Giraudia sphacelarioides (Phaeophyceae) at the Canary Islands and in Danish waters: a study in ecotypic differentiation and its biogeographical implications

Comparative culture studies on isolates from Lanzarote (Canary Islands) and from Danish waters of Giraudia sphacelarioides show that temperature plays the key role to determine its geographical distribution. Experiments show that the upper lethal temperature is the same for both isolates 26.5—-31.1°C for microthalli, and formation of macrothalli is inhibited between 23.2 and 26.5°C. The lower lethal temperature for both micro- and macrothalli in the Lanzarote isolate is between 10.8° C and 7.6°C, while the Danish isolate survives 54°C. The microthallus is thus the more persistent stage in relation to temperature, while the macrothalli occur only when more suitable conditions exist in nature. In the North Atlantic Ocean G. sphacelarioides is distributed over approximately 30° latitudes with severe winter temperatures especially in Danish waters. This distribution can only be explained by ecotypic differentiation. In Danish waters salinity decreases from c. 30 ‰ in the northern Kattegat to below 8 ‰ in the inner parts and therefore becomes an important factor for the immigration of species into the Baltic Sea. Combined salinity (30–20–10–5 ‰) and temperature (4 to 30°C) experiments show that the Lanzarote isolate only grows at 20 ‰ in an attenuated temperature interval and at 10 ‰ only fertile microthalli are observed, however, with limited liberation of swarmers. The Danish isolate grows and reproduces also at salinities from 20–5 ‰ both as microand macrothalli, but in a still more attenuated temperature interval, and the morphology of the macrothalli becomes increasingly aberrant vs. decreasing salinity. This is in agreement with the fact that G. sphacelarioides is reported from the northern part of Kattegat with salinity from 28—-25 ‰, and it is only recorded a few times in the southern part of Kattegat and limited by the 10 ‰ isohaline.     

CULTURE STUDIES ON REPRODUCTION OF SPERMATOCHNUS PARADOXUS (PHAEOPHYCEAE,CHORDARIALES)1

The life history of Spermatochnus paradoxus (Roth) Kütz. isolated from the Mediterranean Sea was studied in culture. Meiospores develop to a microscopic stage (microthallus) which at 20°C perpetuates asexually by plurilocular sporangia and formation of new microthalli. At 9°C microthalli act as homothallic gametophytes. Fusion of isogametes results in a diploid microthallus which, after differentiation of an apical cell, leads back to Spermatochnus plants. In addition, gametes develop without fusion to form haploid macrothalli, the further fate of which has not been determined. Chromosome numbers alternate between n = 20 ± 2 in the microthalli and 2n = 41 ± 4 in macrothalli.     

RELATION OF TEMPERATURE TO DEVELOPMENT OF THE MACROTHALLUS OF DESMOTRICHUM UNDULATUM1,2

Desmotrichum undulatum (J. Agardh) Reinke (Phaeophyta) was found in the winter months in the littoral zone of a tidal marsh in Virginia. When field collections were maintained in culture media at 21 C, most cells of the thallus developed into plurilocular sporangia. Released zoospores developed into microthalli from which clonal cultures were established. At 21 C microthalli produced sporangia which released zoospores, subsequently developing into more microthalli. However, microthalli at 6 C formed filaments which subsequently developed into thalloid plants. When the thalloid plants of Desmotrichum formed in culture were subjected to 21 C, plurilocular sporangia were formed. These results support the proposition that the seasonal periodicity of Desmotrichum is due to a temperature-regulated phenomenon in the development of macrothalli.     

