BIOTIN LIBERATION BY THE LICHEN ALGA COCCOMYXA SP. AND BY CHLORELLA PYRENOIDOSA

The unicellular green alga Coccomyxa, a component of the lichenPeltigera aphthosa, liberated about 7.2mµg biotin permg dry weight of cells into the culture medium during a growthperiod of 15–20 days. The corresponding figure for thefree-living alga Chlorella pyrenoidosa was 0.45mµg ofbiotin. Chromatographic analysis indicated that this was freebiotin and not a bound form of the vitamin. The biotin concentrationof rinsed Coccomyxa cells was 1.88mµg per mg dry weightof cells, of which less than 0.01mµg was extractable byhot water. Cells of Chlorella contained 0.16mµg of biotinper mg dry weight, of which 0.11mµg was extractable byhot water. The biotin content of Coccomyxa, which was about12 times that of Chlorella, is thus almost entirely in the boundform. The importance of biotin in the symbiotic interactionsbetween the alga and the fungus in Peltigera is discussed. ¹Present address: University Department of Agriculture, Oxford,England. ²Present address: Institute of Marine Resources, Universityof California, La Jolla, California, U.S.A.     

Effects of Metabolic Inhibitors on the Calcification of a Freshwater Green Alga Gloeotaenium loitlesbergarianum Hansgirg. 2. Effects of Some Inhibitors of Protein Synthesis

The effects of five inhibitors of protein synthesis, viz. streptomycin,aurin tricarboxylic acid, tetracycline, chloramphenicol, andcycloheximide, on the calcification of Gloeotaenium loitlesbergarianumHansgirg, a freshwater green alga were studied. Streptomycinhad no effect while aurin tricarboxylic acid at 50 µgml^–1 and tetracyline, chloramphenicol and cycloheximideat 20 µg ml^–1 completely inhibited calcificationin the alga. High concentrations of chloramphenicol and cycloheximidewere not completely inhibitory when added 26 h and 32 h respectivelyafter the material was incubated in the induction medium. Itis concluded that the effects by these substrates are the resultsof inhibition of protein synthesis, which is directly or indirectlylinked to calcification. calcification, Gloeotaenium loitlesbergarianum Hansgirg, green alga, chlorophyceae, protein synthesis inhibitors     

Effects of Radiations on Blue-green Algae: I. The Production and Characterization of a strain of Anacystis nidulans resistant to Ultraviolet radiation

The unicellular blue-green alga Anacystis nidulans was exposedto ultraviolet radiation during several successive subcultures.The ultraviolet-trained strain so obtained was then comparedwith the untrained control and found to be relatively more resistantto ultraviolet, penicillin, and streptomycin, and more sensitiveto isoni-azid. It was further characterized by decreased carotenoid/chlorophyllratio and by not having fully overcome the division-inhibitingeffect of ultraviolet radiation. It was able to grow betterthan the untrained strain in a medium containing high concentrationsof nitrite as the sole nitrogen source.     

Effects of Radiations on Blue-green Algae: II. Effects in Growth

The unicellular blue-green alga Anacystis nidulans was repeatedlytreated with X-rays and radiophosphate (32P) during successivesubcultures. The strains so obtained were characterized by comparisonwith the untreated control strain, with respect to their resistanceto ultraviolet light, X-rays, streptomycin, and isoniazid. The³²P-treated strain was found to be relatively more resistantto streptomycin than the untreated strain and the X-rayed strainwas found to be relatively rnore sensitive to isoniazid thanthe control. In old cultures, cells of the X-rayed strain weresignificantly smaller than those of the untreated strain. The effects of X-rays on cell- and heterocyst dimensions ofthe nitrogen-fixing alga Chlorogloea fritschii Mitra were studied.In the irradiated material the cell diameter and heterocystbreadth were greater, rather than smaller, than in unirradiatedmaterial.     

ADAPTATION OF A BLUE-GREEN ALGA TO SODIUM SELENATE AND CHLORAMPHENICOL

The pattern of growth of the unicellular blue-green alga Anacystisnidulans in gradually increasing concentrations of sodium selenateand chloramphenicol during successive subcultures was studied.An increase in tolerance to sodium selenate of about twelvetimes occurred during ten transfers of the alga in increasingconcentrations of the drug. The tolerance was partially lostafter the resistant cells had been given the same number oftransfers in a selenate-free medium. ¹ Present address: Botany Department, The University, Udaipur,Raj., India.     

