Zooplankton biomass gradient off south-western Nova Scotia: nearshore ctenophore predation or hydrographic separation?

A persistent large-scale cross-shelf gradient in zooplanktonbiomass >1050 µm was evident off south-western NovaScotia during annual spring surveys between 1985 and 1987, withrelatively low levels inshore and higher levels offshore. Conversely,the abundance of the tentaculate ctenophore Pleurobrachia pileuswas the greatest inshore, and distributed reciprocally to zooplankton>1050 µm. The principle prey of both adult ctenophoresand post-larval cod is zooplankton >1050 µm (primarilycalanoid copepods), and cod growth rates are strongly influencedby prey biomass. Ctenophore predation appears to have been responsiblefor the low nearshore zooplankton biomass, whereas the influenceof hydrographic factors on the zooplankton gradient was minimal.On a smaller scale, persistent, abrupt changes in zooplanktonbiomass >1050 µm and ctenophore density existed 3–30km from shore, in contrast to linear gradients in water density(₁) during a 5 week sampling period in spring 1987. Ctenophoreswere confined to depths <55 m and zooplankton >1050 µmpredominantly occurred at depths >55 m. High concentrationsof chlorophyll and phaeopigment were evident at depths <55m also suggesting intense predation by ctenophores on largeherbivores. The relatively high proportion of smaller zooplankton(153–308 –m) in the nearshore is also consistentwith the predation hypothesis. The reduced growth experiencedby post-larval cod inshore appears generated by ctenophore predationof a common prey resource.     

Ova production by hydromedusae from the NE Pacific

Gonads of hydromedusae had a dry wt of 18 of wet wt, with carbonand nitrogen compos ition equalling 40 and 10 of dry wt, respectively.These values are 4 times higher than for whole specimens. Gonadsof mature medusae represented 2–15 of total wet wt (10–50of total dry wt). For Phialidium gregarium (the most numeroushydromedusa in surface waters of Saanich Inlet, BC), gonadsvaried in size seasonally and were largest in May when foodwas most abundant and when daily rations were maximum. Diametersof ova ranged from 70 to 200 µm; estimated dry wts equalled0.03–0.8 µg and estimated carbon weights were 0.01–0.3µg. Medusae released up to > 10 000 ova/female/day.This rep resented 0.1–4 of total dry wt/day (1–16of carbon). Egg production was dependent on nutritional stateand on female biomass; ova size, on the other hand, was independentof female biomass both within and among species. For the hydromedusaein Saanich Inlet, carbon flux of ova was estimated to equalonly about 50 of metabolic carbon losses because reproductiveindividuals represented only a small part of the total hydromedusapopulation.     

Growth and feeding rates of the newly hatched larval ctenophore Mnemiopsis leidyi A. Agassiz (Ctenophora, Lobata)

Mnemiopsis leidyi: larvae depend on microplankton (<200 µm) prey duringthe first few days following hatching until larvae are >0.5mm in length and can successfully capture and consume mesozooplanktonprey. Feeding and growth rates of newly hatched M. leidyi larvaewere measured in controlled laboratory experiments. When fednatural microplankton assemblages, newly hatched larvae consumedsignificant quantities of both autotrophic and heterotrophicprey, including diatoms, phototrophic, heterotrophic and mixotrophicdinoflagellates, euglenoid flagellates, aloricate and tintinnidciliates, and rotifers. Average per capita clearance rates were1.99–7.59 mL individual^–1 h^–1 ( = 4.01 mL individual^–1 h^–1; SD = 1.95)and total per capita ingestion was 0.01–4.70 µgC individual^–1 day^–1 x 10² ( = 0.83 µg C individual^–1 day^–1 x 10²; SD =1.89). Larval growth rates were –0.13 to 0.56 mm individual^–1day^–1 (equivalent to –1.72 to 4.33 µg C individual^–1day^–1) over a range of larval sizes from 0.5 (<0.5µg C) to 5 mm (85 µg C). A diet consisting entirelyof microplankton prey supported larval growth for >2 weeks,and growth rate decreased when larvae reached 4–5 mm inlength, corresponding to the beginning of their morphologicaltransition from tentaculate to lobate feeding mode. The grossgrowth efficiency of larvae fed natural microplankton assemblageswas 3%.     

Expression, localization, and functional evaluation of CFTR in bovine corneal endothelial cells

