Studies on the phytoplankton ecology of the trondheemsfjord. II. Chloroplast pigments in relation to abundance and physiological state of the phytoplankton

The quantitative composition of the chloroplast pigments of phytoplankton sampled weekly at one station in the Trondheimsfjord was studied by circular paper chromatography throughout 18 months. The concentrations of total chlorophyll a (T-chl a obtained by the trichromatic method) as well as of chromatographically purified chlorophyll a (chl a) followed the variations in phytoplankton concentration. Two spring blooms and a weak autumn flowering of phytoplankton were clearly reflected in the pigment contents found, namely 14–16 mg T-chl a/m³ for the spring maxima, corresponding to nearly 300 mg T-chl a/m² for the euphotic zone; and 3–4 mg/m³ or 32 mg/m² for the autumn peak. The concentrations between blooms amounted to ≈ 1 mg T-chl a/m³, while concentrations down to 0.03 mg/m³ were found for winter samples.The content of T-chl a was high in diatom cells prior to a bloom (20–40 × 10^?9 mg/cell). During rapid growth (a more or less exponential phase) the cell content of chloroplast pigments decreased (to 5–10 × 10^?9 mg). No degradation product of chlorophylls could be detected during this phase and the percentage of chl a (of T-chl a) was high (70–80 %). At the peak of the bloom, and especially when the nitrate content in the surrounding water had been exhausted, low values for T-chl a were found ($\text{0.3–0.5 × 10}{}^{\mathrm{<mtext>9</mtext><mtext>?</mtext>}}\text{mg/cell}$). As soon as the cell counts started to fall, or even before the decline could be clearly detected, the percentage of chl a dropped (to 40-20 %) and derived chlorophylls (not phaeophytin a) were present in the samples. Model studies with cultured algae showed a similar behaviour.It is concluded that the proportion of chl a to T-chl a and the occurrence of chlorophyll derivatives in phytoplankton samples can give valuable information on the stage of development of the algal populations involved.     

Cd transfer in the deposit-feeder Prosobranch Hydrobia ulvae (Pennant) from benthic diatoms: the kinetics of rapid Cd assimilation and efflux

The kinetics of Cd trophic transfer from benthic diatoms to the Prosobranch mud snail Hydrobia ulvae was described experimentally in microcosms using Cd contaminated microalgae (0.71, 3.63 and 8.54 μg Cd mg Chl a⁻¹). The depurated mud snails (2 ind. cm⁻²) were allowed to feed on the stable Cd pre-contaminated benthic diatoms at the concentration of 2 mg Chl a dm⁻³ to ensure that the algal food availability was not a limiting factor. Weight-specific ingestion rate (IR) and assimilation efficiency (AE) were calculated by an indirect mass-balance method on the basis of metal residues in the snail tissues, and metal loss (efflux rate, Δe) was estimated for the time intervals when a decrease or no change in the tissue metal concentrations occurred.A similar pattern of consumption was observed in all experiments: ingestion was rapid over the first 4 h, followed by slower ingestion period (between 4 and 16 h). The feeding behaviour of H. ulvae was not affected by the different diatom Cd concentrations. An analogous two-phasic pattern was observed in the tissue Cd concentration changes. Net accumulation of Cd in the snails was observed for the two highest exposures, indicating that the Cd threshold concentration in food above which metal is retained in the body, lies between 0.71 and 3.63 μg Cd mg Chl a⁻¹. The respective 16-h AEs were 0.024% and 0.004% potentially due to rapid gut-passage of microalgae and/or diminished nutritional value of the food. The efflux rates, calculated for the last 12 h of exposure, were positively related to the concentration of Cd in the snail tissues and microalgae. This study demonstrated that trophic transfer should be considered as a source of Cd accumulation in snails and the ability of H. ulvae to enhance their rate of Cd elimination in response to elevated metal concentrations in the ambient environment is relevant for models predicting metal bioaccumulation and toxicity in coastal and estuarine systems.     