Thiamine requirements of various plant cells in suspension culture

The thiamine requirements of cells of several plant speciesin suspension culture were investigated. Omission of thiaminefrom the medium leads to a rapid and complete cessation of growthin subcultures of soybean, tobacco and rice cells. The criticallevels of thiamine content in these cells are considered tobe in the vicinity of 0.6, 0.5 and 0.2 µg per g dry weight,respectively. Soybean cells can grow satisfactorily when suppliedwith an equimolar mixture of two thiamine precursors, pyrimidineand thiazole moieties. Neither moiety alone can substitute forthiamine. On the other hand, Rula and peanut cells can be successfullysubcultured for ten passages in the absence of externally suppliedthiamine. When grown without thiamine, Rula cells had an averagethiamine content of 0.5-0.6 µg in darkness and 3.5 µgper g dry weight in the light. The relationship between thethiamine requirement and the degree of dedifferentiation incultured cells is discussed. ¹ Present address: Section of Phytochemical Research, Researchand Development Division, Eisai Co., Ltd., Kawashima, Gifu 112,Japan. (Received December 24, 1975; )     

Tentoxin Inhibits Both Photophosphorylation in Thylakoids and the ATPase Activity of Isolated Coupling Factor F1 from the Cyanobacterium Anacystis nidulans

Tentoxin strongly inhibited the ATPase activity of isolatedcoupling factor 1 (AF₁) from the cyanobacterium Anacystis nidulans,with 50% inhibition occurring at 0.3 µM. When thylakoidsfrom A. nidulans were preincubated with 0.3 µM tentoxinfor 30 min, photophosphorylation was inhibited by 50%. Measurementsof fluorescence from 9-aminoacridine indicated that tentoxininhibited the utilization of the proton gradient by ATP formationin thylakoids. These results indicate that tentoxin is a strongenergy-transfer inhibitor of photophosphorylation in A. nidulans.Tentoxin decreased the level of ATP in intact cells both inthe light and in darkness, its effects being much stronger inthe dark. Tentoxin at 50 µM strongly inhibited the growthof the cells. ³Present address: Corporate Research and Development Laboratory,Tonen Co. 1-3-1 Nishi-tsurugaoka, Ohi-machi, Saitama, 354 Japan ⁴Present address: Technology and Engineering Laboratories, AjinomotoCo., Inc. Suzuki-cho 1, Kawasaki, 210 Japan     

COMPONENTS OF THE ELECTRON-TRANSFERRING SYSTEM IN ACETOBACTER SUBOXYDANS AND RECONSTRUCTION OF THE LACTATE OXIDATION SYSTEM

1. Cytochromes a₁⁵⁹⁰, b⁵⁶⁰, c₁⁵⁵⁴ and c₁⁵⁵² were isolated andpurifiedfrom a strain of Acetobacter suboxydans. The proceduresusedwere described in detail.
2. The main cytochrome band at550-560 mµ in intact cellssplitted at liquid air temperatureinto two bands, 551 mµ(strong) and 559 mµ (weak).
3. Optical and physiological properties of the four cytochromeswere investigated. Lactic dehydrogenase activity was found tobe associated with cytochrome c₁⁵⁵⁴. The two c₁-type cytochromes,especially cytochrome c₁⁵⁵⁴, persisted in their reduced formafter the purification through many steps.
4. By some combinationsof isolated components reconstruction ofthe oxygen uptake systemcould be realized.
5. The oxygen-consuming activity of purifiedoxidase preparationswas accelerated by a-tocopherol but notby Emasoll 4130 andTween 80.
6. Some discussions were made onthe nature of terminal oxidase,the role of cytochrome c₁⁵⁵²in the electron-transport system,and persistence of reducedstate of c₁-type cytochromes.
7. A possible scheme of the electron-transferringsystem of Acetobactersuboxydans was presented.