Growth and reproduction of Scytosiphon lomentaria (Fucophyceae) in relation to temperature in two populations from Denmark

Two strains of Scytosiphon lomentaria from Denmark have been grown under long-day conditions on a temperature-gradient plate. The material from north-west Jutland (strain No. 46) has a reduced prostrate system (a few-celled lump) whereas the other material from the Sound (strain No. S41) has a well-developed crust. This difference plays a significant role in growth and reproductive patterns. Strain No. 46 rapidly produces a great number of cylindrical macrothalli. Within a four-week experimental period, formation of swarmers from plurilocular sporangia on the macrothalli takes place and results in a maximum dry weight of 32.9 mg at 18.2°C.
Swarmers from the macrothalli of strain S41 always develop into knot-filamentous or crust-shaped thalli. The development of the macrothalli, therefore, takes a longer time than in strain 46 and the maximum dry weight is only 16.5 mg at 16°C even within an experimental period of six weeks. The reproductive pattern is more complex than in strain 46. The crusts produce unilocular sporangia at temperatures between 16°C and 23.8°C, and function, therefore, as the reproductive system during the summer as macrothalli disappear at temperatures above 18°C both in nature and in culture. Formation of plurilocular sporangia on macrothalli starts when they are from 6–9 weeks old at temperatures between 11°C and 18°C.
The temperature range for growth in the two strains also differs: Strain 46 grows from 7.3–24.4°C while strain S41 grows at least from 4–5.1°C to an upper limit of 27.1°C, but lower limit has not been determined precisely in the present experiment. These results indicate that temperature ecotypes exist, even within a limited geographic area.     

Temperature requirements ofScytosiphon lomentaria (Scytosiphonales,Phaeophyta) from the Gulf of Thessaloniki,Greece, in relation to geographic distribution

Temperature requirements for growth, reproduction and formation of macrothalli of a day-neutral strain ofScytosiphon lomentaria from the Gulf of Thessaloniki were experimentally determined and correlated with the geographic distribution in the North Atlantic Ocean. The microthallus grew in a wider temperature interval and better at higher temperatures than did the macrothallus. Germlings acclimated to 5 or 15°C grew sufficiently (>20% of maximum rate) and developed into macrothalli at 5–25°C and 5–27°C. Macrothalli acclimated to 10 or 15°C grew sufficiently at 5–20°C. Macrothalli acclimated to 15°C survived at −1°C and reproduced at 5 to 23°C. Regardless of the acclimation temperature, germlings and macrothalli grew optimally (>80% of maximum rate) at 15–25°C and at 10–15°C. The experimental data explain only the southern distribution boundary ofScytosiphon in the North Atlantic. This boundary is composite in nature: on the European coasts it is a growth boundary, whereas on the American coasts it is a lethal one.     

STUDIES ON THE AUTECOLOGY OF THE MARINE DIATOM THALASSIOSIRA NORDENSKIÖLDIICLEVE. 1. THE INFLUENCE OF DAYLENGTH,LIGHT INTENSITY,AND TEMPERATURE ON GROWTH1

The marine diatom Thalassiosira nordenskiöldii Clave was grown at 48 different combinations of daylength (9:15, 12:12, 15:9 LD), light intensity (0.011, 0.027, 0.066, 0.100 ly/min [g cal/cm²/min]), and temperature (0, 5, 10, 15 C). Growth occurred at all combinations of light and temperature except at 15 C at the highest light level. Maximum growth (K = 1.8 doublings/day) occurred at 10 C under the 15:9 LD cycle. At 15 C the maximum rate was 1.7 doublings/day but occurred at the shortest day-length (9:15 LD). The maxima at 5 and 0 C were 1.32 and 0.67 doubling/day, respectively. At 0 C growth was similar over a wide range of light intensities (K = 0.6–0.65), with, maximum growth being attained at a much lower light intensity than at 5 C. Above 5 C there was a decrease in the light intensity at which maximum growth occurred and excessive light became inhibitory to growth. At 15 C the light intensity at which maximum growth occurred was greater with shorter day-lengths. The temperature optimum was 10 C at 15:9 and 15 C at 9:15 LD. The chlorophyll a content of the cells was greatest under low light intensities and short daylengths, while temperature had a variable effect. The response of Thalassiosira in the laboratory contrasts with, its apparent preference for low temperatures in nature (0–5 C). The experiments suggest that the termination of the bloom of Thalassiosira in Narragansett Bay and elsewhere is not solely temperature dependent.     

