Reference #: ESK-1025-122460
Submit Date: 06/26/2002 14:57:16-0500

Circadian regulation of memory formation in Aplysia

ABSTRACT:
Sensitization in Aplysia affords a superb opportunity to investigate the regulation of learning and memory by the circadian clock. Sensitization, a non-associative form of learning by which a noxious stimulus increases the duration of a reflex, has been studied extensively in Aplysia. Many of the signaling pathways and physiological processes involved in both short-term sensitization (STS) and long-term sensitization (LTS) are well understood. Thus, we investigated the modulation of learning and memory by the circadian clock in Aplysia. To determine whether Aplysia exhibit diurnal rhythms in sensitization, entrained animals (12:12 LD) were subjected to LTS or STS training during the day and the night. No significant difference was found in STS between animals trained in the day (ZT 3, 6, 9) or the night (ZT 15, 18, 21). However, animals exhibited a diurnal rhythm of LTS with peak retention occurring at ZT 9. To investigate if this rhythm persisted in constant darkness (DD), animals were trained on the 2nd day of DD. Animals subjected to LTS training during the subjective day (CT 3, 9) showed significantly greater sensitization 24 h post-training than animals trained at subjective night (CT 15, 21). Moreover, animals trained during the subjective day demonstrated significantly longer lasting sensitization (as much as 3 days post-training) than animals trained at night. Training time determined the rhythm since animals trained during the night but tested during the day demonstrated no learning. These results indicate that the circadian oscillator exerts strong modulatory influences on the formation of long-term memory in Aplysia. Further studies are underway to determine the molecular pathways by which the circadian oscillator modulates learning and memory processes in Aplysia. Supported by NS 28462.

Keywords: Circadian, Learning, Memory, Aplysia

Reference #: LON-1017-357782
Submit Date: 03/28/2002 16:46:58-0500

Influence of the nutritional state on phytoplankton response to UV-B radiation at three different latitudes (Rimouski, Canada, Ubatuba, Brazil and Ushuaia, Argentina).

ABSTRACT:
The increase of the ultraviolet-B radiation (UV-B, 280-320 nm) may have harmful effects on the lower levels of the food web. However, assessing this is complex because the phytoplankton response to UV-B is quite variable. In addition, nutrient stress may increase the sensitivity to UV-B through the alteration of several mechanisms of photo-protection, defense or reparation, but results from the literature are somewhat contradictory. To test this, natural phytoplankton communities obtained from large mesocosms were incubated, with or without addition of nitrate, in UV-transparent plastic bags exposed to natural and enhanced UV-B conditions at the surface of the mesocosms. Incubations were performed at the beginning, in the middle and at the end of a phytoplankton bloom that developed during each mesocosm experiment, providing different nutrient status before nitrate supplementation. Responses, in terms of photosynthesis (PAM fluorescence) and pigments, are compared between a north-temperate mesotrophic site (Rimouski, Canada), a tropical oligotrophic site (Ubatuba, Brasil) and a cold-temperate site at the southern tip of South America (Ushuaia, Argentina). Preliminary results show strong photoinhibition after 24 h of surface incubation. Nitrate addition reduces photoinhibition during the post-bloom period, when cells are nutrient stressed. Phytoplankton communities from the south temperate and tropical site show greater UV-B tolerance than phytoplankton from the north-temperate site.

Keywords: UV-B, phytoplankton, nutrient limitation, photoinhibition

Reference #: RET-1017-513340
Submit Date: 03/30/2002 12:18:15-0500

CDOM Effects on Aquatic Photosynthesis in the Coastal Arctic Ocean: Trade-Offs between UV Protection and Competition for PAR.

