Fast-start escape performance across temperature and salinity gradients in mummichog Fundulus heteroclitus

Fast-start predator-escape performance of mummichogs Fundulus heteroclitus was tested across field-informed variation in temperature (24, 30 and 36°C) and salinity (2, 12 and 32 ppt). Performance was similar across temperatures and salinities when fish were allowed to acclimate to these conditions. However, when mummichogs experienced acute temperature changes, performance exhibited thermal dependence in two contrasting ways. Fast-start turning rates and linear speeds varied directly with the temperature at which the manoeuvre was executed, but these aspects of performance varied inversely with acclimation temperature, with cool-acclimated fish exhibiting faster starts across test temperatures. Temperature effects were consistent across salinities. These results suggest that while mummichogs increase performance with acute temperature increases, long-term rises in sea temperature may cause these fish to become more susceptible to predation during abrupt cooling events, such as when storm events flood shallow water estuaries with cool rainwater.     

Environmental Optima for Seven Strains of Pseudochattonella (Dictyochophyceae,Heterokonta)

The ichthyotoxic flagellate Pseudochattonella has formed recurrent blooms in the North Sea, Skagerrak and Kattegat since 1998. Five strains of Pseudochattonella farcimen and two strains of P. verruculosa were examined in an assay comparing the light response of specific growth rates over a range of temperatures and salinities to get further knowledge on the autecology of members of this genus. Temperature optima were lower in P. farcimen (9°C–15°C) than in P. verruculosa (12°C–20°C). P. farcimen also showed a somewhat lower salinity optimum (18–26) than P. verruculosa (20–32). All strains showed light‐dependent growth responses reaching saturation between 18 and 52 μmol · photons · m^?2 · s^?1 at optimal temperature and salinity conditions. Compensation point estimates ranged from 4.2 to 15 μmol · photons · m^?2 · s^?1. Loss rates increased with temperature and were lowest at salinities close to optimal growth conditions. Blooms of P. farcimen have been recorded in nature under conditions more similar to those minimizing loss rates rather than those maximizing growth rates in our culture study.     

The effects of different temperature and salinity levels on the acute toxicity of zinc in the Pink Shrimp (Farfantepenaeus paulensis)

The purpose of this study was to measure the acute toxicity of zinc (Zn) on Farfantepenaeus paulensis at different salinities and temperatures by monitoring oxygen consumption. This aspect of the effect of zinc has not been studied in this important commercial species before. First, we examined the acute toxicity of zinc in F. paulensis at 24, 48, 72, and 96?h medium lethal concentration (LC₅₀). One hundred and fifty shrimp were employed for the routine metabolism measurement utilizing sealed respirometers. Ten shrimp were subjected to oxygen consumption measurements in one of the four concentrations of zinc (control, 0.5, 1.0, 2.0, and 3.0 mg?L^?1) at three salinities (36, 20, and 5) and three temperatures (25°C, 20°C, and 15°C). Zinc was significantly more toxic at a salinity of 5 than at 20 or 36. The oxygen consumption was estimated through experiments performed on each of the 12 possible combinations of three temperatures (25°C, 20°C, and 15°C) and three salinities (36, 20, and 5). The shrimp showed a significant reduction in oxygen consumption at a salinity of 5. The results show that the oxygen consumption decreases with respect to the zinc concentration in all temperatures studied. At the highest zinc concentration employed (3.0?mg?L^?1), the salinity 5 and the temperature at 25°C, oxygen consumption decreases 60.92% in relation to the control. The results show that zinc is more toxic to F. paulensis at lower salinities. The significance of the findings for the biology of the species close to sources of zinc is discussed.     

The effect of acute warming and thermal acclimation on maximum heart rate of the common killifish Fundulus heteroclitus

Common killifish Fundulus heteroclitus were acclimated to ecologically relevant temperatures (5, 15 and 33°C) and their maximum heart rate (f_Hmax) was measured at each acclimation temperature during an acute warming protocol. Acclimation to 33°C increased peak f_Hmax by up to 32% and allowed the heart to beat rhythmically at a temperature 10°C higher when compared with acclimation to 5°C. Independent of acclimation temperature, peak f_Hmax occurred about 3°C cooler than the temperature that first produced cardiac arrhythmias. Thus, when compared with previously published values for the critical thermal maximum of F. heteroclitus, the temperature for peak f_Hmax was cooler and the temperature that first produced cardiac arrhythmias was similar to these critical thermal maxima. The considerable thermal plasticity of f_Hmax demonstrated in the present study is entirely consistent with eurythermal ecology of killifish, as shown previously for another eurythermal fish Gillichthys mirabilis.     