The combined effect of temperature and salinity changes on osmoregulation and haemocyanin concentration in Saduria entomon (Linnaeus, 1758)

Global warming is having an impact on the temperature and salinity of Baltic Sea waters. Therefore, it is important to determine the conditions in which animals can exist and how these changes may influence their functioning. Hence, the purpose of this research was to determine the broad tolerance limits of temperature and salinity of the glacial relict Saduria entomon by studying its behaviour, osmoregulatory ability and haemocyanin concentration. This effect of temperature was confirmed in the laboratory for individuals acclimated to different salinity and temperature regimes. Changes in the physiological parameters of S. entomon at various temperatures (5.5–21.5°C) and salinity levels (1–15 PSU) were recorded. There were statistically significant differences in haemolymph osmotic pressure under the influence of salinity and temperature. The mean haemolymph osmotic pressures were the lowest at 1 PSU at all the temperatures examined and the highest at 15 PSU and high temperatures 16.5 and 21.5°C. The haemocyanin concentration decreased significantly with increasing temperature at 1 PSU. There was a significant difference in haemocyanin concentration due to salinity at temperatures of 5.5 and 10.0°C (the haemocyanin concentration decreased with increasing salinity). The results showed that, although S. entomon is classified as a cold-water animal, it can survive at high temperatures above 16.5°C at least for a short time, as it is capable of osmoregulation. The tolerance to temperature changes was better than expected.     

Relative importance of temperature and other factors in determining geographic boundaries of seaweeds: Experimental and phenological evidence

Experimentally determined ranges of thermal tolerance and requirements for completion of the life history of some 60 seaweed species from the North Atlantic Ocean were compared with annual temperature regimes at their geographic boundaries. In all but a few species, thermal responses accounted for the location of boundaries. Distribution was restricted by: (a) lethal effects of high or low temperatures preventing survival of the hardiest life history stage (often microthalli), (b) temperature requirements for completion of the life history operating on any one process (i.e. [sexual] reproduction, formation of macrothalli or blades), (c) temperature requirements for the increase of population size (through growth or the formation of asexual propagules). Optimum growth/reproduction temperatures or lethal limits of the non-hardiest stage (often macrothalli) were irrelevant in explaining distribution. In some species, ecotypic differentiation in thermal responses over the distribution range influenced the location of geographic boundaries, but in many other species no such ecotypic differences were evident. Specific daylength requirements affected the location of boundaries only when interacting with temperature. The following types of thermal responses could be recognised, resulting in characteristic distribution patterns: (A) Species endemic to the (warm) temperate eastern Atlantic had narrow survival ranges (between ca 5 and ca 25°C) preventing occurrence in NE America. In species with isomorphic life histories without very specific temperature requirements for reproduction, northern and southern boundaries in Eur/Africa are set by lethal limits. Species with heteromorphic life histories often required high and/or low temperatures to induce reproduction in one or both life history phases which further restricted distribution. (B) Species endemic to the tropical western Atlantic also had narrow survival ranges (between ca 10 and ca 35°C). Northern boundaries are set by low, lethal winter temperatures. Thermal properties would potentially allow occurrence in the (sub) tropical eastern Atlantic, but the ocean must have formed a barrier to dispersal. No experimental evidence is so far available for tropical species with an amphi-Atlantic distribution. (C) Tropical to temperate species endemic to the western Atlantic had broad survival ranges (<0 to ca 35°C). Northern boundaries are set by low summer temperatures preventing (growth and) reproduction. Thermal properties would permit occurrence in the (sub)tropical eastern Atlantic, but along potential “stepping stones” for dispersal in the northern Atlantic (Greenland, Iceland, NW Europe) summer temperatures would be too low for growth. (D) In most amphi-Atlantic (tropical-) temperate species, northern boundaries are set by low summer temperatures preventing reproduction or the increase of population size. On European shores, species generally extended into regions with slightly lower summer temperatures than in America, probably because milder winters allow survival of a larger part of the population. (E) Amphi-Atlantic (Arctic-) temperate species survived at subzero temperatures. In species with isomorphic life histories not specifically requiring low temperatures for reproduction, southern boundaries are set by lethally high summer temperatures on both sides of the Atlantic. None of the species survived temperatures over 30°C which prevents tropical occurrence. Species with these thermal responses are characterized by distribution patterns in which southern boundaries in Eur/Africa lie further south than those in eastern N America because of cooler summers. In most species with heteromorphic life histories (or crustose and erect growth forms), low temperatures were required for formation of the macrothalli (either directly or through the induction of sexual reproduction). These species have composite southern boundaries in the north Atlantic Ocean. On American coasts, boundaries are set by lethally high summer temperatures, on European coasts by winter temperatures too high for the induction of macrothalli. Species with this type of thermal responses are characterized by distribution patterns in which the boundaries in Eur/Africa lie further north than those in eastern N America because of warmer winters. Paper presented at the XIV International Botanical Congress (Berlin, 24 July–1 August, 1987), Symposium 6-15, “Biogeography of marine benthic algae”.     

