First account of apochlorotic diatoms from mangrove waters in Florida

ABSTRACT. From January to December 2004, monthly samples were collected from the mangrove salt marsh of J.U. Lloyd State Park, Florida, to examine the spatial and temporal distributions of heterotrophic diatoms in this subtropical region. Four non-pigmented (i.e. apochlorotic), heterotrophic diatom morphotypes were isolated from mangrove neuston and plankton sites. Colorless diatoms were numerically significant in neuston during the fall and winter months and counts peaked at 174 × 10³ cells/L in December. Heterotrophic diatoms were most prevalent in mangrove plankton in October and averaged 55.5 × 10³ cells/L. Valve morphology was detailed for mangrove morphotypes (I, II, V, and VI). However, only one type (I) was named with confidence ( Nitzschia leucosigma ). The other three types failed to conform closely to published diagnostic features suggesting that either characters are more variable than accepted or these types were new species. Growth responses to changes in salinity and irradiance were detailed in the laboratory. All morphotypes were euryhaline, tolerating salinities between 10‰ and 40‰; N. leucosigma was most salt tolerant and grew from 10‰ to 60‰. Maximum growth was achieved between 20‰ and 40‰. Growth was not significantly different for heterotrophic diatoms during light and dark treatments or for diatoms grown with or without bacteria.     

Salinity tolerance of stable fly (Diptera: Muscidae)

Effects of salinity on the survival, growth, and development of stable fly, Stomoxys calcitrans (L.), were investigated in the laboratory. Larvae failed to develop to pupation when reared in media containing a salinity of 40 parts per thousand (ppt) sodium chloride (NaCl). Maximum salinity supporting larval development equaled the salinity of seawater (34 ppt); the larval LC90 was 24.2 ppt. Deleterious effects of high salinity decreased as larvae matured. Six-day-old larvae reared at a salinity of 34 ppt weighed 79% less than controls, compared with a 36% difference in 9-d-old larvae; by pupation, the difference was only 24%. Salinity did not influence the duration of larval, pupal, or adult stages. Survival of pupae was unimpaired despite a slight increase in number of pupal deformities, and normal adults emerged. Eggs were highly tolerant to saline. They hatched at salinity concentrations lethal to larvae; greater than 50% hatch occurred even when eggs were maintained at 80 ppt NaCl. Sensitivity of larvae to salinities close to that of seawater might be important for control of stable flies inhabiting marine areas.     

Can differences in salinity tolerance explain the distribution of four genetically distinct lineages of Phragmites australis in the Mississippi River Delta?

In the Mississippi River Delta, the common wetland grass, Phragmites australis, displays high genetic diversity, as several genetically distinct populations are co-occurring. Differences in salinity tolerance may be an important factor determining these populations’ distribution in the delta. Our study investigated the salt tolerance of four genotypes exposed to 0, 10, 20, 30, and 40 ppt salinity. The growth rate, biomass, and the light-saturated photosynthetic rate were stimulated at 10 ppt salinity and inhibited at salinities higher than 20 ppt, compared to controls. Increased concentrations of Cl^? and Na⁺ were found in the roots and older leaves of plants exposed to high salinities. Salt tolerance levels differed between genotypes. High salinity tolerance was mainly achieved by reduced water uptake and vacuole compartmentalization of toxic ions. The most tolerant genotype sustained biomass and photosynthesis even at 40 ppt, whereas the most sensitive genotype did not survive salinities higher than 20 ppt. Our findings show that the observed occurrence of different genotypes in the Mississippi River Delta is correlated to genetically determined differences in salinity tolerance. Further investigations are needed to better understand the role that salinity tolerance plays in the invasion of certain introduced P. australis genotypes.     

Salinity tolerance in Hyalophysa chattoni (Ciliophora, Apostomatida), a symbiont of the estuarine grass shrimp Palaemonetes pugio

The apostome ciliate Hyalophysa chattoni, a symbiont of the estuarine grass shrimp Palaemonetes pugio, was tested for its growth and reproductive ability in a wide range of salinities from 0.1 to 55 ppt. Shrimp, with their attached ciliates, were slowly acclimated to different salinities in order to assess protozoan cell size and division. The trophont and tomont stages of the ciliate life cycle were analyzed. In both stages, cell size increased with salinity from 0.1 to 20 ppt. Cell size leveled in the 20-35 ppt range, and decreased at higher salinities. The number of daughter cells produced per tomont cyst correlated with increased cell size, and also correlated with increased salinity. Additionally, increased salinity correlated with an increase in the percentage of cells able to divide and excyst as tomite stages. These results indicate that H. chattoni is able to grow and divide more effectively at salinities closer to seawater than in the estuarine environment from which they were collected. Though able to survive salinities from 0.1 to 55 ppt, the species is better adapted for an existence in the higher salt concentrations.     