ABSTRACT:
Coastal environment in the Arctic Ocean are strongly affected by the input of freshwaters because of the many large rivers which discharge from circumpolar land masses into the sea. These waters are rich in chromophoric dissolved organic matter (CDOM) composed of fulvic and humic acids that are likely to vary in concentration with changes in climate. Although downstream rivers are typically thought of as heterotrophic ecosystems, autochthonous photosynthetic carbon production is critically important for metazoan food webs in such systems (Thorp & Delong in press Oikos ) and their downstream coastal environments. CDOM protects phytoplankton against ultraviolet radiation because of it spectral absorption characteristics, and riverine CDOM is known to have UV absorption per units organic carbon that is 10 to 150 times greater than marine CDOM (Carder et al. 1989 Limnol. Oceanogr.34:68-81). However, CDOM also absorbs strongly in the blue region of the PAR spectrum which is the most efficient waveband for photosynthesis (Markager & Vincent 2000 Limnol. Oceanogr. 45:642-650). We evaluated these effects using a variety of models. Spectral attenuation was estimated by equations derived from previous work in the Hudson Bay region (Laurion et al 1997 Photochem. Photobiol. 65:107-114). The effects of CDOM on UV-inhibition of photosynthesis were examined using the index T* (weighted transparency; Gibson et al. 2000 Arctic 53: 372-82). The PAR effects were evaluated using a primary production model that incorporates temperature (Rae & Vincent 1998 J. Plankton. Res.20:1293-1312) and by an index of spectral matching for photosynthesis (Ae; Markager & Vincent 2001. J. Plankton Res. 23: 1373-84). These modelling results will be validated in the coming field season by a series of bioptical measurements and experiments in Hudson Bay.

Keywords: CDOM, climate, photosynthesis, ultraviolet

Reference #: LAU-1017-605735
Submit Date: 03/31/2002 13:54:27-0500

UV-acclimation of cultured phytoplankton exposed to natural and enhanced UVB radiation and methodological aspects of MAA quantification.

ABSTRACT:
Bloom-forming dinoflagellates often synthesize high concentrations of mycosporine-like amino acids (MAAs) as a protection from high PAR and UV radiation, which may afford them a competitive advantage over other species. Photoprotection and long-term acclimation to natural and enhanced UVB radiation were examined during 4 weeks in three dinoflagellates and one diatom. Semi-continuous, nutrient-replete cultures were maintained outdoors under natural light, with or without additional UVB (from lamps). The photosynthetic performance (XE-PAM fluorometry) and the concentration and composition of MAAs and photoprotective carotenoids (PPCs; comprising xanthophylls) were followed weekly. A great variety of MAAs was found in the dinoflagellates (up to 10, identified by co-chromatography and LC-MS). Large differences between sp. (and between 2 strains of the same sp.) were observed. In most cases, the composition and concentration of MAAs and PPCs increased under enhanced UVB. Growth rate and photosynthetic performance were sometime lower under enhanced UVB, while in other cases photoacclimation seemed to occur. The least affected sp. was Alexandrium tamarense who responded most rapidly to enhanced UVB. The algae also responded to changes in natural incident radiation. Some methodological aspects of MAA quantification were also investigated (with 4 sp. of dinoflagellates). Our results indicate how freezing (liquid-N) likely breaks the cells, mobilizing the water-soluble MAAs in the filter moist (otherwise highly packaged in fresh cells), while the organelles containing the pigments remain relatively intact. The implications of standard sample handling on the evaluation of MAA concentration in algae and on the estimation of the absorption of suspended material in water from in vivo spectroscopy (filter pad technique) will also be discussed.

Keywords: Alexandrium tamarense, photoprotection strategies, photosynthetic performance, in vivo absorption

Reference #: NOZ-1019-159186
Submit Date: 04/18/2002 13:01:19-0500

Effects of enhanced ultraviolet-B radiation on photosynthetic activity of natural phytoplankton populations measured by fluorescence (PAM) and ¹⁴C-tracer methods

