Temporal variations in phytoplankton, particulates, and colored dissolved organic material based on optical properties during a Long Island brown tide compared to an adjacent embayment

Since 1985, the coastal embayments of Long Island, New York, have been plagued with recurrent blooms, aptly called brown tides, of the pelagophyte Aureococcus anophagefferens. The distinct ocean color observed during these blooms suggests that optical methods can be used as a tool to study, detect, and track brown tides. Thus, the goal of our project was to compare the optical properties and pigment composition during bloom and non-bloom conditions and assess temporal variations in the phytoplankton and other constituents in the seawater associated with bloom development. From 17 May to 8 June 2000, we measured a time series of particle size distributions and concentrations as well as size-fractioned algal pigments and optical properties in two Long Island embayments where brown tides are known to occur. During our study, A. anophagefferens represented an insignificant contribution to the algal community in West Neck Bay (WNB), whereas a bloom developed in Quantuck Bay (QB). Initially, temperature and salinity were similar at the two locations; however, bulk optical properties, chlorophyll, and particle concentrations were nearly a factor of 2 greater at QB. Bulk optical properties remained constant at WNB, yet increased exponentially at QB as the bloom developed. The composition of particulates, including phytoplankton, varied little at QB, and the optical properties suggested the dominance of A. anophagefferens (confirmed by microscopy). The largest temporal variations were observed in the colored dissolved organic material (CDOM); the colloidal (0.2–0.7 μm) fraction, exhibiting a strong protein-like signal, increased dramatically at the height of the bloom. At WNB particle sizes and algal composition varied despite the invariant bulk optical properties; CDOM variations were minimal. Overall, the optical properties in the two bays demonstrated that at QB temporal variations were dominated by biomass and colloidal protein changes, whereas shifts in the algal community occurred at WNB. This study demonstrates the utility of in situ optical observations to resolve temporal changes in the ecological conditions associated with algal bloom development.     

Prasinoviruses of the marine green alga Ostreococcus tauri are mainly species specific

Prasinoviruses infecting unicellular green algae in the order Mamiellales (class Mamiellophyceae) are commonly found in coastal marine waters where their host species frequently abound. We tested 40 Ostreococcus tauri viruses on 13 independently isolated wild-type O. tauri strains, 4 wild-type O. lucimarinus strains, 1 Ostreococcus sp. ("Ostreococcus mediterraneus") clade D strain, and 1 representative species of each of two other related species of Mamiellales, Bathycoccus prasinos and Micromonas pusilla. Thirty-four out of 40 viruses infected only O. tauri, 5 could infect one other species of the Ostreococcus genus, and 1 infected two other Ostreococcus spp., but none of them infected the other genera. We observed that the overall susceptibility pattern of Ostreococcus strains to viruses was related to the size of two host chromosomes known to show intraspecific size variations, that genetically related viruses tended to infect the same host strains, and that viruses carrying inteins were strictly strain specific. Comparison of two complete O. tauri virus proteomes revealed at least three predicted proteins to be candidate viral specificity determinants.     

Genome-wide metabolic network reconstruction of the picoalga Ostreococcus

The green picoalga Ostreococcus is emerging as a simple plant model organism, and two species, O. lucimarinus and O. tauri, have now been sequenced and annotated manually. To evaluate the completeness of the metabolic annotation of both species, metabolic networks of O. lucimarinus and O. tauri were reconstructed from the KEGG database, thermodynamically constrained, elementally balanced, and functionally evaluated. The draft networks contained extensive gaps and, in the case of O. tauri, no biomass components could be produced due to an incomplete Calvin cycle. To find and remove gaps from the networks, an extensive reference biochemical reaction database was assembled using a stepwise approach that minimized the inclusion of microbial reactions. Gaps were then removed from both Ostreococcus networks using two existing gap-filling methodologies. In the first method, a bottom-up approach, a minimal list of reactions was added to each model to enable the production of all metabolites included in our biomass equation. In the second method, a top-down approach, all reactions in the reference database were added to the target networks and subsequently trimmed away based on the sequence alignment scores of identified orthologues. Because current gap-filling methods do not produce unique solutions, a quality metric that includes a weighting for phylogenetic distance and sequence similarity was developed to distinguish between gap-filling results automatically. The draft O. lucimarinus and O. tauri networks required the addition of 56 and 70 reactions, respectively, in order to produce the same biomass precursor metabolites that were produced by our plant reference database.     

