Effects of UV radiation of different wavebands on pigmentation, 15N-ammonium uptake, amino acid pools and adenylate contents of marine diatoms

Three marine diatoms Lauderia annulata Cleve, Odontella sinensis (Greville) Grunow and Thalassiosira rotula Meunier were exposed to ultraviolet (UV) radiation of different wavebands under controlled laboratory conditions (0.035 vol% CO₂, 18 °C). Several changes in the patterns of pigments in these organisms were seen depending on the waveband of UV radiation and species examined. UV-B and UV-B plus UV-A radiation led to a reduction in the overall pigment content of all three diatoms. The uptake of ¹⁵N-ammonium was less affected by 5-h UV-A (WG 320) but significantly reduced after UV-B and UV-B plus UV-A exposure. The pattern of free amino acid pools varied depending on the applied UV wavebands and the tested diatom. The main protein-bound amino acids of T. rotula decreased after 5-h UV irradiance except leucine. Contents of adenosine 5′-mono-, di-, and triphosphate (AMP, ADP and ATP) were affected differently by UV radiation; ATP values increased at the end of UV-B and UV-B plus UV-A exposure. These results have been discussed with reference to the impact of the different UV sources and the influence on the nitrogen metabolism in connection to pigments and supply with energy. Received: 13 May 1997 / Accepted: 11 October 1997     

In situ measurements of photosynthetic irradiance responses of two Red Sea sponges growing under dim light conditions

Photosynthetic responses to irradiance by the photosymbionts of the two Red Sea sponges Theonella swinhoei (Gray) and Clionavastifica (Hancock) growing under dim light conditions were measured in situ (in September 1997) using a newly developed underwater pulse amplitude modulated (PAM) fluorometer. Relative rates of photosynthetic electron transport (ETR) were calculated as the effective quantum yield of photosystem II (Y ) multiplied with the photosynthetic photon flux (PPF). Photosynthesis versus irradiance (P-I ) curves, obtained within minutes, showed that individual specimens of both sponges, growing under very low light conditions, feature lower light saturation points as well as lower maximal ETRs than individuals growing under higher light. Evaluations of such curves using low irradiances of the actinic light source (20 to 130 μmol photons m⁻² s⁻¹) showed a general decrease in Y, with a shoulder from the lowest irradiance applied till 20 to 30 μmol photons m⁻² s⁻¹. Point measurements yielded ETRs close to what could be estimated from the P-I curves. These point measurements also revealed good correlations between the diurnally changing ambient irradiances (1 to 50 μmol photons m⁻² s⁻¹) and average ETR values for both species. Further analysis showed that although Y values varied considerably between the different point measurements, they did not decrease significantly with light under these very low irradiances. Therefore, PPF rather than Y seems to determine the in situ diel photosynthetic performance at the low ambient irradiances experienced by these sponges. Received: 22 November 1997 / Accepted: 8 April 1998     

Impact of UV-B radiation on uptake of 15N-ammonia and 15N-nitrate by phytoplankton of the Wadden Sea

Natural marine phytoplankton populations from the German Wadden Sea and unialgal cultures of the haptophycean Phaeocystis pouchetii were tested in 1989 under controlled UV-B stress conditions. Assimilation of ¹⁵N-nitrate in phytoplankton consisting mainly of P. pouchetii, or in pure cultures of this alga, was found to be very sensitive to enhanced UV-B dosage in comparison ¹⁵N-ammonia uptake. In contrast, in phytoplankton samples containing Ceratium spp., Coscinodiscus sp., Noctiluca sp. or others, rate of ¹⁵NO₃ ^- uptake was higher and only slightly affected by UV-B irradiance compared to the P. pouchetii sample. UV-B inhibitory effect on uptake of inorganic nitrogen by P. pouchetii was more pronounced under strong white-light conditions and after a UV-B pre-illumination period of several hours than under low white light. Pools of glutamine and alanine decreased after UV-B exposure. Results are discussed with reference to the damaging effects of white light and UV-B on nitrogen metabolism.     

