First description of the environmental niche of the epibenthic dinoflagellate species Coolia palmyrensis,C. malayensis,and C. tropicalis (Dinophyceae) from Eastern Australia

Environmental variables such as temperature, salinity, and irradiance are significant drivers of microalgal growth and distribution. Therefore, understanding how these variables influence fitness of potentially toxic microalgal species is particularly important. In this study, strains of the potentially harmful epibenthic dinoflagellate species Coolia palmyrensis, C. malayensis, and C. tropicalis were isolated from coastal shallow water habitats on the east coast of Australia and identified using the D1‐D3 region of the large subunit (LSU) ribosomal DNA (rDNA). To determine the environmental niche of each taxon, growth was measured across a gradient of temperature (15–30°C), salinity (20–38), and irradiance (10–200 μmol photons · m^?2 · s^?1). Specific growth rates of Coolia tropicalis were highest under warm temperatures (27°C), low salinities (ca. 23), and intermediate irradiance levels (150 μmol photons · m^?2 · s^?1), while C. malayensis showed the highest growth at moderate temperatures (24°C) and irradiance levels (150 μmol photons · m^?2 · s^?1) and growth rates were consistent across the range of salinity levels tested (20–38). Coolia palmyrensis had the highest growth rate of all species tested and favored moderate temperatures (24°C), oceanic salinity (35), and high irradiance (>200 μmol photons · m^?2 · s^?1). This is the first study to characterize the environmental niche of species from the benthic harmful algal bloom genus Coolia and provides important information to help define species distributions and inform risk management.     

EXCYSTMENT AND GROWTH OF CHRYSOPHYTES AND DINOFLAGELLATES AT LOW TEMPERATURES AND HIGH SALINITIES IN ANTARCTIC SEA-ICE1

Extreme environmental conditions have been thought to limit algal growth in the upper sea-ice. In McMurdo Sound, Antarctica, chrysophyte statocysts (stomatocysts) and dinoflagellate hypnozygotes (resting cysts) overwinter in first- and second-year land-fast sea-ice exposed to temperatures of -20° C or lower. In early November, when temperatures in the upper ice are < ?8°C and brine salinities are >126 psu, dinoflagellate cysts activate and shortly thereafter excyst. During early November, chrysophyte statocysts also begin to excyst. Net daily primary production occurs in the sea-ice brine at temperatures as low as ?7.1° C, at brine salinities as high as 129 psu, and at average photon flux densities as low as 5 μmol photons.m^?2.s^?1. Dinoflagellate densities were >10⁶ vegetative cells.L^?1 of ice while temperatures in the upper ice were between ?6.8 and ?5.8° C and brine salinities were ～100 psu. Chrysophyte densities reached >10⁶.L^?1 of ice by early December. High densities of physiologically active clyo- and halotolerant algae can occur in the upper land-fast sea-ice under extreme conditions of temperature and salinity.     

LOW THERMAL LIMIT OF GROWTH RATE OF SYMBIODINIUM CALIFORNIUM (DINOPHYTA) IN CULTURE MAY RESTRICT THE SYMBIONT TO SOUTHERN POPULATIONS OF ITS HOST ANEMONES (ANTHOPLEURA SPP.; ANTHOZOA,CNIDARIA)1

Symbiodinium californium (#383, Banaszak et al. 1993 ) is one of two known dinoflagellate symbionts of the intertidal sea anemones Anthopleura elegantissima, A. xanthogrammica, and A. sola and occurs only in hosts at southern latitudes of the North Pacific. To investigate if temperature restricts the latitudinal distribution of S. californium, growth and photosynthesis at a range of temperatures (5°C–30°C) were determined for cultured symbionts. Mean specific growth rates were the highest between 15°C and 28°C (μ 0.21–0.26 · d^?1) and extremely low at 5, 10, and 30°C (0.02–0.03 · d^?1). Average doubling times ranged from 2.7 d (20°C) to 33 d (5, 10, and 30°C). Cells cultured at 10°C had the greatest cell volume (821 μm³) and the highest percentage of motile cells (64.5%). Growth and photosynthesis were uncoupled; light‐saturated maximum photosynthesis (P_max) increased from 2.9 pg C · cell^?1 · h^?1 at 20°C to 13.2 pg C · cell^?1 · h^?1 at 30°C, a 4.5‐fold increase. Less than 11% of daily photosynthetically fixed carbon was utilized for growth at 5, 10, and 30°C, indicating the potential for high carbon translocation at these temperatures. Low temperature effects on growth rate, and not on photosynthesis and cell morphology, may restrict the distribution of S. californium to southern populations of its host anemones.     