ABSTRACT:
During summer 2000, a 10-day mesocosm experiment was carried out in order to assess the effects of enhanced UV-B radiation on the photosynthetic characteristics of a phytoplankton community of surface waters of the St. Lawrence Estuary (Québec, Canada). Triplicates of mesocosms were submitted to three UVB treatments: (1) natural UVB (NUV-B, control), (2) low UVB enhancement (LUV-B), and (3) high UVB (HUV-B) enhancement. Water samples were collected 2 times per day (05h00 and 13h00). The potential and the actual photochemical efficiency of the reaction centres of PSII (F_v/F_m and F/F'_m, respectively), and the photosynthetic capacity (P^B_max) and efficiency (^B) were estimated using the pulse amplitude modulation (PAM) fluorescence and ¹⁴C-tracer methods, respectively. Throughout the study, F_v/F_m ranged from 0.3 to 0.58, and F/F'_m varied between 0.15 and 0.53. P^B_max varied between 1.96 and 23.13 mg C mg Chl a^-1h^-1 while ^B ranged from 0.014 to 0.034 mg C mg Chl a^-1 ((E m^-2 s^-1) h^-1)^-1. There was no evidence for significant differences in these parameters between the 3 spectral treatments, except during the last three days of experiment when nutrient-limited conditions appeared. The lack of significant change in F_v/F_m despite the enhancement of UV-B (LUV-B and HUV-B) suggests that damage to the photosynthetic reaction centres did not occur. On the other hand, diurnal changes in F_v/F_m, F/F'_m, P^B_max, and ^B were observed during most of the days, with minima values measured at noon. The decrease in P^B_max, and ^Bvalues at noon obviously indicates photoinhibition. The recovery of F_v/F_m, the morning after, suggests that regulation, rather than damage to PS II, indeed, occurred.

Keywords: UV radiation, Phytoplankton, Fluorescence, ¹⁴C

Reference #: DE-1017-736939
Submit Date: 04/02/2002 01:35:20-0500

Photoecological chararcterisation of an epilithic ecosystem at a high mountain locality (Central Spain)

ABSTRACT:
Epilithic ecosystems in high mountains are exposed to extreme solar UV radiation and microclimatic conditions. Study of effects of UV radiation in paralell with microclimatic measurements are not common in experimental field conditions, specially in the mediterranean region. UV radiation was measured during a growing season at Sierra de Gredos (2000 m a.s.l., 40.5 N, 5.5 W), closed to lichens samples of Rhizocarpon geographicum, with the DLR-Biofilm (Bacillus subtilis spores, type TKJ 6312 and type HA-101), biosensor which quantifies the UV biologically effective irradiation (ADN target). An electronic UV dosimeter (Optometer, Giga-Herzt Optik, Puchheim, Germany), was used as an international standardized measure with a sensitivity similar to erythema, simultaneously for calibration. Microclima (temperature, relative humidity) at the experimental side was determined by a microclimatic station (Squirrel, U.K.), including also a PAR sensor (Sky sensor). The application of Radiative transfer modeling for estimation of UV radiation climate at ideal conditions (i.e. clear sky), provide ratios of irradiances UV-B/UV-A lower than the ratios of maximum BED UV-B/BED (UV-A) obtained with the TKJ 6312 Biofilm Ecodosimeter (DLR), being these 100 times higher as the first. A correlation analysis between the Biofilm data and the optometer erythema irradiances showed a 10 times higher sensitivity of the Biofilm, demonstrated specially at the campaigns of June, in the mornings. A 40 % higher sensitivity of the Biofilm in the UV-B range was obtained by the correlation UV-B/PAR calculated between the Biofilm irradiances and PAR data. The design of an experiment with lichens samples with- and without cortex demonstrated the main protection function of the cortex against microclima conditions and UV radiation, specially at summer solstice.

Keywords: photoecological, epilithic, ultraviolet, cortex

Reference #: MEA-1017-708166
Submit Date: 04/01/2002 17:18:55-0500

The Measurement of Ultraviolet Radiation Induced DNA Damage in Dosimeters Along a Latitudinal Gradient

