Temperature-influenced variations in speciation and chemical composition of marine phytoplankton in outdoor mass cultures

Between September, 1976 and July, 1977 Phaeodactylum tricornutum Bohlin was replaced as the dominant species by Skeletonema costatum (Grev) Cleve as temperatures fell below 10°C in the fall in an outdoor pond supplied with a mixture of waste water and sea water. Phaeodactylum tricornutum returned in the spring as the major species when temperatures rose above 10°C. In an adjacent pond in which only nitrogen and phosphorus were added in excess, however, P. tricornutum dominated throughout the entire study period even through the temperature varied between 0 and 25°C. We suspected that the difference inspecies dominance in the two ponds occurred because Skeletonema costatum requires silicon, which was present in sufficient quantities only in the waste-water-enriched pond. whereas Phaeodatylum tricornutum does not have a specififc requirement for this nutrient. The cellular chemical composition of P. tricornutum varied in a U-shaped fashion with changing temperature: minimum values for the cellular carbon, nitrogen, and chlorophyll contents were displayed at 15–20°C and maximum values at 3 and 15°C. Both the cellular carbon: nitrogen and carbon: chlorophyll ratios by weight were invariant with changing temperatures at ≈6: 1 and 50: 1 respectively, indicating nutrient saturation. Only under conditionsof nutrient saturation, which can be established in various ways, can the influence of temperature on phytoplankton physiology be separated from nutrient-related factors.     

High predictability of direct competition between marine diatoms under different temperatures and nutrient states

The distribution of marine phytoplankton will shift alongside changes in marine environments, leading to altered species frequencies and community composition. An understanding of the response of mixed populations to abiotic changes is required to adequately predict how environmental change may affect the future composition of phytoplankton communities. This study investigated the growth and competitive ability of two marine diatoms, Phaeodactylum tricornutum and Thalassiosira pseudonana, along a temperature gradient (9–35°C) spanning the thermal niches of both species under both high‐nitrogen nutrient‐replete and low‐nitrogen nutrient‐limited conditions. Across this temperature gradient, the competitive outcome under both nutrient conditions at any assay temperature, and the critical temperature at which competitive advantage shifted from one species to the other, was well predicted by the temperature dependencies of the growth rates of the two species measured in monocultures. The temperature at which the competitive advantage switched from P. tricornutum to T. pseudonana increased from 18.8°C under replete conditions to 25.3°C under nutrient‐limited conditions. Thus, P. tricornutum was a better competitor over a wider temperature range in a low N environment. Being able to determine the competitive outcomes from physiological responses of single species to environmental changes has the potential to significantly improve the predictive power of phytoplankton spatial distribution and community composition models.     

EFFECTS OF VARIATION IN TEMPERATURE. I. ON THE BIOCHEMICAL COMPOSITION OF EIGHT SPECIES OF MARINE PHYTOPLANKTON1

The influence of temperature on the biochemical composition of eight species of marine phytoplankton was investigated. Thalassiosira pseudonana Hasle and Heim-dal, Phaeodactylum tricornutum Bohlin and, Pavlova lutheri Droop (three of eight species studied) had minimum values of carbon and nitrogen quotas at intermediate temperatures resulting in a broad U-shaped response in quotas over the temperature range of 10 to 25°C. Protein per cell also had minimum values at intermediate temperatures for six species. For T. pseudonana, P. tricornutum, and P. lutheri, patterns of variation in carbon, nitrogen, and protein quotas as a function of temperature were similar. Over all species, lipid and carbohydrate per cell showed no consistent trends with temperature. Only chlorophyll a quotas and the carbon: chlorophyll a ratios (θ) showed consistent trends across all species. Chlorophyll a quotas were always lower at 10°C than at 25°C. Carbon: chlorophyll a ratios (θ) were always higher at 10°C than at 25°C. We suggest that although θ consistently increases at lower temperatures, the relationship between temperature and θ ranges from linear to exponential and is species specific. Accordingly, the interspecific variance in θ that results from species showing a range of possible responses to temperature increases as temperature declines and reaches a maximum at low temperatures. High photon flux densities appear to increase the potential interspecific variance in the carbon: chlorophyll a ratio and therefore exacerbate these trends.     