Proteolysis of chloroplast thylakoid membranes. I. Selective degradation of thylakoid pigment-protein complexes at the outer membrane surface

Isolated pea thylakoids were experimentally unstacked in low-salt buffer and incubated with Pronase or trypsin. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that brief treatment with a very low concentration (1 μg/ml) of either enzyme had an effect primarily on the light-harvesting chlorophyll $\text{a}\text{b}$-protein complexes, which are more sensitive to proteolytic attack than the other proteins of the thylakoid membranes. This mild proteolysis cleaves a ~1000-dalton portion from the predominant 28,000-dalton polypeptide of these complexes. Extensive proteolysis (100 μg Pronase/ml for 15 min) degraded almost all membrane polypeptides not associated with the pigment-protein complexes and degraded the chlorophyll $\text{a}\text{b}$-protein complexes further than milder proteolysis. Pronase treatment of thylakoids in the presence of horseradish peroxidase was used to monitor membrane breakage during proteolysis. Treatment with 100 μg Pronase/ ml enabled considerable amounts of peroxidase activity, and presumably, proteolytic enzymes to enter into the intrathylakoid space. This trapping of peroxidase activity was seen only minimally with milder proteolysis (1 μg Pronase/ml). These results suggest that brief exposure to low concentrations of proteolytic enzymes affects only the outer, stromal thylakoid surface, while at higher concentrations, significant proteolysis takes place at both sides of the membrane.     

The mechanism of anion inhibition of pork heart aspartate aminotransferase

The mechanism of anion inhibition of the reaction of the pork heart extramitochondrial aspartate aminotransferase (EC 2.6.1.1) with erythro-β-hydroxy-l-aspartate was investigated. This reaction produces a mixture of complexes, one of which is characterized by an absorption maximum at 492 nm. Spectrophotometric analysis of equilibrium mixtures of aspartate aminotransferase and erythro-β-hydroxy-l-aspartate, in different buffers, indicated that acetate, chloride, and cacodylate were competitive inhibitors of hydroxyaspartate binding. Pyrophosphate, however, was not a competitive inhibitor. Between pH 4.5 and 9.0 the affinity of the enzyme for the monovalent anions decreased as the pH increased. The data indicated that the anion binding group had a pK_a in the range from pH 6 to 7, depending upon the anion studied. From pH 4.5 to 9.0, the substrate dissociation constant and the distribution of enzyme-substrate complexes were both unaffected by pH. By stopped-flow spectrophotometry, an initial rapid relaxation ($\text{t}\text{1}\text{2}\text{= 2–8}\text{ms}$) was associated with an increase in absorbance at 492 nm, and this rate depended upon both substrate and buffer concentrations. A slower relaxation ($\text{t}\text{1}\text{2}\text{= 180}\text{ms}$) was associated with a decrease in the absorbance at 492 nm to approximately 70% of the value attained in the first rapid reaction. The rate of this slower reaction was largely independent of substrate and buffer concentrations. Kinetic analysis of the rates of the first relaxation in several different concentrations of Tris-acetate buffer of pH 8 showed that the rate of association decreased with increasing acetate concentration whereas the reaction rate for dissociation was unaffected. Thus, acetate appears to exert its inhibitory effect by preventing the formation of the enzyme-substrate complex rather than by displacing the substrate from the enzyme.     

Photosynthetic electron transport,ATP synthesis and nitrogenase activity in isolated heterocysts of Anabaena cylindrica

Isolated heterocysts of the N₂-fixing blue-green alga Anabaena cylindrica contain the Photosystem I components P-700, bound and soluble ferredoxins and ferredoxin-NADP reductase. They also show Photosystem I activity being able to photoreduce both methylviologen and NADP when ascorbate+dichlorophenol-indophenol acts as reductant. They photophosphorylate (64 μmol ATP produced/mg chlorophyll $\text{a}\text{h}$) and carry out oxidative phosphorylation (8.7 μmol ATP produced/mg chlorophyll $\text{a}\text{h}$). Ninety per cent of the total cell-free extract nitrogenase activity is located in the heterocyst fraction of aerobic cultures.     