Growth and photosynthesis in seedlings of Hizikia fusiformis (Harvey) Okamura (Sargassaceae, Phaeophyta) cultured at two different temperatures

This study examined temperature acclimation, growth, and photosynthetic characteristics of the zygote-derived seedlings of Hizikia fusiformis (Harvey) Okamura (Sargassaceae). The seedlings were cultured at 15°C or 25°C for 4 weeks. The average relative growth rate was significantly higher in seedlings acclimated at 25°C. The photosynthetic rate measured at 15°C was much higher in seedlings grown at 15°C than those grown at 25°C, indicating photosynthetic acclimation to a lower temperature. At 35°C, the photosynthetic rate of 15°C-grown seedlings was drastically decreased, whereas that of 25°C-grown seedlings was significantly increased. The maximum relative electron transport rate (rETR_max) measured at the respective growth temperature was significantly higher in seedlings grown at 25°C than at 15°C. At a measuring temperature of 35°C, the rETR_max in both 15°C- and 25°C-grown seedlings were considerably reduced with regard to those measured at 15°C or 25°C. Our results suggested that, compared with the seedlings grown at 25°C, those acclimated at a lower temperature could be disadvantaged under adverse conditions such as increased temperatures.     

Salinity affects growth but not thermal preference of adult mummichogs Fundulus heteroclitus

The effects of an ecologically relevant range of salinities (2, 12, 22, 32) on thermal preferences and growth of adult mummichogs Fundulus heteroclitus were determined for fish from a southern Chesapeake Bay population. Salinity did not affect the mean temperature selected by F. heteroclitus in a thermal gradient, which was identified as 26.6°C based on observations of 240 individuals. Salinity and temperature had significant and interacting effects on growth rates of F. heteroclitus measured over 12 weeks. Growth rates were highest overall and remained high over a broader range of temperatures at moderate salinities (12 and 22), while high growth rates were shifted toward lower temperatures for fish grown at a salinity of 2 and higher temperatures at a salinity of 32. Significant reductions in growth relative to the optimal conditions (28.6°C, salinity of 22) were observed at the coolest (19.6°C) and warmest (33.6°C) temperature tested at all salinities, as well as temperatures ≥ 26.6°C at a salinity of 2, ≥ 28.6°C at a salinity of 12 and ≤ 26.6°C at a salinity of 32. Growth rates provide a long-term, organismal measure of performance and results of this study indicate that performance may be reduced under conditions that the highly euryhaline F. heteroclitus can otherwise easily tolerate. The combination of reduced salinity and increased temperature that is predicted for temperate estuaries as a result of climate change may have negative effects on growth of this ecologically important species.     