Environmental controls on growth and lipid content for the freshwater diatom, Fragilaria capucina: A candidate for biofuel production

The use of microalgae for biofuel production has the potential to reduce fossil fuel consumption. Ideal candidate species of microalgae for bio-oil production need both relatively high growth rates and lipid content. Here, we report on the effects of temperature, nutrients (N, Si), and salinity on growth rates and lipid content of the common freshwater diatom, Fragilaria capucina (Desm), isolated from western Lake Erie. At low NaCl salinity, growth rate increased rapidly from 10 to 20°C, and then further increased slowly from 20 to 30°C, with a maximum specific growth rate of 0.61?day^?1. Growth rate declined with increasing salinity (e.g., reduced by ca. 50 and 100% at 137 and 274?mmol?L^?1 NaCl, respectively), and increased with increased N and Si concentration until ca. 100?μmol?L^?1 for each (with >85% of maximum growth rate at 10?μmol?L^?1). Lipid content (% total lipid per dry mass) in nutrient-replete cultures was 14% and (1) increased to >30% at low N and, especially, low Si; (2) was lower at 30°C vs. 20 or 10°C; and (3) decreased with salinity. Thus, F. capucina accumulates lipid to high levels even under N, Si, and temperature levels that permit a high growth rate for this species, and hence, this species is a candidate for use in biofuel production.     

OLISTHODISCUS LUTEUS (CHRYSOPHYCEAE) I. EFFECTS OF SALINITY AND TEMPERATURE ON GROWTH. MOTILITY AND SURVIVALS1, 2

The effect of salinity and temperature on Olisthodiscus luteus Carter has been examined to across the relative importance of these factory on dynamics of natural population. A salinity range 2–50% was observed with increased tolerance to low salinity (<5%.) at higher temperature (20–30°C). Slinities at 4–5%. Had densities of 10³ cells/ml^?1, and growth >0.5 division day^?1 at temperature of 15–30°C higher salinities (5–50%.) variable but distinct optima for density, growth and motility were observed 5, 10 and 30°C. Density and motility showed no clear optima from 10–10%.15–25°C where maximum growth rates >1.0 division/day^?1 were common. Temperature increased from (0.5–1.9 division. Day^?1) and increases of three orders of magnitude (10^2?10³) for maximum densities. Temperature optima 20°C for growth 5–35%. And 25°C for >40%. were observed. The implications of these findings to natural populations of O. luleus are discussed.     

Temperature × light interaction and tolerance of high water temperature in the planktonic freshwater flagellates Cryptomonas (Cryptophyceae) and Dinobryon (Chrysophyceae)

Using microcosm experiments, we investigated the interactive effects of temperature and light on specific growth rates of three species each of the phytoplanktonic genera Cryptomonas and Dinobryon. Several species of these genera play important roles in the food web of lakes and seem to be sensitive to high water temperature. We measured growth rates at three to four photon flux densities ranging from 10 to 240 μmol photon · m^?2 · s^?1 and at 4–5 temperatures ranging from 10°C to 28°C. The temperature × light interaction was generally strong, species specific, and also genus specific. Five of the six species studied tolerated 25°C when light availability was high; however, low light reduced tolerance of high temperatures. Growth rates of all six species were unaffected by temperature in the 10°C–15°C range at light levels ≤50 μmol photon · m^?2 · s^?1. At high light, growth rates of Cryptomonas spp. increased with temperature until the temperature optimum was reached and then declined. The Dinobryon species were less sensitive than Cryptomonas spp. to photon flux densities of 40 μmol photon · m^?2 · s^?1 and 200 μmol photon · m^?2 · s^?1 over the entire temperature range but did not grow under a combination of very low light (10 μmol photon · m^?2 · s^?1) and high temperature (≥20°C). Among the three Cryptomonas species, cell volume declined with temperature and the maximum temperature tolerated was negatively related to cell size. Since Cryptomonas is important food for microzooplankton, these trends may affect the pelagic carbon flow if lake warming continues.     