(Received May 16, 1960; )     

Regulation of Tracheary Element Differentiation by Exogenous L-Methionine in Callus of Soya Bean Cultivars

The relationship between the induction of tracheary elementdifferentiation and exogenous L-methionine was examined in agar-growncultures of soya bean callus initiated from Glycine max L. ‘Wayne’and ‘Clark 63’. Although Wayne is a normal cultivarsoya bean, seedlings of Clark 63 exhibit abnormal growth at25 °C due to exessive ethylene biosynthesis at this temperature.Wayne callus showed increased xylogenesis in the presence ofexogenous L-methionine (3.7 µg 1^–1) in comparisonto IAA–KN controls at both 20 and 25 °C. Clark 63callus produced greater numbers of tracheary elements in responseto exogenous L-methionine only at 25 °C. The induction ofxylem differentiation was independent of the maintenance temperatureof the stock cultures of both cultivars. Xylogenesis initiatedbyan IAA–KN medium was inhibited by the addition of AgNO₃(20 mg 1^–1) to the extent of 76.5 per cent in cv. Wayneand 6 per cent in cv. Clark 63. The inhibitory effect was partiallyreversed by the addition of L-methionine (3.7 µg 1^–1)to the IAA–KN–AgNO₂ medium. These data support thehypothesis that xylogenesis in vitro involves auxin, cytokininand ethylene. differentiation, xylogenesis, L-methionine, ethylene, Glycine max L., soya bean, callus culture, auxin, kinetin     

Cyanobacteria and cyanobacterial toxins in three alkaline Rift Valley lakes of Kenya--Lakes Bogoria, Nakuru and Elmenteita

For decades frequent mass mortalities of Lesser Flamingos (Phoeniconaiasminor Geoffroy) have been observed at alkaline-saline KenyanRift Valley lakes. To estimate the potential influence of toxiccyanobacteria on these mass deaths, the phytoplankton communitieswere investigated in Lakes Bogoria, Nakuru and Elmenteita. Cyanobacterialtoxins were analyzed both in the phytoplankton from the threelakes and in isolated monocyanobacterial strains of Arthrospirafusiformis, Anabaenopsis abijatae, Spirulina subsalsa and Phormidiumterebriformis. Lake Bogoria was dominated by the cyanobacteriumA. fusiformis. In L. Nakuru and L. Elmenteita the phytoplanktonmainly consisted of A. fusiformis, A. abijatae and Anabaenopsisarnoldii, and in L. Nakuru an unknown Anabaena sp. was alsofound. Furthermore, this is the first time A. abijatae and theunknown Anabaena sp. have been found in Kenyan lakes. Phytoplanktonwet weight biomass was found to be high, reaching 777 mg L^–1in L. Bogoria, 104 mg L^–1 in L. Nakuru and 202 mg L^–1in L. Elmenteita. Using HPLC, the cyanobacterial hepatotoxinsmicrocystin-LR, -RR -YR, -LF and -LA and the neurotoxin anatoxin-awere detected in phytoplankton samples from L. Bogoria and L.Nakuru. Total microcystin concentrations amounted to 155 µgmicrocystin-LR equivalents g^–1 DW in L. Bogoria, and 4593µg microcystin-LR equivalents g^–1 DW in L. Nakuru,with anatoxin-a concentrations at 9 µg g^–1 DW inL. Bogoria and 223 µg g^–1 DW in L. Nakuru. In L.Elmenteita phytoplankton, no cyanobacterial toxins were found.A. fusiformis was identified as one source of the toxins. Theisolated strain of A. fusiformis from L. Bogoria was found toproduce both microcystin-YR (15.0 µg g^–1 DW) andanatoxin-a (10.4 µg g^–1 DW), whilst the A. fusiformisstrain from L. Nakuru was found to produce anatoxin-a (0.14µg g^–1 DW). Since A. fusiformis mass developmentsare characteristic of alkaline-saline lakes, health risks towildlife, especially the Arthrospira-consuming Lesser Flamingo,may be expected.     

Methanol Accumulation in Maturing Seeds

During in vitro growth and maturation of soybean seeds, cessationof embryo growth and dry weight accumulation occurred in thepresence of abundant C and N nutrients. Axis followed by cotyledontissues changed from green to yellow, and post-harvest germinationpotential declined if cultured after yellowing of axis tissues.A tissue specific accumulat;on of methanol occurred during thein vitro culture of immature seeds (i.e. initially 50 to 70mg fresh weight) to maturity in liquid medium. Methanol accumulatedto 3.0 g m^–3 or 50 µg seed^–1 in the medium,while methanol decreased from 37 to about 3.0 µg g^–1fresh weight in cotyledons. By contrast, axis tissues increased20-fold in methanol concentration to 90 µg g^–1 during20 d in culture. Ethanol was present only in trace amounts inaxis tissues and medium. Addition of exogenous methanol vapourto in situ grown seeds during precocious maturation decreasedsubsequent seedling vigour and germination with increasing levelsof exposure. Methanol accumulation in axis tissues during thegermination phase was not correlated with high temperature andtissue water content treatments which simulated pre-harvestdeterioration of seeds. However, the accumulation of methanolduring in vitro seed development and maturation in liquid culturemay contribute to reduced post-harvest germination performance. Key words: Soybean, Glycine max, seed maturation, in vitro, methanol     

