Effects of various temperature cycles on the larval development of the gastropod molluscCrepidula fornicata

Veligers ofCrepidula fornicata (L.) were reared for 12 days at constant temperatures of 15°, 20°, 25°, 30° and 35°C, and at 5 C° daily cycles of equal periodicity (COEP) over the temperature ranges 15° to 20°C, 20° to 25°C, 25° to 30°C and 30° to 35°C. COEP consisted of equal periods (6 h) of maximum temperature, minimum temperature, and uniformly increasing and decreasing temperature each 24 h period. Survival was high and not influenced by cyclic or constant temperature from 15° to 30°C. At 35°C and COEP 30° to 35°C, all larvae died before Day 6. Shell growth rate increased markedly over the range 15° to 25°C, and growth rates at cyclic temperatures in this range were intermediate between growth rates at the corresponding constant temperatures. Larvae reared at COEP 15° to 20°C and COEP 30° to 35°C had discontinuities in their shells due to inhibition of shell secretion during the adverse part of each temperature cycle. Groups ofc. fornicata veligers were exposed for 2 days to daily temperature cycles of equal and unequal periodicity in the critical 30° to 35°C range. [Cycles of unequal periodicity (COUP) consisted of unequal periods (varying between 3 and 15 h) of maximum and minimum temperature and uniformly increasing and decreasing temperature each 24 h period.] These veligers showed shell growth although their body tissue declined, as indicated by decreasing carbon content per larva. Least shell growth and most body tissue loss occurred in those cycles with the longest exposure to higher temperature. Larvae exposed for arious days to the mildest 30° to 35°C COUP (15 h at 30°C, 3 h increasing temperature, 3 h at 35°C and 3 h decreasing temperature) recovered and resumed normal growth when transferred to constant 30°C, but their growth was retarded in proportion to the number of days in the temperature cycle. Rates of shell growth of veligers in temperature cycles show an immediate effect of environmental temperature, while changes in carbon content per larva better reflect the effects of temperature on general metabolism and survival.     

Anaerobic heat production of bivalves (Polymesoda caroliniana andModiolus demissus) in relation to temperature,body size,and duration of anoxia

Anaerobic heat-production rates of two co-occurring species of estuarine bivalves (a clam and a mussel) were measured with double-twin heat-flow calorimeters, one at 20°C, the other at 30°C. There is no significant difference between the two species in metabolic rates. There is evidence of initial aerobic metabolism in some individuals, as shown by high initial rates exponentially decreasing with time, while others had fluctuating but stable average metabolic activity from the beginning. During aerobic as well as anaerobic metabolism, the bivalves showed rhythmic periods of activity and quiescence. The two species differed in their rhythmic pattern of active and resting metabolism. In the case ofPolymesoda caroliniana, periods of resting metabolism tend to be longer and periods of active metabolism shorter at 30°C than at 20°C. There is a similarity between thermograms ofModiolus demissus at 20° and 30°C. Following acute temperature changes from 5° to 20° and 30°C, the bivalves showed stable metabolic rates in a matter of hours. The stabilized average rates [pooled averages for both species of 1.34×10^-4 (standard error of the mean=0.17×10^-4) W g^-1 dry weight of tissue at 20°C and 2.10×10^-4 (SE=0.20×10^-4) W g^-1 at 30°C] signify a temperature coefficient (Q₁₀) of 1.56 between 20° and 30°C, or partial temperature acclimation. Subtracting heat production as a result of physical activity, i.e., considering only resting metabolism, the corresponding means and standard errors of the means are 1.24×10^-4 and 0.14×10^-4 W g^-1 at 20°C and 1.91×10^-4 and 0.077×10^-4 W g^-1 at 30°C. Anaerobic heat production rate at 20°C is proportional to body size (r=0.84, 9 degrees of freedom, DF). ForM. demissus, measured anaerobic heat production is on the order of 7.5% of the level of aerobic respiration reported in the literature.     

