Genetic differentiation of high-temperature tolerance in the kelp Undaria pinnatifida sporophytes from geographically separated populations along the Pacific coast of Japan

The kelp Undaria pinnatifida has a widespread latitudinal range in Japan, with populations exposed to very different temperature regimes. To test the hypothesis that U. pinnatifida exhibits genetic differentiation in its temperature response, juvenile sporophytes from a warmer location (Naruto, southern Japan) and two colder locations (Okirai Bay and Matsushima Bay, northern Japan) were collected and transplanted to long lines, cultivated under the environmental conditions in Matsushima Bay. These plants were bred using successive self-crossing methods for three generations and the characteristics of photosynthesis, growth, survival, and nitrogen contents of the third-generation juvenile sporophytes (2–3 cm) then were measured and compared. The plants from Naruto showed significantly higher photosynthetic activities and respiration than those from the northern populations at warmer temperatures of 20–35°C. The juvenile sporophytes from all three locations had similar growth rates below 18°C, but significant differences were observed at 18–24°C. The optimum temperatures for growth were 14–16°C in plants that originated from Okirai Bay and Matsushima Bay and 18°C in plants that originated from Naruto. These results reflected the differences in latitude. Dead plants were observed at high temperatures of 22 and 24°C in the northern population plants, whereas no plants from Naruto died. Juvenile sporophytes from Naruto exhibited the greatest capacity to accumulate high nitrogen reserves. These results suggest that the differences in high-temperature tolerance in juvenile U. pinnatifida sporophytes from geographically separated populations are due to genetic differentiation rather than phenotypic plasticity.     

Growth of Ecklonia cava (Laminariales, Phaeophyta) sporophytes transplanted to a locality with different temperature conditions

Transplanting experiments were carried out to determine whether the small type sporophytes with short stipe of Ecklonia cava Kjellman (Laminariales, Phaeophyta) growing in a locality with warm temperatures, change into larger type with a long stipe when transplanted to a locality with cooler temperatures. Juvenile E. cava sporophytes, having a stipe shorter than 5 cm long were collected from Tei in Tosa Bay (southern Japan) (seawater temperature 15–29°C) and transplanted to Nabeta Bay (central Japan) (seawater temperature 13–25°C), where larger type E. cava sporophytes characterized by long stipe (ca 1 m) grow. They were attached to artificial reefs at the sea bottom (9 m depth) in Nabeta Bay to monitor their growth. For comparison, juvenile E. cava sporophytes of almost similar size growing in Nabeta Bay were also transplanted in the same way to the same experimental site. Observations of growth of sporophytes from Tei and Nabeta were carried out monthly for 2 years from November 1995 to October 1997. The transplanted Tei and Nabeta sporophytes showed an increase in stipe length and diameter from winter to spring, whereas almost no increase was observed during summer and autumn. At the end of the study period, the stipe of Nabeta sporophytes reached 25.6 cm in length and 17.0 mm in diameter, whereas that of Tei sporophytes reached 11.1 cm in length and 11.2 mm in diameter. The primary blade length was 16.0 cm in Nabeta sporophytes, whereas it was 5.5 cm in Tei sporophytes. Thus, Tei sporophytes still remained smaller than Nabeta sporophytes even under the same environmental conditions.     

Temperature requirements for the growth of young sporophytes of Undaria pinnatifida and Undaria undarioides (Laminariales, Phaeophyceae)

The relative growth rate of young sporophytes of Undaria pinnatifida (Harvey) Suringar and Undaria undarioides (Yendo) Okamura was examined in order to understand the difference in distribution of these two species around the coast of Japan. The optimal temperature for growth of both species was similar at 20°C and the upper critical temperature for growth was also similar, at 27°C for U. pinnatifida and 26°C for U. undarioides. Therefore, the optimal and upper critical temperatures for growth of the young sporophytes are not the main factors determining the distribution of each species. Next, the lower critical temperatures for growth were examined. For the young sporophytes of U. pinnatifida, the lower limit was less than 5°C while for those of U. undarioides it was 15°C. Thus, the difference in the lower critical temperature for growth between the two species was approximately 10°C. During the period of young sporophyte growth in the field, the temperature at the mouth of Ise Bay, Japan, where U. pinnatifida occurs, ranges from 12.7°C in December to 13.1°C in April, with a minimum of 7.9°C in February. Our experiments indicate that young sporophytes are able to grow throughout this period. The temperature off Hamajima, Japan, where U. undarioides occurs, ranges from 19.1°C to 14.8°C during the same time period. Again, young sporophytes are able to growth throughout this period, although minimum winter temperatures are only just high enough for growth. These natural temperature ranges during the growth season of the sporophytes agree well with the experimentally determined temperature requirements for growth of each species. Therefore, the difference between the two species in the critical temperature required for growth of the young sporophytes, especially in the low temperature range, is one of the major factors determining the distribution pattern of each species.     