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

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

Growth and grazing responses of Chrysochromulina ericina (Prymnesiophyceae): the role of irradiance, prey concentration and pH

The effect of irradiance, prey concentration and pH on the growth and grazing responses of the mixotrophic prymnesiophyte Chrysochromulina ericina under N-and P-replete conditions was studied using the pedinophyte Marsupiomonas pelliculata as prey. The two organisms were inoculated in monocultures and in mixed cultures at different predator: prey ratios at three irradiances and allowed to grow for 4–7 days. All cultures were non-axenic. Algal densities and pH were monitored throughout the experiments and growth and grazing rates were measured. An increase in growth of C. ericina cultures at irradiances of 25 and 70 μmol photons m⁻² s⁻¹ was observed after the addition of prey, while growth of C. ericina cultures at the high irradiance (150 μmol photons m⁻² s⁻¹) was unaffected by the addition of prey. However, although the growth of C. ericina increased at low irradiance (25 μmol photons m⁻² s⁻¹), it did not reach the same level as monocultures at the high irradiance (150 μmol photons m⁻² s⁻¹), suggesting that phagotrophy can only partly replace photosynthesis in C. ericina. Maximum growth rates of C. ericina at irradiances of 25 and 70 μmol photons m⁻² s⁻¹ were obtained at concentrations of > 0.15–0.3×10⁵ M. pelliculata ml⁻¹, corresponding to 50–100 μg C 1⁻¹. Ingestion of M. pelliculata cells by C. ericina did not generally follow Michaelis—Menten kinetics. Deviation from the expected saturation kinetics was especially pronounced at irradiances of 70 and 150 μmol photons m⁻² s⁻¹. At these irradiances ingestion of M. pelliculata cells by C. ericina decreased at high concentrations of M. pelliculata, indicating an increased uptake of bacterial prey in these cultures. The growth rate of C. ericina was affected in both monocultures and in mixed cultures when pH increased above 8.6, and growth stopped around pH 9. The prey alga M. pelliculata tolerated high pH better and, consequently, took over in the mixed cultures when pH exceeded 9. The ecological significance of mixotrophy in the genus Chrysochromulina is discussed. Published online: 4 July 2002     

Optimization of pigment content and the limits of photoacclimation for Ulva rotundata (Chlorophyta)

Two vegetative clones (designated 11/85 and 7/86 in accordance with month/year of collection) of the chlorophyte macroalga Ulva rotundata were collected in the vicinity of Beaufort, North Carolina, USA. Each was grown in an outdoor continuous-flow system in summer (>-20°C) of 1986 and late winter (10° to 17°C) of 1987 in graded scalar quantum irradiances ranging from 9 to 100% of full sunlight, with and without NH ₄ ⁺ enrichment. The pigment content of plants from each irradiance was determined following 4 to 8 d sunny weather. Chlorophyll (chl) and carotenoid content were inverse curvilinear functions of irradiance. The chl a:b and carotenoid: chl ratios were positively related to irradiance. The close nonlinear relationship between chl (a+b) and the chl a:b ratio was independent of clone, temperature or NH ₄ ⁺ -enrichment. Chl (a+b) content was linearly correlated with light-regulated growth rate in the summer, but showed a marked hysteresis in the relationship in winter due to photoinhibition. The photon growth yield (PGY, i.e., the biomass yield per unit absorbed light) was maximal for plants grown at slightly subsaturating irradiances, and dropped off sharply at lower irradiances. At higher irradiances, PGY declined gradually in summer and markedly in winter. Light absorption exceeded growth needs at full sunlight, suggesting that U. rotundata was incapable of further reducing its pigment content when growth rate was light-saturated. This, along with the linear chlgrowth relationship, is consistent with photosynthetic feedback regulation of chl content. Regardless of the mechanism, chl regulation may operate within the constraints of a resource tradeoff between light harvesting and carboxylation capacities, such that pigmentation must be optimized rather than maximized.     