Effects of temperature and salinity on larval development ofNecora puber (Brachyura: Portunidae)

Temperature and salinity affected both length of larval development and mortality inNecora puber collected in the Ría de A Coruña during December 1984 and January 1985. Development time decreased considerably with increased temperature. This decrease was sharper when temperature increased from 15° to 20°C than when it increased from 20° to 25°C. At 35S, average development took 48, 32 and 28 d at 15°, 20° and 25°C, respectively. At the three salinities tested (25, 30 and 35), larval development was completed only at 15°C, at 20°C/30 and 35S, and at 25°C/35S. Development times at 15° and 20°C were highly significantly different at both 35 and 30S (P 0.01). However, there were no significant differences between development times at 20° and 25°C (P > 0.05). Within any one specific temperature series, no significant difference was observed between the salinity values tested (P > 0.05). The duration of each of the five zoeal stages was similar within each and the same temperature/salinity combination, whereas the duration of the megalop was twice as long as any of the zoeal stages. The combination of the lowest temperature (15°C) and the highest salinity (35) tested resulted in the greatest larval survival of 28%. Highest mortality occurred at 25°C, at which temperature development was completed only at 35S. A sharp drop in larval survival was observed in the transition period Zoea V — megalop in all combinations of temperature and salinity tested. Within the limits of tolerance to temperature and salinity, the former effected more pronounced differences in the duration of larval development, while salinity appeared to constitute a limiting factor for survival.     

Seasonal oxygen consumption of the saltmarsh lsopod Sphaeroma rugicauda

Oxygen consumption of the saltmarsh isopod Sphaeroma rugicauda (Leach) was measured on 10 occasions during 1973. It was found that the metabolism depended upon both body size and exposure temperature. For most of the year, slope values relating oxygen consumption with size were between 0.5 and 0.9, but during August they were greater than 1.0. Within the environmental temperature range the R-T curve was strictly temperature-dependent, but during the summer there was a translation and rotation of the upper part of the curve to the right. A plateau of temperature-independent metabolism occurred between 30° and 35°C, which are temperatures approaching the critical maximum for the species. Thermal acclimation for 7 days at 20°C resulted in an extended plateau of temperature-independent metabolism between 15° and 35°C.     

Laboratory study of survival and duration of individual zoeal stages as a function of temperature in the brachyuran crab Cancer magister

Larvae were hatched from ovigerous Dungeness crabs, Cancer magister, collected from Puget Sound Basin, Washington, USA, in April, 1986, and the effects of temperature on rates of survival and development were studied for each of the five zoeal stages both in small batch-culture and in individual culture. Culture method had little effect on the results at 10°, 15°, and 20°C. Increased mortality was measured at all stages at 20°C, with 100% mortality occurring during the terminal fifth stage. Fifth stage larvae may also show higher mortality at 15°C than at 10°C. Stage duration varied inversely with temperature at all stages, although differences between 10° and 15°C were greater than between 15° and 20°C. The results indicate that survival and stage duration are independent of the values for the previous and subsequent stages, that variability among larvae in instar duration increases with temperature, and that the terminal fifth zoeal stage is the most sensitive to temperature stress. Duration of a late zoeal instar is not related to its earlier development rate nor can early development rates be used to predict whether individual zoeae will successfully develop to the megalopa. Measurements of megalopa dry weights indicate no differences due either to previous culture temperatures or to total time to the megalopa. Predictive models of larval transport that require estimates of larval duration should account for both changes in temperature response that can affect individual stage duration, and variability among individuals in stage duration that can influence the degree of larval dispersion.     

Individual effects and interactions of salinity,temperature, and zinc on larval development of the grass shrimp Palaemonetes pugio. I. Survival and developmental duration through metamorphosis

Larvae of the estuarine grass shrimp Palaemonetes pugio (Holthuis) were reared from hatch through successful completion of metamorphosis in 80 combinations of salinity (3 to 31%), temperature (20° to 35°C), and zinc (0.00 to 1.00 ppm Zn⁺⁺). Response-surface methodology was employed to depict the individual effects and interactions of the three factors on survival and developmental duration through total larval development. Outside the optimal salinity-temperature conditions of 17 to 27 S and 20° to 27°C, viability of larvae was reduced by both the individual effects of salinity and temperature and interactions between the two factors. Survival capacity of larvae and resistance adaptations to salinity and temperature were progresively reduced by zinc concentrations from 0.25 to 1.00 ppm Zn⁺⁺. Response-surface analysis of the data suggested that the duration of total larval development of P. pugio was least at salinities from 18 to 23 and at temperatures from 30° to 32°C. At both higher and lower salinity-temperature conditions and in increasing zinc concentrations from 0.25 to 1.00 ppm Zn⁺⁺, developmental rates were retarded. A significant zinc-temperature interaction existed, whereby increasing zinc concentrations reduced both survival and developmental rates of larvae more at suboptimal temperatures. Larval resistance to zinc toxicity was least at supraoptimal salinities, indicative of a significant zinc-salinity interaction. The reduced viability, restricted euryplasticity, and retarded developmental rates of P. pugio larvae developing in media with low-level zinc contamination would limit the distributive properties of the pelagic phase in the life cycle of the species and reduce recruitment both into and out of the parent estuarine population.     