Morphological and physiological differences among cultivation lines of <Emphasis Type="Italic">Undaria pinnatifida</Emphasis> in a common garden experiment using a tank culture system

Undaria pinnatifida is grown for food and industrial materials worldwide; therefore, advanced breeding is needed to meet quality and productivity requirements. In this study, we examined regional lines of U. pinnatifida from five cultivation sites in Japan with different environmental conditions: Oga (OGA, the northern Sea of Japan coast), Hirota Bay (HRT, the northeastern Pacific coast), Matsushima Bay (MAT, the northeastern Pacific coast), Naruto (the Seto Inland Sea coast) and Shimonoseki (SIM, the southern Sea of Japan coast). The sporophytes of these lines were cultured in a tank culture system under controlled environmental conditions, and their morphological characteristics, nutrient uptake kinetics (V _max, K _s and V _max/K _s ), and carbon, nitrogen and phosphorus contents were determined. Sporophytes from MAT grew faster, whereas those from SIM were smaller than those from the other sites. Although the blade thickness of sporophytes cultivated in the sea significantly differs among cultivation sites in the previous study, there was no significant difference in blade thickness among the regional lines cultivated in the tank. Sporophytes from OGA had the greatest V _max/K _s values and significantly greater nitrogen contents than the other lines. Therefore, the morphological characteristics of MAT and SIM sporophytes, and the nutrient uptake kinetics of OGA sporophytes may have a genetic origin. This indicates that these lines may represent useful resources for selective breeding, with MAT sporophytes providing faster growth and OGA sporophytes being well-adapted to low-nutrient conditions.     

Effects of temperature and nutrients on microscopic stages of the bull kelp (Nereocystis luetkeana,Phaeophyceae)

Warming ocean temperatures have been linked to kelp forest declines worldwide, and elevated temperatures can act synergistically with other local stressors to exacerbate kelp loss. The bull kelp Nereocystis luetkeana is the primary canopy-forming kelp species in the Salish Sea, where it is declining in areas with elevated summer water temperatures and low nutrient concentrations. To determine the interactive effects of these two stressors on microscopic stages of N. luetkeana, we cultured gametophytes and microscopic sporophytes from seven different Salish Sea populations across seven different temperatures (10–22°C) and two nitrogen concentrations. The thermal tolerance of microscopic gametophytes and sporophytes was similar across populations, and high temperatures were more stressful than low nitrogen levels. Additional nitrogen did not improve gametophyte or sporophyte survival at high temperatures. Gametophyte densities were highest between 10 and 16°C and declined sharply at 18°C, and temperatures of 20 and 22°C were lethal. The window for successful sporophyte production was narrower, peaking at 10–14°C. Across all populations, the warmest temperature at which sporophytes were produced was 16 or 18°C, but sporophyte densities were 78% lower at 16°C and 95% lower at 18°C compared to cooler temperatures. In the field, bottom temperatures revealed that the thermal limits of gametophyte growth (18°C) and sporophyte production (16–18°C) were reached during the summer at multiple sites. Prolonged exposure of bull kelp gametophytes to temperatures of 16°C and above could limit reproduction, and therefore recruitment, of adult kelp sporophytes.     