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.     

Effects of light and temperature on the growth of Takayama helix (Dinophyceae): mixotrophy as a survival strategy against photoinhibition

Takayama helix is a mixotrophic dinoflagellate that can feed on diverse algal prey. We explored the effects of light intensity and water temperature, two important physical factors, on its autotrophic and mixotrophic growth rates when fed on Alexandrium minutum CCMP1888. Both the autotrophic and mixotrophic growth rates and ingestion rates of T. helix on A. minutum were significantly affected by photon flux density. Positive growth rates of T. helix at 6–58 μmol photons · m^?2 · s^?1 were observed in both the autotrophic (maximum rate = 0.2 · d^?1) and mixotrophic modes (0.4 · d^?1). Of course, it did not grow both autotrophically and mixotrophically in complete darkness. At ≥247 μmol photons · m^?2 · s^?1, the autotrophic growth rates were negative (i.e., photoinhibition), but mixotrophy turned these negative rates to positive. Both autotrophic and mixotrophic growth and ingestion rates were significantly affected by water temperature. Under both autotrophic and mixotrophic conditions, it grew at 15–28°C, but not at ≤10 or 30°C. Therefore, both light intensity and temperature are critical factors affecting the survival and growth of T. helix.     

Diversity in the influence of temperature on the growth rates of freshwater algae, and its ecological relevance

1. Growth rates of seven species of planktonic algae were determined in culture over a range of temperature from 2 to 35 °C. Additional observations on growth and viability were made for 13 species in the temperature range 20–35 °C. 2. There was a wide range of growth rates between species at their optimal temperatures, from 1.7 divisions day^?1 (Asterionella formosa) to 0.3 divisions day^?1 (Ceratium furcoides). 3. There were considerable differences between species for growth at low and high temperature. Certain algae, including the diatom A. formosa and the flagellates Cryptomonas marssonii, Dinobryon divergens and Eudorina unicocca var. unicocca, had growth rates of 0.4 divisions day^?1 or more at 5 °C. The cyanophyte Tychonema (formerly Oscillatoria) bourrellyi, the xanthophyte Tribonema sp., the desmid Staurastrum cingulum and the large dinoflagellate C. furcoides grew poorly or not at all at this temperature. All 21 species tested could grow at 25 °C, but many – including most of the diatoms, some cyanophytes, and all the flagellates – failed to grow persistently at 30 °C. Only Aphanizomenon flos‐aquae survived with moderate increase at 35 °C, a lethal temperature for the other species. 4. The applicability was considered of proposed quantitative formulations of the rate‐temperature relationship. Simple exponential relationships applied only to very limited lower ranges of temperature. The relationship proposed by B?lehrádek was a better fit over a wider temperature range, but still excluded rate‐decline at high temperature. 5. The interspecific differences found are of potential significance for restrictions in natural distributions associated with season, altitude (especially above 500 m) and latitude.     

Effect of temperature on growth and ingestion rates of Favella sp

This study describes the effect of temperature on the growthand ingestion rates of the tintinnid, Favella sp. cultured withthe dinoflagellate Heterocapsa triquetra. In vivo fluorescencewas used to monitor the change in density of the H. triquetrapopulation over 4- to 5-day periods in control tubes containingonly algae, and in experimental tubes containing algae and tintinnids.A ‘switchover point’ occurred in the temperaturedependency of the growth rate such that below 11.4°C, H.triquetra grew more quickly than Favella sp. and above thistemperature the situation was reversed. Ingestion rates of Favellaon H. triquetra were found to be temperature dependent in anonlinear fashion. The rate doubled (from 2.5 to 5.3 cells animal^–1h^–1) between 11.4 and 16.4°C whereas there was nochange in ingestion rates between 8.0 and 11.4°C, or between16.4 and 21.1°C.     