Presence of peptide hormones that control gonadotropin secretion in extrahypothalamic areas of the brain.

The hypocholesterolemic drug clofibrate (ethyl-α-$\text{p}$-chlorophenoxyisobutyrate) was found to strongly suppress 3-hydroxy-3-methylglutaryl coenzyme A reductase (EC 1.1.1.34) activity in cultured mouse L cells at concentrations of 20 – 50 μg/ml. The half-life ($\text{t1}\text{2}$) of the reductase (approximately 120 min) was strongly reduced when L cells were incubated with cycloheximide plus a maximal inhibitory concentration of clofibrate (50 μg/ml), resulting in a $\text{t1}\text{2}$ value of 10 min. Preliminary kinetic analysis of the inhibition suggested that clofibrate increased the rate of inactivation (or degradation) of the reductase without affecting the rate of enzyme synthesis.     

Use of natural polymers as immobilizing agents and effects on the growth of Dunaliella salina and its glycerol production

Agar-agar, agarose, carrageenan and calcium alginate were used for the immobilization of Dunaliella salina cells. Out of the four, agar-agar was found to be the most effective and therefore the study was carried out on it using different pH values ranging from 6 to 10 and cell densities from 0.1 to 0.8 μg chlorophyll (chl, a) per bead to find which are is best suited for glycerol production. The maximum glycerol production of 9.2 μM/mg chl a was recorded in agar-agar immobilized algae and this was followed by 8.4 μM/mg chl a in calcium alginate. The maximum cell number 6.2 × 10⁹/ml and the specific growth rate (μ) of 0.80 l/day were reached at pH 8 in agar-agar immobilized algae. It was shown that the maximum amount of glycerol was produced when the cell density was 0.8 μg chl a/ block. Changing the medium after 24 hours affected the rate of glycerol production at different pH values. Using a cell density of 0.8 μg chl a/block at 16 W/m² light intensity increased the glycerol production in comparison with the use of free living cells.     

Temporal variability in egg production rates of Acartia tonsa Dana in Long Island Sound

The relationship between week-by-week variations in the in situ egg production rates of Acartia tonsa Dana and changes in chlorophyll concentration in several size fractions was investigated by incubating adult females in natural sea water for 24-h periods. Our results indicate that the egg production of A. tonsa in Long Island Sound was better related to the 10 μm chlorophyll size fraction than to the total chlorophyll concentration. The < 10 μm size fraction comprised the greatest percentage of the chlorophyll during July and August when the water column was stratified. Egg production rates were lowest (8.7 eggs · female⁻¹ · day⁻¹) in early August when less than 0.5 μg chlorophyll 1 ⁻¹ was observed in the 10 μm chlorophyll a size fraction. Following destratification in late August, the “fall” diatom bloom occurred and egg production rates increased to the maximum observed rate of 56.6 eggs · female⁻¹ · day⁻¹. At this time, the concentration of the 10μm chlorophyll size fraction was 5.5 μg 1⁻¹. Maximum egg production rates were observed at chlorophyll concentrations as low as 0.8 μg 1⁻¹ in the 10 μm size fraction.     

Quantitation of the diastereoisomers of l-buthionine-(R,S)-sulfoximine in human plasma: a validated assay by capillary electrophoresis

An assay for the diastereoisomers of the biochemical modifier $\text{l}\text{-buthionine}\text{-(R,S)-}\text{sulfoximine}$ (BSO) in human plasma has been developed using capillary electrophoresis (CE). Separation of the diastereoisomers is achieved by the micellar electrokinetic chromatography (MEKC) mode of CE. Plasma is injected directly onto the separation capillary without any extraction step, and BSO is detected directly by ultraviolet absorbance measurements at 190 nm without prior derivatization. The whole assay, including capillary conditioning, takes approximately 30 min. Intra- and inter-day R.S.D. values are approximately 7% at sample concentrations around 25 μg ml⁻¹, and approximately 3% at sample concentrations around 500 μg ml⁻¹. The limit of detection in plasma is 3.9 μg ml⁻¹ (S/N = 2). The assay has been used to quantitate the diastereoisomers of BSO in patient samples in a pharmacokinetic study.     