The effect of irradiance and temperature responses and the phenology of a native alga,Undaria pinnatifida (Laminariales), at the southern limit of its natural distribution in Japan

Phenology, irradiance, and temperature characteristics of an edible brown alga, Undaria pinnatifida (Laminariales), were examined from the southernmost natural population in Japan, both by culturing gametophytes and examining the photosynthetic activity of sporophytes using dissolved oxygen sensors and pulse amplitude-modulated chlorophyll fluorometer (IMAGING-PAM). Our surveys confirmed that sporophytes were present between winter and early summer, but absent by July. IMAGING-PAM experiments were used to measure maximum effective quantum yield (ΦII at 0 μmol photons m^?2 s^?1) for each of 14 temperatures (8–36 °C). Oxygen production was also determined over a coarser temperature gradient. Net photosynthesis and ΦII (at 0 μmol photons m^?2 s^?1) were observed to be temperature-dependent; the maximum ΦII was estimated to be 0.67, occurred at 21.2 °C, and was nearly identical to the optimal temperature of the net photosynthetic rate (21.7 °C). A net photosynthesis–irradiance (P–E) model revealed that saturation irradiance (E _k) was 119.5 μmol photons m^?1 s^?1, and the compensation irradiance (E _c) was 17.4 μmol photons m^?1 s^?1. Culture experiments on the gametophytes revealed that most individuals could not survive temperatures over 28 °C and that growth rates were severely inhibited. Based on our observations, temperatures greater than 20 °C are likely to influence photosynthetic activity and gametophyte survival, and therefore, it is possible that this species might become locally extinct if seawater temperatures in this region continue to rise.     

Morphometric study of Ecklonia cava (Laminariales, Phaeophyta) sporophytes in two localities with different temperature conditions

Sporophytes of Ecklonia cava Kjellman (Laminariales, Phaeophyta) were collected seasonally from within 3–4 replicate, 1‐m² quadrates, haphazardly placed in dense assemblages at 6–9 m depth in Tei, Tosa Bay (southern Japan; water temperature 15–29°C) from 1995 to 1996, and in Nabeta Bay, Shimoda (central Japan; water temperature 13–25°C) from 1996 to 1997. Growth rings were checked for all samples and mean values of each biometric parameter of sporophytes 1‐year‐old and over were compared. The plant length (stipe length + primary blade length) was always shorter in Tei sporophytes (24–52 cm) than Nabeta sporophytes (70–100 cm), the difference being mainly owing to the shorter stipe length in Tei sporophytes (7–14 cm) than in Nabeta sporophytes (54–83 cm). However, the primary blade length was sometimes longer in Tei sporophytes (12–38 cm) than in Nabeta sporophytes (14–21 cm). Stipe diameter, longest bladelet length and primary blade width were mostly less in Tei sporophytes (8.6–12.4 mm, 5.5–7.0 cm and 23.4–38.0 cm, respectively) than Nabeta sporophytes (16.4–20.2 mm, 9.2–12.0 cm and 43.0–52.6 cm, respectively). Nevertheless, the number of bladelets of sporophytes from Tei (15–28) and Nabeta (18–29) were within the same range. At Tei, 32–43% of the sporophytes had wrinkled blades in summer and autumn, whereas wrinkled primary blades or bladelets were not observed in Nabeta sporophytes throughout the experimental period. These morphometric differences of E. cava between the two localities are suggested to be dependent on environmental factors, especially seawater temperature.     

Effects of experimental thinning on the growth and maturation of the brown alga Undaria pinnatifida (Laminariales; Phaeophyta) cultivated in Matsushima Bay,northern Japan

In northern Japan, massive production of high-quality specimens of the kelp Undaria pinnatifida prior to the traditional harvest season is strongly needed to meet commercial demand. To address this need, we tested the effects of controlled thinning by cutting small plants on the growth and maturation of sporophytes cultivated in Matsushima Bay, northern Japan. In early December 2009, the stocking densities of cultivated kelps were thinned to 10 and 5 plants per 4 cm thread section in two experimental groups. In contrast, no thinning was conducted during cultivation until March 2010 in the control group (about 16–20 plants per 4 cm thread section). Morphological features, photosynthesis, and carbon and nitrogen contents were compared among the three groups. Compared to kelps of control group, total length, stipe width, the length and width of sporophyll, and dry weights of blade and sporophyll showed significantly higher values in kelps of the two experimental groups. However, stipe length of kelps of control group was significantly greater than those of the two experimental groups. The photosynthetic rates and nitrogen contents of kelps of the two experimental groups were significantly greater than those of the control from January to March. No significant differences occurred in all these parameters between kelps of the two experimental groups. Based on these results, the growth and maturation of U. pinnatifida sporophytes can be promoted greatly by experimental thinning, and this will improve production of high-quality specimens of kelps and increase economic returns before the traditional harvest season.     