Effects of temperature and irradiance on quantum yield of PSII photochemistry and xanthophyll cycle in a tropical and a temperate species

The effect of a wide range of temperatures (?15 and 60°C) in darkness or under strong irradiation [1,600 μmol(photon) m^?2 s^?1] on quantum yield of photosystem II photochemistry and xanthophyll cycle pigments was investigated in a tropical fruit crop (Musa sp.) and a temperate spring flowering plant (Allium ursinum L.). In darkness within the nonlethal thermal window of A. ursinum (from ?6.7 to 47.7°C; 54.5 K) and of Musa sp. (from ?2.2°C to 49.5°C; 51.7 K) maximal quantum yield of PSII photochemistry (F_v/F_m) was fairly unaffected by temperature over more than 40 K. At low temperature F_v/F_m started to drop with ice nucleation but significantly only with initial frost injuries (temperature at 10% frost damage; LT₁₀). The critical high temperature threshold for PSII (T_c) was 43.8°C in A. ursinum and 44.7°C in Musa sp. Under strong irradiation, exposure to temperatures exceeding the growth ones but being still nonlethal caused photoinhibition in both species. Severity of photoinhibition increased with increasing distance to the growth temperature range. ΔF/F_m′ revealed distinctly different optimum temperature ranges: 27–36°C for Musa sp. and 18–27°C for A. ursinum exceeding maximum growth temperature by 2–7 K. In both species only at temperatures > 30°C zeaxanthin increased and violaxanthin decreased significantly. At nonlethal low temperature relative amounts of xanthophylls remained unchanged. At temperatures > 40°C β-carotene increased significantly in both species. In Musa sp. lutein and neoxanthin were significantly increased at 45°C, in A. ursinum lutein remained unchanged, neoxanthin levels decreased in the supraoptimal temperature range. In darkness, F_v/F_m was highly temperature-insensitive in both species. Under strong irradiation, whenever growth temperature was exceeded, photoinhibition occurred with xanthophylls being changed only under supraoptimal temperature conditions as an antiradical defence mechanism.     

Combined effects of seawater temperature and nutrient condition on growth and survival of juvenile sporophytes of the kelp Undaria pinnatifida (Laminariales; Phaeophyta) cultivated in northern Honshu, Japan

Recently, withering of farmed juvenile sporophytes of the kelp Undaria pinnatifida (Harvey) Suringar has led to reduced production of this species in northern Japan, possibly because of the high water temperature and low nutrient concentration in cultivation areas. This problem may be solved by introducing parental plants with greater tolerance to high temperature and low nutrient conditions. We examined the combined effects of various temperatures (15, 20, 24, and 27 °C) and nutrient availabilities (seawater enriched with 25 % PESI medium and non-enriched seawater) on the growth and survival of cultivated juvenile sporophytes (1–2 cm) collected from Matsushima Bay, Miyagi Prefecture in northern Japan and Naruto, Tokushima Prefecture in southern Japan. The relative growth rates of juvenile sporophytes from both locations were significantly greater at 15 and 20 °C than at 24 and 27 °C. The juvenile sporophytes cultured in enriched medium had significantly higher relative growth rates than those cultivated in non-enriched seawater. Dead juveniles were observed in non-enriched seawater at all temperatures and the survival percentage decreased with increasing seawater temperatures. Compared to the juvenile sporophytes from Matsushima Bay, those from Naruto showed greater tolerance to high temperature even under the low nutrient condition. These results suggest that the withering of juvenile sporophytes is caused by the combined effects of low nutrient availability and high temperature. A potential solution to this problem is to introduce ecotypes with greater tolerance to high temperature and low nutrient conditions from a warmer region of Japan.     