Intra-colonial variability in light acclimation of zooxanthellae in coral tissues of Pocillopora damicornis

We investigated heterogeneity of light acclimation of photosynthesis in sun- and shade-adapted coenosarc and polyp tissues of Pocillopora damicornis. The zooxanthellar community within P. damicornis colonies at Heron Island is genetically uniform, yet they showed a large degree of plasticity in their photo-physiological acclimation linked to light microclimates characterised by fibre-optic microprobes. Microscale scalar irradiance measurements showed higher absorption in polyp than coenosarc tissues and higher absorption in the more densely pigmented shade-adapted polyps than in sun-adapted polyps. The combination of an O₂ microelectrode with a fibre-optic microprobe (combined sensor diameter 50–100 μm) enabled parallel measurements of O₂ concentration, gross photosynthesis rate and photosystem II (PSII) quantum yield at the coral surface under steady-state conditions as a function of increasing irradiances. Lower O₂ levels at the tissue surface and higher compensation irradiance indicated a higher respiration activity in sun-adapted polyp tissue as compared to shade-adapted polyps. Shade-adapted coenosarc and polyp tissues exhibited lower maxima of relative electron transport rates (rETR_max) (84±15 and 41±10, respectively) than sun-adapted coenosarc and polyp tissues (136±14 and 77±13, respectively). Shade-adapted tissues showed stronger decrease of rETR at high scalar irradiances as compared to sun-adapted tissues. The relationship between the relative PSII electron transport and the rate of gross photosynthesis, as well as O₂ concentration, was non-linear in sun-adapted tissues over the entire irradiance range, whereas for shade-adapted tissues the relationship became non-linear at medium to high scalar irradiances >200 μmol photons m⁻² s⁻¹. This suggests that rETR measurements should be used with caution in corals as a proxy for photosynthesis rates. The apparently high rates of photosynthesis (oxygen evolution rates) suggest that there must be a considerable electron transport rate through the photosystems that is not observed by the rETR measurements. This may be accounted for by vertical heterogeneity of zooxanthellae in the tissue and the operation of an alternative electron pathway such as cyclic electron flow around PSII.     

Inhibition of photosynthesis by ultraviolet radiation as a function of dose and dosage rate: Results for a marine diatom

The effects of ultraviolet radiation on phytoplankton are usually described as a function of dose (J m^–2, weighted appropriately). Experiments conducted in 1988 and 1989 on a marine diatom,Thalassiosira pseudonana (Clone 3H), demonstrate that during lightlimited photosynthesis in visible radiation, the inhibition of photosynthesis by supplemental ultraviolet radiation (principally UV-B: 280 to 320 nm) is a function of irradiance (W m^–2) as well as of dose: for equal doses of UV-B, a relatively short exposure to high UV-B irradiance is more damaging to photosynthesis than a longer exposure to lower irradiance. In fact, photoinhibition by UV-B is well described as a monotonic, nonlinear function of irradiance for time scales of 0.5 to 4 h. A nitrate-limited culture was about nine times more sensitive to UV-B than was a nutrient-replete culture, but the kinetics of photoinhibition were similar. These results have some bearing on efforts to describe the effects of ultraviolet radiation on marine primary productivity. Action spectra of photoinhibition by UV can be constructed, but they should only be used to describe photoinhibition for specified time scales. Vertical profiles of relative photoinhibition must be interpreted cautiously because photoinhibition by UV-B is likely to be a function of incubation time and results must therefore be interpreted in the context of vertical mixing.     