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

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

Environmental and nutritional factors which regulate population dynamics and toxin production in the dinoflagellate Alexandrium catenella

The effects of environmental and nutritional factors on population dynamics and toxin production were examined in Alexandrium catenella, maintained in enriched K media in laboratory cultures. Starting with a density of 50 cell ml⁻¹, the dinoflagellate population typically showed a lag phase and an exponential growth phase which lasted 14 days each, and then entered the stationary phase, with a maximal capacity of 12–18,000 cell ml⁻¹-. Population densities showed distinct diurnal patterns, with population growth beginning 2–4 hours in darkness. The optimal physical conditions for growth were pH 8.5,salinity of 30–35‰, temperature of 20–25°C, and photoperiod of 14//10D to 16L/8D. The cell cycle was determined by flow cytometry on synchronized batch cultures maintained at optimal pH, salinity, temperature and under 5 different photoperiod regimes. It was found that the G₁ phase was timed to end at approximately 3 h after onset of darkness, and the G₂/M phase had begun at 4 hours. Nutrient supply markedly affected population growth. Under optimal physical conditions, the optimal concentrations for macronutrients and micronutrients were: NH⁺⁻⁴- 0.025–0.2 mM,NO⁻³ 0.22–8.83 mM, glycerophosphate0.04–0.06 mM, silicate 0.1–0.54 mM; FeEDTA 0.07–0.11 mM;Co 0.1 μM, Cu 0.005–0.04 μM; Mn 0.22–7.2 μM;Mo 0.03–0.6 μM; Se 0.02–0.1 μM; Zn 0.04–1.6μM; thiamin 0.075–6 μM; vitamin B₁₂0.0004–0.004 μM; biotin 0.007–0.015 μM; EDTA5–40 μM. The toxin profile of A. catenella was determined by HPLC and found to include in descending order: GTX-4, GTX-3, GTX-1, B2, neosaxitoxin, saxitoxin. Toxin content per cell was highest in cell populations in the early exponential phase. The highest toxin per litre medium was recorded at 20°C at the beginning of the stationary phase,when cell density was highest and toxin/cell was still relatively high. At10°C, the cell density was low while the amount of toxin/cell was high;while at 30°C, the population at full capacity was low and the toxin/cell was also low. The population and toxin data thus provided an explanation for the peak level of PSP contamination in shellfish during the months of March–April around the eastern and southern side of Hong Kong and a minor peak extending to the western side in September–October, when the physical conditions of the seawater provided the right environment for toxin accumulation. Toxin content in the dinoflagellate reached its maximum during the S-phase of the cell cycle. Nitrogen restriction in the medium reduced population growth and toxin production, while phosphorus restriction reduced only population growth but enhanced toxin accumulation in the cells. This revised version was published online in August 2006 with corrections to the Cover Date.     

Growth, maturation and photosynthesis of the brackish water alga Rhizoclonium sp. (Cladophoraceae, Chlorophyta) in relation to salinity

The effects of salinity on growth, maturation and photosynthesis were examined in the filamentous alga Rhizoclonium sp. (Cladophoraceae, Chlorophyta) growing in a brackish water habitat in a canal draining into Tokyo Bay, Japan. In this habitat Rhizoclonium sp. was exposed to a wide salinity range, both daily, 5–23‰ during November 1996, and hourly, 6–24‰ during the spring tide day. From the results of culture experiments, growth and maturation of Rhizoclonium sp. occurred in the wide salinity range of 10–40‰ at 20 μmol photons m‐²s‐¹ at 20°C, but did not occur at salinity of 0‰. Light saturation on the photosynthesis‐irradiance curve at 20°C at 20‰ was reached at 100 μmol photons m‐²s‐¹, which is characteristic for shade‐adapted algae. On the photosynthesis‐salinity curve at 20°C at saturated irradiance (160 μmol photons m‐²s‐¹), the net photosynthetic rate increased with increasing salinity up to 30‰ but decreased at 40‰. On the photosynthesis–salinity curve at 20°C at 20 μmol photons m‐²s‐¹ (at near in situ irradiance), the photosynthetic rates were almost the same in the salinity range from 0 to 40‰. Therefore, this species is able to grow, reproduce and photosynthesize with a relative efficiency in a wide salinity range, which shows that it is well adapted to a brackish water environment.     

