.0 mg L⁻¹) were more effective at 60 ppt salinity and 30 °C. At 140 ppt salinity, microalgal growth response was less obvious at any of the corresponding phosphorus concentrations or temperatures. In both salinity experiments, Dunaliella salina bloomed easily and was predominant among the microalgae. Our observations indicate that Dunaliella salina populations and the overall rich microalgal profile of the saltworks, along with their performance in laboratory mono–and mixed cultures hold promise for mass cultivation within the M. Embolon saltworks basins.     

GROWTH AND ORGANIC OSMOLYTES OF GEOGRAPHICALLY DIFFERENT ISOLATES OF MICROCOLEUS CHTHONOPLASTES (CYANOBACTERIA) FROM BENTHIC MICROBIAL MATS:RESPONSE TO SALINITY CHANGE1

The comparative growth and osmotic acclimation often culture strains of the marine benthic cyanobacterium Microcoleus chthonoplastes Thuret isolated from microbial mats in Germany, Spain, Egypt, the United States, Mexico, Chile, and Australia were investigated in salinities ranging from freshwater to twice seawater. All isolates showed a broad growth versus salinity response consistent with the dominance of this species in intertidal and hypersaline microbial communities. Growth optima, salinity preferences, and maximum growth rates differed for each isolate and could be related to the habitat from which they were isolated. This is most obvious when comparing strains from brackish habitats with those from a hypersaline lake. While the former isolates exhibited sharply pronounced growth optima under hyposaline conditions, cultures from the hypersaline environment grew best in salinity more than double seawater. The major low-molecular weight organic compounds present in all M. chthonoplastes strains were the carbohydrates glycosylglycerol and trehalose. This was proven by using ¹³C-nuclear magnetic resonance spectroscopy. Glycosylglycerol was synthesized and accumulated with increasing salinities, indicating its role as an osmolyte. In contrast, trehalose was present in relatively high concentrations under hyposaline conditions only. Differences in the patterns of growth versus salinity, as well as in those of osmotic acclimation among the M. chthonoplastes isolates, point to the development of different physiological ecotypes within the species.     

Effects of NaCl salinity on growth, morphology, photosynthesis and proline accumulation of Salvinia natans

The effects of NaCl salinity on growth, morphology and photosynthesis of Salvinia natans (L.) All. were investigated by growing plants in a growth chamber at NaCl concentrations of 0, 50, 100 and 150 mM. The relative growth rates were high (ca. 0.3 d⁻¹) at salinities up to 50 mM and decreased to less than 0.2 d⁻¹ at higher salinities, but plants produced smaller and thicker leaves and had shorter stems and roots, probably imposed by the osmotic stress and lowered turgor pressure restricting cell expansion. Na⁺ concentrations in the plant tissue only increased three-fold, but uptake of K⁺ was reduced, resulting in very high Na⁺/K⁺ ratios at high salinities, indicating that S. natans lacks mechanisms to maintain ionic homeostasis in the cells. The contents of proline in the plant tissue increased at high salinity, but concentrations were very low (<0.1 μmol g⁻¹ FW), indicating a limited capacity of S. natans to synthesize proline as a compatible compound. The potential photochemical efficiency of PSII (F_v/F_m) of S. natans remained unchanged at 50 mM NaCl but was reduced at higher salinities, and the photosynthetic capacity (ETR_max) was significantly reduced at 50 mM NaCl and higher. It is concluded that S. natans is a salt-sensitive species lacking physiological measures to cope with exposure to high NaCl salinity. At low salinities salts are taken up and accumulate in old leaves, and high growth rates are maintained because new leaves are produced at a higher rate than for plants not exposed to salt.     

Tolerance and Resistance in Gastropod Mollusks Hydrobia ulvaeand H. ventrosafrom the White Sea to Abiotic Environmental Factors

Tolerance to salinity changes and resistance to desiccation, fresh water, and freezing were studied in two hydrobiid species from the White Sea, Hydrobia ulvae(Pennant) and H. ventrosaMontagu. It was shown that H. ventrosahas a greater tolerance to low salinities in the range of 6–10 but is less tolerant to high salinities (35–45). The interspecies differences in low salinity tolerance persisted after the acclimation of snails to 20, 16, and 12. A comparison of survival in fresh water and under desiccation conditions suggests that H. ulvaeis more resistant to these factors. In fresh water, LT₅₀was 30 and 60 days for H. ventrosaand H. ulvae, respectively. Under desiccation conditions, LT₅₀was 6 and 25 days for H. ventrosaand H. ulvae, respectively. At subzero temperatures, H. ventrosawas shown to be a superior survivor. Within the same species of mud snail, the detrimental effect of freezing depended on the salinity: survival decreased with decreasing salinity. These data suggest significant differences in the mechanisms of resistance and tolerance to abiotic environmental factors between the two species. Despite the partial overlapping of their ecological niches, the interspecies differences may play an important role in the distribution and spatial structure dynamics of coexisting populations of these species in the White Sea region.     

Salinity effects on the growth,mortality and shell strength of Balanus amphitrite from the Salton Sea,California

The Salton Sea, the largest lake in California, has a salinity of around 43 g l-1 that is increasing by about 0.4 g l-1 y-1. A 15 month microcosm experiment was conducted to determined the effects of salinity (30, 39, 48, 57, and 65 g l-1) and tilapia ( Oreochromis mossambicus) on an assemblage of benthic and planktonic Salton Sea algae and invertebrates, including the barnacle Balanus amphitrite. Eleven months after the microcosms were established, acrylic plates containing newly settled B. amphitrite collected at the Salton Sea were placed in the microcosms to determine the effects of salinity on their growth and shell strength. The Brody-Bertalanffy growth model was fitted to the B. amphitrite growth data. Growth was fastest at 48 g l-1 and slowest at 65 g l-1. B. amphitrite grown at 39–48 g l-1 were the largest and required the greatest force to break, but the strength of the barnacle shell material declined steadily as the salinity increased. However, B. amphitrite at the higher salinities were shorter and had thicker walls relative to their diameters, which may have increased their structural stability. The effects of salinity on the mortality of adult B. amphitrite was determined in laboratory aquaria set up at 43, 60, 70, 75, 80, 90, and 100 g l-1. Salinities were achieved in two ways: by salt addition and by evaporation. Calculated 12-day LC50 values were 83 g l-1 when salinities were achieved through salt addition and 89 g l-1 when salinities were achieved through evaporation. Differences in B. amphitrite mortality between the two methods illustrate the importance of producing experimental salinity levels carefully. B. amphitrite is expected to become extinct within the Salton Sea when the salinity reaches 70–80 g l-1 and to show marked declines in abundance at salinities as low as 50 g l-1. This revised version was published online in July 2006 with corrections to the Cover Date.