UV absorption by mycosporine-like amino acids in Phaeocystis antarctica Karsten induced by photosynthetically available radiation

Mycosporine-like amino acids (MAAs), which occur in diverse taxonomic groups, exhibit in vivo absorption maxima between 310 nm and 360 nm and may play a photoprotective role against ultraviolet (UV) exposure. Using cultures of colonial Phaeocystis antarctica, we examined the relationship between MAA concentration, in vivo UV absorption, photoprotective (carotenoid) and photosynthetic pigments, and photosynthetically available radiation (PAR, 350–700 nm). UV absorption was high; chlorophyll-specific absorption, a ^* _ph, at 330 nm ranged from 0.06 to 0.41 m²/mg chlorophyll a. Values of a ^* _ph (330) were 4–13 times greater than a ^* _ph (676). Mycosporine-glycine, shinorine, and mycosporine-glycine valine are responsible for the strong in vivo UV absorption. The sum of all MAAs increased with irradiance when normalized to chlorophyll a or carbon concentrations, whereas individual MAAs varied independently from each other. Mycosporine-glycine concentrations showed no statistically significant change over the range of light intensities, whereas mycosporine-glycine and shinorine concentrations increased at higher irradiances. The relative fluorescence yield for chlorophyll a was low in the UV region compared to the visible region, implying that absorbed UV radiation (<375 nm) is transferred inefficiently to chlorophyll a in the reaction center. Quantitative estimates of UV screening by MAAs are attributed to elevated MAA concentrations and increased diameter at high light. Received: 31 March 1999 / Accepted: 13 July 2000     

Effect of feeding regime and irradiance on the photophysiology of the symbiotic sea anemone Aiptasia pulchella

To determine how the animal and algal components of the symbiotic sea anemone Aiptasia pulchella respond to changes in food availability and culture irradiance, sea anemones from a single clone were maintained at four irradiance levels (320, 185, 115, and 45 E m^-2 s^-1) and either starved or fed for 5 wk. Changes in protein biomass of sea anemones maintained under these conditions were not related to the productivity of zooxanthellae, since the protein biomass of fed A. pulchella decreased with increase in irradiance and there was no difference in protein biomass among starved sea anemones at the four irradiance levels. Except for the starved high-light sea anemones, the density of symbiotic zooxanthellae was independent of culture irradiance within both starved and fed. A. pulchella. Starved sea anemones contained over twice the density of zooxanthellae as fed sea anemones. Within both starved and fed individuals, chlorophyll per zooxanthella increased with decreasing culture irradiance while algal size remained constant (in fed sea anemones) at about 8.80 m diameter. Chlorophyll a: c ₂ ratios of zooxanthellae increased with decreasing culture irradiance in zooxanthellae from starved sea anemones but remained constant in zooxanthellae from fed sea anemones. As estimated from mitotic index data, the in situ growth rates of zooxanthellae averaged 0.007 d^-1 and did not vary with irradiance or feeding regime. Photosynthesis-irradiance (P-I) responses of fed A. pulchella indicated an increase in photosynthetic efficiency with decreasing culture irradiance. But there was no consistent pattern in photosynthetic capacity with culture irradiance. Respiration rates of fed sea anemones also did not vary in relation to culture irradiance. The parameter I _k , defined as the irradiance at which light-saturated rates of photosynthesis are first attained, was the only parameter from the P-I curves which increased linearly with increasing culture irradiance. The daily ratio of net photosynthesis to respiration for A. pulchella ranged from 1.6 to 2.8 for sea anemones maintained at the three higher irradiances, but was negative for those maintained at 45 E m^-2 s^-1. Since the final protein biomass was greatest for sea anemones maintained at the lowest irradiance, these results indicate that sea anemone growth cannot be directly related to productivity of zooxanthellae in this symbiotic association.     

Ecotypic differentiation in the marine diatom Skeletonema costatum: influence of light intensity on the photosynthetic apparatus