A phosphate-regulated promoter for fine-tuned and reversible overexpression in Ostreococcus: application to circadian clock functional analysis

BACKGROUND: The green picoalga Ostreococcus tauri (Prasinophyceae), which has been described as the smallest free-living eukaryotic organism, has minimal cellular ultra-structure and a very small genome. In recent years, O. tauri has emerged as a novel model organism for systems biology approaches that combine functional genomics and mathematical modeling, with a strong emphasis on light regulated processes and circadian clock. These approaches were made possible through the implementation of a minimal molecular toolbox for gene functional analysis including overexpression and knockdown strategies. We have previously shown that the promoter of the High Affinity Phosphate Transporter (HAPT) gene drives the expression of a luciferase reporter at high and constitutive levels under constant light. METHODOLOGY/PRINCIPAL FINDINGS: Here we report, using a luciferase reporter construct, that the HAPT promoter can be finely and reversibly tuned by modulating the level and nature of phosphate in culture medium. This HAPT regulation was additionally used to analyze the circadian clock gene Time of Cab expression 1 (TOC1). The phenotype of a TOC1ox/CCA1:Luc line was reverted from arrhythmic to rhythmic simply by adding phosphate to the culture medium. Furthermore, since the time of phosphate injection had no effect on the phase of CCA1:Luc expression, this study suggests further that TOC1 is a central clock gene in Ostreococcus. CONCLUSIONS/PERSPECTIVES: We have developed a phosphate-regulated expression system that allows fine gene function analysis in Ostreococcus. Recently, there has been a growing interest in microalgae as cell factories. This non-toxic phosphate-regulated system may prove useful in tuning protein expression levels quantitatively and temporally for biotechnological applications.     

A Description of Occurrence and Morphology of a New Species of Red-Water Forming Strombidium (Spirotrichea, Oligotrichia)

We describe a red-water ciliate, Strombidium lingulum n. sp., collected from a marine fjord in British Columbia (BC), Canada. In August, 1995, red-brown streaks were observed in the waters of Kyuquot Sound. BC. These streaks were composed of a ciliate population with an abundance in the surface of ˜ 1.5 × 10³ cells ml^-1. Density was reduced to < 50 cells ml^-1 below the surface. The bloom persisted for only a few hours; cells were observed for 3-4 days and were only occasionally observed in the weeks after the bloom. The red waters were speculated to be formed by a combination of downwelling events and an observed phototactic migration of the ciliate. As the ciliate was positively phototactic and pigmented, it may be mixotrophic; it was certainly heteroirophic, as it contained dinoflagellates and small ciliates in food vacuoles. Ciliates were preserved in Lugol's iodine and then both protargol stained and prepared for scanning electron microscopy.     

Irish kefir-like grains: their structure, microbial composition and fermentation kinetics

The structure of six Irish kefir samples was studied in the electron microscope, and the microbial composition and fermentation kinetics during growth in 10% reconstituted skim milk at 21°C. The microbial composition of the six samples was similar; at the end of the fermentation the counts of lactococci, leuconostocs, lactobacilli, acetic acid bacteria and yeasts were 10⁹, 10⁸, 5 × 10⁶, 10⁵ and 10⁶ ml⁻¹ respectively; the levels of acetic acid bacteria and lactobacilli showed some intersample differences. Lactate was the major metabolite followed in order by ethanol, acetate and acetoin. The final concentrations of L-lactate produced (66–90 mmol kg⁻¹) were 10-fold higher than those of D-lactate. Acetate and ethanol concentrations varied from 4 to 14 and 2 to 40 mmol kg^−'1 respectively. The rates of citrate utilization and concentration of acetoin produced during growth differed between samples. Scanning electron microscopy showed not only variation between the interior and exterior of the sample but also large variation between different sections of the interiors and exteriors of the same sample. Long and short, and straight and curved rods and yeasts were seen in all samples, the curved rods observed in the interior, but lactococci were seen on the surface of only one sample. There were no gross differences in structure between samples.     