The enzyme "aldehyde oxidase" is an iminium oxidase. Reaction with nicotine delta 1'(5') iminium ion.

The second of the two reaction steps involved in the metabolic transformation of (?)-nicotine to (?)-cotinine $\text{(}\text{3}\text{) (}\text{i.}\text{e.}$, the oxidation of the intermediate $\text{2}\text{)}$ is mediated mainly, if not solely, by the enzyme aldehyde oxidase (EC 1.2.3.1). Of the molecular species that constitute $\text{2}$, nicotine Δ^1′(5′) iminium ion $\text{(}\text{2a}\text{)}$ appears to serve as the substrate. The enzyme has a strong affinity for $\text{2a}$, as shown in a study on the inhibition of the oxidation of 3-(aminocarbonyl)-1-methylpyridinium chloride. This study gave a value of K_i = 6 μM; K_m = 2 μM (pH 7.4). Mainly in view of this finding, “iminium oxidase” seems to be a more adequate name than “aldehyde oxidase” for this enzyme.     

Cardiovascular effects and pharmacokinetics of the carboxylic ionophore monensin in dogs and rabbits

Monensin, a carboxylic ionophore, produces strong pressor, positive chronotropic effects and elevates the blood glucose level when injected intravenously (100 μg/kg) into pentobarbital anesthetized dogs or administered orally (2 mg/kg) to conscious dogs. Intravenously administered monensin disappeared from the blood rapidly with a $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of ca. 2.5 min and, in the conscious dogs, ingested monensin showed a peak plasma level 90 min after feeding; this coincided with the time of maximum increase in arterial blood pressure and blood glucose. In conscious rabbits, although higher doses of monensin were administered, 200 μg/kg intravenously and 10 mg/kg orally, its cardiovascular effects were less than observed in the dog and were slower in onset. This correlated with slower clearing of injected monensin from the blood ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 8}\text{min}$) and slower entry of ingested monensin from the gut into the blood. Rabbit plasma and tissue levels were higher 17 hr after oral ingestion of monensin than six hr after ingestion.     

Treadmilling of actin at physiological salt concentrations: An analysis of the critical concentrations of actin filaments

Treadmilling of actin was investigated at physiological salt concentrations (100 mm-KCl, 0.5 to 2.0 mm-MgCl₂, 200 μm-ethyleneglycol-bis(β-aminoethyl ether)N,N′-tetraacetic acid or 50 μm-CaCl₂ at 37 °C. The concentration at which monomers bind to the lengthening end of filaments with the same rate as subunits are released (low critical concentration c₁ was determined by mixing unmodified actin filaments with various concentrations of monomeric actin labeled with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole. Above a monomeric actin concentration of about 0.12 μm, incorporation of actin molecules into filaments was detected, whereas below this concentration no incorporation was found (c₁ = 0.12 μm). Combination of various concentrations of labeled monomers with labeled filaments permitted determination of the net critical concentration ($\text{c}{}_1$) at which filaments lengthen at one end with the same rate as they shorten at the other end ($\text{c}{}_1\text{= 0.16}\text{μm}$). A lower limit of the high critical concentration at the shortening end (c_h) was estimated by measuring the release of subunits from labeled filaments in the presence of various concentrations of unlabeled monomers (c_h >0.5 μm). The differences in the three critical concentrations demonstrate that under physiological conditions actin filaments lengthen at one end by, on the average, one subunit during the time that four association reactions take place at the two ends (efficiency parameters $\text{s =}\text{1}\text{4}$). The small difference between the low and the net critical concentration suggests that the rates of both association and dissociation are considerably greater at the lengthening end than at the shortening end of actin filaments.     