Interactive Effects of CO2, Temperature,Irradiance, and Nutrient Limitation on the Growth and Physiology of the Marine Diatom Thalassiosira pseudonana (Coscinodiscophyceae)

The marine diatom Thalassiosira pseudonana was grown in continuous culture systems to study the interactive effects of temperature, irradiance, nutrient limitation, and the partial pressure of CO₂ (pCO₂) on its growth and physiological characteristics. The cells were able to grow at all combinations of low and high irradiance (50 and 300 μmol photons · m⁻² · s⁻¹, respectively, of visible light), low and high pCO₂ (400 and 1,000 μatm, respectively), nutrient limitation (nitrate-limited and nutrient-replete conditions), and temperatures of 10–32°C. Under nutrient-replete conditions, there was no adverse effect of high pCO₂ on growth rates at temperatures of 10–25°C. The response of the cells to high pCO₂ was similar at low and high irradiance. At supraoptimal temperatures of 30°C or higher, high pCO₂ depressed growth rates at both low and high irradiance. Under nitrate-limited conditions, cells were grown at 38 ± 2.4% of their nutrient-saturated rates at the same temperature, irradiance, and pCO₂. Dark respiration rates consistently removed a higher percentage of production under nitrate-limited versus nutrient-replete conditions. The percentages of production lost to dark respiration were positively correlated with temperature under nitrate-limited conditions, but there was no analogous correlation under nutrient-replete conditions. The results suggest that warmer temperatures and associated more intense thermal stratification of ocean surface waters could lower net photosynthetic rates if the stratification leads to a reduction in the relative growth rates of marine phytoplankton, and at truly supraoptimal temperatures there would likely be a synergistic interaction between the stresses from temperature and high pCO₂ (lower pH).     

Photosynthetic Rates, Gross Patterns of Carbon Dioxide Assimilation and Activities of Ribulose Diphosphate Carboxylase in Marine Algae Grown at Different Temperatures

Studies of the marine green flagellate Dunaliella tertiolecta have confirmed and extended previous observations of Steemann Nielsen and his colleagues. Algae, grown at 12°C, assimilated carbon dioxide under light-saturated conditions more rapidly than did those grown at 20°C; for both, the assimilation rate being higher at 20°C than at 12°C. Cells grown at the lower temperature contained higher concentrations of soluble protein, higher activities of ribulose diphosphate carboxylase and showed an enhanced relative rate of protein synthesis during the photosynthetic assimilation of carbon dioxide. This appears to represent true adaptation since it allowed the growth rate at 12°C to be almost the same as that at 20°C. Studies of the marine diatom Phaeodactylum tricornutum have not revealed the same picture of temperature adaptation. Cultures grown at 5°C had significantly higher rates of photosynthesis than did those grown at 10°C, but the same was not true when algae grown at 10°C were compared with those grown at 20°C. In this organism, growth at the lower temperatures reduced its ability to photosynthesize at 20°C. Cells grown at the lower temperatures contained more protein than did those grown at 20°C; this was particularly marked in cells growing at 5°C, a temperature which reduced the growth rate. The relative rate of protein synthesis was higher in Phaeodactylum grown at lower temperatures; but this difference was most marked when the measurements were made at 20°C.     

Temperature effects on growth and cell size in the marine calcareaous dinoflagellate Thoracospaera heimii

Growth experiments were carried out on the marine calcareous dinoflagellate Thoracosphaera heimii. Two strains (A603, GeoB 86) of the phototrophic, predominantly vegetative coccoid T. heimii were cultured at different temperature and nutrient levels. For the temperature experiment a gradient box was developed to allow the simultaneous testing of a wide range of temperatures on phytoplankton. During the investigations T. heimii was growing from 14 to 27°C. Exponential growth rates do not show an unimodal response curve vs. temperature: values rise with increasing temperatures toward maximal growth rates around 27°C. At low temperatures exponential growth is extremely long (over 50 days). In f/2 culture medium T. heimii (A603) is less efficient at high temperatures than at low temperatures, final yield was about five times higher at 16°C than at 27°C. Growth rate and final yield at 27°C are approximately the same for all experiments, despite different nutrient levels. Mean shell diameters show no clear relation to growth temperature. Calcification of T. heimii shells is inversely related to temperature.     