ABSTRACT:
DNA damage induced by ultraviolet radiation (UV) was measured in DNA dosimeters along a latitudinal transect from 41 S to 3 N in the southeastern Pacific Ocean. DNA dosimetry is a useful tool for estimating the potential for DNA damage in biological systems in the marine environment. Quartz cuvettes containing calf thymus DNA were incubated daily under ambient solar UV. A radioimmunoassay was used to measure direct DNA damage, such as cyclobutane pyrimidine dimers (CPD) and pyrimidine(6-4)pyrimidinone dimers ([6-4]PD), and indirect DNA damage, such as 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo). Irradiance measurements were taken daily along the latitudinal gradient. DNA damage in dosimeters was compared to solar UV measurements. CPD and (6-4)PD induction levels were closely correlated with ultraviolet-B radiation (UVB), whereas 8-oxodGuo levels were closely related to ultraviolet-A radiation (UVA). We found that CPD and (6-4)PD levels increased latitudinally with increasing irradiance. A correlation between increasing latitude and 8-oxodGuo was also observed in the dosimeters. The ratio of (6-4)PDs to CPDs decreased with increasing latitude.

Keywords: cyclobutane pyrimidine dimer, pyrimidine(6-4)pyrimidinone, 8-oxo-7,8-dihydro-2'-deoxyguanosine, latitudinal gradient

Reference #: VAS-1017-693974
Submit Date: 04/01/2002 13:54:56-0500

Responses of marine microbial communities to ultraviolet radiation in the North Water Polynya, High Arctic

ABSTRACT:
The annual thinning of the stratospheric ozone layer results in an increase of ultraviolet-B radiation (UVBR, 280-320 nm) reaching the surface of the Earth from polar to sub-polar latitudes. Consequently, the influence of enhanced UVBR on individual components of marine planktonic communities has increasingly drawn the attention of researchers. In this context, the present study aimed at assessing the potential short-term effects of UVBR on microbial communities (pico- and nanophytoplankton and heterotrophic bacteria) belonging to surface waters of the North Water (NOW), High Arctic. During fall 1999, small volume incubations of natural planktonic community were performed during 12/12 h day/night cycles at 11 stations from 18^th September to 1^st October 1999. During the photoperiod, the samples received constant artificial photosynthetically available radiation (PAR, 400-700 nm) with or without artificial gradient of ultraviolet radiation (UVR, 280-400 nm). Initial concentrations of pico- and nanophytoplankton were in the range 18-4067 and 272-3080 cells mL^-1, respectively. Bacteria initial concentrations varied from 146 to 680*10³ bacteria mL^-1. Dose-response curves showed a delayed cell-cycle and reduced chlorophyll a fluorescence for picophytoplankton, suggesting that picophytoplankton might be affected with increasing UVR cumulative doses. On the other hand, the response of nanophytoplankton cells was more variable with respect to increased UVR cumulative doses. This could be explained by the high species-diversity of this size-class. With respect to UVR levels, bacteria did not show any variation in abundance, cell size or DNA content. Results of the present study suggest that when assessing the effect of UVR on the microbial food, the temporal variations of the incident irradiance, and/or the composition of the microbial communities have to be taken into account.

Keywords: UV-B radiation, North Water, Arctic , Picophytoplankton

Reference #: FRA-1017-692828
Submit Date: 04/01/2002 13:52:23-0500

Biological weighting functions for the effect of UV radiation on carbon partitioning in microalgae.

ABSTRACT:
UV radiation clearly inhibits phytoplankton photosynthesis, with direct effects on both photosystem II and the enzyme, Rubisco, that catalyses the first reaction of the photosynthetic carbon reduction cycle. The subsequent partitioning of fixed carbon into macromolecular pools (carbohydrates, lipids, and proteins) is also affected by UV exposure, although relative changes in allocation are not well-documented and vary considerably. The wavelength specificity of inhibition of photosynthesis has been described by spectral weighting functions, or biological weighting functions (BWFs) that combine the effect of UV radiation with interactive effects of longer wavelengths. BWFs permit one to compare the effects of different radiation sources or various ozone depletion scenarios. In contrast to photosynthesis, no data are available from which BWFs for partitioning can be determined, as experimental techniques have varied widely. These BWFs are essential for predicting the effects of increased UV-B on other trophic levels, and for analyzing the cost and benefit of synthesizing protective compounds. Using a polychromatic approach, we are developing BWFs for the partitioning of ¹⁴C in Thalassiosira pseudonana (3H) at photosynthetically saturating irradiance. We are comparing these functions to BWFs calculated from simultaneous measurements of primary productivity. We have found consistent differences in sensitivity to UV exposure among the pools, and are testing these differences for significance using a variety of model and calculation approaches.