Combined effects of temperature and salinity on fed and starved larvae of the mediterranean mussel Mytilus galloprovincialis and the Japanese oyster Crassostrea gigas

The combined effects of temperature, salinity and nutrition on survival and growth of larvae of the Mediterranean mussel Mytilus galloprovincialis and the Japanese oyster Crassostrea gigas were studied over a period of 7 d in the laboratory. Ripe adults, collected in spring and summer 1987 from natural populations in the Bay of Arcachon, France, were induced to spawn. Larvae of both species were cultured at four temperatures (15°, 20°, 25° and 30°C), four salinities (20, 25, 30 and 35S) per temperature, and two levels of nutrition (fed and unfed) per temperature/salinity combination. The fed larvae received a mixed algal diet of 50 cells each of Isochrysis galbana and Chaetoceros calcitrans forma pumilum per microlitre. In both bivalve species, larvae survived over a wide range of temperature and salinity, with the exception of mussel larvae, which died at 30°C. Statistical analysis indicated that nutrition had the greatest effect on larval development, explaining 64 to 75% of the variance in growth of M. galloprovincialis and 54 to 70% in growth of Crassostrea gigas. Unfed mussel larvae displayed little growth. Compared with temperature, the effect of salinity was very slight. M. galloprovincialis larvae exhibited best growth at 20°C and 35S and C. gigas at 30°C and 30S.     

Synergistic effects of cadmium and salinity combined with constant and cycling temperatures on the larval development of two estuarine crab species

The developmental stages from megalopa to third crab of the blue crab Callinectes sapidus Rathbun were tested in 12 combinations of cadmium (0, 50, and 150 ppb) and salinity (10, 20, 30, and 40) at 25°C. A reduction in survival and a significant delay in development from megalopa to third crab occurred within each salinity regime in 50 ppb compared with the control. Comparison of the delay in development within each salinity regime revealed that the sublethal effect of cadmium was most pronounced in the salinities normally preferred by C. sapidus. A similar comparison within each cadmium concentration, however, showed that the developmental time from megalopa to third crab was approximately the same irrespective of salinity. The developmental stages from hatch to first crab of the mud-crab Rhithropanopeus harrisii (Gould) were examined in 63 combinations of cadmium (0, 50, and 150 ppb), salinity (10, 20, and 30), constant temperature (20°, 25°, 30°, and 35°C) and cycling temperature (20° to 25°C, 25° to 30°C, and 30° to 35°C). The results indicated that cycling temperatures may have a stimulating effect on survival of the larvae compared to constant temperatures, both in the presence and in the absence of cadmium. Effects of cadmium and salinity and their interaction on the survival of the larvae from zoeae to megalopa were documented at most of the temperatures by analyses of variance. The zoeal larvae were more susceptible to cadmium than the megalopa. Effects of different combinations of cadmium and salinity on the duration of larval development were assessed by a t-test.     

Influence of light and temperature on the growth rate of estuarine benthic diatoms in culture

Four species of estuarine benthic diatoms: Amphiprora c. f. paludosa W. Smith, Nitzschia c. f. dissipata (Kützing) Grunow, Navicula arenaria Donkin, and Nitzschia sigma (Kützing) W. Smith were grown in unialgal cultures. The growth rates of the diatoms were determined as the rate of increase of the chlorophyll a content of the cultures. The diatoms were cultured at different combinations of temperture, daylength, and quantum irradiance. The highest growth rates of Navicula arenaria occurred at 16° to 20°C; the other 3 species had their optimum at 25°C or higher. The small-celled species had higher growth rates at their optimum temperature, but at lower temperatures the growth rates of all 4 species became very similar. The minimum daily quantum irradiance that could effect light-saturated growth at 12° and 20°C ranged from 2.5 to 5.0 E.m^-2.day^-1. At 12°C, two species had their highest growth rates under an 8 h daily photoperiod. At 20°C, the three species tested all had highest growth rates under 16 h daily photoperiod. The growth response of the benthic diatoms is comparable to that of several cultures of planktonic diatoms, as described in the literature. The influence of temperature and quantum irradiance on the diatoms in the present investigation was comparable to the influence of temperature and light intensity on the ¹⁴C-fixation of marine benthic diatoms (Colijn and van Buurt, 1975).     