STOICHIOMETRIC RESPONSES OF PHYTOPLANKTON SPECIES TO THE INTERACTIVE EFFECT OF NUTRIENT SUPPLY RATIOS AND GROWTH RATES1

Three species of phytoplankton, Rhodomonas sp., Phaeodactylum tricornutum Bohlin, and Isochrysis galbana Parke, were cultivated in semicontinuous culture to analyze the response of carbon (C):nitrogen (N):phosphorus (P) stoichiometry to the interactive effect of five N:P supply ratios and four growth rates (dilution rates). The relationship between cellular N and P quotas and growth rates fits well to both the Droop and Ågren’s functions for all species. We observed excess uptake of both N and P in the three species. N:P biomass ratios showed a significant positive relationship with N:P supply ratios across the entire range of growth rates, and N:P biomass ratios converged to an intermediate value independent of N:P supply ratios at higher growth rates. The effect of growth rates on N:P biomass ratios was positive at lower N:P supply ratios, but negative at higher N:P supply ratios for both Rhodomonas sp. and I. galbana, while for P. tricornutum this effect was negative at all N:P supply ratios. A significant interactive effect of N:P supply ratios and growth rates on N:P biomass ratios was found in both Rhodomonas sp. and P. tricornutum, but not in I. galbana. Our results suggest that Ågren’s functions may explain the underlying biochemical principle for the Droop model. The parameters in the Droop and Ågren’s functions can be useful indications of algal succession in the phytoplankton community in changing oceans.     

锦州湾浮游植物群落结构特征及其对环境变化的响应

锦州湾是我国北方污染严重的海湾,以水体的富营养化和重金属污染为特征。基于2011年8月(夏季)和2012年5月(春季)在锦州湾进行的航次调查,研究了该湾水采浮游植物的群落结构、时空分布及其对生态环境变化的响应。研究结果表明:锦州湾海域浮游植物群落主要由硅、甲藻组成,其生态类型主要为温带近岸型。春季和夏季共鉴定出浮游植物4门41属62种,硅藻在两个季节的物种数和细胞丰度上均占绝对优势,且底栖硅藻比例较高。夏季浮游植物细胞丰度平均值为41.44×103个/L,主要优势种为海链藻Thalassiosira spp.和叉角藻Cerarium furca;春季浮游植物细胞丰度平均值为13.80×103个/L,主要优势种为新月柱鞘藻Cylindrotheca closterium和中肋骨条藻Skeletonema costatum。锦州湾春季和夏季浮游植物群落组成差异明显,冗余分析(Redundancy analysis,RDA)表明硝酸盐浓度和水温分别是夏季和春季影响浮游植物群落结构的最重要环境因子。与历史资料相比,锦州湾优势种发生了显著变化,适于富营养化环境的微型浮游植物和部分耐污种在群落中占优势,表明人类活动引起的水体富营养化以及其它污染物,可能对浮游植物种类组成及分布产生了一定影响。     

The influence of temperature on growth rate and length of larval life of the gastropod, Crepidula plana Say

The relationship between rate of larval development and the potential to prolong larval life was examined for larvae of the marine prosobranch gastropod Crepidula plana Say. Larvae were maintained in clean glass dishes at constant temperatures ranging from 12–29°C and fed either Isochrysis galbana Parke (ISO) or a Tahitian strain of Isochrysis species (T-ISO). Under all conditions, larvae grew at constant rates, as determined by measurements of shell length and tissue biomass. Most larvae eventually underwent spontaneous metamorphosis. Regardless of temperature, faster growth was associated with a shorter planktonic stage prior to spontaneous metamorphosis. Within an experiment, higher temperatures generally accelerated growth rates and reduced the number of days from hatching to spontaneous metamorphosis. However, growth rates were independent of temperature for larvae fed ISO at 25 and 29°C and for larvae fed T-ISO at 20 and 25°C. Where growth rates were unaffected by temperature, time to spontaneous metamorphosis was similarly unaffected. Maximum durations of larval life at a given temperature were shorter for larvae of Crepidula plana than for those of the congener C. fornicata (L.), although both species grew at comparable rates. Interpretations of the ecological significance of these interspecific differences in delay capabilities will require additional data on adult distributions and larval dispersal patterns in the field.     