Keywords: biological weighting functions, carbon partitioning, photosynthesis, mycosporine-like amino acids

Reference #: STR-1017-687302
Submit Date: 04/01/2002 12:36:31-0500

Modeling Acute Exposure and Dose to Solar Radiation

ABSTRACT:
One of the major technical challenges in calculating solar flux on the human form has been the complexity of the surface geometry (i.e. the surface normal vis a vis the incident radiation). The American Cancer Society reports that over 80% of skin cancers occur on the face, head, neck, and back of the hands. The quantification, as well as the mapping of the anatomical distribution of solar radiation on the human form is essential if we are to study the etiology of skin cancers or cataracts or immune system suppression. Utilizing advances in computer graphics, including high-resolution 3-dimensional mathematical representations of the human form, the calculation of incident flux has been attained to sub-centimeter precision. Lighting detail included partitioning of direct beam and diffuse skylight, shadowing effects, and gradations of model surface illumination depending on model surface geometry and incident light angle. With the incorporation of ray tracing and radiosity algorithms, the results are not only realistic renderings, but also an accurate representation of the distribution of light on the model. The calculation of light illumination for various receptor points across the anatomy provides information about differential exposure [Watts per square meter] as a function of model posture, orientation relative to the sun, and sun elevation. Illustration of instantaneous exposure is achieved using a false color rendering - mapping light intensity to color - creating exposure isopleths. The integration of a geodesic sun-tracking model into the lighting module allowed specific sun exposure scenarios to be simulated, with instantaneous exposure, as well as the cumulative dose [ Joules per square meter] calculated for a given latitude, date, time of day, and duration. This approach may find application in the determination of the reduction in exposure that one achieves by wearing a hat, shirt, or sun glasses. More fundamentally, such an analysis tool could estimate the "dose" factor needed to develop dose-response functions for sunlight-induced disease.

Keywords: exposure modeling, sunlight exposure , sunlight dose, 3D graphic model

Reference #: FRI-1017-684002
Submit Date: 04/01/2002 11:39:53-0500

Determination of slow recovery of photosynthesis after UV exposure in open ocean Antarctic phytoplankton populations

ABSTRACT:
Ultraviolet radiation-induced (UV) damage and repair to Antarctic phytoplankton photosynthesis was examined during the austral spring in surface coastal waters near Palmer Station (PAL) and in the open ocean waters of the Weddell-Scotia Confluence (WSC) from 1997 to 1999. Predicted productivity was compared to rates measured in time course experiments using UV-transmitting and UV-opaque tanks under natural irradiance for exposure periods up to 12 hours. Predicted productivity was calculated from biological weighting functions (BWF) measured from seawater collected at the same time, combined with full band spectral irradiance (290-700 nm, at 1 nm resolution) at 1-minute intervals. Spectral irradiance was comprised of irradiances of 290-320 nm measured with the Smithsonian Institution SR-18 scanning UV-B radiometer, combined with UV-A and PAR irradiances from either the Palmer Station SUV-100 scanning radiometer or, for the WSC, the output of a radiative transfer model (System for Transfer of Atmospheric Radiation - STAR). BWFs were determined from 1-hour incubations and in the case of Palmer Station assemblages, included an irradiance-based model to incorporate the rapid recovery from UV damage. In contrast, BWFs for WSC assemblages supported a cumulative exposure model in which repair was excluded. However, the longer term time series experiments indicated that WSC phytoplankton are capable of slow rates of recovery and it is important to account for this when modeling the effects of UV exposure.