PHYLOGENETIC ANALYSIS AND GENOME SIZE OF OSTREOCOCCUS TAURI (CHLOROPHYTA, PRASINOPHYCEAE)

Ostreococcus tauri Courties et Chrétiennot-Dinet is the smallest described autotrophic eukaryote dominating the phytoplanktonic assemblage of the marine Mediterranean Thau lagoon (France). Its taxonomic position was partly elucidated from ultrastructure and high-pressure liquid chromatography (HLPC) pigment analysis. The sequence analysis of the 18S rDNA gene of O. tauri measured here is available in EMBL Nucleotide Sequence Database (accession number: Y15814) and allowed to clarify its phylogenetic position. O. tauri belongs to the Prasinophyceae and appears very close to Mantoniella, a typical scaly Prasinophyceae, morphologically very different from the naked and coccoid Ostreococcus. An electrophoretic analysis of O. tauri shows that the nucleus contains 10.20 mbp. This small genome, fragmented into 14 chromosomes ranging in size from 300 to 1500 kbp, confirms the minimalist characteristics of Ostreococcus tauri.     

Food intake and growth in the blue-spotted trevally, Caranx bucculentus Alleyne and Macleay 1877, with reference to predation on penaeid prawns

Blue-spotted trevally, Caranx bucculentus , were fed different rations of pilchard and prawn in order to investigate feeding and growth relationships. Maintenance rations at 25.5° C amounted to 3.7% B.W. day⁻¹ and 2.7% B.W. day⁻¹ for prawns and pilchards, respectively. Additional feeding experiments at 28.9° C yielded a maintenance ration of prawns of 3.8% B.W. day⁻¹, suggesting there is very little if any temperature effect on the feeding-growth relationship over the range studied. Fish fed twice or more each day consumed about 7.3 ± 1.4% B.W. day⁻¹.
Given the biomass of this trevally in Albatross Bay, Gulf of Carpentaria, and the contribution of prawns to its diet, we estimate consumption of commercial prawns at 25 ± 5 g.ha⁻¹ day⁻¹ or 11 g kg⁻¹ day⁻¹.     

Size-dependent mortality of red sea bream, Pagrus major, juveniles released with fluorescent otolith-tags in News Bay, Japan

Totals of 2^.67 x 10⁵ and 7^.56 x 10⁵ juvenile red sea bream of three size groups (10, 20 and 40 mm t.l.) marked with a fluorescent substance in the otolith were released in News Bay, Oita Prefecture, Japan, in July 1987 and June 1988, respectively; the aim was to estimate growth and mortality of different developmental stages.
Of fish released in 1987 and 1988, 10 618 and 4413, respectively were recaptured during those two years. Released fish remained in the bay until the end of summer, and afterwards migrated out towards open waters. Fish of the 40-mm group released in 1987 grew to over 200 mm t.l. in one year. Mean growth rate for 19 days after release was higher in the 40-mm group (0^.87 mm day⁻¹) than in the 20-mm group (0^.74mm day⁻¹). Survival rates over 19 days were 59^.0 and 10^.1 % for 40-mm and 20-mm fish, respectively, in 1987, and those over 30 days were 69^.2, 3^.3 and 0^.0% for 40-mm, 20-mm and 10-mm fish, respectively, in 1988.
Cannibalism was indicated by the presence of marked otoliths for 20-mm fish in the stomachs of a few 40-mm individuals recaptured 2 days after release. Size-dependent growth and size-selective mortality were both noted in juvenile red sea bream, i.e. the relative size differential between larger and smaller individuals was maintained in the period between marking and recapture, and mortality was inversely proportional to size.     

The effect of a calcium-channel antagonist, nifedipine and agonist, Bay K-8644, on the phytochrome-controlled swelling of etiolated wheat protoplasts

The effect of external Ca²⁺ and Ca²⁺-channel modulators on the phytochrome-controlled swelling of etiolated wheat ( Triticum aestivum L. cv. Arminda) mesophyll protoplasts has been studied. The red light (R)-stimulated swelling of the protoplasts requires Ca²⁺ in the surrounding medium and maximum response was observed in a medium containing I m M CaCI₂. Far-red light (FR) irradiation of protoplasts in the presence or absence of Ca²⁺ does not influence the protoplast volume. The Ca²⁺-channel antagonist nifedipine prevents R-induced protoplast swelling at very low concentrations (0.1 μ M ). The Ca²⁺ -channel agonist Bay K-8644 stimulates the swelling of protoplasts incubated in darkness or irradiated with FR. Action of nifedipine depends on whether it is applied before or after the R pulse. The results are compatible with the hypothesis that phytochrome controls the activity of dihydropyridine-sensitive L-type Ca²⁺ channels.     