Abundance and Biomass of Heterotrophic Flagellates, and Factors Controlling Their Abundance and Distribution in Sediments of Botany Bay

The abundance and biomass of heterotrophic flagellates were estimated monthly in sediments of Botany Bay during March 1999-February 2000. The annual abundance and biomass were in the ranges of 0.46-4.70 x 10(5) cells/cm(3) and of 0.30-8.61 micro g C/cm(3), respectively. The majority of heterotrophic flagellates (93-100%) were less than 10 mm in length and few flagellates were larger than 10 mm. Of the total microbial carbon biomass, heterotrophic flagellates made up about 5% (but at times up to 35%). The contribution of heterotrophic flagellates varied from month to month, and among the sites. The abundance of heterotrophic flagellates was negatively correlated with sediment grain size and positively correlated with the abundance of bacteria, algae (autotrophic flagellates and diatoms), and their probable grazers. A best subsets regression analysis showed that bacterial and algal abundance are the most important factors controlling the abundance of heterotrophic flagellates. When the previously reported grazing rates on bacteria were applied, heterotrophic flagellates would consume a maximum of 64% of bacterial standing stock daily in Botany Bay, suggesting that heterotrophic flagellates are important as bacterivores. However, the importance of heterotrophic flagellate grazing probably varies significantly among the sites and from month to month.     

Phenotypic plasticity with respect to salt stress response by Lotus glaber: the role of its AM fungal and rhizobial symbionts

Our hypothesis is that Lotus glaber (a glycophytic species, highly tolerant to saline-alkaline soils) displays a plastic root phenotypic response to soil salinity that may be influenced by mycorrhizal and rhizobial microorganisms. Uninoculated plants and plants colonised by Glomus intraradices or Mesorhizobium loti were exposed to either 150 or 0 mM NaCl. General plant growth and root architectural parameters (morphology and topology) were measured and phenotypic plasticity determined at the end of the salt treatment period. Two genotypes differing in their salt tolerance capacity were used in this study. G. intraradices and M. loti reduced the total biomass of non-salinised, sensitive plants, but they did not affect that of corresponding tolerant ones. Root morphology of sensitive plants was greatly affected by salinity, whereas mycorrhiza establishment counteracted salinity effects. Under both saline conditions, the external link length and the internal link length of mycorrhizal salt-sensitive plants were higher than those of uninoculated control and rhizobial treatments. The topological trend (TT) was strongly influenced by genotype x symbiosis interaction. Under non-saline conditions, nodulated root systems of the sensitive plant genotype had a more herringbone architecture than corresponding uninoculated ones. At 150 mM NaCl, nodulated root systems of tolerant plants were more dichotomous and those of the corresponding sensitive genotype more herringbone in architecture. Notwithstanding the absence of a link between TTs and variations in plant growth, it is possible to predict a dissimilar adaptation of plants with different TTs. Root colonisation by either symbiotic microorganisms reduced the level of root phenotypic plasticity in the sensitive plant genotype. We conclude that root plasticity could be part of the general mechanism of L. glaber salt tolerance only in the case of non-symbiotic plants.     

Physiological responses to hyper-saline waters in sailfin mollies (Poecilia latipinna)