Reactivation of Cytoplasmic Streaming in a Tonoplast-Permeabilized Cell Model of Acetabularia

To find whether cytoplasmic streaming in Acetabularia is controlledby Ca²⁺, a tonoplast-permeabilized cell model was prepared usinga vacuolar perfusion technique. The cytoplasmic streaming remainedalmost normal after perfusion with EGTA medium (10 mM EGTA,40 mM PIPES, 5mM MgCl₂ and 800 mM sorbitol, pH 6.9), but stoppedwithin 10 min when saponin medium (EGTA medium plus 50 µg/mlsaponin, 50 µg/ml hexokinase and 5 mM glucose) was perfused.This model system was reactivated with a solution containing0.5 mM ATP and different concentrations of Ca²⁺ (reactivationmedium). With the reactivation medium at pCa 6–5, theresumed streaming lasted for about 10 min before the cytoplasmaggregated. At pCa 4–3, the streaming was observed onlyfor a few minutes because the cytoplasm aggregated quickly.At pCa 7, no reactivated movement was observed. Reactivationwas not induced in an ATP- or Mg²⁺-deficient medium even inthe presence of an adequate concentration of Ca²⁺, and was inhibitedby 50 µg/ml cytochalasin B or 1 mM N-ethylmaleimide. We concluded from these observations that the cytoplasmic streamingin Acetabularia is very likely to be driven by the actomyosinsystem in the presence of Mg-ATP and Ca²⁺ at pCa 6–5. (Received October 31, 1984; Accepted April 1, 1985)     

Effects of Sucrose Concentration on the Photosynthetic Ability of Rose Shoots In Vitro

Reducing the concentration of sucrose in the culture mediumover successive subcultures has been tested as a method forincreasing the ability of rose shoots grown in vitro (Rosa cvsIceberg and Peace) to take up CO₂. Shoots maintained on ‘constant’10, 20 and 40 g I^–1 sucrose showed decreased levels ofCO² uptake at higher sucrose concentrations, although cv. Peacegrew least at 10 g l^–1 and showed correspondingly lowamounts of CO₂ uptake compared with 20 and 40 g l^–1. Bothcultivars died when sucrose was omitted from the medium. Assucrose concentration was reduced in the medium, so CO₂ uptakeof shoots initially cultured on 20 and 40 g l^–1 sucrosewas found to increase, although a concentration of 10 gl ^–1sucrose seemed to be limiting, below which the growth and chlorophylllevels of shoots declined. Rosa hybrid, rose, shoot culture in vitro, photosynthetic ability, sucrose, infra-red gas analysis     

UPTAKE OF ACETATE BY NEOTRICULA APERTA (GASTROPODA: POMATIOPSIDAE), THE SNAIL HOST OF SCHISTOSOMA MEKONGI IN THE LOWER MEKONG BASIN

All three races of Neotricula aperta, an epilithic, schistosometransmitting, snail of the Mekong and Mul rivers of NortheastThailand and southern Laos, were found to take up acetate froma dilute solution. After 48 h incubation the mean specific netuptake rates (µmol^–1 g^–1 h^–1), from750 µM acetate, were: 1.86, -race; 1.39, ß-raceand 3.25, y-race. Over 48 h the snails were able to achievereductions in the ambient acetate concentration of up to 60%.Incubations under bacteriostatis suggested that bacteria arenot involved in the uptake of acetate by N. aperta. The uptakecharacteristics conform to the Michaelis-Menten model. The transportconstants, J_max (µmol^–1 g^–1 h^–1) andK_t (µM) were 1.10 and 102 respectively (-race). Racialdifferences in uptake characteristics are discussed in relationto micro-habitat differences. HPLC indicated concentrations of acetate in y-N. aperta microhabitatsof around 325 µM. This suggests a pool size sufficientto satisfy only 6% of the snail's basal metabolic rate (BMR).Levels within the epilithic aufwuchs, however, are probablyhigh enough to provide for more than 50% of the BMR. The possible role of acetate in the energy metabolism of N.aperta is discussed. Short-chain carboxylic acids (such as acetate),arising from the decomposition of the aufwuchs, could representsources of fermentable organics that may be taken up by N. apertasnails and used to supplement their nutrition during times offood shortage. However, further investigations involving ¹⁴C-labellingtechniques are required. The findings of this investigationhave implications for the chemical ecology and life-cycle ofN. aperta. (Received 16 June 1994; accepted 28 July 1994)     