The fauna of the muddy sediments of Lough Neagh, with particular reference to eutrophication

SUMMARY. The main groups of animals found in the muddy sediments of Lough Neagh were Chironomidae (Diptera) and Oligochaeta (mainly Tubificidae). At 8 m depth, the average biomass of the main species in these groups was: Chironomus anthracinus , 2.64gm⁻²; Procladius , 342.8 mgm⁻²; tubificids ( Tubifex, Potamothrix, Aulodrilus, Limnodrilus ), 418.7mgm⁻². At 25m depth C. anthracinus and Procladius were less abundant, C. plumosus was present and among the tubificids Limnodrilus had a higher density (up to 50000m⁻²) often an order of magnitude greater than at 8m. Kinnego Bay, a semi-enclosed, polluted area of the lough, had fewer chironomids than the open lough, with chiefly C. plumosus and Procladius. Limnodrilus was more abundant than at 8m. Dero obtusa (Naididae) was also present, sometimes in large numbers (31000m⁻²).
The response of this fauna to eutrophication in L. Neagh appears to be a diminution in the number of species present, with C. plumosus gradually replacing C. anthracinus as the dominant Chironomus , and tubificids, particularly Limnodrilus , becoming more abundant, A further stage, shown in Kinnego Bay, has Procladius as the most numerous' chironomid. Average total biomass at the three sites was 3.9gm⁻² at 8m, 13.2gm⁻² at 25 m in the main lake, 2.8gm⁻² in Kinnego Bay. At 8m depth, C. anthracinus contributed 76% of the total biomass, at 25m Limnodrilus contributed 74% and C. anthracinus 15%, and in Kinnego Bay, Limnodrilus contributed 40%, C. plumosus 28% and Procladius 20%.     

HARBOR PORPOISE (PHOCOENA PHOCOENA) ABUNDANCE IN ALASKA: BRISTOL BAY TO SOUTHEAST ALASKA, 1991-1993

Between 1991 and 1993, Alaska harbor porpoise ( Phocoena phocoena ) abundance was investigated during aerial surveys throughout much of the coastal and offshore waters from Bristol Bay in the eastern Bering Sea to Dixon Entrance in Southeast Alaska. Line-transect methodology was used, and only those observations made during optimal conditions were analyzed. Survey data indicated densities of 4.48 groups/100 km², or approximately 3,531 harbor porpoises (95% C. I. 2,206-5,651) in Bristol Bay and 0.54 groups/100 km², or 136 harbor porpoises (95% C. I. 11-1,645) for Cook Inlet. Efforts off Kodiak Island resulted in densities of 1.85 groups/100 km², or an abundance estimate of 740 (95% C. I. 259-2,115). Surveys off the south side of the Alaska Peninsula found densities of 2.03 groups/100 km² and an abundance estimate of 551 (95% C. I. 423-719). Surveys of offshore waters from Prince William Sound to Dixon Entrance yielded densities of 4.02 groups/100 km² and an abundance estimate of 3,982 (95% C. I. 2,567-6,177). Combining all years and areas yielded an uncorrected density estimate of 3.82 porpoises per 100 km², resulting in an abundance estimate of 8,940 porpoises (CV = 13.8%) with a 95% confidence interval of 6,746-11,848. Using correction factors from other studies to adjust for animals missed by observers, the total number of Alaska harbor porpoises is probably three times this number.     

Differential Inhibition of Secretagogue-Stimulated Sodium Uptake in Adrenal Chromaffin Cells by Activation of D4 and D5 Dopamine Receptors

Abstract: Recent studies have demonstrated that D1-selective and D2-selective dopamine receptor agonists inhibit catecholamine secretion and Ca²⁺ uptake into bovine adrenal chromaffin cells by receptor subtypes that we have identified by PCR as D5, a member of the D1-like dopamine receptor subfamily, and D4, a member of the D2-like dopamine receptor subfamily. The purpose of this study was to determine whether activation of D5 or D4 receptors inhibits influx of Na⁺, which could explain inhibition of secretion and Ca²⁺ uptake by dopamine agonists. D1-selective agonists preferentially inhibited both dimethylphenylpiperazinium- (DMPP) and veratridine-stimulated ²²Na⁺ influx into chromaffin cells. The D1-selective agonists chloro-APB hydrobromide (CI-APB; 100 µ M ) and SKF-38393 (100 µ M ) inhibited DMPP-stimulated Na⁺ uptake by 87.5 ± 2.3 and 59.7 ± 4.5%, respectively, whereas the D2-selective agonist bromocriptine (100 µ M ) inhibited Na⁺ uptake by only 22.9 ± 5.0%. Veratridine-stimulated Na⁺ uptake was inhibited 95.1 ± 3.2 and 25.7 ± 4.7% by 100 µ M CI-APB or bromocriptine, respectively. The effect of CI-APB was concentration dependent. A similar IC₅₀ (∼18 µ M ) for inhibition of both DMPP- and veratridine-stimulated Na⁺ uptake was obtained. The addition of 8-bromo-cyclic AMP (1 m M ) had no effect on either DMPP- or veratridine-stimulated Na⁺ uptake. These observations suggest that D1-selective agonists are inhibiting secretagogue-stimulated Na⁺ uptake in a cyclic AMP-independent manner.     