Three genetically distinct clones of Skeletonema costatum (Grev.) Cleve were grown at 20°C under high (274 E m^-2 s^-1) and low (27 E m^-2 s^-1) light conditions and their photoadaptive photosynthetic responses compared. When all three clones were grown under low light, pigment analyses and fluorescence excitation spectra demonstrated that the accessory pigments, chlorophyll c and fucoxanthin, became more important in light-harvesting compared to chlorophyll a. Photosynthetic unit sizes increased for Photosystems I and II in low light, but photosynthesis vs irradiance characteristics were not reliable predictors of photosynthetic unit features. Fluorescence excitation spectra and photosynthesis vs irradiance (P-I) relationships indicated that changes in energy transfer occurred independent of changes in pigment content. Large increases in accessory pigment content were not accompanied by large increases in excitation from these pigments. Changes in energy transfer properties were as important as changes in PSU size in governing the photoadaptive responses of S. costatum. When the three clones were grown under identical conditions, each had a separate and distinct pattern of photoadaptation. Significant differences among clones were found for pigment ratios, photosynthetic unit sizes for Photosystems I and II and efficiency of energy transfer between pigments. These strikingly different photoadaptive strategies among clones may partially account for the great ecological success of the diatom species. This is the first quantitative investigation of the importance of both chlorophyll c and fucoxanthin to the adaptive responses of diatoms to light intensity, and represents the most complete characterization of the photoadaptive responses of a single species of marine phytoplankter to differences in light environment.     

Effect of UV-B radiation on the marine diatoms Lauderia annulata and Thalassiorsira rotula grown in different salinities

The marine diatoms Lauderia annulata Cleve and Thalassiosira rotula Meunier were grown at different salinities (20, 35 and 45) and exposed to different levels of midultraviolet, UV-B) 439, 717 and 1230 J m^-2 d^-1, weighted) for 2 d. A low UV-B dose (439 J m^-2 d^-1) usually caused a slight increase in biomass production (dry weight) compared to non-UV-B irradiated cells. Enhanced UV-B radiation (717 J m^-2 d^-1) depressed protein and pigment content (chlorophyll a, chlorophyll c ₁+c₂ and carotenoids), especially in algae grown at 20 or 35 salt concentration of the nutrient solution. The effect of UV-B radiation (717 J m^-2 d^-1) on the pattern and concentration of amino acids was species-dependent. Aspartic acid was reduced in all tested diatoms. A drastic increase in glutamine and a reduction in glutamic acid pools could be observed in L. annulata samples, but no significant variation of the impact of UV-B was found in dependence on the salt concentration of the nutrient medium. T. rotula cells grown at 35 S showed an increase of glutamic acid and a decrease of glutamine levels after UV-B radiation. The results are discussed in relation to the impact of UV-B upon carbon and nitrogen metabolism.     

Light regime in an Arctic fjord: a study related to stratospheric ozone depletion as a basis for determination of UV effects on algal growth

Solar radiation as a primary abiotic factor affecting productivity of seaweeds was monitored in the Arctic Kongsfjord on Spitsbergen from 1996 to 1998. The radiation was measured in air and underwater, with special emphasis on the UV-B (ultraviolet B, 280–320 nm) radiation, which may increase under conditions of stratospheric ozone depletion. The recorded irradiances were related to ozone concentrations measured concurrently in the atmosphere above the Kongsfjord with a balloon-carried ozone probe and by TOMS satellite. For comparison, an ozone index (a spectroradiometrically determined irradiance of a wavelength dependent on ozone concentration, standardized to a non-affected wavelength) was used to indicate the total ozone concentration present in the atmosphere. Weather conditions and, hence, solar irradiance measured at ground level were seldom stable throughout the study. UV-B irradiation was clearly dependent on the actual ozone concentration in the atmosphere with a maximal fluence rate of downward irradiance of 0.27 W m⁻² on the ground and a maximal daily fluence (radiation exposure) of 23.3 kJ m⁻². To characterize the water body, the light transmittance, temperature and salinity were monitored at two different locations: (1) at a sheltered shallow-water bay and (2) at a wave-exposed, deep-water location within the Kongsfjord. During the clearest water conditions in spring, the vertical attenuation coefficient (K _d) for photosynthetically active radiation (PAR) was 0.12 m⁻¹ and for UV-B 0.34 m⁻¹. In spring, coinciding with low temperatures and clear water conditions, the harmful UV radiation penetrated deeply into the water column and the threshold irradiance negatively affecting primary plant productivity was still found at about 5–6 m depth. The water body in spring was characterized as a Jerlov coastal water type 1. With increasing temperature in summer, snow layers and glacier ice melted, resulting in a high discharge of turbid fresh water into the fjord. This caused a stratification in the optical features, the salinity and temperature of the water body. During melt-water input, a turbid freshwater layer was formed above the more dense sea water. Under these conditions, light attenuation was stronger than defined for a Jerlov coastal water type 9. Solar radiation was strongly attenuated in the first few metres of the water column. Consequently, organisms in deeper water are protected against harmful UV-B radiation. In the surface water, turbidity decreased when rising tide caused an advection of clearer oceanic water. In the course of the summer season, salinity continuously decreased and water temperature increased particularly in shallow water regions. The impact of global climate change on the radiation conditions under water and its effects on primary production of seaweeds are discussed, since organisms in the eulittoral and upper sublittoral zones are affected by UV radiation throughout the polar day. In clearer water conditions during spring, this may also apply to organisms inhabiting greater depths. Received: 20 June 2000 / Accepted: 17 October 2000     