THE RATIO OF CALCAREOUS AND ORGANIC SHELL COMPONENTS OF FRESHWATER SPHAERIID CLAMS IN RELATION TO WATER HARDNESS AND TROPHIC CONDITIONS

Shells from 14 populations of sphaeriid clams including Sphaeriumstriatinum, S. simile, Pisidium walkeri, Musculim partumeiumand M. iransversum were analyzed for organic carbon (µgCmg^–1 shell), nitrogen (µg,N mg^–1 shell) andCaCO_s (%CaCO₃ of total clam dry weight). Habitat waters wereassessed for total hardness (expressed as ppm CaCo₃), ppm Ca,ppm Mg, conductivity (µmho) and suspended organic Carbon(µgCl^–1). For all populations, shell organic C andN are positively correlated and there is an inverse relationshipbetween the amounts of shell CaCO₃ and shell organic carbon.Trophic considerations give the best correlation with shelltype at the generic level of consideration since species ofMusculium are found at the opposite end of the trophic scale(eutrophic) from all other populations studied. For S. striatinum,the most extensively studied species, the amount of shell CaCO₃is inversely related to water hardness. The selection of shellsin the Sphaeriidae is discussed in relation to structural-functionalneeds and habitat conditions ¹ Present Address: Department of Biology, Syracuse University,Syracuse, New York 13210, U.S.A. ² Present Address: Department of Zoology, Miami University,Oxford, Ohio 45056, U.S.A. (Received 5 December 1978;     

Growth and swainsonine production of Swainsona galegifolia (Andr.) R. Br. untransformed and transformed root cultures

Untransformed and transformed root cultures of Swainsona galegifollawere established for swainsonine production. Transformed rootsgrew faster and produced higher swainsonine levels (62.3 µgg^–1 DW) than untransformed roots (23.6 ,µg g^–1DW) or roots of intact plants (8.7 µg g^–1 DW). Transformationof a number of plant genotypes using A. rhizogenes strain LBA9402 showed that plant genotype Influences swainsonine levelin transformed roots but that a wide range of swainsonine levelscan be induced by separate transformation events in the samegenotype. Enhancement of swainsonine production was attemptedby treatment with sugars and induction of polyploid roots. Key words: Agrobacterium rhizogenes, root cultures, Swainsona galegifolia, swainsonine     

Xylem fluxes of fixed N through nodules of the legume Acacia littorea and haustoria of an associated N-dependent root hemiparasite Olax phyllanthi

Nodulated 1-1.5-year-old plants of Acacia littorea grown inminus nitrogen culture were each partnered with a single seedlingof the root hemiparasite Olax phyllanthi. Partitioning of fixedN between plant organs of the host and parasite was studiedfor the period 4–8 months after introducing the parasite.N fluxes through nodules of Acacia and xylem-tapping haustoriaof Olax were compared using measured xylem flows of fixed Nand anatomical information for the two organs. N₂ fixation duringthe study interval (635 µg N g FW nodules^–1 d^–1)corresponded to a xylem loading flux of 0.20 µg N mm^–2d^–1 across the secretory membranes of the pencycle parenchymaof the nodule vascular strands. A much higher flux of N (4891µg mm^–2 d^–1) exited through xylem at the junctionof nodule and root. The corresponding flux of N from host xylemacross absorptive membranes of the endophyte parenchyma of Olaxhaustorium was 1.15 µg N mm^–1 d^–1, six timesthe loading flux in nodules. The exit flux from haustorium toparasite rootlet was 20.0 pg N mm^–1 d^–1, 200-foldless than that passing through xylem elements of the nodule.Fluxes of individual amino compounds in xylem of nodule andhaustorium were assessed on a molar and N basis. N flux valuesare related to data for transpiration and partitioning of Cand N of the association recorded in a companion paper. Key words: Olax phyllanthi, host-parasite relationships, N flux, Acacia, N₂ fixation     