The effect of salinity and cyclic temperature on larval development of the mud-crab Rhithropanopeus harrisii (Brachyura: Xanthidae) reared in the laboratory

Larvae of Rhithropanopeus harrisii (Gould) were reared from hatching to the first or second crab stages in 11 combinations of salinities and cyclic temperatures (5, 20, and 35 S at 20° to 25°C, 25° to 30°C, and 30° to 35°C; 25 S at 20° to 25°C and 30° to 35°C). The larvae survived to the megalops and first crab stages in all salinities and cycles of temperature other than 5 S at 30° to 35°C. The best survival to the megalops (94%) and first crab (90%) stages occurred in 20 S, 20° to 25°C. In all other combinations of salinities and temperatures there was a reduction in survival to the first crab stage. The duration of the larval stages was affected significantly by temperature, whereas the effect of salinity on the mean days from hatching to the first crab stage was not consistent at the different temperature cycles. Development to the first crab stage required the shortest time in 20 S, 30° to 35°C (mean 12.3 days), and the longest time in 5 and 35 S, 20° to 25°C (mean 22.6 days and 21.6 days, respectively). Megalops larvae reared in 35 S at all cycles of temperature, as well as larvae in 20 and 25 S, 30° to 35°C, showed a high percentage of abnormality, with the highest percentage occurring in 35 S, 30° to 35°C. It appears that larval development of R. harrisii is strongly influenced by environmental factors and not solely related to genetic differences.This research was supported by grants from the Nordic Council for Marine Biology and the U.S. Atomic Energy Commission [Grant No. At-(40-1)-4377].Contribution No. 116, Zoological Museum, University of Oslo, Norway.     

High-temperature tolerance of photosynthesis in the red alga Chondrus crispus

Chondrus crispus (Stackhouse) is a perennial red seaweed, common in intertidal and shallow sublittoral communities throughout the North Atlantic Ocean. In the intertidal zone, C. crispus may experience rapid temperature changes of 10 to 20C° during a single immerison-emerision cycle, and may be exposed to temperatures that exceed the thermal limits for long-term survival. C. crispus collected year-round at Long Cove Point, Chamberlain, Maine, USA, during 1989 and 1990, underwent phenotypic acclimation to growth temperature in the laboratory. This phenotypic acclimation enhanced its ability to withstand brief exposure to extreme temperature. Plants grown at summer seawater temperature (20°C) were able to maintain constant rates of lightsaturated photosynthesis at 30°C for 9 h. In contrast, light-saturated photosynthetic rates of plants grown at winter seawater temperature (5°C) declined rapidly following exposure to 30°C, reached 20 to 25% of initial values within 10 min, and then remained constant at this level for 9 h. The degree of inhibition of photosynthesis at 30°C was also dependent upon light intensity. Inhibition was greatest in plants exposed to 30°C in darkness or high light (600 mol photons m^-2s^-1) than in plants maintained under moderate light levels (70 to 100 mol photons m^-2s^-1). Photosynthesis of 20°C-acclimated plants was inhibited by exposure to 30°C in darkness or high light, but the degree of inhibition was less than that exhibited by 5°C-grown plants. Not only was light-saturated photosynthesis of 20°C plants less severely inhibited by exposure to 30°C than that of 5°C plants, but the former also recovered faster when they were returned to growth conditions. The mechanistic basis of this acclimation to growth temperature is not clear. Our results indicate that there were no differences between 5 and 20°C-grown plants in the thermal stability of respiration, electron transport associated with Photosystems I or II, Rubisco or energy transfer between the phycobilisomes and Photosystem II. Overall, our results suggest that phenotypic acclimation to seawater temperature allows plants to tolerate higher temperatures, and may play an important role in the success of C. crispus in the intertidal environment.     

Temperature-influenced infection rates in the Chondrus crispus—Petersenia pollagaster pathosystem: a regression analysis

Cross-infection experiments were performed to determine the influence of temperature on infection rate in the Chondrus crispus Stackhouse-Petersenia pollagaster (Petersen) Sparrow pathosystem. C. crispus thalli were collected at Pubnico Harbor, Nova Scotia, Canada in the fall of 1981 to 1984. Infective zoospores were used to inoculate healthy thalli at five different temperatures. The highest infection rate was obtained at 20°C, while significantly lower rates were obtained at temperature extremes. The parasite's life cycle, consisting of infection of healthy thalli, endobiotic development, and release of zoospores, was completed in 48 to 72 h at 15° to 20°C.     