Keywords: UV inhibition of photosynthesis, Antarctic phytoplankton

Reference #: HEL-1017-494888
Submit Date: 03/30/2002 06:59:09-0500

Photorepair mechanisms and protective compounds in two zooplanktonic species, Daphnia menucoensis (Cladocera) and Metacyclops sp. (Copepoda), from freshwater bodies of Patagonia, Argentina

ABSTRACT:
Specimens of Daphnia menucoensis, Cladocera (from Laguna Cacique Chiquichano, 43 S) and Metacyclops sp., Copepoda (from Laguna Parque de la Ciudad, 43 S) were used in experiments designed to evaluate the effectiveness of a) photorepair mechanisms, and b) UV-absorbing compounds to cope with detrimental effects of UV-B (280-320 nm). In both species UV-B caused a significant dose-dependent mortality, with Metacyclops sp. being more resistant than D. menucoensis, having a maximum mortality of 30% and 100%, respectively after receiving a dose of 150 KJ m^-2. A significant decrease of mortality (i.e., higher survival) were observed in both species when exposed also to PAR (60 W m^-2), suggesting an active photorepair. Although this mechanism was more evident in D. menucoensis, the effectiveness of photorepair (i.e., increased survival divided by total death) was about the same for both species. Biological weighting functions (BWFs) also suggested the higher resistance to UV-B wavelengths of copepods as compared to cladocerans. This higher resistance seems to be related to the presence of mycosporine like aminoacids -MAAs- (i.e., shinorine and porphyra-334), and carotenoids, which would add an adaptive advantage to Metacyclops sp. This work was supported by Fundación Antorchas (project 13887-83) and Fundación Playa Unión.

Keywords: UVR, photorepair, zooplankton, Patagonia

Reference #: SAR-1017-328019
Submit Date: 03/28/2002 08:57:38-0500

St.Lawrence Estuary planktonic community exposed to enhanced ultraviolet radiation and dissolved hydrocarbons: a mesocosm approach

ABSTRACT:
The combined effects of the Water Soluble Fraction (WSF) of a crude oil and ultraviolet-B radiation (UVBR) on a natural planktonic community were examined as part of a large experimental program designed to study the effects of different UVBR intensities on the planktonic assemblage of the lower St. Lawrence Estuary. Nine 1800L mesocosms were attached to a wharf structure in a marina and filled with seawater pumped at 5m depth about 3 km off the coast of Rimouski. Water in mesocoms was used to fill 9L Teflon bags which were kept immerged into the mesocoms and subjected to two UVBR regimes: natural UVBR (NUVB), and enhanced UVBR (HUVB), which was expected to mimic 60% ozone depletion condition. The experiment with dissolved hydrocarbons was carried out over 5 days by adding a known among of water soluble petroleum hydrocarbons (WSF) obtained from crude oil to 9L bags in triplicate for both light conditions. Three bags were also kept without WSF as controls. Combined effects of both stresses (light conditions and dissolved hydrocarbons) were investigated by measuring a series of biological and chemical parameters. The composition of hydrocarbons extracted at the end of the experiment was clearly different with respect to UVB treatments as revealed by their synchronous fluorescence spectra. In NUVB + hydrocarbons bags, the chemical composition was preserved almost intact as the initial WSF used. In bags with high HUVB + hydrocarbons, fluorescence spectra showed a relative enrichment in smaller and fluorescent compounds which seems to indicate a drastic change in the chemical composition of WSF and the possible generation of new light aromatic polar compounds. Secondly, total abundance of cells < 20 um was 60%, 79% and 84% lower in HUVB controls, NUVB + hydrocarbons, and HUVB + hydrocarbons treatments, respectively, when compared to NUVBc treatment. Finally, mean cell size was higher under HUVB than under NUVB, and higher in HUVB + hydrocarbons bags than in HUVB controls which is indicating that cells were not dividing normally. Our results clearly demonstrate that the natural phytoplankton community of the St.Lawrence Estuary can be directly affected by WSF and UVBR in a synergic manner.