Decomposition of the tropical macroalga Caulerpa cupressoides (West) C. Agardh: Field and laboratory studies

The decomposition of the marine tropical green macroalga Caulerpa cupressoides (West) C. Agardh was studied in order to assess its importance as a means of supplying nutrients to the sediments of seagrass beds which are in the early stages of colonization. Caulerpa is a colonizer species in the succession of seagrass beds. The dynamics of Caulerpa decomposition were also compared to that of other macroalgae and marine vascular plants.Caulerpa lost 50% of its original biomass in 7 days in litter bags positioned in the water column and sediments of Tague Bay lagoon, St. Croix, U.S. Virgin Islands. This rate is extremely rapid in comparison to that of vascular plants. Caulerpa was allowed to decompose in flasks for 141 days. During this time reducing conditions (Eh < ? 100 mv) were established within 7 days and subsequently up to 1.8 mmol dissolved nitrogen was released from 25 g wet weight algae. The predominant form of nitrogen released was dissolved organics. Nitrate and nitrite were found only in trace concentrations after reducing conditions were established. The $\text{C}\text{N}$ ratio in the particulate matter of decomposing Caulerpa decreased significantly over time in the flasks and increased significantly in the sediments. The low percent N and high $\text{C}\text{N}$ ratios of decomposing Caulerpa suggest it would be poor quality food for detritivores.The amount of nitrogen released during the decomposition of Caulerpa was extrapolated to conditions in nature and was found sufficient to support a minimum of 10% of the nitrogen requirement of seagrasses as they colonize Tague Bay lagoon.     

Antenna function of a chlorophyll ab protein complex of Photosystem I

The functional role of a chlorophyll $\text{a}\text{b}$ complex associated with Photosystem I (PS I) has been studied. The rate constant for P-700 photooxidation, K_P-700, which under light-limiting conditions is directly proportional to the size of the functional light-harvesting antenna, has been measured in two PS I preparations, one of which contains the chlorophyll $\text{a}\text{b}$ complex and the other lacking the complex. K_P-700 for the former preparation is half of that of the preparation which has the chlorophyll $\text{a}\text{b}$ complex present. This difference reflects a decrease in the functional light-harvesting antenna in the PS I complex devoid of the chlorophyll $\text{a}\text{b}$ complex. Experiments involving reconstitution of the chlorophyll $\text{a}\text{b}$ complex with the antenna-depleted PS I preparation indicate a substantial recovery of the K_P-700 rate. These results demonstrate that the chlorophyll $\text{a}\text{b}$ complex functions as a light-harvesting antenna in PS I.     

Kinetic parameters for the binding of p-nitrophenyl alpha-d-mannopyranoside to concanavalin A.