HCO-dependentfluid secretion by the corneal endothelium controls corneal hydrationand maintains corneal transparency. Recently, it has been shown thatmRNA for the cystic fibrosis transmembrane conductance regulator (CFTR) is expressed in the corneal endothelium; however, protein expression, functional localization, and a possible role in HCO transport have not been reported. Immunoblotting for CFTR showed asingle band at ~170 kDa for both freshly isolated and primary cultures of bovine corneal endothelial cells. Indirectimmunofluorescence confocal microscopy indicated that CFTR locates tothe apical membrane. Relative changes in apical and basolateralchloride permeability were estimated by measuring the rate offluorescence quenching of the halide-sensitive indicator6-methoxy-N-ethylquinolinium iodide during Clinflux in the absence and presence of forskolin (FSK). Apical andbasolateral Cl permeability increased 10- and 3-fold,respectively, in the presence of 50 µM FSK. FSK-activated apicalchloride permeability was unaffected by H₂DIDs (250 µM);however, 5-nitro-2-(3-phenylpropyl-amino)benzoic acid (NPPB; 50 µM) and glibenclamide (100 µM) inhibited activated Clfluxes by 45% and 30%, respectively. FSK-activated basolateral Cl permeability was insensitive to NPPB, glibenclamide,or furosemide but was inhibited 80% by H₂DIDS.HCO permeability was estimated by measuring changesin intracellular pH in response to quickly lowering bath[HCO]. FSK (50 µM) increased apicalHCO permeability by twofold, which was inhibited42% by NPPB and 65% by glibenclamide. BasolateralHCO permeability was unaffected by FSK. Genistein(50 µM) significantly increased apical HCO andCl permeability by 1.8- and 16-fold, respectively. When50 µM genistein was combined with 50 µM FSK, there was no furtherincrease in Cl permeability; however,HCO permeability was reduced to the control level.In summary, we conclude that CFTR is present in the apical membrane ofbovine corneal endothelium and could contribute to transendothelialCl and HCO transport. Furthermore,there is a cAMP-activated Cl pathway on the basolateralmembrane that is not CFTR.

     

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     

Spatial heterogeneity of zooplankton biomass and size structure in southern Quebec lakes: variation among lakes and within lake among epi-, meta- and hypolimnion strata

Environmental control of zooplankton biomass size structure(53–100, 100–202, 202–500 and >500 µm)was investigated in the three limnetic strata of 25 southernQuébec Shield lakes, Canada. Among-lake differences werethe greatest source of variation of zooplankton biomass, whereasthe strong lake–by–stratum interaction observedindicated that the vertical variations of zooplankton biomassand its size fractions were not constant from lake to lake.The analysis of spatial and local factors based on thermal stratais consistent with conceptual models of predation and nutrientcontrol on the biomass and size structure of the zooplankton.Productivity of the aquatic systems, which was driven by lakedepth, flushing rate and total phosphorus concentration, wasthe primary factor influencing total zooplankton biomass andsize structure at among-lake scale in epilimnetic waters. Theeffects of the planktivorous fish on the large zooplankton biomass(>500 µm) was more clearly perceived when the effectof lake depth was removed by partial redundancy analysis. Thisstudy showed that although bottom-up and top-down forces arecomplementary in structuring of zooplankton communities, theycan also act differently on the community attributes (e.g. biomassand size structure). Among-lake zooplankton biomass is predictablefrom lake trophy, but the size structure and vertical distributionof zooplankton communities appear to be controlled by lake stratificationand by inference to interactions with size selective predationby fish. In metalimnetic waters, the 53–100 and 100–202µm zooplankton biomass fractions were primarily dependenton abiotic factors, while the 202–500 and >500 µmfractions were related to planktivory and picophytoplanktonconcentrations. The well-oxygenated and cold hypolimnetic watersof some lakes offered a refuge from surface turbulence and planktivoryto large zooplankton size fractions (202–500 and >500µm).     

Anatomic distribution of pulmonary vascular compliance

Presson, Robert G., Jr., Said H. Audi, Christopher C. Hanger, Gerald M. Zenk, Richard A. Sidner, John H. Linehan, Wiltz W. Wagner, Jr., and Christopher A. Dawson. Anatomic distribution ofpulmonary vascular compliance. J. Appl.Physiol. 84(1): 303-310, 1998.Previously, thepressure changes after arterial and venous occlusion have been used tocharacterize the longitudinal distribution of pulmonary vascularresistance with respect to vascular compliance using compartmentalmodels. However, the compartments have not been defined anatomically.Using video microscopy of the subpleural microcirculation, we havemeasured the flow changes in ~40-µm arterioles and venules aftervenous, arterial, and double occlusion maneuvers. The quasi-steadyflows through these vessels after venous occlusion permitted anestimation of the compliance in three anatomic segments: arteries >40µm, veins >40 µm, and vessels <40 µm in diameter. We foundthat ~65% of the total pulmonary vascular compliance was in vessels<40 µm, presumably mostly capillaries. The transient portions ofthe pressure and flow data after venous, arterial, and double occlusionwere consistent with most of the arterial compliance being upstreamfrom most of the arterial resistance and most of the venous compliancebeing downstream from most of the venous resistance.

     

The influence of irradiance on growth, photosynthesis and respiration of Gyrodinium cf. aureolum

The bloom-forming marine dinoflagellate Gyrodinium cf. aureolumwas grown in batch cultures over a range of irradiances (35–380µmolm^–2 s^–1 and growth, photosynthesis and respirationrates determined. Saturation of growth occurred at irradiancesof 100µmol m^–2 s^–1 Below this light level,decreases in growth rates and cell size, and a relative increasein carbon specific respiration rates, were observed. On theother hand, photosynthesis-irradiance relationships determinedfrom dissolved oxygen incubations showed that on a cellularand carbon basis, cultures grown at low irradiances had higherrates of light-limited and light-saturated photosynthesis, mainlyas a result of large increases in cell chlorophyll content.This adaptation strategy enables low-light-grown organisms toexploit available high irradiance through a relatively highphotosynthetic capacity. In cells grown at higher light levels(>100µmol m^–2 s^–1), excess photosynthatemay be diverted to storage rather than used for growth.     