Temperature requirements for the growth and maturation of the gametophytes of Undaria pinnatifida and U. undarioides (Laminariales, Phaeophyceae)

Gametophytes of two Undaria species, U. pinnatifida and U. undarioides (Laminariales, Phaeophyceae), were studied to determine their water temperature requirements in order to understand their different distributions in Mie Prefecture, Japan. The optimal temperature for growth was 20°C for gametophytes of both species, and the upper critical temperature for growth was also the same for both species at 28°C. Therefore, the optimal and critical temperatures for growth of the gametophytes are not the main factors determining distribution. The optimal temperature for maturation of U. pinnatifida was approximately 10–15°C, whereas it was closer to 20–21°C for U. undarioides, a difference between these species of at least 5°C. In autumn and early winter, the seawater temperature at the mouth of Ise Bay, where U. pinnatifida is distributed, ranges from 21.6°C (October) to 12.7°C (December), and off Hamajima, where U. undarioides is found, the range is from 22.7°C (October) to 19.1°C (December). The seawater temperatures from October to December, which is the maturation season for the gametophytes, agreed well with the optimal temperature requirements for maturation of the gametophytes of both species. Thus the difference in the maturation temperature range of the gametophytes is a major factor determining distribution of these Undaria species along the Japanese coast.     

Compensation of the brown alga Undaria pinnatifida (Laminariales; Phaeophyta) after thallus excision under cultivation in Matsushima Bay, northern Japan

In recent years, the crop yield of cultivated Undaria pinnatifida (Harvey) Suringar has not been able to meet commercial demand and so advances in cultivation technology are strongly needed to increase production. Interestingly, cultivation work has shown the yield of U. pinnatifida sporophytes may be increased significantly by thallus excision, which may cause compensatory growth of the remaining tissues. To test this hypothesis and clarify correlative mechanisms, we examined seasonal morphological characteristics, photosynthetic rates, nutrient uptake rates, and carbon and nitrogen contents of U. pinnatifida sporophytes after thallus excision at a point 30 cm from the meristem in late February and compared these parameters with control kelps grown without excision, which were cultivated together in Matsushima Bay, northern Japan. Compared to control kelps, the length and dry weight of blades increased significantly after excision, and the growth phase was prolonged for about 1 month. The photosynthetic rates, nutrient uptake rates, and carbon and nitrogen contents of excised kelps were significantly higher than those of the controls. After vegetative growth stopped, resources accumulating in thalli were translocated significantly to sporophylls for maturation, indicating maturation was not negatively affected by thallus excision. These results indicate U. pinnatifida exhibits a very strong compensatory ability in response to thallus excision and consequently, the yield could be increased due to an increase in harvest frequency.     

Thermal factors affecting egg development in the wandering glider dragonfly, <Emphasis Type="Italic">Pantala flavescens</Emphasis> (Odonata: Libellulidae)

The wandering glider dragonfly, Pantala flavescens (Fabricius), arrives in Japan from tropical regions every spring. The offspring colonize areas throughout Japan, with rapid increases in populations in the autumn, but all individuals die in the winter, suggesting low tolerance to low temperatures. However, few quantitative data on egg development and water temperature have been reported for this species. Females at the reproductive stage were collected from fields throughout the flying season and their eggs released using an artificial oviposition technique. Almost all of the eggs were fertilized. Egg size was stable throughout the seasons. Most eggs hatched within a period of 5 days at high water temperatures (35 and 30 °C), which were recorded in the shallow ponds and rice paddy fields from summer to early autumn. However, the egg-stage duration increased with declining water temperature. All eggs in water at 15 °C had failed to hatch by 90 days. The calculated critical temperature of water was determined to be approximately 14.3 °C; the total effective temperature for the egg stage was about 80 degree-days. Thus, low water temperatures in winter may prevent P. flavescens overwintering in Japan.     