Effects of temperature and salinity on embryonic development of turbot (Scophthalmus maximus L.) from the North Sea, and comparisons with Baltic populations

Optimum temperature and salinity conditions for viable hatch were studied for turbot (Scophthalmus maximus L.) from the North Sea. Temperatures ranging from 6 to 22°C and salinities from 5 to 35‰ were used. Optimum conditions were observed to be between 12 and 18°C at salinities between 20 and 35‰. This contrasted with corresponding data for turbot from the southern Baltic proper, according to which survival sharply decreased in temperatures below 14°C and was high in salinities of 10 to 15‰. Thus, it is concluded that Baltic and Atlantic turbot should be considered as different races.     

The Influence of Salinity and Temperature on Seed Germination in Salicornia bigelovii

Seeds of Salicornia bigelovii were germinated at 4.4°C, 15.5°C, and 26.6°C in saline solution containing from 0% to 8.08% sea salt. At 4.4°C, germination was delayed until the 26th day, but the final germination per cent was high in all salinities. At 15.5°C, germination was delayed until the 19th day, and the germination per cent was higher in the higher salinities. At 26.6°C, the germination began within one day and the germination per cent was higher at the lower salinities. With the exception of 26.6°C data, the maximum germination occurred at a sea salt concentration at 4.04 % which is very close to the salinity of the sea.     

A laboratory investigation of temperature and salinity tolerances of juvenile Metapenaeus bennettae Racek and Dall (Crustacea: Penaeidae)

Temperature and salinity tolerances of juvenile Metapenaeus bennetlae Racek and Dall were estimated by abrupt exposure to critically high or low levels of each factor following acclimation to 12 combinations of temperature (17, 22, 27 and 32°C) with salinity (5, 20 and 35‰.). No significant differences were found between tolerances of males and females. Acclimation temperature influenced both temperature and salinity tolerances, while acclimation salinity affected only the salinity tolerance. Irrespective of temperature and salinity acclimation levels, juvenile M. bennettae were able to tolerate temperatures from 8.1 to 32.9°C and salinities from 1.0 to 62.0‰ These findings are discussed in relation to similar published studies.     

Temperature and salinity effects on the respiratory metabolism of the first zoeal stage of Macrobrachium holthuisi Genofre & Lobão (decapoda: Palaemonidae)

Oxygen consumption rates of stage I Macrobrachium holthuisi Genofre & Lobão zoeae were measured in 24 different temperature and salinity combinations using Cartesian diver microrespirometers. Metabolic rates varied little with salinity at 15°C while at 20°C a marked elevation occurred in 0 and 35‰ At 25°C, a slight elevation occurred in 0‰; rates remained constant, however, in the other salinities. At 30°C, respiratory rates were similar to those recorded at 25°C except for decreases at 0 and 28‰ salinity. Q₁₀ values in the different salinities were usually highest between 15 and 20°C. Statistical analyses showed that while both temperature, salinity and their interaction significantly influenced larval respiratory rates, temperature had the more pronouced effect. Larval metabolism is salinity independent over the salinity range encountered in the larval biotope (7–21‰) at temperatures of 15–30°C.     

The effects of salinity on the cellular permeability and cytotoxicity of Heterosigma akashiwo