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

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

Photosynthetic and respiratory responses of Gracilaria parvispora from the southeastern Gulf of California

Photosynthetic and respiratory responses (P–E curves) of Gracilaria parvispora from the southeast Gulf of California were studied at four temperatures (20, 25, 30, 35 °C) and salinity (25, 30, 35, 40 psu) combinations. The alga showed acclimation in its photosynthetic and respiratory responses to tropical temperature as well as to oceanic salinity. A positive effect of temperature on photosynthetic rate (P _max) was observed for all salinities. Photosynthetic rates for treatments at 20 and 25 °C were lower (<9.2 mg O₂?g dry weight (dw)^?1?h^?1) than for treatments at 30 and 35 °C (>12 mg O₂ g dw^?1?h^?1). G. parvispora showed limited tolerance to low salinities (25 psu) and low temperatures (20 °C) and the interaction between temperature and salinity was significant (analysis of variance, P?<?0.05). Responses to salinity indicated adaptation to oceanic salinity. Photosynthetic responses were lower at 25 psu than at higher salinities. The lowest P _max values (6.2–8.2 mg O₂?g dw^?1?h^?1) were observed at the lowest salinity (25 psu) regardless of temperature. Compensation and saturation irradiances (26–170 and 57–149 μmol photons m^?2?s^?1, respectively) indicate adaptation to lower irradiances in shallow (1–2 m depth) habitats, where turbidity can be high, and the capacity of shade adaptation has been developed. Results suggest distribution of this species is mainly related to salinity or temperature. The potential mariculture efforts of G. parvispora would be limited by low temperatures in winter, and indicate that this species will probably not be able to spread further due to low temperatures (<15 °C) in the upper part of the Gulf of California.     

THE ACCLIMATED RESPONSE OF GROWTH,PHOTOSYNTHESIS, COMPOSITION,AND CARBON BALANCE TO TEMPERATURE IN THE PSYCHROPHILIC ICE DIATOM NITZSCHIA SERIATA1

Nitzschia seriata Cleve, a common member of marine bottom ice communities in the Arctic, was grown in unialgal batch cultures to test for compensatory mechanisms for the low temperatures (?1.8° C) typical of its natural habitat. The upper lethal limit for growth was between 12° and 15°C, and the optimum was between 6° and 12° C. The Arrhenius function adequately (R²= 73%) fitted the relationship between growth rate and temperature from – 1.6° up to 10° C, with an average Q₁₀ of 1.9 over the entire range. Light-saturated and light-limited rates of photosynthesis (normalized to chlorophyll a or cell carbon) showed complete compensation from 12° to 4° C. Photosynthetic rates, especially at light saturation, declined rapidly at temperatures below 4° C. Susceptibility to photoinhibition was greatest at the lowest growth temperatures. Cellular composition (chlorophyll a, protein, polysaccharide, and lipid contents) was not systematically related to temperature in any simple way, although cell size (carbon per cell) was maximal at the lowest growth temperature. Dark respiration was unmeasurably low (<0.015 day^?1) at all growth temperatures. The strategy of adaptation in N. seriata may be characterized as optimizing efficiency and compensation, rather than maximization, of growth rate.     

Growth of the conchocelis phase of Porphyra columbina (Bangiales, Rhodophyta) at different temperatures and levels of light, nitrogen and phosphorus

Temperature, light, nitrogen and phosphorus all had significant effects on the growth of conchocelis colonies of Porphyra columbina Montagne when grown in vitro using a shell substrate. High rates of growth were recorded at 15°C and at 8°C under low light levels. These fight and temperature conditions are similar to those found in the subtidal environment of southern New Zealand coastlines. Little growth occured at 22°C. Nitrogen stimulated growth at concentrations far greater than are likely to be found in situ, while at concentrations of 120 μmol/L and above phosphorus had an inhibitory effect on growth, The culture parameters were strongly interactive in their effect on growth, in particular temperature and light. Conchosporangia formed in all treatments 14 days after alteration of the photoperiod to 10 h light: 14 h dark. Optimal conditions for culture of the conchocelis of P. columbina from southern New Zealand are a water temperature of approximately 15°C, light levels between 10 and 50 μmol m^?2s^?1 and seawater nitrogen levels maintained above 100 μmol/L.     