The influence of temperature and salinity on the duration of embryonic development,fecundity and growth of the amphipod Echinogammarus marinus Leach (Gammaridae)

The effects of salinity and temperature on the duration of embryonic development, fecundity and growth of the amphipod Echinogammarus marinus Leach from the Mondego estuary (Portugal) were studied in laboratory experiments. Combinations of three temperatures (10, 15 and 20 °C) and four salinities (10, 15, 20 and 25 ‰) were used. The duration of embryonic development was 33 ± 0.7 d (mean ± S.E.) at 10 °C, 32 ± 0.5 d at 15 °C, and 17 ± 0.3 d at 20 °C. Analysis of variance demonstrated that the duration of E. marinus embryonic development, reared under different combinations of salinity and temperature, was significantly affected only by temperature (P < 0.001). A positive correlation between the number of newborn juveniles and the size of E. marinus females (as head length) was observed. The number of juveniles released per female was higher at 10 °C and lower at 20 °C. Analysis of variance showed that only temperature significantly affected the number of juveniles released per female (P < 0.001). Experimental data were used to calibrate the von Bertalanffy growth model. Results showed that growth was continuous throughout life under all laboratory conditions. Intrinsic growth rates were higher at 20 °C and lower at 10 °C. Analysis of covariance applied over the initial 90 d after hatching showed significant differences between growth rates of E. marinus under different salinity and temperature conditions. Extrapolation of laboratory data to the field scenario suggests that E. marinus in the Mondego estuary have a multivoltine life cycle.     

Effects of temperature,irradiance, and daylength on the marine diatom leptocylindrus danicus cleve. I. Photosynthesis and cellular composition

Rates of ¹⁴C uptake and cellular composition of C, N, and Chl a in the marine diatom Leptocylindrus danicus Cleve were measured in axenic batch culture under 49 combinations of temperature (5, 10, 15, 20 °C), daylength (15: 9, 12: 12, 9: 15 LD), and irradiance (at least four irradiances per daylength). ¹⁴C uptake exhibited a temperature-dependent daylength effect. Similar P-I curves characterized cells grown under 15: 9 and 12: 12 LD; P_max values were 17.2, 11.2, 4.3, and 1.8 pg C. pg Chl a^?1. h^?1 at 20, 15, 10, and 5°C, respectively. Under 9:15 LD at 20 and 15°C, the lightsaturated photosynthetic rate was ≈50% that in cells grown under longer daylengths. ¹⁴C uptake was independent of daylength at 10 and 5°C. The initial slope, a, of cells grown under long daylengths increased by five-fold between 5 and 20 °C. α values of cells grown under 9: 15 LD at 15 and 20 °C were depressed relative to longer daylengths. Chl a was inversely related to irradiance, and increased with temperature from 10 to 20 °C, whereas cell carbon and nitrogen showed a similar temperature dependence but was not influenced by irradiance or daylength. The C : N ratio and cell volume were independent of temperature, irradiance, and daylength. Both the C : Chl a and N : Chl a ratios increased with irradiance by greater amounts at lower temperatures.     

Effects of low temperature on growth and non-structural carbohydrates of the imperial bromeliad <Emphasis Type="Italic">Alcantarea imperialis</Emphasis> cultured in vitro

The imperial bromeliad Alcantarea imperialis grows naturally on rocky outcrops (‘inselbergs’) in regions where daily temperatures vary from 5 to 40°C. As carbohydrate metabolism is altered in response to cold, it could lead to reprogramming of the metabolic machinery including the increase in levels of metabolites that function as osmolytes, compatible solutes, or energy sources in order to maintain plant homeostasis. The aim of this study was to evaluate the effects of different temperatures on plant growth and non-structural carbohydrates in plants of A. imperialis adapted to low temperature. Seedlings of A. imperialis were grown in vitro under a 12-h photoperiod with four different day/night temperature cycles: 5/5°C, 15/15°C, 15/30°C (dark/light) and 30/30°C. Plants were also cultivated at 26°C in ex vitro conditions for comparison. The results showed an inverse relationship between temperature and germination time and no differences in the percentage of germination. Plants maintained for 9 months at 15°C presented a reduced number of leaves and roots, and a dry mass four times lower than plants grown at 30°C. Sugar content was higher in plants grown at 15°C than at 30°C. However, the highest amount of total sugar was found in plants growing under warm day/cold night conditions. Myo-inositol, glucose, fructose and sucrose were found predominantly under high temperatures, while under low temperatures, sucrose was apparently replaced by trehalose, raffinose and stachyose. Starch content was highest in plants grown under high temperatures. The lowest starch content was detected under low temperatures, suggesting its conversion into soluble carbohydrates to protect the plants against cold. These results indicated that low temperature retarded growth of A. imperialis and increased sugar levels, mainly trehalose, thus suggesting that these sugar compounds could be involved in cold tolerance.     