A laboratory study using the fish‐killing raphidophyte Heterosigma akashiwo was conducted to examine its capability to grow at salinities below oceanic, and to test the perceived relationship between reduced salinities and increased cytotoxicity. A nonaxenic strain of H. akashiwo isolated from the U.S. Pacific Northwest was exposed to a combination of three salinity (32, 20, and 10) and five temperature (14.7°C, 18.4°C, 21.4°C, 24.4°C and 27.8°C) conditions. Our results demonstrate that cell permeability and cytotoxicity are strongly correlated in unialgal cultures of H. akashiwo, which both increased as salinity decreased from 32 to 10. Furthermore, over a broad median range of salinities (10 and 20), neither temperature nor specific growth rate was correlated with cytotoxicity. However, in cultures grown at the salinity of 32, both temperature and specific growth rate were inversely proportional to toxicity; this relationship was likely due to the effect of contamination by an unidentified species of Skeletonema in those cultures. The presence of Skeletonema sp. resulted in a cytotoxic response from H. akashiwo that was greater than the response caused by salinity alone. These laboratory results reveal the capability of H. akashiwo to become more toxic not only at reduced salinities but also in competition with another algal species. Changes in cell permeability in response to salinity may be an acclimation mechanism by which H. akashiwo is able to respond rapidly to different salinities. Furthermore, due to its strong positive correlation with cytotoxicity, cellular permeability is potentially associated with the ichthyotoxic pathway of this raphytophyte.     

Effects of temperature,salinity and body size on routine metabolism of coastal largemouth bass Micropterus salmoides

Routine metabolism (i.e. standard metabolism plus a low level of activity) of coastal largemouth bass Micropterus salmoides from Mobile‐Tensaw Delta, AL, U.S.A. was examined as a function of temperature (15, 20, 25 and 30° C), salinity (0, 4, 8 and 12) and body mass (range 24–886 g) using flow‐through respirometry. Functionally, a cubic relationship best described the effect of salinity on respiration; the magnitude of these effects increased with temperature and body mass. The best model predicted that specific respiration (mg O₂ g^?1 h^?1) at temperatures >20° C was lowest at salinities of 0·0 and 9·7, and elevated at 3·2 and 12·0; salinity had little to no effect at temperatures ≤20° C. Respiration increased exponentially with temperature, but when compared with previously published respiration rates for M. salmoides from northern latitudes, predicted respiration was higher at cool temperatures and lower at high temperatures. The reduced energetic cost near the isosmotic level (i.e. c. 9) may be an adaptive mechanism to tolerate periods of moderate salinity levels and may help explain why M. salmoides do not flee an area in response to increased salinity. Further, these results suggest that salinity has high energetic costs for coastal populations of M. salmoides and may contribute to the observed slow growth and small maximum size within coastal systems relative to inland freshwater populations.     

Dense winter bloom of the dinoflagellate Heterocapsa triquetra below the thick surface ice of brackish Lake Shihwa,Korea

We investigated the seasonal abundance of the dinoflagellate Heterocapsa triquetra (Ehrenberg) F. Stein, as well as the relevant in situ environmental factors, in brackish Lake Shihwa, Korea. We also examined the growth rates and morphological characteristics of the species in laboratory cultures. In the field, the population densities of H. triquetra remained at low levels from late spring to early summer, and then completely disappeared from August to November 2007. Interestingly, a dense bloom of H. triquetra appeared below the ice surface on 17 January 2008; identities of the cells were confirmed by rDNA sequence comparisons. The second peak reached a density of 672 × 10³ cells L^?1 on 28 March 2008, at a water temperature of 9.1°C. Laboratory experiments showed that growth rates of H. triquetra increased with incremental temperature increases within the range of 10 and 20°C. The highest growth rate reached by H. triquetra was 0.62 d^?1 at 20°C with a salinity of 30. Above 25°C, the dinoflagellate was unable to grow between salinities of 10 and 15, and reached only relatively low growth rates (<0.12 d^?1) under other salinity conditions. However, under continuous cultures at 5°C and 8°C, H. triquetra cells retained its growth capability for more than 12 days, implying that H. triquetra can survive and grows even at very low temperatures. The equivalent spherical diameter (ESD) of H. triquetra did not change markedly between 10 and 25°C, but the equivalent spherical diameter was significantly different at 5°C. The cell volume buildup of H. triquetra at low temperatures is one of the important survival strategies to overcome the harsh environmental conditions. These characteristics make H. triquetra a consistently dominant dinoflagellate in Lake Shihwa during the cold winter season.     