We examined the ionoregulatory physiology and biochemistry of the teleost sailfin molly (Poecilia latipinna), an inhabitant of salt marshes along the gulf coast, during exposure to hyper-saline waters (salinity range 35-95 ppt). Mollies were able to tightly control plasma Na(+) and Cl(-) concentrations and tissue water levels up to 65 ppt, but at higher salinities plasma ion levels began to rise and muscle water content dropped. Still, even at the highest salinity (90 ppt) plasma Na(+) and Cl(-) levels were only 32% and 39%, respectively, above levels at 35 ppt. Drinking rates at 60 ppt climbed 35%, while gut Na(+)/K(+)-ATPase (NAK) activity rose 70% and branchial NAK activity jumped 200%. The relatively small rise in drinking rate, in the face of a more than doubling of the osmotic gradient, suggests that a reduction in branchial water permeability significantly limited water loss and associated salt load. At 80 ppt, a salinity where plasma ion levels just begin to rise, drinking rate rose more rapidly, but gut and gill NAK activity did not, suggesting that mollies employed other pathways (perhaps renal) of salt excretion. At higher salinities, plasma ion levels continued to rise and muscle water content fell slightly indicating the beginnings of internal osmotic disturbances. To evaluate the energetic costs of hyper-salinity on mollies we measured the rate of O(2) consumption and found it rose with salinity, in sharp contrast to virtually all species previously examined. Interestingly, despite higher metabolism, growth was unaffected by hyper-salinity.     

Germination ecology of coastal plants in relation to salt environment

Responses of seed germination to salinity were examined using 37 species collected from salt marshes, cliffs, and fore (unstable) and hind (stable) sand dunes along Japanese coasts. For comparison, seed germination of nine inland species was also examined. The soil salinities in salt marshes ranged from 150 to 300 mmol/L NaCl, whereas those in fore and hind dunes ranged from 0 to 150 mmol/L NaCl, with a few exceptions. Cliff soils showed relatively high salinities up to 300 mmol/L NaCl. Ciff and foredune soils that encountered a typhoon and storm showed high salinities >300 mmol/L NaCl. Salt tolerance in seed germination of coastal plants was ordered by comparing the responses of percentage and rate of germination to salinity conditions up to 200 mmol/L NaCl, being in the order of salt marsh>cliff>foredune≅hind dune≅inland. Thse results indicate that salt tolerance in seed germination of coastal plants is closely related to the salinity conditions of their habitats. Germination experiments under favorable conditions showed that a high percentage of the seeds of salt marsh species germinate rapidly, those of diff species germinate slowly and those of foredune species exhibit a low percentage and low rate of germination. It seems that these germination characteristics contribute to the success of germination at the ‘safe site’ and the subsequent survivorship of emerged plants in their natural habitats.     

Methane emissions along a salt marsh salinity gradient

The seasonal flux of methane to the atmosphere was measured at three salt marsh sites along a tidal creek. Average soil salinities at the sites ranged from 5 to 17 ppt and fluxes ranged from below detection limits (less than 0.3 mgCH₄ m^-2 d^-1) to 259 mgCH₄ m^-2 d^-1. Annual flux to the atmosphere was 5.6 gCH₄ m^-2 from the most saline site, 22.4 gCH₄ m^-2 from the intermediate site, and 18.2 gCH₄ m^-2 from the freshest of the three sites. Regression of the amount of methane in the soil with flux indicates that changes in this soil methane can account for 64% of the observed variation in flux. Data on pore water distributions of sulfate suggests that the activity of sulfate reducing bacteria is a primary control on methane flux in these transitional environments. Results indicate that relatively high emissions of methane from salt marshes can occur at soil salinities up to approximately 13 ppt. When these data are combined with other tidal marsh studies, annual CH₄ flux to the atmosphere shows a strong negative correlation with the long term average soil salinity over a range from essentially fresh water to 26 ppt.     

Survival and development of horseshoe crab (Limulus polyphemus) embryos and larvae in hypersaline conditions

The horseshoe crab Limulus polyphemus spawns in the mid- to upper intertidal zone where females deposit eggs in nests below the sediment surface. Although adult crabs generally inhabit subtidal regions of estuaries with salinities from 5 to 34 ppt, developing embryos and larvae within nests are often exposed to more extreme conditions of salinity and temperature during summer spawning periods. To test whether these conditions have a negative impact on early development and survival, we determined development time, survival, and molt cycle duration for L. polyphemus embryos and larvae raised at 20 combinations of salinity (range: 30-60 ppt) and temperature (range: 25-40 degrees C). Additionally, the effect of hyperosmotic and hypoosmotic shock on the osmolarity of the perivitelline fluid of embryos was determined at salinities between 5 and 90 ppt. The embryos completed their development and molted at salinities below 60 ppt, yet failed to develop at temperatures of 35 degrees C or higher. Larval survival was high at salinities of 10-70 ppt but declined significantly at more extreme salinities (i.e., 5, 80, and 90 ppt). Perivitelline fluid remained nearly isoosmotic over the range of salinities tested. Results indicate that temperature and salinity influence the rate of crab development, but only the extremes of these conditions have an effect on survival.     