CHARACTERIZATION OF A LYTIC VIRUS INFECTIOUS TO THE BLOOM-FORMING MICROALGA AUREOCOCCUS ANOPHAGEFFERENS (PELAGOPHYCEAE)

Aureococcus anophagefferens Hargraves and Sieburth has caused recurring monospecific blooms in Long Island embayments since it was first described in 1985. It was termed the "brown tide," due to the resulting water color, and has had a devastating effect on Long Island's (New York) marine ecosystem. In 1992, a virus that was capable of causing lysis of A. anophagefferens was isolated and maintained in culture. We report on the further characterization of this virus, Aureococcus anophagefferens virus-1 (AaV-1), indicated by a buoyant density of 1.2776 g·mL⁻¹ in a CsCl equilibrium gradient. Electron microscopy revealed a phage with a hexagonal head and tail similar to previously described phages. By using adenovirus for calibration, the virus was found to have a head 50—55 nm wide and a tail 70–75 nm long. The viral band was infectious to A. anophagefferens after dialysis. The virus was composed of at least 16 distinct polypeptides ranging in molecular weight from 20 to 230 kDa. The adsorption coefficient for the virus was 7.2 × 10⁻⁹ mL·min⁻¹, and the burst size was calculated to be 9.4 viruses per A. anophagefferens cell at 20° C. Complete lysis of A. anophagefferens occurred with a titer as low as 893 viruses·mL⁻¹, and the lower limit of infectivity was 93 viruses·mL⁻¹. The virus lost its infectivity between 30° and 40° C. These results suggest that AaV-1 is highly infectious and that the role of the virus in preventing or ending A. anophagefferens blooms needs further investigation.     

Activity of methanotrophic bacteria in Green Bay sediments

Abstract Sediment pore water samples obtained from a 19 m station in Green Bay in Lake Michigan were examined for levels of ambient dissolved methane and copper, and for the potential for in situ methane oxidation by methanotrophs found within surface sediments. The in situ methane concentration in the upper oxic sediment layer ranged from 20–150 μmol · 1⁻¹ at this station. The activity of methanotrophs and the kinetics of methane oxidation in these sediments were demonstrated by the uptake of radiolabeled methane. K_s values varied between 4.1–9.6 nmol · cm³ of sediment slurry. High V_max values (12.7–35.2 nmol · cm⁻³ · h⁻¹) suggest a large population of methanotrophs in the sediments. An average methane flux to the oxic sediments of 0.24 mol · m⁻² · year⁻¹ was calculated from the pore water methane gradients. Pore water concentrations of copper in the upper sediment layer ranged from 10–120 nmol · 1⁻¹. Based upon the copper concentration, other measured parameters, and equilibrium conditions defined by WATEQF4, an estimate for dissolved free Cu²⁺ concentration of 5–38 nmol · 1⁻¹ pore water was obtained. Several factors control the rate of methane oxidation, including oxygen, methane, and the bioavailability of free Cu²⁺.     