The combined effects of temperature,salinity, and declining oxygen tension on oxygen consumption in the marine pulmonate Amphibola crenata (Gmelin, 1791)

Oxygen consumption of Amphibola crenata (Gmelin) was measured in various salinity-temperature combinations (< 0.1‰ to 41‰ salinity and 5 to 30°C) in air, and following exposure to declining oxygen tensions. In all experimental conditions, respiration varied with the 0.44 power of the body weight (sd = 0.14). The aquatic rate was consistently higher than the aerial rate of oxygen consumption, although at 30 °C the two rates were similar. Oxygen consumption increased with temperature up to 25 °C in all salinities; the lowest values were recorded at temperatures below 10 °C and at 30 °C in the most dilute medium. At all exposure temperatures, the oxygen consumption of Amphibola decreased regularly with salinity down to 0.1 ‰, and following exposure to concentrated sea water (41‰). Salinity had the least effect at 15 °C which was the acclimation temperature. In general, all of the temperature coefficients (Q₁₀ values) were low, < 1.65. However, Q₁₀ values above 2.8 were recorded at a salinity of 17.8‰ between 10 and 15 °C. Oxygen consumption of all size classes of Amphibola was more temperature dependent in air than in water and small individuals show a greater difference between their aerial and aquatic rates than larger snails. The rates of oxygen consumption in declining oxygen tensions were expressed as fractions of the rates in air saturated sea water at each experimental salinity-temperature combination. The quadratic coefficient B₂ becomes increasingly more negative with both decreasing salinity and temperatures up to 20 °C. At higher temperatures (25 and 30 °C) the response is reversed such that O₂ uptake in snails becomes increasingly independent of declining oxygen tensions at higher salinities. On exposure to a salinity of 4‰, Amphibola showed no systematic response to declining oxygen tension with respect to temperature. The ability of Amphibola to maintain its rate of oxygen consumption in a wide range of environmental conditions is discussed in relation to its potential for invading terrestrial habitats and its widespread distribution on New Zealand's intertidal mudflats.     

Acute osmotic tolerance of cultured cells of the oyster pathogen Perkinsus marinus (Apicomplexa : Perkinsida)

Cultured Perkinsus marinus cells were exposed for 24 hr to salinities of 0, 3, 6, 9, 12 and 22 ppt at temperatures of 1, 5, 10, 15 and 28°C in artificial seawater (ASW) and to the same salinities at 28°C in ASW with the osmotic concentration adjusted with sucrose to the equivalent of 22 ppt. At 28°C mortality increased as salinity decreased below 22 ppt. Mortality was greater than 99% at 0 ppt and greater than 90% at 3 ppt. Mortality was 70% at 6 ppt, 43% at 9 ppt and 20% at 12 ppt. Mortality was low (<5%) and equal to that at 22 ppt in all treatments where osmotic concentration was maintained with sucrose. Mortality occurred rapidly, within 5 min of exposure to experimental conditions. In the region where mortality was most sensitive to salinity changes (6–12 ppt), lower temperature caused an increase in mortality, but the temperature effect was significant only at 9 ppt.     

Effects of temperature and salinity on the eggs and early larvae of Caranx mate (Cuv. & Valenc.) (pisces: carangidae) in Hawaii

Eggs and larvae of the carangid fish, Caranx mate (Cuv. & Valenc.), were incubated at various temperature (17.2 to 33.1 °C) and salinity (10 to 42 ‰) combinations in five experiments. The following rates were directly proportional to temperature: embryonic development, yolk absorption, eye and jaw development, and increase in length. Unfed C. mate larvae attained a maximum size at 25 °C and 20 ‰ Eyes and jaws of larvae were functional by the end of the yolk sac stage at all temperature and salinity levels tested.Hatching success and larval survival at the end of the yolk sac stage were generally greater than 50 % between 22° and 32°C. Hatching success and larval survival at the end of the yolk sac stage were reduced at salinity extremes, especially in low temperature-low salinity and high temperature-high salinity combinations. The frequency of morphological abnormalities was also high at extreme temperatures and salinities.The incipient upper thermal TL_m for unfed C. mate larvae acclimated to 23.8°C increased from 31.5°C for newly hatched larvae, to 34.2°C for 72 h larvae, but decreased to 32.0°C for starving larvae after the exhaustion of the yolk supply.     