Growth and survival rates of large-type sporophytes of Ecklonia cava transplanted to a growth environment with small-type sporophytes

Stipe lengths of sporophytes of Ecklonia cava Kjellman have been reported to be longer along the southeast than southwest coast of the Izu Peninsula, central Japan. Two bays in this region that have natural populations of E. cava, but with different stipe lengths, were chosen for transplant experiments to examine if stipe length was an environmentally controlled trait. Transplant experiments were carried out in order to determine whether large-type sporophytes of E. cava with long stipes growing in Nabeta Bay (southeast Izu Peninsula, Japan) would turn into small-type sporophytes with short stipes when transplanted to Nakagi Bay (southwest Izu Peninsula). Ten juvenile sporophytes of E. cava (stipe length < 5 cm) were collected from Nabeta Bay (large-type habitat) and transplanted to Nakagi Bay (short-type habitat) in December 1995. As a transplant control, ten juvenile sporophytes of E. cava growing in Nakagi Bay were also transplanted to the same artificial reefs. Growth and survival rates of the sporophytes were monitored monthly for 3 y until December 1998. The transplanted sporophytes showed an increase in their stipe length and diameter from winter to spring, whereas almost no increase was observed from summer to autumn. However, the elongation was greater in Nabeta sporophytes than in Nakagi sporophytes. The primary blade length increased mainly from winter to early spring and decreased largely in autumn. Average primary blade lengths were similar in both Nabeta and Nakagi sporophytes from the end of the first year of transplanting. Although ca. 70% of both Nabeta and Nakagi sporophytes survived during the first 2 y after transplantation, no Nakagi sporophytes and only two Nabeta sporophytes survived to the end of the 3 y study period. Despite transplantation to Nakagi Bay, where short sitpes are naturally present, the sporophytes from Nabeta Bay persisted in having longer stipes, which suggests that stipe length is genetically, rather than environmentally, controlled.     

Low-temperature tolerance of juvenile tarpon <Emphasis Type="Italic">Megalops atlanticus</Emphasis>

The tarpon Megalops atlanticus is a tropical to subtropical species whose pole-ward distribution is thought to be limited by low water temperatures. In the western north Atlantic Ocean juvenile tarpon occur in estuaries of the South Atlantic Bight (SAB) north of Florida near the northern limit of its distribution, but it is currently unknown whether these individuals can survive winter, grow to maturity, and contribute to the adult population. As a first step to determine whether juvenile tarpon can survive winter conditions in the SAB, we conducted laboratory experiments to estimate minimum lethal temperatures of tarpon exposed to 1) ambient fluctuating winter water conditions and 2) a constant rate of temperature decline. Juvenile tarpon exposed to ambient winter water conditions had a mean ± standard deviation (SD) minimum lethal temperature of 13.7 ± 3.4 °C. When exposed to a constant rate of temperature decline (2 °C day^?1), mean ± SD minimum lethal temperature (9.2 ± 0.8 °C) was lower than when tarpon were exposed to ambient fluctuating conditions. A combination of our results with all published data on the cold tolerance of juvenile tarpon resulted in an overall mean ± SD minimum lethal temperature of 12.0 ± 2.8 °C. Based on available long-term temperature records from SAB estuaries, overwinter survival of juvenile tarpon is unlikely in most aquatic habitats (e.g., tidal creeks, flats, open water). Similar to other estuarine transient fishes, juvenile tarpon likely exploit seasonably favorable nursery habitats and then migrate to other locations to overwinter.     

Compensatory abilities depending on seasonal timing of thallus excision of the kelp Undaria pinnatifida cultivated in Matsushima Bay, northern Japan

Improved cultivation technology for the kelp Undaria pinnatifida is greatly needed to increase production to meet increasing commercial demand. A previous cultivation trial indicated that the crop yield of U. pinnatifida sporophytes could be increased greatly by thallus excision in late February due to compensatory growth of the remaining tissues. To develop this potential new cultivation technology, it is essential to identify the time period during which this kelp can compensate and its physiological responses to thallus excision. In this study, U. pinnatifida sporophytes were excised at about 30 cm above the meristem at the beginning of January, February, March, and April, respectively. Morphological features, photosynthesis, nutrient uptake, and carbon and nitrogen contents of excised kelps were measured and compared with these parameters in control kelps grown without excision. Both experimental and control kelps were farmed together in Matsushima Bay, northern Japan. The kelps excised in January and February showed significant increases in the lengths and dry weights of the blade, photosynthetic rates, nutrient uptake rates, and carbon and nitrogen contents compared with the control kelps, and the growth phase was prolonged for at least 1 month. No significant increases were found in dry weights and carbon and nitrogen contents of sporophylls until early April, which indicated that the maturation period was delayed. At the end of this experiment, the nitrogen contents of sporophyll tissues formed after excisions were significantly lower than those of tissues formed before excisions. In contrast, the kelps excised in March and April showed no significant increases in morphological and physiological parameters compared with control kelps. These results suggest that U. pinnatifida sporophytes exhibited great compensation when excisions were conducted during the growing phase in January and February but not in March and April when the maturation phase had started. The regulation of resource allocation to growth and maturation after thallus excisions in January and February likely results in prolongation of the growth phase and maturation phase in excised kelps.     