Light acclimation states of phytoplankton in the Southern Ocean, determined using photosynthetic pigment distribution

In high-latitude waters such as the Southern Ocean, the primary production of phytoplankton supports the ecosystem. To understand the photo-acclimation strategy of such phytoplankton within cold environments, the vertical distribution profile of photosynthetic pigments was analyzed in the Southern Ocean. Samples were taken along 110°E during the austral summer, and along 150°E and around the edge of the seasonal sea ice of the Antarctic Continent during the austral autumn. Pigment extraction methods were optimized for these samples. The standing crop of chlorophyll a was larger in the region along the edge of the seasonal sea ice than at sampling stations in open ocean areas. Chlorophyll concentration seemed to be dependent on the formation of thermo- and haloclines along the edge of the seasonal sea ice, but not in the open ocean where such clines are less pronounced. The marker pigments fucoxanthin and/or 19′-hexanoyloxyfucoxanthin were dominant at most sampling stations throughout the water column, while other marker pigments such as alloxanthin were quite low. This indicated that diatoms and/or haptophytes were the major phytoplankton in this area. Comparison of the relative ratio of fucoxanthin with that of 19′-hexanoyloxyfucoxanthin allowed some stations to be characterized as either diatom-dominant or haptophyte-dominant. The relative ratio of xanthophyll-cycle pigments (diadinoxanthin plus diatoxanthin) to chlorophyll a was high in surface waters and decreased gradually with depth. This suggests that near the ice edge during summer in the Southern Ocean, both diatoms and haptophytes acclimate to their light environments to protect their photosystems under high-light conditions.     

四溴双酚A(TBBPA)对中肋骨条藻的毒性效应研究

为研究四溴双酚A(tetrabromobisphenol A,TBBPA)对海洋微藻的毒性效应,本文设置五个不同浓度组(0、1.0、5.0、10.0、20.0 mg·L-1)进行中肋骨条藻(Skeletonema costatum)培养实验,在96 h内取样分析其光合色素含量、可溶性蛋白含量、丙二醛(MDA)含量和超氧化物歧化酶(SOD)活性的变化。结果表明,较低浓度组(1.0和5.0 mg·L-1)叶绿素a、叶绿素c和类胡萝卜素含量48 h之前被显著诱导,最大值出现在24 h;较高浓度组(10.0和20.0 mg·L-1)三种色素含量在48 h之前被显著抑制,24 h达最低值;72 h之后各浓度组均恢复到对照组水平。不同浓度TBBPA胁迫下,中肋骨条藻的可溶性蛋白含量、SOD活性和MDA含量一般被显著诱导,SOD活性和MDA含量在72 h和96 h时随TBBPA浓度升高而增加。虽然1.0 mg·L-1TBBPA对中肋骨条藻生长不具有可观测效应,但已影响到其生理生化指标。目前海水中TBBPA浓度较低,尚不会对中肋骨条藻产生毒性影响。     

Effects of altered photic regimes on diel patterns of species-specific photosynthesis