Keywords: Water Soluble Fraction of crude oil, ultraviolet-B radiation, Natural planktonic community, Mesocosm

Reference #: PEL-1017-262837
Submit Date: 03/27/2002 13:50:39-0500

Combined effects of UVB and dissolved hydrocarbons on marine microbial community

ABSTRACT:
In August 2001, a mesocosm experiment was designed to study the combined effects of light quality and dissolved hydrocarbons on natural assemblages of marine nanophytoplankton (2-20 micron) and bacteria. We tested the hypothesis that interactions of natural solar radiation, especially UVB radiation (280-320nm) and environmental contaminants like the water soluble fraction of hydrocarbons from crude oil (WSF) could induce additive or synergic harmful ecological effects on phytoplanktonic and bacterial communities. A time-series experiment was carried out for 7 days under 3 light conditions conducted on 3 land-based tanks of 1300 L each capacity: ambiant UVB radition (NUVB), enhanced UVB radiation by lamps (HUVB), and dark. Each tank contained 4 groups of 9L-Teflon bags (in triplicate) which were filled with similar unaltered and unfiltered seawater just collected from the estuary. Three groups (3 bags x 3) were contaminated by low-, medium, and high-oil treatment concentrations corresponding to concentrations of ~ 10, 20 and 50 mg.L-1 WSF, respectively. The forth group kept without WSF served as the uncontaminated control. Both light and WSF treatment effects were evaluated by measuring many biological and physico-chemical parameters during the course of the experiment. Some quantitative ratios of dissolved PAHs were calculated from chromatographic data to characterize the chemical weathering processes. Changes in nanophytoplankton and bacteria abundance, in term of light scattering propreties and cell fluorescence were investigated by flow cytometry. Bacterial densities were significantly higher in oiled mesocosms relative to controls, and specifically more important under dark conditions. Contrasting to bacteria, nanophytoplankton was more inhibited in all treatments and light conditions. Our results clearly indicate interactive effects of WSF of crude oil and UVB radiation which substantially increase the toxicity of dissolved oil for a part of plankton communities and demonstrate a need to consider such interactions in high latitude regions supporting marine traffic and possible oil spills.

Keywords: Phototoxicity, UVB radiation, dissolved hydrocarbons, marine microbial community

Reference #: TAI-1016-613276
Submit Date: 03/20/2002 02:17:03-0500

Mycosporine-like amino acids in the marine dinoflagellate Scrippsiella sweeneyae: induction by ultraviolet radiation

ABSTRACT:
The increased UV-B radiation (280-320 nm) reaching the Earth's surface due to the depletion of stratospheric ozone has raised the question of the effect of this enhanced radiation on marine ecosystems. UV-B radiation may impair the light-dependent responses of marine phytoplankton. UV-B has a high energy level per photon and is affectively absorbed by nucleic acids, proteins, and pigments. To counteract harmful UV effects aquatic plants have evolved UV-protective mechanisms such as the production of UV-absorbing sunscreen functions. One of the UV-absorbing compounds is known as mycosporine-like amino acids (MAAs). These compounds presumably are synthesized by marine algae and have absorption maxima ranging from 310 nm to 360 nm. In the present study we have investigated the spectral absorption characteristics of the marine dinoflagellate Scrippsiella sweeneyae exposed to four different spectral compositions and five relative intensities of UV-B to UV-A (320-340 nm) + photosynthetically available radiation (PAR: 400-700 nm). MAAs induced by UV radiation (UVR) were identified as shinorine, palythine, porphyra-334 and two unidentified MAAs, for which the maximum absorption was determined to be at 310 nm and 360 nm, respectively. Production of UVR induced MAAs was dependent on the dosage of UVR. Greater induction of MAAs was observed at shorter wavelengths. The composition of MAAs varied with increasing light intensity. UV-B radiation was observed to decrease growth rates and increase cell volumes. Induced MAAs was linearly correlated to cell volume. This result may suggest that the cells protect themselves from UVR by inducing MAAs production and enhancing cell volumes.

Keywords: Cell volume, Mycosporine-like amino acids, Scrippsiella sweeneyae, UV-absorbing compounds

Reference #: BOU-1016-575691
Submit Date: 03/19/2002 15:55:48-0500

Effects of UVB radiation on phytoplankton : the role of D1 protein.