Effects of extreme changes of sea water temperature and salinity on the development of the sand dollar <Emphasis Type="Italic">Scaphechinus mirabilis</Emphasis>

The combined effects of temperatures of 14, 17, 20, 22, and 25°C and salinities of 36–12‰ on embryos and larvae of the sand dollar Scaphechinus mirabilis was studied. Embryonic development is the most sensitive stage in the early ontogenesis of S. mirabilis. It is completed at a temperature of 14–20°C in a salinity range of 36–24‰ and at temperature of 22°C to 26‰. The fertilization proceeds in wider ranges of temperature and salinity. Among the swimming larvae, blastulae showed the greatest resistance to variations of these environmental factors. All the larvae survived at a temperature of 14–22°C and a salinity of 36–20‰, and more than 70% of them at 18‰. The pluteus I is the most vulnerable stage; probably this is related to the formation of the larval skeleton and transition to phytoplankton feeding. The survival of larvae at the age of 20 days was 100% at 14–22° C and a salinity of 36–24‰, most of them survived at 14–20°C and a salinity 18‰. The temperature 25 ° C is the most damaging for early development of S. mirabilis. The duration of development of that species lasts 28.5–29 days at 20°C and a salinity of 32.2–32.6‰. At 20 and 22°C, the larvae settled and completed metamorphosis more quickly if sand from the parental habitat was present. The larvae did not settle during the experiment (14 days) at 14 ° C and in the absence of sand.     

Combined effect of temperature and salinity on the development of the holothurianEupentacta fraudatrix

Temperature (25, 22, 16, and 12°C) and salinity (32–14‰) effects on the development of the low-boreal holothurianEupentacta fraudatrix were investigated. By studying the desalination resistance of adult holothurians,E. fraudatrix was shown to be a stenohaline species. The lower salinity limit at which both the larvae and adults survived was 22‰. Fertilization and development to the stage of free-swimming blastula occurred at the bottom. Embryogenesis, a critical stage of development, was successfully completed at a salinity of 32–26‰ and temperature of 22–16°C. The fertilization and development of a free-swimming blastula proved to be most resistant to temperature changes. The blastulae that developed at lowered temperatures (16–12°C) were capable of further development and settling at the same temperatures, which is likely associated with the peculiarities of the species range. If the early development proceeded at a higher temperature (22°C), the larvae failed to adapt to and perished from sharp temperature decreases at later stages of development. Thus, the lecithotrophic larva and a short period of larval development in the pelagial larvae (3–3.5 days from fertilization to settlement) ofE. fraudatrix are caused by the stenohalinity and environmental conditions of the species and, in turn, contribute to the fact that the young animals settle in the vicinity of their parents.     

Respiratory changes in the euryhaline clam, Mulinialateralis (Say), over a range of temperature and salinity combinations

The combined effects of five temperatures (15, 20, 25, 30, and 32 °C) and five salinities (10, 15, 20, 25, and 35%.) on respiratory metabolism in the euryhaline clam, Mulinia lateralis (Say), were determined from polarographic measurements of oxygen consumption. Although both the effects of temperature and salinity were statistically significant as well as their interaction effects, the effect of temperature was greater. Euryhalinity (previously ascribed to M. lateralis based only on its geographical distributions) was reflected physiologically by the few significant differences between respiration rates in various salinities at a given temperature. Significant differences were most often between rates in 20%. and the 10%. or 35%. extremes. Consistently highest rates in 20%. may reflect a salinity preferendum since this salinity was similar to long-term mean habitat salinity.     

Exposure of goldsinny, rock cook and corkwing wrasse to low temperature and low salinity: survival, blood physiology and seasonal variation