Ecology of a saline stream: community responses to spatial gradients of environmental conditions

Spatial changes in structural and functional characteristics of fish and macroinvertebrate communities in eastern Kentucky were investigated in a drainage system chronically exposed to high levels of chloride salts from nearby oilfield operations. Salinity levels at biological monitoring stations ranged from 0.12–31.3‰. Lotic regions with salinities greater than 10‰ were dominated by larvae of the dipterans Ephydra and Culicoides. In regions with salinities less than 10‰ species richness increased more or less linearly with decreasing levels of chloride salts. Ephemeropterans appeared to be one of the major invertebrate groups least tolerant of elevated NaCl levels and were absent in regions with salinities greater than 2‰ Availability of food resources, such as periphyton and particulate organic matter, did not appear to be grossly altered in disturbed regions, and it is suggested that the observed distribution of macroinvertebrate fauna was largely in response to taxonomic differences in salt tolerance. Fish seemed to be more tolerant of highly saline conditions, and several species were observed in regions experiencing salinities as high as 15‰. Accordingly, assemblages of fish taxa along the salinity gradient may have been influenced by trophic factors, such as spatial limitations in availability of invertebrate prey.     

Long-term hyposaline and hypersaline stresses produce distinct antioxidant responses in the marine alga Dunaliella tertiolecta

Tolerance to salinity stress in higher plants correlates to levels of antioxidant enzymes and/or substrates. Do hyperosmotic and hypoosmotic stress induce antioxidant responses in salt tolerant algae, and if so, are these responses the same for both excess and minimal salinity? To answer these questions, cultures of the marine alga Dunaliella tertiolecta (Chlorophyta) were grown in seven salinities covering a 60-fold range from 0.05 to 3.0 mol/L NaCl. Long-term effects of salinity on growth and antioxidant parameters were determined. Growth rates were reduced at the salinity extremes (0.05 mol/L NaCl and 3 mol/L NaCl) indicating the cultures were stressed. The levels of six antioxidant enzymes and three antioxidant substrates were quantified at these growth salinities. Compared to growth at optimum salinities (i.e. 0.2-0.5 mol/L NaCl), high salinities produced a 260% increase in monodehydroascorbate reductase, a doubling of ascorbate peroxidase activity and a three-fold increase in the rate of dark respiration. Cells acclimated to low growth salinities (hyposaline stress, i.e. < 0.2 mol/L NaCl) showed major increases in glutathione and alpha-tocopherol coupled with decreases in Fv/Fm ratios and in total and reduced ascorbate compared to moderate and high external salinities. Cell volumes remained unchanged, except at the lowest salinity where they doubled. Catalase, superoxide dismutase, dehydroascorbate reductase and glutathione reductase activities were not altered by extreme salinities. The involvement of oxidative stress at both salinity extremes is implied by the alterations in antioxidant enzymes and substrates, but the specific changes are very different between hypo and hypersaline stresses.     

Growth and physiological parameters of whiting (Sillaginodes punctata) in relation to salinity

This study assessed the impact of salinity on whiting (Sillaginodes punctata) in an attempt to understand the mechanisms by which salinity could potentially influence habitat selection and growth of King George whiting in southern Australia. The experiment included whiting of two age classes, young of the year (YOY) and 2⁺ year, at three salinities (30, 40, 50 ppt). YOY whiting showed no significant difference in length or weight gain, specific growth rate, feed intake, food conversion ratio or condition factor when exposed to the three salinities for 72 day. Plasma osmolality of YOY whiting was not significantly different at any salinity, although it was significantly lower than that of 2⁺ year whiting. The 2⁺ year whiting showed significantly higher plasma osmolality than the YOY. Blood plasma potassium and chloride levels of 2⁺ year fish at 50 ppt were significantly higher than those at 30 ppt and 40 ppt. Blood sodium levels at 50 ppt were significantly higher than at 30 ppt but the sodium level at 40 ppt was not different from 30 ppt or 50 ppt. Haematocrit of 2⁺ whiting was significantly higher at 30 than at 50 ppt while haematocrit at 40 ppt was not different from 30 or 50 ppt. The 2⁺ year‐old whiting had a more pronounced increase in plasma osmolality and plasma ions at high salinities, indicating poorer osmoregulatory capacity in older fish. This study provides physiological evidence to partially explain habitat occupancy and growth in relation to salinity of different age groups of whiting in southern Australia.     