Physiological performance of the cold-water coral Dendrophyllia cornigera reveals its preference for temperate environments

Cold-water corals (CWCs) are key ecosystem engineers in deep-sea benthic communities around the world. Their distribution patterns are related to several abiotic and biotic factors, of which seawater temperature is arguably one of the most important due to its role in coral physiological processes. The CWC Dendrophyllia cornigera has the particular ability to thrive in several locations in which temperatures range from 11 to 17 °C, but to be apparently absent from most CWC reefs at temperatures constantly below 11 °C. This study thus aimed to assess the thermal tolerance of this CWC species, collected in the Mediterranean Sea at 12 °C, and grown at the three relevant temperatures of 8, 12, and 16 °C. This species displayed thermal tolerance to the large range of seawater temperatures investigated, but growth, calcification, respiration, and total organic carbon (TOC) fluxes severely decreased at 8 °C compared to the in situ temperature of 12 °C. Conversely, no significant differences in calcification, respiration, and TOC fluxes were observed between corals maintained at 12 and 16 °C, suggesting that the fitness of this CWC is higher in temperate rather than cold environments. The capacity to maintain physiological functions between 12 and 16 °C allows D. cornigera to be the most abundant CWC species in deep-sea ecosystems where temperatures are too warm for other CWC species (e.g., Canary Islands). This study also shows that not all CWC species occurring in the Mediterranean Sea (at deep-water temperatures of 12–14 °C) are currently living at their upper thermal tolerance limit.     

Effects of temperature on growth of Vallisneria americana in a sub-tropical estuarine environment

The submersed aquatic vegetation (SAV) species Vallisneria americana Michx. (tape grass) is a valuable resource in the Caloosahatchee estuary and in many other aquatic systems. Given the variable nature of freshwater inflows and environmental conditions in the Caloosahatchee, it is necessary to understand how tape grass will respond to high and low salinity conditions at different light and temperature levels. Specifically, quantitative information is needed as input to modeling tools that can be applied to predict growth and survival of tape grass under a range of environmental conditions present in the estuary. We determined growth rates for small and medium sized tape grass plants obtained from the Caloosahatchee estuary, southwest coastal Florida, USA in freshwater (0.5 psu) under high (331 μE m^?2 s^?1) and low light (42 μE m^?2 s^?1) and at 10 psu under high light conditions. We ran six treatments at five temperatures spanning 13–32 °C for 8–9 weeks. The optimum temperature for growth was roughly 28 °C, with a minimum threshold temperature of 13 °C and a maximum threshold temperature of 38 °C. Plants grew fastest in freshwater, at high light and temperatures greater than 20 °C. The slowest growth rates were observed at 13 °C regardless of salinity, light or plant size. Our results suggest that tape grass growth is strongly influenced by water temperature and that additional stressors such as low light and elevated salinity can reduce the range of temperature tolerance, especially at colder water temperatures.     

Influence of temperature on the expression of manganese toxicity by two soybean varieties

Summary Two soybean varieties (Glycine max) were grown in nutrient solution to investigate their response to manganese toxicity at two different temperature regimes. Dry matter yields of both varieties were markedly reduced by lower temperature (21°C day/18°C night). At these temperatures leaf crinkle symptoms of Mn toxicity were very severe on Bragg and moderate on Lee at high levels of Mn in solution (15 ppm). However increasing the temperature to 33°C day/28°C night completely eliminated symptoms on both varieties. High levels (15 ppm) of Mn in nutrient solution decreased yields of both varieties at low temperature with Bragg showing the greater reduction. At high temperature neither variety showed yield reductions at 15 ppm Mn. Higher concentrations of Mn in shoots and roots were obtained at higher temperature, indicating that increased tolerance was not associated with lower plant Mn levels. Lee consistantly contained higher levels of Mn in the shoots than Bragg in the 15 ppm Mn solution at both temperatures although appearing to be more tolerant at low temperatures. The implications of these results for environmental effects on the expression of Mn toxicity in the field are discussed. re]19751202     