ABSTRACT:
In the context of a study comparing tropical with temperate phytoplankton communities for their response to an increase in UV-B radiation, we examined the role of the D1 protein, essential for photosynthesis and dynamically regulated in a damage/repair cycle. Inactivating the repair (re-synthesis) of this protein through high light or UV photodamage (or using antibiotics such as lincomycin) leads to the inhibition of photosynthesis. To determine D1 repair activity, small UV-transparent bags were filled with natural seawater, and incubated at sea surface with or without the addition of lincomycin. Photoinhibition was followed using variable fluorescence (Fv/Fm, from a Walz Xe-PAM instrument) and actual degradation of the D1 protein was assessed from immunoblots. The bag incubations took place under two conditions: natural solar illumination (NUVB), and natural solar illumination augmented in UV-B (using UV-B lamps: HUVB). The natural seawater used to fill the bags came from two mesocosms (1800 L) exposed to these light conditions and followed through time (7-10 days). This was part of a bigger mesocosm experiment run at three different latitudes. Here results are compared between a tropical site located at Ubatuba, Brasil and a temperate site periodically exposed to the Antarctic ozone hole: Ushuaia, Argentina (but not under the ozone hole at the time of the experiment). Preliminary results show that the inhibition of D1 protein synthesis led to a dramatic decrease in Fv/Fm in both sites, reaching values generally lower than 0.25. Photoinhibition occurred more rapidly in Ubatuba than in Ushuaia. In Ubatuba near lethal values (0.25) were reached faster (~ 10 min) under the HUVB light treatment than under the NUVB light treatment (~ 20 min). In Ushuaia, however, low Fv/Fm values were reached in about the same time (~ 45 min) for both light treatments. These results suggest that the D1 repair cycle is very active in Ubatuba and accelerates under high UVB radiation while in Ushuaia, the cycle does not seem affected by the different light treatments. This study confirms the crucial role of D1 protein in the photosynthetic process of phytoplankton.

Keywords: D1 Protein, Ultraviolet radiation, Phytoplankton

Reference #: LAC-1017-354282
Submit Date: 03/28/2002 15:05:10-0500

Mesocosm experiments performed at three different latitudes to assess the effects of increased UV-B radiation on phytoplankton.

ABSTRACT:
Mesocosm experiments were performed in the coastal environments of Rimouski (Canada), Ubatuba (Brasil), and Ushuaia (Argentina) to examine the response of planktonic ecosystems from high and low latitudes to realistic future levels of UV-B radiation. In each experiment, nine transparent polyethylene bags were filled with filtered seawater and submitted to various light treatments. The ultraviolet radiation enhancement was provided by UV-B lamps suspended over the mesocosms. In Rimouski and Ushuaia, UV-B lamps were turned on from 10:00 to 15:00 and 11:00 to 16:00 respectively, while in Ubatuba, they were adjusted using a computer-controlled feedback system that allowed UV-B enhancement to vary throughout the day as is naturally observed in the environment. Water samples were collected daily every morning to evaluate the biological and chemical state of the mesocosms including nutrients, phytoplankton abundance and biomass, and physico-chemical variables such as temperature, pH, salinity, oxygen, and alkalinity. The duration of the experiments varied between 7 to 10 days. Phytoplankton blooms occurred during the Rimouski and Ushuaia experiments; but in Ubatuba, algal biomass decreased gradually from day one onwards. Replicability of mesocosms of a same experiment can be compromised by the technique used to fill them up. Not being able to collect the water mass that was used to fill up all the mesocosms in a single trip as well as the dynamics of the environment where water was collected are factors that could explain why certain differences were observed. Nonetheless, replicability was generally good in the three experiments of this project. The mesocosm design used in this series of outdoor experiments provided conditions that mimicked relatively well the natural environment. Furthermore, the computer-controlled UV-B lamp enhancement system, although still being adjusted, appears to be promising for future research.

Keywords: Mesocosm, Phytoplankton, UV-B