Effects of Grazing by Flagellates on Competition for Ammonium between Nitrifying and Heterotrophic Bacteria in Soil Columns

The enhanced mineralization of immobilized nitrogen by bacteriophagous protozoa has been thought to favor the nitrification process in soils in which nitrifying bacteria must compete with heterotrophic bacteria for the available ammonium. To obtain more insight into this process, the influence of grazing by the flagellate Adriamonas peritocrescens on the competition for ammonium between the chemolithotrophic species Nitrosomonas europaea and the heterotrophic species Arthrobacter globiformis in the presence of Nitrobacter winogradskyi was studied in soil columns, which were continuously percolated with media containing 5 mM ammonium and different amounts of glucose at a dilution rate of 0.007 h^-1 (liquid volumes). A. globiformis won the competition for ammonium. The grazing activities of the flagellates had two prominent effects on the competition between N. europaea and A. globiformis. First, the distribution of ammonium over the profile of the soil columns was more uniform in the presence of flagellates than in their absence. In the absence of flagellates, relatively high amounts of ammonium accumulated in the upper layer (0 to 3 cm), whereas in the underlying layers the ammonium concentrations were low. In the presence of flagellates, however, considerable amounts of ammonium were found in the lower layers, whereas less ammonium accumulated in the upper layer. Second, the potential ammonium-oxidizing activity of N. europaea was stimulated in the presence of flagellates. The numbers of N. europaea at different glucose concentrations in the presence of flagellates were comparable to those in the absence of protozoa. However, in the presence of flagellates, the potential ammonium-oxidizing activities were four to five times greater than those in the absence of protozoa.     

Competition between Salicornia europaea and Atriplex prostrata (Chenopodiaceae) along an experimental salinity gradient

Salicornia europaea L. is a halophyte that often occupies the lowestand most saline (>3.5% total salt) areas of salt marshes. Atriplexprostrata Boucher is less salt tolerant than S. europaea and oftengrows in a less saline (<2.0% total salts) zone adjacent to S. europaea. The purpose of this experiment was to determine thecompetitive outcome when these two species are grown at differentsalinities to ascertain the extent salinity and competition affect plantzonation. Plants were grown in a de Wit replacement series at 85, 170,and 340 mM NaCl in half-strength Hoagland's no. 2 nutrient solution fortwo months. There was a significant effect of salt concentration,competition, and their interaction on biomass production of S. europaea plants. However, only salt concentration significantly affectedbiomass production of A. prostrata plants. Results of thisexperiment confirmed the results of other studies that demonstrated thatthe more salt tolerant species were less competitive at lower salinities. Atriplex prostrata was the better competitor at 85 mM NaCl, whereasS. europaea was the better competitor at 340 mM NaClbecause growth of A. prostrata was inhibited. At 170 mMNaCl, A. prostrata biomass production decreased more than S. europaea biomass in mixed culture.     

Comparison of two commercial formulations of Bacillus thuringiensis var. israelensis for the control of Anopheles aquasalis (Diptera: Culicidae) at three salt concentrations

Anopheles aquasalis larvae are salt water tolerant, preferring concentrations between 10 and 20 parts per thousand (ppt). The larvicidal efficacy of two formulations of Bacillus thuringiensis var. israelensis (Vectobac-12AS and Bactivec), was investigated against An. aquasalis at salinities of 0, 10, and 20 ppt. A probit analysis was used to calculate the lethal concentrations (LC50 and LC95) for each product at each salinity. The LC50 and LC95 were higher for Bactivec than Vectobac-12AS, and for Bactivec, the LC50 and LC95 increased with salinity. Vectobac-12AS should thus be preferred to Bactivec for An. aquasalis control, especially in saline breeding habitats.     