Diel patterns of photosynthesis were measured for two polar diatoms (Coscinodiscus sp. and Porosira pseudodenticulata) collected in September 1985 from McMurdo Sound, Antarctica, and four temperate dinoflagellates (Gonyaulax hyalina, Gymnodinium splendens, Dinophysis caudata, and Glenodinium sp.) collected in July 1985 and January 1986 from the Southern California Bight, California, USA. For phytoplankton incubated under three combinations of photoperiod and irradiance, distinct diel patterns of light-saturated (P _max) and light-limited (P _L ) photosynthesis were found for (i) different species isolated from the same environment, and (ii) polar diatoms and temperate dinoflagellates. The time of day when the maximum rate of P _max occurred was influenced by both irradiance and daylength for the polar diatoms but not by daylength for three out of four temperate dinoflagellates. The range of values of the ratio of maximum to minimum rates of photosynthesis (P _max:P _min) was similar for polar diatoms and temperate dinoflagellates. The results of this study suggest that changes in irradiance or photoperiod could influence species-specific patterns of photosynthesis in nature. As a consequence, in light-limited environments differential reproductive success could result from these diel patterns, and ultimately be reflected in temporal and spatial differences in community structure.     

Photoadaptation of photosynthesis in Gonyaulax polyedra

Gonyaulax polyedra Stein exhibited a combination of photoadaptive strategies of photosynthesis when only a single environmental variable, the light intensity during growth, was altered. Which of several biochemical/physiological adjustments to the light environment were employed depended on the level of growth irradiance. The photoadaptive strategies employed over any small range of light levels appeared to be those best suited for optimizing photosynthetic performance and not photosynthetic capacity. (Photosynthetic performance, P _i, is defined as the rate of photosynthesis occurring at the level of growth irradiance.) Among all photosynthetic parameters examined, only photosynthetic performance showed a consistent correspondence to growth rates of G. polyedra. Above 3500 to 4000 W cm^-2, where photosynthetic performance was equal to photosynthetic capacity, cells were not considered light-limited in either photosynthesis or growth. At these higher light levels, photosynthetic perfomance, cell volume, growth rates and respiration rates remained maximal; photosynthetic pigment content varied only slightly, while the photosynthetic capacity of the cells declined. At intermediate light levels (3000 to 1500 W cm^-2), photosynthesis, not growth, was light-limited, and photoadaptive strategies were induced which enhance absorption capabilities and energy transfer efficiencies of chlorophyll a to the reaction centers of G. polyedra. Photosynthetic capacity remained constant at about 280 mol O₂ cm^-3 h^-1, while photosynthetic performance ranged from 100 to 130 mol O₂ cm^-3 h^-1. Major increases in photosynthetic pigments, especially peridinin-chlorophyll a-proteins and an unidentified chlorophyll c component, accompanied photoadaptation to low irradiances. Maximal growth rates of 0.3 divisions day^-1 were maintained, as were respiration rates of about-80 mol O₂ cm^-3 h^-1 and cell volumes of about 5.4×10^-8 cm^-3 cell^-1. Below about 1250 W cm^-2, photosynthesis in G. polyedra was so light-limited that photosynthetic performance was unable to support maximal growth rates. Under these conditions, G. polyedra displayed photostress responses rather than photoadaptive strategies. Photostress was manifested as reduced cell volumes, slower growth, and drastic reductions in pigmentation, photosynthetic capacity, and rates of dark respiration.     

Light absorption by a marine diatom: experimental observations and theoretical calculations of the package effect in a small Thalassiosira species

The relationship between in vivo light absorption efficiency of whole cells and in vitro absorption efficiency of algal pigments has been examined experimentally in the marine diatom Thalassiosira sp. In vitro absorption spectra were obtained for cells disrupted by either ultrasonic treatment or high-pressure shearing stress in a low-temperature (-40°C) pressure cell. A dimensionless measure of the magnitude of the package effect (Q _a ^*), calculated from the ratio of whole-cell to disrupted-cell absorption, ranged from about 0.5 at the blue absorption peak of chlorophyll a (λ=435 nm) to 0.7 at the red chlorophyll a peak (λ=670 nm) to 1.0 at the absorption minimum (λ=600 nm). Cell diameter was found to be an inappropriate measure of size for assessing the magnitude of the package effect. Instead, the effective optical diameter for calculation of intracellular self-shading was found to be less than the cell diameter. This observation is consistent with the fact that most algal pigments are contained within chloroplasts, and that chloroplast volume is necessarily smaller than cell volume.     