Wrasse used as cleaner fish with farmed Atlantic salmon Salmo salar can be subjected to large and rapid temperature and salinity fluctuations in late autumn and early winter, when summer-warmed surface water is affected by early snowmelt episodes. Because of their containment in sea cages, wrasse which are essentially acclimated to summer temperatures may be rapidly exposed to winter conditions. Short-term tolerance of low temperature and low salinity by three species of wrasse, goldsinny Ctenolabrus rupestris rock cook Centrolabrus exoletus corkwing Crenilabrus melops caught during the summer, and winter-caught corkwing, was investigated. A 3–day period at 30 or 32‰ salinity and temperature 8, 6 or 4° C (for summer-caught fish; 4° C only for winter-caught) was followed by a decline in salinity to 24, 16 or 8‰ over c. 36 h, followed by a further 24 h at these salinities held constant, at each of the three temperatures. Controls in 30 or 32‰ were maintained at 8, 6 or 4° C. Mortality of summer-caught corkwing and rock cook was high at 4° C, whereas the influence of salinity on mortality was small. Mortality of goldsinny was low or zero in all treatments. Surviving corkwing and rock cook after 3 days at 4° C and 32‰ salinity had elevated plasma osmolality: in summer-caught corkwing, plasma [Cl°] and [Na⁺] were high, whereas in rock cook only [Na⁺] was high. Haematocrit was low in summer-caught corkwing, high in rock cook. In survivors of all three species at the end of the experiment, values of all these parameters were comparable with those of fish at the beginning of the experiment, except that survivors at low salinity (8, 16‰) had low plasma osmolality, at all temperatures, and in surviving rock cook in these treatments haematocrit was high and plasma [Cl^?] was low. Winter-caught corkwing had higher osmolality, [Na⁺] and [Cl^?] than summer-caught corkwing; there was no difference in haematocrit. Survival of wintercaught corkwing exposed to four salinities at 4° C was much higher than that of summercaught corkwing under the same conditions. Little change in blood physiology was recorded for winter-caught corkwing, with only fish subjected to 8‰ and 4° C showing signs of osmoregulatory stress. The interspecific and seasonal differences in survival and blood physiology at low temperature and low salinity are discussed in relation to wrasse survival over winter, both in the field and in salmon farms.     

Hot and salty: the temperature and salinity preferences of a temperate estuarine shrimp larva, Upogebia pusilla (Decapoda: Thalassinidea)

At a time when global climate changes are forcing life to adapt to a warming and salinity-changing environment, it is essential to understand how future changes in ocean chemistry will affect species. This study evaluates the combined effects of temperature and salinity on survival and development of Upogebia pusilla larvae. Combinations were made from three temperatures (18, 23, and 28°C) and three salinities (15, 25, and 35). Survival, larval duration and megalopa size were compared between treatments. U. pusilla larvae developed optimally in the highest salinity (35) and higher temperatures (23–28°C). Low salinities and temperatures did not support larval survival and development, with salinity being the main restricting factor for survival, while temperature affected mainly the duration of the larval stages. Larvae at higher temperatures (23–28°C) presented a higher development rate but no differences were found in megalopa size.     

Reproductive isolating mechanisms contributing to asymmetric hybridization in Killifishes (Fundulus spp.)

When species hybridize, one F1 hybrid cross type often predominates. Such asymmetry can arise from differences in a variety of reproductive barriers, but the relative roles and concordance of pre-mating, post-mating prezygotic, and post-zygotic barriers in producing these biases in natural animal populations have not been widely investigated. Here, we study a population of predominantly F1 hybrids between two killifish species (Fundulus heteroclitus and F. diaphanus) in which >95% of F1 hybrids have F. diaphanus mothers and F. heteroclitus fathers (D♀ × H♂). To determine why F. heteroclitus × F. diaphanus F1 hybrids (H♀ × D♂) are so rare, we tested for asymmetry in pre-mating reproductive barriers (female preference and male aggression) at a common salinity (10 ppt) and post-mating, pre-zygotic (fertilization success) and post-zygotic (embryonic development time and hatching success) reproductive barriers at a range of ecologically relevant salinities (0, 5, 10, and 15 ppt). We found that F. heteroclitus females preferred conspecific males, whereas F. diaphanus females did not, matching the observed cross bias in the wild. Naturally rare H♀ × D♂ crosses also had lower fertilization success than all other cross types, and a lower hatching success than the prevalent D♀ × H♂ crosses at the salinity found in the hybrid zone centre (10 ppt). Furthermore, the naturally predominant D♀ × H♂ crosses had a higher hatching success than F. diaphanus crosses at 10 ppt, which may further increase their relative abundance. The present study suggests that a combination of incomplete mating, post-mating pre-zygotic and post-zygotic reproductive isolating mechanisms act in concert to produce hybrid asymmetry in this system.