Influence of temperature changes on oxygen uptake and ammonia and phosphate excretion,in relation to body size and weight,in Oikopleura dioica (Appendicularia)

The relationship between the rates of oxygen consumption, ammonia and phosphate excretion of a pelagic tunicate, the larvacean Oikopleura dioica Fol, 1872 were assessed as a function of size, dry weight and ash-free dry weight at 15°, 20° and 24°C. O. dioica has higher respiration and excretion rates than copepods of similar weight, but the weight exponent of the allometric power function: Y=aX ^b is similar to that of other poikilotherms. Temperatures above 20°C have a depressing effect on respiration and ammonia excretion. 90% of the variance in metabolic rates is explainable by body mass and temperatures Q₁₀ values for oxygen consumption, ammonia and phosphate excretion, respectively, are 2.45, 1.86 and 1.75 between 15° and 20°C, and 3.75, 2.90 and 3.60 between 20° and 24°C. Metabolic quotients (O:N, O:P, N:P) indicate a protein-oriented diet. The results of this study suggest weak metabolic regulation in O. dioica, an energetic strategy which allows an immediate response to favourable changes in feeding conditions.     

Effect of phosphate and ammonium levels on photosynthetic and respiratory responses of the red alga Gracilaria verrucosa

Gracilaria verrucosa (Hudson) Papenfuss exposed to nutrient enriched media (0.1 mM PO₄; 1.0 mM NH ₄ ⁺ ) by pulse feeding 2 h every third day for a period of 5 wk at 20°C and 25–30 salinity showed significantly higher rates of photosynthesis regardless of photon flux density correlated with increased pigment levels. Algae in nonenriched media showed significantly higher levels of soluble carbohydrates and decreased levels of phycoerythrin and chlorophyll a. Photosynthetic and respiratory responses to temperature 15°, 25°, 30°C and salinity (15, 25, 30 S) combinations indicate broad tolerances by both nutrient enriched and non-nutrient enriched algae. Photosynthetic and respiratory rates were highest at the high temperatures. Pulse-fed algae had significantly higher photosynthetic rates than non-nutrient enriched plants at all temperature and salinity combinations. Non-nutrient enriched algae had significantly higher respiratory rates than nutrient enriched algae at only 30°C and 15. The respiratory rates of both nutrient enriched and non-nutrient algae decreased under combinations of higher temperatures and salinities. G. verrucosa, grown without nutrients, has lower tolerances to environmental stresses.     

Effect of freezing on photosynthesis of intertidal macroalgae: relative tolerance of Chondrus crispus and Mastocarpus stellatus (Rhodophyta)

The effect of freezing on photosynthetic metabolism was studied in the red algae, Chondrus crispus and Mastocarpus stellatus. Plants of both species were collected from the intertidal at Chamberlain or Kresge Point, Maine, USA (43°56N, 69°54W) between February and March 1987. Photosynthetic rates were measured immediately after freezing at-20°C and following recovery periods in seawater. Photosynthesis in C. crispus declined rapidly following freezing, falling to 70% of control values within 1 h and 30% after 3 h exposure. Minimum photosynthetic rates (7 to 9% of controls) occurred following freezing exposures of 12 h or more. Full photosynthetic recovery in C. crispus after 3 h at-20°C required 48 h. Photosynthesis in C. crispus did not fully recover in plants frozen for 6 h or more. In contrast, photosynthesis in M. stellatus was relatively unaffected by freezing exposures of <12 h. Twelve hours or more at-20°C reduced photosynthesis to 55% of controls. Photosynthesis in M. stellatus fully recovered from 24 h at-20°C within 24 h. In both species the reduction of photosynthesis by freezing was associated with damage to the plasma membrane and reduced efficiency of energy transfer from phycobilisomes to chlorophyll a, but did not appear to involve ribulose-1,5-bisphosphate carboxylase oxygenase activity. The freezing tolerance of C. crispus and M. stellatus positively correlates with their respective intertidal distributions, suggesting that freezing may be involved in controlling the distributions of these species on the shore.     