EFFECTS OF LIGHT INTENSITY AND TEMPERATURE INTERACTIONS ON GROWTH CHARACTERISTICS OF PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE)1

Cell division rate, carbon fixation per cell, cell width and chloroplast length of Phaeodactylum tricornutum Bohlin were determined at 30 different combinations of light intensity and temperature. Division rate peaked at 23° C or less depending on light intensity. For each light intensity studied, carbon fixation increased directly with growth temperature from 14 to 25° C. The slope of this relationship was modified by light intensity. Cells grown at 23–25° C tended to be larger than those grown at lower temperatures, possibly due to increased carbon fixation per cell coupled with lower division rates. Chloroplasts were largest at a combination of temperatures above 21° C and low light intensities. This effect could cause cells to sink at a higher than normal rate due to reduced vacuole size and is presented as a possible mechanism affecting the distribution of P. tricornutum.     

TEMPERATURE EFFECTS ON MICROALGAL PHOTOSYNTHESIS‐LIGHT RESPONSES MEASURED BY O2 PRODUCTION,PULSE‐AMPLITUDE‐MODULATED FLUORESCENCE,AND 14C ASSIMILATION1

Short‐term temperature effects on photosynthesis were investigated by measuring O₂ production, PSII‐fluorescence kinetics, and ¹⁴C‐incorporation rates in monocultures of the marine phytoplankton species Prorocentrum minimum (Pavill.) J. Schiller (Dinophyceae), Prymnesium parvum f. patelliferum (J. C. Green, D. J. Hibberd et Pienaar) A. Larsen (Coccolithophyceae), and Phaeodactylum tricornutum Bohlin (Bacillariophyceae), grown at 15°C and 80 μmol photons · m^?2 · s^?1. Photosynthesis versus irradiance curves were measured at seven temperatures (0°C–30°C) by all three approaches. The maximum photosynthetic rate (P^C_max) was strongly stimulated by temperature, reached an optimum for Pro. minimum only (20°C–25°C), and showed a similar relative temperature response for the three applied methods, with Q₁₀ ranging from 1.7 to 3.5. The maximum light utilization coefficient (α^C) was insensitive or decreased slightly with increasing temperature. Absolute rates of O₂ production were calculated from pulse‐amplitude‐modulated (PAM) fluorometry measurements in combination with biooptical determination of absorbed quanta in PSII. The relationship between PAM‐based O₂ production and measured O₂ production and ¹⁴C assimilation showed a species‐specific correlation, with 1.2–3.3 times higher absolute values of P^C_max and α^C when calculated from PAM data for Pry. parvum and Ph. tricornutum but equivalent for Pro. minimum. The offset seemed to be temperature insensitive and could be explained by a lower quantum yield for O₂ production than the theoretical maximum (due to Mehler‐type reactions). Conclusively, the PAM technique can be used to study temperature responses of photosynthesis in microalgae when paying attention to the absorption properties in PSII.     

Effect of temperature on the functional response of Adalia bipunctata to Myzus persicae

The effect of temperature on the functional response of female adults of the two-spot ladybird, Adalia bipunctata L. (Coleoptera: Coccinellidae) was examined in petri dish arenas containing sweet pepper leaves infested with different densities of the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae). The predator showed a type II functional response at three tested temperatures ranging from 19°C to 27°C. The theoretical maximum number of prey captured by the predator increased with temperature. Based on the random predator equation, the estimated attack rates ranged from 0.13 h^?1 at 19°C to 0.35 h^?1 at 27°C on a leaf area of 20–25 cm². There was no significant difference between the attack rates of the predator at 23°C and 27°C. Handling time significantly decreased as temperature increased from 19°C (0.39 h) to 27°C (0.24 h). This study shows that A. bipunctata displays high predation rates on M. persicae for a wide range of temperatures, indicating its potential for augmentative releases against this aphid pest. The limitations of the predictions generated by functional response experiments are discussed.     