Use of immobilized algae for estimating bioavailable phosphorus released by zooplankton

Cells of the green alga Selenastrum capricomuxum were immobilizedin permeable alginate beads to prevent them from being grazedby zooplankton. Algae were able to grow in these beads and wereused as a new technique to estimate bioavailable phosphorus(P) released by zooplankton. P-limited algal cells were encapsulatedin alginate beads and used to measure P-release by Daphnia pulexfeeding on P-saturated and P-limited free algal cells. Daphnidsgrazing on P-saturated cells released 20 times more P availablefor the immobilized algae than animals grazing on P-limitedcells (0.06 versus 0.003 µg P mg^–1 Daphnia-DW h^–1).     

In vitro Shoot and Root Formation in the Apple Cultivar Akero

Regulation of in vitro shoot and root formation and the histologicalorigin of newly formed shoots was studied in the apple cultivarÅkerö. Both composition of mineral elements and benzylaminopurine(BAP) concentration affected shoot multiplication. Similar numbersof shoots were obtained with Lepoivre and MS medium after twosucceeding subcultures, but Murashige and Skoog medium was preferabledue to production of longer shoots. The optimum BAP concentrationwax around 8.8 µM. Higher concentrations caused vitrifiedshoots. The rooting ability increased with numbers of subcultures.Also the concentration of indol-3-yl butyric acid (IBA) affectedrooting. A strong interaction between numbers of subculturesand IBA concentration was obtained. After insufficient numbersof subcultures, when shoots were still difficult to root, increasingIBA concentration exerted little effect on rooting. When shootshad reached an ‘easy-to-root condition’ root initiationdepended on IBA concentration, showing an optimum at 2.5 µM.Supraoptimal IBA concentrations delayed root initiation. Dark treatment of shoots during the root-initiation phase increasedrooting ability. The most positive effect was obtained at suboptimalIBA concentrations. Anatomical studies revealed both axillaryand adventitious shoots. Two kinds of adventitious structureswere demonstrated. Malus domestica Borkh. apple cultivar Åkerö, in vitro propagation, anatomy, origin of shoots     

On the trophic fate of Phaeocystis pouchetii (Harlot). III. Functional responses in grazing demonstrated on juvenile stages of Calanus finmarchicus (Copepoda) fed diatoms and Phaeocystis

The objective of this study was to quantify the functional responsein feeding rate in the various developmental stages of Calanusfinmarchicus to different concentrations of the diatoms Thalassiosiranordenskioeldii and Porosira glacialis, and the haptophyseanPhaeocystis pouchetii. Grazing of copepodite stage I–VC.finmarchicus was measured using two different approaches.Feeding rates were obtained from either incubation experiments,estimating the rate of removal of particles from suspension,or by quantifying the turnover rate of the plant pigments inthe gut. Clearance as a function of algal concentration (1–30µg plant pigment 1^–1) was described in juvenilestages of C.finmarchicus fed the diatoms T.nordenskioeldii [20µm equivalent spherical diameter (ESD)], P.glacialis (40µm ESD), and two size categories (30–100 µmand >100 µm ESD) of the gelatinous alga P.pouchetii.When the copepodite stages were fed T.nordenskioeldii, the gutcontent of plant pigments was in general higher than when fedP.glacialis. Rates obtained were variable when the same copepoditestages were offered the two size categories of P.pouchetii,but within the same order of magnitude as those obtained forthe larger diatom. At unialgal diets, diatoms were more readilyconsumed than the larger size fraction among colonies of P.pouchetiiby copepodite stage I–III C.finmarchicus. But given anappropriate prey size, C.finmarchicus grazed both diatoms andcolonies of gelatinous algae at equal rates. A linear relationshipbetween gut content and food concentrations <10 µgchlorophyll 1^–1 was found. This indicates that the ingestionrate in C.finmarchicus is directly proportional to the ambientfood concentration during the most productive period in Mayand June in high latitudes irrespective of algal species present. ¹Present address: Marine Biological Laboratory, University ofCopenhagen, Strandpromenaden 5, DK-3000 Helsingør, Denmark ²Present address: Greater Copenhagen Council, Gl. KøgeLandevej 1–3, DK-2550 Valby, Denmark