Genetic variability and differentiation in the temperature niche component of the diatom Thalassiosira pseudonana

The acclimated reproduction rates of 14 clones of the diatom Thalassiosira pseudonana were measured at 12°, 16°, 20°, and 24°C. Reproduction rate increased monotonically with an increase in temperature in all 14 clones. Significant genetic variability in reproduction rates and electrophoretic mobility of isozymes were observed among clones within a population from a single water bottle collected in a warm core eddy overlying slope water. The major genetic differentiation was between neritic and oceanic populations, with neritic clones having higher reproduction rates at all 4 temperatures. Surprisingly small genetic differences were observed among clones from neritic waters around the world. The slopes of the temperature-reproduction rate plots of all 14 clones were quite similar.Woods Hole Oceanographic Institution Contribution No. 4679     

Influence of food concentration,temperature and salinity on the larval development ofBalanus amphitrite

Influence of food concentration (0.5, 1 and 2 x 10⁵ cell ml^–1 ofSkeletonema costatum), temperature (20 and 30°C) and salinity (15, 25 and 35) on the larval development ofBalanus amphitrite (Cirripedia: Thoracica) was examined. The mortality rate at 20°C was lower than at 30°C in general. Increase in food concentration from 0.5 to 1 x 105 cells ml^–1 improved the survival rate, but this was not evident when food concentration was increased to 2 x 105 cells ml^–1. The results indicate that food availability and temperature jointly determine the energy allocation for metamorphic progress. It was observed that the influence of the tested variables varied with instar. At 20 °C the mean duration of the second instar exceeded 3 d and was much longer than other instar durations. The fourth, fifth and sixth instars and the total naupliar period showed that the effect of different salinities at given food concentrations was negligible at 20°C, while at 30°C there was a marked decrease in duration with increasing salinity.     

Aspects of the biology of resting spores of Thalassiosira nordenskioeldii and Detonula confervacea

Large numbers of resting spores of Thalassiosira nordenskioeldii Cleve and Detonula confervacea (Cleve) Gran were produced when these species were grown at low levels of ammonia and nitrate. The production of resting spores by T. nordenskioeldii was inversely related to temperature. At 0° and 5°C between 68 and 96% of the total cells were resting spores, while at 15°C resting spores were not produced. Resting spores of both species would not survive 7 days in the dark at 20°C. At 0°, 5°, 10° and 15°C, the length of time that the resting spores of both T. nordenskioeldii and D. confervacea remained viable was inversely related to temperature. At 0°C, T. nordenskioeldii remained viable for 576 days. The data suggest that the production of resting spores by these two species does not aid them in the survival of unfavorably high temperatures such as are found in temperate estuaries during the summer. Rather, they appear to be an adaptation for the survival of long periods of darkness in polar regions.     

Temperature ecotypes near the southern boundary of the kelp Laminaria saccharina

Effects of temperature on survival, growth, and photosynthesis were compared for two USA populations of Laminaria saccharina Lamour. One population was located in New York State, near the southern latitudinal boundary of the species in the western North Atlantic. This southern boundary population was exposed to ambient temperatures 20°C for about 6 wk each summer. The second population was located in Maine, toward the center of the latitudinal range of the species, and was rarely exposed to temperatures>17°C. sporophytes from the New York (NY) population exhibited greater tolerance of high temperature than plants from the Maine (ME) site. Juvenile sporophytes from the two sites had similar rates of survivorship and growth at temperatures below 20°C, but showed different responses at 20°C in laboratory experiments. NY plants survived and grew for 6 wk at 20°C. ME plants showed negative growth during wk 2 and 100% mortality during wk 3. NY and ME plants held in situ at the NY site during June to September, 1985, also exhibited differential survivorship when ambient temperatures exceeded 20°C. Results of photosynthesis and dark respiration measurements on NY and ME plants grown at various temperatures suggested that the high-temperature tolerance of NY plants was attributable to their ability to maintain positive daily net C-fixation at 20°C. The high-temperature tolerance of the NY plants appeared to be due to genetic adaptation and is probably crucial to the persistence of the species near its southern boundary.     

Effects of acute changes in temperature and salinity on pulsation rates in ephyrae of the scyphozoan Aurelia aurita

The response of Aurelia aurita ephyrae to abrupt temperature and salinity differentials is expressed as changes in bell pulsation rates. Acute temperature rate-responses of Texas (USA) ephyrae reflect a reduced temperature sensitivity over a broad range (10° to 35°C), with a Q₁₀ value of 0.97 between 20° and 25°C. The initial relationship between salinity change and pulsation rate is linear and direct. This pattern is disrupted after 24 h, with those ephyrae experiencing a salinity decrease pulsing significantly faster than those experiencing no change or an increase in salinity. This response to low salinities dissipates after 2 days. Holding osmotic pressure constant and disrupting ionic ratios has more of an immediate and persistent effect than solely decreasing salinity.