The effect of light and temperature on the growth and photosynthesis of Gracilariopsis chorda (Gracilariales, Rhodophtya) from geographically separated locations of Japan

The effect of light and temperature on the growth and photosynthesis of the Japanese agarophyte, Gracilariopsis chorda (Gracilariaceae, Rhodophyta), was determined to better understand its physiology so that we could identify candidates for mass cultivation. Above the photosynthetic active radiation of 66 μmol photons m^?2 s^?1, photosynthetic rates saturated for all strains that were collected from six different locations (Hokkaido, Chiba, Tokushima, Saga, Kagoshima, and Okinawa); furthermore, either photosynthesis or growth was observed at all temperature treatments examined in our study (4–32 °C for photosynthesis, 16–32 °C for growth experiments). We identified a temperature range for optimal photosynthesis and growth, which occurred within 20.1–29.1 °C and roughly correlated with the water temperatures of the collection locations and strongly suggests that this species tolerates a wide variety of water temperature. In particular, the Kagoshima strain had the widest range of optimal temperatures (20.8–29.1 °C), whereas the Saga strain had the narrowest range (23.1–27.3 °C). It is important to note that all the optimal temperature ranges overlapped among the strains; therefore, no definitive distinction can be determined. The broad tolerance to temperatures commonly observed from northern to southern Japan suggests that the cultivation of this species should succeed during spring to summer in the majority of the coastal regions in Japan.     

The endemic kelp Lessonia corrugata is being pushed above its thermal limits in an ocean warming hotspot

Kelps are in global decline due to climate change, which includes ocean warming. To identify vulnerable species, we need to identify their tolerances to increasing temperatures and determine whether tolerances are altered by co-occurring drivers such as inorganic nutrient levels. This is particularly important for those species with restricted distributions, which may already be experiencing thermal stress. To identify thermal tolerance of the range-restricted kelp Lessonia corrugata, we conducted a laboratory experiment on juvenile sporophytes to measure performance (growth, photosynthesis) across its thermal range (4–22°C). We determined the upper thermal limit for growth and photosynthesis to be ~22–23°C, with a thermal optimum of ~16°C. To determine if elevated inorganic nitrogen availability could enhance thermal tolerance, we compared the performance of juveniles under low (4.5 μmol · d⁻¹) and high (90 μmol · d⁻¹) nitrate conditions at and above the thermal optimum (16–23.5°C). Nitrate enrichment did not enhance thermal performance at temperatures above the optimum but did lead to elevated growth rates at the thermal optimum. Our results indicate L. corrugata is likely to be extremely susceptible to moderate ocean warming and marine heatwaves. Peak sea surface temperatures during summer in eastern and northeastern Tasmania can reach up to 20–21°C, and climate projections suggest that L. corrugata's thermal limit will be regularly exceeded by 2050 as southeastern Australia is a global ocean-warming hotspot. By identifying the upper thermal limit of L. corrugata, we have taken a critical step in predicting the future of the species in a warming climate.     

Critical thermal minima and maxima of three freshwater game-fish species acclimated to constant temperatures

A total of 120 critical thermal maxima (CT maxima) and 120 critical thermal minima (CT minima) were determined for channel catfish, largemouth bass and rainbow trout acclimated to three constant temperatures: 20, 25 and 30 °C in catfish and bass, and 10, 15 and 20 °C in trout. Highest mean CT maximum and lowest mean CT minimum measured over these acclimation temperatures were 40.3 and 2.7 °C (catfish), 38.5 and 3.2 °C (bass) and 29.8 and ∼ 0.0 °C (trout). Temperature tolerance data were precise with standard deviations generally less than 0.5 °C. Channel catfish had the largest thermal tolerance scope of the three species while rainbow trout had the lowest tolerance of high temperatures and the highest tolerance of low temperatures. In all species CT minima and CT maxima were highly significantly linearly related to acclimation temperature. Within each species, slopes relating CT maxima to acclimation temperature were approximately half as large as those relating CT minima to acclimation temperature, suggesting that acclimation temperature has a greater influence on tolerance to low rather than high temperatures. Slopes relating both CT minima and CT maxima to acclimation temperature for the two warm-water species were similar and approximately twice those for the rainbow trout. This revised version was published online in July 2006 with corrections to the Cover Date.