Effect of temperature on growth of some avirulent fungi and cross-protection against the wheat take-all fungus

The linear growth rates of Gaeumannomyces graminis var. graminis, G. graminis var. tritici, Phialophora radicicola var. graminicola and a lobed hyphopodiate Phialophora sp. were studied on agar at various temperatures between 5 and 30 °C and on wheat roots at two temperature regimes (12 h at 7°/12 h at 13 °C and 12 h at 17°/12 h at 23 °C). On agar at 30 °C, the isolates of G. graminis graminis grew faster than those of G. graminis tritici and Phialophora sp. but three isolates of G. g. graminis grew more slowly than the other two fungi at 5 and 10 °C. Two other isolates of G. g. graminis were cold-tolerant and had growth rates comparable to those of G. g. tritici and Phialophora sp. at 10 °C. The growth rates of Australian isolates of P. radicicola graminicolu were similar to that of a British isolate and were about a third to a half those of the other three fungi at most temperatures. The growth rates of the fungi on wheat roots at the low and high temperature regimes were correlated with the growth rates on agar at 10 and 20 °C respectively. The correlation was better at low temperatures r= 0.81) than at high temperatures (r = 0.62). Cross-protection experiments using two G. g. graminis isolates which grow poorly at temperatures below 15 °C and a cold-tolerant isolate each of G. g. graminis and Phialophora sp. showed that, while all four fungi protected wheat against take-all at high temperatures (17/23 °C) as evidenced by less severe disease and significantly greater dry weights, only the cold-tolerant fungi were effective at low temperatures (7/13 °C). The use of cold-tolerant isolates of avirulent fungi in field experiments may result in better protection in the early stages of wheat growth when Australian soil temperatures are mostly below 15 °C.     

The effect of temperature on growth and lipid and fatty acid composition on marine microalgae used for biodiesel production

Cultivation temperature is one of the major factors affecting the growth and lipid accumulation of microalgae. In this study, the effects of temperature on the growth, lipid content, fatty acid composition and biodiesel properties of the marine microalgae Chaetoceros sp. FIKU035, Tetraselmis suecica FIKU032 and Nannochloropsis sp. FIKU036 were investigated. These species were cultured at different temperatures (25, 30, 35 and 40 °C). The results showed that the specific growth rate, biomass and lipid content of all microalgae decreased with increasing temperature. With regards to fatty acids, the presence of saturated fatty acids (SFAs) in T. suecica FIKU032 and Nannochloropsis sp. FIKU036 decreased with increasing temperature, in contrast with polyunsaturated fatty acids (PUFAs). Moreover, Chaetoceros sp. FIKU035 was the only species that could grow at 40 °C. The highest lipid productivity was observed in Chaetoceros sp. FIKU035 when cultivated at 25 °C (66.73 ± 1.34 mg L^?1 day^?1) and 30 °C (61.35 ± 2.89 mg L^?1 day^?1). Moreover, the biodiesel properties (cetane number, cold filter plugging point, kinematic viscosity and density) of the lipids obtained from this species were in accordance with biodiesel standards. This study indicated that Chaetoceros sp. FIKU035 can be considered as a suitable species for biodiesel production in outdoor cultivation.     