Comparative NMR studies of diffusional water permeability of red blood cells from different species: XVIII platypus (Ornithorhynchus anatinus) and saltwater crocodile (Crocodylus porosus)

As part of a programme of comparative measurements of P _d (diffusional water permeability) the RBCs (red blood cells) from an aquatic monotreme, platypus (Ornithorhynchus anatinus), and an aquatic reptile, saltwater crocodile (Crocodylus porosus) were studied. The mean diameter of platypus RBCs was estimated by light microscopy and found to be ～6.3 μm. P _d was measured by using an Mn²⁺‐doping 1H NMR (nuclear magnetic resonance) technique. The P _d (cm/s) values were relatively low: ～2.1×10^?3 at 25°C, 2.5×10^?3 at 30°C, 3.4×10^?3 at 37°C and 4.5 at 42°C for the platypus RBCs and ～2.8×10^?3 at 25°C, 3.2×10^?3 at 30°C, 4.5×10^?3 at 37°C and 5.7×10^?3 at 42°C for the crocodile RBCs. In parallel with the low water permeability, the E _a,d (activation energy of water diffusion) was relatively high, ～35 kJ/mol. These results suggest that “conventional” WCPs (water channel proteins), or AQPs (aquaporins), are probably absent from the plasma membranes of RBCs from both the platypus and the saltwater crocodile.     

EFFECTS OF LIGHT AND TEMPERATURE ON NET PHOTOSYNTHESIS AND DARK RESPIRATION OF GAMETOPHYTES AND EMBRYONIC SPOROPHYTES OF MACROCYSTIS PYRIFERA1

The rates of net photosynthesis as a function of irradiance and temperature were determined for gametophytes and embryonic sporophytes of the kelp, Macrocystis pyrifera (L.) C. Ag. Gametophytes exhibited higher net photosynthetic rates based on oxygen and pH measurements than their derived embryonic sporophytes, but reached light saturation at comparable irradiance levels. The net photosynthesis of gametophytes reached a maximum of 66.4 mg O₂ g dry wt^?1 h^?1 (86.5 mg CO₂ g dry wt^?1 h^?1), a value approximately seven times the rate reported previously for the adult sporophyte blades. Gametophytes were light saturated at 70 μE m^?2 s^?1 and exhibited a significant decline in photosynthetic performance at irradiances 140 μE m^?1 s^?1. Embryonic sporophytes revealed a maximum photosynthetic capacity of 20.6 mg O₂ g dry wt^?1 h^?1 (25.3 mg CO₂ g dry wt^?1 h^?1), a rate about twice that reported for adult sporophyte blades. Embryonic sporophytes also became light saturated at 70 μE m^?2 s^?1, but unlike their parental gametophytes, failed to exhibit lesser photosynthetic rates at the highest irradiance levels studied; light compensation occurred at 2.8 μE m^?2 s^?1. Light-saturated net photosynthetic rates of gametophytes and embryonic sporophytes varied significantly with temperature. Gametophytes exhibited maximal photosynthesis at 15° to 20° C, whereas embryonic sporophytes maintained comparable rates between 10° and 20° C. Both gametophytes and embryonic sporophytes declined in photosynthetic capacity at 30° C. Dark respiration of gametophytes was uniform from 10° to 25° C, but increased six-fold at 30° C; the rates for embryonic sporophytes were comparable over the entire range of temperatures examined. The broader light and temperature tolerances of the embryonic sporophytes suggest that this stage in the life history of M. pyrifera is well suited for the subtidal benthic environment and for the conditions in the upper levels of the water column.