Effects of temperature, salinity and irradiance on the growth of the harmful red tide dinoflagellate Cochlodinium polykrikoides Margalef (Dinophyceae)

The effects of temperature, salinity and irradiance on the growthof the harmful red tide dinoflagellate Cochlodinium polykrikoideswere examined in the laboratory. From 60 different combinationsof temperature (10–30°C) and salinity (10–40)under saturated irradiance, C. polykrikoides exhibited its maximumspecific growth rate of 0.41 day^-1 at a combination of 25°Cand salinity of 34. Optimum growth rates of >0.3 day^-1 wereobserved at temperatures ranging from 21 to 26°C and atsalinities from 30 to 36. The organism did not grow at temperatures10°C and only grew at salinities >30 if the temperaturewas >15°C. It was able to grow in temperatures rangingfrom 15 to 30°C and at salinities from 20 to 36. These valuesclosely resembled those observed for this species in situ. Itappears as if C. polykrikoides is a stenohaline organism thatprefers high salinities, indicative of offshore waters. Temperaturehad the greatest influence on the growth rate, followed by salinity,and then the interaction between temperature and salinity. Theoptimum irradiance for growth was >90 µmol m^-2 s^-1.Photoinhibition did not occur at 230 µmol m^-2 s^-1, whichwas the maximum irradiance used in this study.     

Modulation of physiological performance by temperature and salinity in the sugar kelp Saccharina latissima

The sugar kelp Saccharina latissima experiences a wide range of environmental conditions along its geographical and vertical distribution range. Temperature and salinity are two critical drivers influencing growth, photosynthesis and biochemical composition. Moreover, interactive effects might modify the results described for single effects. In shallow water coastal systems, exposure to rising temperatures and low salinity are expected as consequence of global warming, increased precipitation and coastal run‐off. To understand the acclimation mechanisms of S. latissima to changes in temperature and salinity and their interactions, we performed a mechanistic laboratory experiment in which juvenile sporophytes from Brittany, France were exposed to a combination of three temperatures (0, 8 and 15°C) and two salinity levels (20 and 30 psu (practical salinity units)). After a temperature acclimation of 7 days, sporophytes were exposed to low salinity (20 psu) for a period of 11 days. Growth, and maximal quantum yield of photosystem II (Fv/Fm), pigments, mannitol content and C:N ratio were measured over time. We report for the first time in S. latissima a fivefold increase in the osmolyte mannitol in response to low temperature (0°C) compared to 8 and 15°C that may have ecological and economic implications. Low temperatures significantly affected all parameters, mostly in a negative way. Chlorophyll a, the accessory pigment pool, growth and Fv/Fm were significantly lower at 0°C, while the de‐epoxidation state of the xanthophyll cycle was increased at both 0 and 8°C compared to 15°C. Mannitol content and growth decreased with decreased salinity; in contrast, pigment content and Fv/Fm were to a large extent irresponsive to salinity. In comparison to S. latissima originating from an Arctic population, despite some reported differences, this study reveals a remarkably similar impact of temperature and salinity variation, reflecting the large degree of adaptability in this species.     