Phytoplankton ecology in an Antarctic lake

SUMMARY. The ecology of the phytoplankton of Heywood Lake, Signy Island, South Orkney Islands, Antarctica was investigated during 1969–72. The lake, which is ice-covered for 8–10 months per year, is moderately eutrophic due to enrichment by seal excreta.
The annual cycle of the phytoplankton is described. During the winter (approximately May-September), very few algal cells could be detected in the water column and ¹⁴C fixation was below measurable limits. In spring (October-November), a rapidly-growing population of algae caused a large increase in the chlorophyll- a concentration (maximum value 170 mg m⁻²) but carbon fixation remained low, with values <500 mg C m⁻² day⁻¹. The algae contributing to this peak were mainly small chlorophytes and chrysophytes. The summer open-water period (December-March) was characterized by a different phytoplankton population dominated by cryptophytes. Chlorophyll levels were lower ( c . 40 mg m⁻²) but ¹⁴C fixation rates >3 g C m⁻² day⁻¹ were measured on bright days. Values for Assimilation Number were very high (maximum value 10.5 mg C h⁻¹ mg⁻¹ (chlorophyll- a ) in January (1971) though temperatures never exceeded 8°C. In autumn, the phytoplankton regressed to winter levels. Both spring and summer algal populations probably overwinter as resting stages.     

Volume changes of Commelina communis guard cell protoplasts in response to K+, light and CO2

The effects of K⁺ concentration, light intensity and CO₂ levels on the volume of Commelina communis L. guard cell protoplasts were studied. Two degrees of swelling response were observed, both dependent on an external supply of K⁺, but not necessarily on the supply of a permeant anion. The presence of K⁺ itself, independent of light or CO₂ level, stimulated swelling at a relatively slow rate. When K⁺, light and low CO₂ conditions were supplied together, the swelling was relatively rapid and of high magnitude. The rapid swelling was specific for K⁺ and Rb⁺ giving a half maximal effect after 2 h at a KCl concentration of about 18 mmol m⁻³. The addition of CaCl₂ at 1 mol m⁻³ inhibited K⁺-dependent swelling under all conditions tested. The response to light and low CO₂ levels by Commelina guard cell protoplasts is thought to reflect a high degree of physiological integrity.     

Winter growth of juvenile plaice on the Port Erin Bay (Isle of Man) nursery ground

Juvenile plaice ( Pleuronectes platessa ) were studied in Port Erin Bay, Isle of Man, U.K. between September and March 1989/1990 and 1990/1991. Plaice (>90 mm) were tagged and individual growth rates calculated for the autumn, winter and over-winter time periods. During the study the population of fish >90 mm remained fairly stable both within a study season and between years. Autumn growth rates ranged from 0 to 0.39 mm day⁻¹ (mean₁₉₈₉=0.13 mm day⁻¹, mean₁₉₉₀=0.10 mm day ⁻¹) and winter 0 to 0.5 mm day⁻¹ (mean₁₉₉₀=0.11 mm day⁻¹ and mean₁₉₉₁=0.17 mm day ⁻¹). In general, growth rates were higher at higher mean seasonal temperatures. However, relative growth rate was significantly higher in the colder winter period of 1991 than 1990.     

DEPTH DISTRIBUTIONS OF DNA DAMAGE IN ANTARCTIC MARINE PHYTO- AND BACTERIOPLANKTON EXPOSED TO SUMMERTIME UV RADIATION

During a survey from January to March 1998, the occurrence of UV-B radiation (UVBR)- induced DNA damage in Antarctic marine phytoplankton and bacterioplankton was investigated. Sampling was done in Ryder Bay, off the British base Rothera Station, 67°S, 68°W (British Antarctic Survey). Samples were taken regularly during the survey period at fixed depths, after which DNA damage was measured in various plankton size fractions (>10, 2–10, and 0.2–2 μm). Incident solar radiation was measured using spectroradiometry, whereas attenuation of biologically effective UVBR was studied using a DNA dosimeter. A diatom bloom was found in the bay during the research period, judging from microscopic observations and HPLC analyses of taxon-specific pigments. The high phytoplankton biomass likely caused strong attenuation of DNA effective UVBR (K_bd-eff). K_bd-eff values ranged from 0.83·m ^{− 1} at the peak of the bloom to 0.47·m ^{− 1} at the end of the season. UVBR-mediated DNA damage, as measured by cyclobutane pyrimidine dimer (CPD) abundance, was detected in all plankton size fractions. Highest levels were found in the smallest size fraction, mainly consisting of heterotrophic bacteria. Clear CPD depth profiles were found during mid-summer (January, beginning of February) with surface levels exceeding 100 CPDs per million nucleotides in the bacterioplankton fraction. At that time, melting of the continuously present shelf ice caused strong salinity gradients in the upper meters, thereby stimulating water column stabilization. At the end of February and beginning of March, this phenomenon was less pronounced or absent. At that time, DNA damage was homogeneously distributed over the first 10 m, ranging between 20 and 30 CPDs per million nucleotides for the smallest size fraction.