The effect of pH in intensive microalgal cultures. II. Species competition

The results of a series of competition experiments between the chlorophyte Dunaliellatertiolecta (Dun) Butcher and the diatom Phaeodactylum tricornutum (TFX-1) Bohlin demonstrate conclusively that Phaeodactylum tricornutum dominates in intensive marine cultures when the pH rises above ≈ 10. This dominance results because of the diatom's unique ability among marine species to tolerate alkaline conditions. When the pH is regulated both freshwater and marine algae, once firmly established in culture at their respective pH optima, can resist invasion from competing species. Hence. pH control may be a method for maintaining species other than P. tricornutum in mass culture. When Dunaliella tertiolecta, however, is grown under even slight pH stress it becomes susceptible to invasion by Phaeodactylum tricornutum. This susceptibility to takeover by P. tricornutum increases with increasing pH. In contrast, the freshwater chlorophyte Chlorella vulgaris Beij., which also is sensitive to increasing pH, is capable of remaining dominant at any pH within its tolerance range when invaded by the pH-insensitive chlorophyte, Scenedesmus obliquus (Turp.) Kutz. Although allelopathic interactions may be responsible for the success of Chlorella vulgaris under seemingly stressful conditions, the success of Phaeodactylum tricornutum at increasingly higher pH seems to be related primarily to the alga's pH tolerance characteristics and not to any chemical interactions with competing species.     

Comparative experimental evolution reveals species-specific idiosyncrasies in marine phytoplankton adaptation to warming

A number of experimental studies have demonstrated that phytoplankton can display rapid thermal adaptation in response to warmed environments. While these studies provide insight into the evolutionary responses of single species, they tend to employ different experimental techniques. Consequently, our ability to compare the potential for thermal adaptation across different, ecologically relevant, species remains limited. Here, we address this limitation by conducting simultaneous long-term warming experiments with the same experimental design on clonal isolates of three phylogenetically diverse species of marine phytoplankton; the cyanobacterium Synechococcus sp., the prasinophyte Ostreococcus tauri and the diatom Phaeodoactylum tricornutum. Over the same experimental time period, we observed differing levels of thermal adaptation in response to stressful supra-optimal temperatures. Synechococcus sp. displayed the greatest improvement in fitness (i.e., growth rate) and thermal tolerance (i.e., temperature limits of growth). Ostreococcus tauri was able to improve fitness and thermal tolerance, but to a lesser extent. Finally, Phaeodoactylum tricornutum showed no signs of adaptation. These findings could help us understand how the structure of phytoplankton communities may change in response to warming, and possible biogeochemical implications, as some species show relatively more rapid adaptive shifts in their thermal tolerance.     

Effects of temperature and dosage on Vairimorpha sp. 696 spore morphometrics,spore yield,and tissue specificity in Heliothis virescens

The effects of temperature and dosage on a new microsporidian species, Vairimorpha sp. 696, were examined in H. virescens. The pathogen was evaluated for tissue specificity, spore size, cumulative percentage mortality, and spore production. All tissues examined bore infection at 32°C. Spore length was significantly longer at 19°C (5.9 μm) than at 32°C (4.7 μm). Spore widths at these two temperatures did not differ significantly. Octospores were not found at either temperature at 8 or 12 days postinoculation. One hundred percent mortality was attained in all dosages administered, but the initial rate of mortaily was more rapid in the higher dosages. Finally, spore yield was greater in larvae administered lower dosages. Maximum spore yield at 27°C was 4.87 × 10⁹ spores/larva.     

Phytoplankton ecology of Loch Achray (Scotland)

Loch Achray is a warm monomictic lake in the Scottish highlands with water temperature ranging from 4 °C to 18.7 °C. The oxygen distribution is mainly clinograde with saturation values ranging from 76 to 112%. The general pattern of nutrient variation is irregular particularly for phosphate. Dissolved silica (measured as silicate) showed a range of 24 μg at. Si l⁻¹; phosphate varied from 0.24 to 0.03 μg at. P l⁻¹ while nitrate ranged from 3.5 to 15.2 μg at. N l⁻¹. The pH remained below 7 for the entire year and the alkalinity was very low, ranging from 2.5 to 6 mg CaCO₃ 1⁻¹. The examination of net samples showed Loch Achray to possess a poor phytoplankton population, consisting mainly of desmids and a few diatoms. The quantitative investigation showed a different picture of variation. There was no clear phytoplankton increase till May when a simultaneous increase occurred involving Melosira, Asterionella, Tabellaria fenestrata and Cyclotella. In July the population was dominated by Anabaena, while Cyclotella and Staurastrum became dominant in August.