ADAPTATION OF PHOTOSYNTHESIS IN LAMINARIA SACCHARINA (PHAEOPHYTA) TO CHANGES IN GROWTH TEMPERATURE1

The effect of growth temperature on photosynthetic metabolism was studied in the kelp Laminaria saccharina (L.) Lamour. Photosynthesis was subject to phenotypic adaptation, with almost constant photosynthetic rates being achieved at growth temperatures between 0 and 20° C. This response involved: (1) an inverse relationship between growth temperature and photosynthetic capacity, (2) a reduction in the Q₁₀ value for photosynthesis of L. saccharina grown at 0 and 5° C compared with 10, 15 and 20° C grown sporophytes, and (3) an acquired tolerance of photosynthesis to temperatures between 15–25° C (which inhibited photosynthesis in 0 and 5° C grown L. saccharina) in sporophytes grown at 10, 15 and 20° C. The physiological basis of these adaptations is discussed in terms of observed changes in activities and kinetics of the Calvin cycle enzyme ribulose-1, 5-bisphosphate carboxylase (oxygenase) and efficiency of light harvesting-electron transport systems.     

THE EFFECT OF SALINITY AND TEMPERATURE ON THE GERMINATION OF POLYMORPHIC SEEDS AND GROWTH OF ATRIPLEX TRIANGULARIS WILLD.

Polymorphic seeds of Atriplex triangularis were germinated at various temperatures (5–15 C, 5–25 C, 10–20 C, 20–30 C) and salinity regimes (0 to 1.5% NaCl) in order to determine their germinability and early seedling growth under these conditions. Larger seeds generally had a higher germination percentage in saline medium. The rate and percentage of germination decreased with increased salinity stress. A thermoperiod of 25 C day and 5 C night, 12 hr/12 hr, temperature enhanced germination of seeds. Early seedling growth is promoted in larger seeds at lower salinity, and at high-day and low-night temperatures. Polymorphic seeds have different physiological requirements which provide alternative situations for seed germination in natural habitats.     

Life History Traits of Two Chaetonotids (Gastrotricha) Under Different Experimental Conditions

Summary

A marine and a freshwater species of Chaetonotida (Gastrotricha) were reared under laboratory conditions. Their life tables and principal demographic parameters were determined at 2 different temperatures (20°and 25°C). At 25°C the data relative to the marine species were collected from 5 cohorts kept at 5 different salinity levels (15, 25, 35, 45, 55°/oo).

A higher temperature increases reproductive activity while shortening its duration in both species, whereas the length of the lifespan remains unaffected. Extreme salinity values (15 and 55°/oo) reduce the maximum longevity of the marine species and have opposite effects on reproductive activity, which is higher at low salinity and becomes lower at high salinity. The postparthenogenetic phase is remarkably long relative to the life cycle: this was observed in all experimental conditions and may be related to the existence of a second reproductive phase, which is hermaphroditic and follows the parthenogenetic one, as recently postulated from morphological data.     

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.     

EFFECTS OF TEMPERATURE,SALINITY, IRRADIANCE AND DIURNAL PERIODICITY ON GROWTH AND PHOTOSYNTHESIS IN THE DIATOM NITZSCHIA AMERICANA; LIGHT-SATURATED GROWTH1

The physiological response of an estuarine clone of Nitzschia americana Fryx3ell was measured under experimental conditions of temperature and salinity which represent the average range of these variables in the Cape Fear River Estuary, North Carolina. The influence of temperature (10, 15, 20, 25, 30°C) and salinity (8, 15, 20, 26, 32‰) on specific growth rates, μ, and parameters of photosynthesis-irradiance curves, α, and P_max were measured during maximum and minimum rates of diurnal photosynthesis using axenic semi-continuous batch cultures maintained at an irradiance saturating for photosynthesis (140 μE m^-2·s-1). There was an increase in μ with increasing temperature up to a broad uptimum (25 ± 2.5°C), above which μ gradually declined. At the predicted optimum temperature of 25°C, μ increased as a linear function of salinity. oth light-limited (α) amd light-saturated (P^max) rates of photosynthesis increased as salinity decreased. The effect of temperature on a and P^max was complex and dependent on salinity. P^max exhibited a diurnal periodicity, whereas estimates of a were not significantly different between sampling periods. Growth efficiencey opf N. americana, calculated as the ratio between specific growth rates and rates of gross photosynthesis, increased with an increase in salinity with a maximum at the predicted optimum temperature and salinity of 25°C and 32‰, suggesting and uncoupling between photosynthesis and growth at nonoptimum growth conditions.