The effects of salinity and sodicity upon nodulation and nitrogen fixation in chickpea (Cicer arietinum)

Production of grain legumes is severely reduced in salt-affected soils because their ability to form and maintain nitrogen-fixing nodules is impaired by both salinity and sodicity (alkalinity). Genotypes of chickpea, Cicer arietinum, with high nodulation capacity under stress were identified by field screening in a sodic soil in India and subsequently evaluated quantitatively for nitrogen fixation in a glasshouse study in a saline but neutral soil in the UK. In the field, pH 8.9 was the critical upper limit for most genotypes studied but genotypes with high nodulation outperformed all others at pH 9.0-9.2. The threshold limit of soil salinity for shoot growth was at ECe 3 dS m(-1), except for the high-nodulation selection for which it was ECe 6. Nodulation was reduced in all genotypes at salinities above 3 dS m(-1) but to a lesser extent in the high-nodulation selection, which proved inherently superior under both non-saline and stress conditions. Nitrogen fixation was also much more tolerant of salinity in this selection than in the other genotypes studied. The results show that chickpea genotypes tolerant of salt-affected soil have better nodulation and support higher rates of symbiotic nitrogen fixation than sensitive genotypes.     

Effects of low-salinity on the growth and development of spotted halibut Verasper variegatus in the larva-juvenile transformation period with reference to pituitary prolactin and gill chloride cells responses

Low-salinity adaptability was investigated in a flatfish spotted halibut Verasper variegatus during the period from late metamorphic larvae to early juveniles by a 20-day rearing experiment under different salinity regimes (1, 4, 8, 16 and 32 ppt). Effects of low-salinity on growth and development were examined and the changes in the prolactin (PRL) production level in the pituitary and the gill chloride cell morphology were examined as physiological backgrounds for low salinity adaptation. PRL cells and chloride cells were identified by immunocytochemistry with a specific antiserum for PRL₁₈₈ and Na⁺,K⁺-ATPase. Most of the fish exposed to over 4 ppt survived for 20 days, but all the fish exposed to 1 ppt died within 5 days. Fish kept in intermediate salinities (8, 16 ppt) grew significantly better than those in the control group (32 ppt). Fish exposed to 4 ppt attained almost the same body length as the control group at 20 days after transfer, although these fish showed an abnormally dark body color as well as delayed development. These results suggested that spotted halibut has a high-adaptability to low-salinity environments and prefers an intermediate salinity near iso-osmolality (about 12 ppt) from the late metamorphic larval stage, but does not completely adapt to a hypoosmotic of 4 ppt salinity or less than half of the osmolality. The percentage of PRL-cell volume to pituitary volume was significantly higher at 4 ppt than in the control group. The chloride cells in gill filaments were significantly larger at 4 ppt than in the control group. These results suggest that juveniles could adapt to a low-salinity environment due to the activation of PRL production and enlargement of chloride cells. These laboratory findings suggest that late metamorphic larvae and early juveniles of spotted halibut may utilize a low salinity environment such as estuarine tidal flats or very shallow coastal areas as their nursery grounds in the sea.     

Effects of salinity and inundation regime on growth and distribution of Schoenoplectus triqueter

In Ireland, Schoenoplectus triqueter is confined to areas in the upper part of the Shannon estuary where average summer soil pore water salinity levels do not exceed 7.0 ppt. Soil-based and nutrient solution-based experiments showed that growth and reproduction of S. triqueter was significantly reduced at salinity of 10 ppt and significantly enhanced at 2.0 ppt compared to a freshwater control. Young plants were less tolerant of salinity than older plants. A transplantation trial showed that S. triqueter could grow at higher salinities in the field but that growth and reproduction were significantly inhibited at higher field salinities. The effect of simulated diurnal tidal inundation on the growth and reproduction of S. triqueter was examined by growing plants in a tank with fluctuating water levels. S. triqueter was able to grow and produce seed when inundated for up to 12 h per 24-h period, indicating a considerable capacity to withstand periodic inundation. Growth responses to simulated tidal inundation were also examined in Bolboschoenus maritimus. Long periods of daily inundation reduced growth of B. maritimus proportionately more than that of S. triqueter. It is concluded that S. triqueter occupies a narrow ecological niche in the Shannon Estuary that is circumscribed by competition from more robust emergent species but is facilitated by the ability of S. triqueter to tolerate lengthy periods of inundation by the tides.