Light-dependence of carbon and sulfur production by polar clones of the genus Phaeocystis

Blooms of the marine prymnesiophyte genus Phaeocystis link the oceanic and atmospheric compartments of the carbon and sulfur cycles. Modeling the fluxes of dimethylsulfide from the ocean to the atmosphere has been limited due to a lack of information on functional responses to environmental variables. In this study, the light-dependence of extracellular carbon production and dimethyl sulfide (DMS) production by non-axenic polar clones of Phaeocystis spp. was examined at different growth stages. Comparative experiments were run with non-axenic arctic clones of the diatoms Thalassiossira nordenskioeldii and Skeletonema costatum. A large portion of carbon incorporated by the colonial stage of Phaeocystis spp. is released extracellularly, in particular in stationary colonies. This extracellular production can be modeled as a function of irradiance, as for carbon incorporation. In Phaeocystis spp., cellular and extracellular carbon incorporation represent different uptake rates, indicating the formation of two distinct carbon pools. The release of extracellular carbon by polar Phaeocystis spp. was not a constant fraction of total production over the irradiance range used. We observed little extracellular carbon production by cells at high irradiance, and maximal rates were observed at intermediate irradiance. Newly incorporated carbon that accumulates in the mucilage of the colonial stage of antarctic Phaeocystis sp. during photosynthesis was not reutilized for cellular growth during the dark period, as observed for temperate clones. In contrast, only a minor fraction of the radiocarbon incorporated by the diatoms was released extracellularly for all growth stages. The production of DMS was an order of magnitude higher for Phaeocystis spp. than for diatoms. The chlorophyll-specific production of DMS and DMSP (dimethylsulphoniopropionate, the precursor to DMS) by Phaeocystis spp. showed a hyperbolic response to irradiance, while arctic diatoms (weak or non-producers of DMS), on the other hand, did not show any light-dependency of DMS production. An inverse relationship between DMS and DMSP production in stationary clones of arctic P. pouchetii was observed, but not for the exponentially growing antarctic clone. Stationary colonies also had higher DMS and dissolved DMSP production rates than exponentially growing ones. These relationships can be extrapolated to the field in areas where Phaeocystis spp. dominates.     

Survival and sex ratios of the intertidal copepod,Tigriopus californicus,following ultraviolet-B (290–320 nm) radiation exposure

The marine harpacticoid copepod, Tigriopus californicus (Baker), is a successful colonizer of supralittoral splash pools from Torch Bay, Alaska, to Baja California, Mexico. As these pools are subject to abundant amounts of direct solar radiation, it was of interest to determine the sensitivity of T. californicus to ultraviolet-B (UV-B, 290 to 320 nm) radiation. During 1980, copepods were raised under diurnal conditions in the laboratory and fed a mixture of unicellular algae and bacteria. Larval and adult stages were irradiated for 0 to 26 h on a rotating turntable under enhanced ultraviolet radiation. Following irradiation, the copepods were maintained in the culture area and checked daily for survival. All life stages of T. californicus tolerated enhanced UV-B radiation irrespective of exposure period; in contrast, survival of an irradiated planktonic copepod, Acartia clausii (Giesbrecht), was significantly lower. Additionally, there appeared to be asex ratio shift in adults that developed from the youngest naupliar stages (N₁/N₂) of T. californicus that were irradiated. Extraction and tentative identification of the pigment(s) responsible for the bright orange color of the carapace of T. californicus were performed. These pigments may function to absorb UV radiation and protect internal structures from photochemically induced damage.