Binding of the chromogenic ligand p-nitrophenyl α-d-mannopyranoside to concanavalin A was studied in a stopped-flow spectrometer. Formation of the protein-ligand complex could be represented as a simple one-step process. No kinetic evidence could be obtained for a ligand-induced change in the conformation of concanavalin A, although the existence of such a conformational change was not excluded. The entire change in absorbance produced on ligand binding occurred in the monophasic process monitored in the stopped-flow spectrometer. The value of the apparent second-order rate constant (k_a) for complex formation (k_a = 54,000 s^?1m^? at 25 °C, pH 5.0, Γ/2 0.5) was independent of the protein concentration when the protein was in the range of 233–831 μm in combining sites and in excess of the ligand. The apparent first-order rate constant (k_?a) for dissociation of the complex was obtained from the rate constant for the decomposition of the complex upon the addition of excess methyl α-d-mannopyranoside (k_?a = 6.2 s^?1 at 25 °C, pH 5.0, Γ/2 0.5). The ratio $\text{k}{}_{\mathrm{<mtext>a</mtext>}}{}_{\mathrm{<mtext>?</mtext><mtext>a</mtext>}}$ (0.9 × 10₄m^?1) was in reasonable agreement with value of 1.1 ± 0.1 × 10⁴m^?1 determined for the equilibrium constant for complex formation by ultraviolet difference spectrometry. Plots of ln($\text{k}{}_{\mathrm{<mtext>a</mtext>}}\text{T}$) and ln($\text{k}{}_{\mathrm{<mtext>a</mtext>}}\text{T}$) vs $\text{1}\text{T}$ were linear (T is temperature) and were used to evaluate activation parameters. The enthalpies of activation for formation and dissociation of the complex are 9.5 ± 0.3 and 16.8 ± 0.2 kcal/mol, respectively. The unitary entropies of activation for formation and dissociation of the complex are 2.8 ± 1.1 and 1.3 ± 0.7 entropy units, respectively. These entropy changes are much less than those usually associated with substantial changes in the conformation of proteins.     

The effects of environmental factors on growth and the chemical and biochemical composition of marine diatoms. I. Light and temperature effects

Temperature and light interact to modify the chemical and biochemical composition of a nitrogen-limited marine diatom, Thalassiosira allenii Takano, grown at a constant dilution rate in continuous culture and under a light:dark cycle.The percent of the total ¹⁴C incorporated into protein, polysaccharide and lipid, the N/C ratio and the C/cell varied with temperature in a markedly non-linear manner. The N/cell was negatively correlated to temperature. The Chl $\text{a}\text{C}$ ratio was positively correlated with temperature under saturating light and non-saturating light for temperatures > 25 °C, but was constant under non-saturating light conditions for temperatures < 25 °C.Productivity index (PI) was negatively correlated to temperature under saturating light conditions, but did not vary under low light. In each case, the variation in PI with temperature was governed by the variation in Chl $\text{a}\text{C}$.The dark carbon loss rate was exponentially related to temperature and independent of light. Variation in the percent of the total ¹⁴C incorporated into protein and polysaccharide, the $\text{N}\text{C}$ ratio and C/cell was primarily due to the effects of N-limitation < 20 °C and primarily due to the effects of temperature > 20 °C. Variation in N/cell was primarily due to the effects of temperature over the entire range of temperature studied. Variation in Chl $\text{a}\text{C}$ was caused by the interaction of temperature and light effects.In most cases, temperature and nutrient effects interacted to govern how a particular parameter varied with temperature while light affected the range of values over which the parameter varied.The percent of the total ¹⁴C incorporated into protein exhibited a significant linear relationship with $\text{N}\text{C}$.The dark carbon loss rate, $\text{N}\text{C}$ ratio and Chl $\text{a}\text{C}$ ratio data were used to test the applicability of a model for the physiological adaptation of unicellular algae. The model, with parameters derived from a non-linear least-squares fit of the dark carbon loss rate data, adequately described the $\text{N}\text{C}$ ratio between 15 and 25 °C at 290 and 137 μE · m^?2 · s^?1, but failed to describe the data at 28 °C and at 48 μE · m^?2 · s^?1. The Chl $\text{a}\text{C}$ ratio was adequately described by the model under all light and temperature conditions.     

EPR study of the effect of formate on cytochrome C oxidase

The addition of formate to oxidized cytochrome $\text{c}$ oxidase (ferrocytochrome $\text{c}$: oxygen oxidoreductase, EC 1.9.3.1) causes the appearance of a high spin heme signal at g = 6 and a splitting of g = 3 signal to g = 2.98 and 3.07. When formate-cytochrome $\text{c}$ oxidase is reduced, the g = 2.98 signal decreases significantly. The spectrophotometric studies showed that formate is a specific ligand to cytochrome $\text{a}$₃. Data suggest that binding of formate to oxidized cytochrome $\text{c}$ oxidase produces a ligand-$\text{a}$₃ interaction leading to the splitting of g = 3 signal hitherto considered as due to cytochrome $\text{a}$. Thus both cytochrome $\text{a}$ and $\text{a}$₃ contribute to the resonance of g = 3 signal of cytochrome $\text{c}$ oxidase.     

Comparative carbon-specific ingestion rates of phytoplankton by Acartia tonsa,Centropages velificatus and Eucalanus pileatus grazing on natural phytoplankton assemblages in the plume of the Mississippi River (northern Gulf of Mexico continental shelf)

During four cruises in continental shelf waters of the northern Gulf of Mexico in the winters of 1981–83, we performed quantitative studies on the grazing of the copepods Acartia tonsa, Centropages velificatus, and Eucalanus pileatus, on phytoplankton using natural particulate assemblages as food. Stations were in, or adjacent to the plume of the Mississippi River, thereby providing wide spectra of phytoplankton and suspended riverine particulate concentrations. Phytoplankton cell volume was converted to carbon, and this, coupled with carbon content measurements of these three copepod species, allowed comparisons of daily ingestion effort even though the copepods were of different sizes. Data were expressed in the same units (% of copepod body carbon ingested copepod ^–1 d^–1) for each species. Over similar ranges of phytoplankton carbon concentrations (0.21–92.06 gCl^–1), Acartia tonsa had higher carbon-specific ingestion rates (x = 22.31%, range = 0.08–152.37%) than C. velificatus (x = 2.8%, range = 0.00–31.09 %) or E. pileatus (x = 1.27%, range = 0.10–2.80%). Carbon-specific ingestion rates increased with increasing phytoplankton carbon concentration for A. tonsa (R² = 0.81) and there was no evidence of saturated feeding on the carbon concentrations offered. A similar, but weaker trend was evident for E. pileatus (R² = 0.71), but not C. velificatus (R² = 0.49). Over a wide range of suspended particulate concentrations (10.6–95.2 mg l^–1), there was no systematic effect of particulates on carbon-specific ingestion rate for any of the three copepod species. However, A. tonsa appeared more adept at grazing in highly turbid water than C. velificatus or E. pileatus.     

Comparing Springtime Ice-Algal Chlorophyll a and Physical Properties of Multi-Year and First-Year Sea Ice from the Lincoln Sea

With near-complete replacement of Arctic multi-year ice (MYI) by first-year ice (FYI) predicted to occur within this century, it remains uncertain how the loss of MYI will impact the abundance and distribution of sea ice associated algae. In this study we compare the chlorophyll a (chl a) concentrations and physical properties of MYI and FYI from the Lincoln Sea during 3 spring seasons (2010-2012). Cores were analysed for texture, salinity, and chl a. We identified annual growth layers for 7 of 11 MYI cores and found no significant differences in chl a concentration between the bottom first-year-ice portions of MYI, upper old-ice portions of MYI, and FYI cores. Overall, the maximum chl a concentrations were observed at the bottom of young FYI. However, there were no significant differences in chl a concentrations between MYI and FYI. This suggests little or no change in algal biomass with a shift from MYI to FYI and that the spatial extent and regional variability of refrozen leads and younger FYI will likely be key factors governing future changes in Arctic sea ice algal biomass. Bottom-integrated chl a concentrations showed negative logistic relationships with snow depth and bulk (snow plus ice) integrated extinction coefficients; indicating a strong influence of snow cover in controlling bottom ice algal biomass. The maximum bottom MYI chl a concentration was observed in a hummock, representing the thickest ice with lowest snow depth of this study. Hence, in this and other studies MYI chl a biomass may be under-estimated due to an under-representation of thick MYI (e.g., hummocks), which typically have a relatively thin snowpack allowing for increased light transmission. Therefore, we suggest the on-going loss of MYI in the Arctic Ocean may have a larger impact on ice–associated production than generally assumed.