Community structure, biomass and productivity of size-fractionated summer phytoplankton populations in lower Narragansett Bay, Rhode Island

Seventeen size-fractionation experiments were carried out duringthe summer of 1979 to compare biomass and productivity in the< 10, <8 and <5 µm size fractions with that ofthe total phytoplankton community in surface waters of NarragansettBay. Flagellates and non-motile ultra-plankton passing 8 µmpolycarbonate filters dominated early summer phytoplankton populations,while diatoms and dinoflagellates retained by 10 µm nylonnetting dominated during the late summer. A significant numberof small diatoms and dinoflagellates were found in the 10–8µm size fraction. The > 10 µm size fraction accountedfor 50% of the chlorophyll a standing crop and 38% of surfaceproduction. The <8 µm fraction accounted for 39 and18% of the surface biomass and production. Production by the< 8 µm fraction exceeded half of the total communityproduction only during a mid-summer bloom of microflagellates.Mean assimilation numbers and calculated carbon doubling ratesin the <8 µm (2.8 g C g Chl a^–1 h^–1; 0.9day^–1)and<5 µm(1.7 g C g Chl a^–1h^–1; 0.5day^–1)size fractions were consistently lower than those of the totalpopulation (4.8 g C g Chl a^–1 h^–1; 1.3 day^–1)and the <10 µm size fraction (5.8 g C g Chl a^–1h^–1; 1.4 day ^–1). The results indicate that smalldiatoms and dinoflagellates in fractionated phytoplankton populationscan influence productivity out of proportion to their numbersor biomass. ¹Present address: Australian Institute of Marine Science, P.M.B.No. 3, Townsville M.S.O., Qld. 4810, Australia.     

Annual patterns of ultraviolet radiation effects on temperate marine phytoplankton off Patagonia, Argentina

We carried out experiments to evaluate the effects of solarultraviolet radiation (UVR; 280–400 nm) upon primary productionof different natural phytoplankton assemblages (i.e. characteristicof a seasonal cycle) from Patagonia (Argentina) from January2001 to January 2002. The short-term impact of UVR (i.e. measuredas radiocarbon incorporation) was assessed by exposing samplesto solar radiation under six radiation treatments: uncoveredquartz tubes and tubes covered with different cut-off Schottfilters (WG295, WG305, WG320, WG360), and Plexiglas UF-3 (cut-offat 400 nm), so that samples received radiation at five differentintervals within the UVR in addition to photosynthetically activeradiation (PAR), and only PAR, respectively. Phytoplankton compositionand abundance allowed us to differentiate pre-bloom, bloom andpost-bloom periods, with pre- and post-bloom samples characterizedby small cells (e.g. flagellates <10 µm), whereas thebloom was dominated by large diatoms (50 µm). Absolutevalues of photosynthesis inhibition were lower during the bloom,but biological weighting functions (i.e. inhibition per unitenergy) indicated that this assemblage was more sensitive toUVR (especially in the UV-B region, 280–320 nm) than thoseof the pre- and post-bloom periods. UV-A radiation (320–400nm) accounted for most of the reduction in carbon incorporation(>60%), especially during the pre- and post-bloom periods.Most of the observed variability was inter-seasonal, althoughsmall intra-seasonal fluctuations were also observed. Our resultsindicate that the taxonomic composition and cellular size areespecially important when addressing UVR effects upon theseassemblages. However, other factors such as mixing can alsocontribute to the variability in responses to UVR.     

Fluid pressure in human dermal fibroblast aggregates measured with micropipettes

Previous studies indicated that connective tissue cells in dermis are involved in control of interstitial fluid pressure (P_if). We wanted to develop and characterize an in vitro model representative of loose connective tissue to study dynamic changes in fluid pressure (P_f) over a time course of a few minutes. P_f was measured with micropipettes in human dermal fibroblast cell aggregates of varying size (<100- and >100-µm diameter) and age (days 1-4) kept at different temperatures (15, 25, and 35°C). Pressures were measured at different depths of micropipette penetration and after treatment with prostaglandin E₁ isopropyl ester (PGE₁), latanoprost (PGF₂), and ouabain. P_f was positive (more than +2 mmHg) during control conditions and increased with increasing aggregate size (day 2), age (day 4 vs. day 1), temperature, and depth of micropipette penetration. P_f decreased from 2.9 to 2.0 mmHg during the first 10 min after application of 10 µl of 1 mM PGE₁ (P < 0.001). P_f increased from 3.0 to 4.8 mmHg (P < 0.01) after administration of 10 µl of 1.4 µM ouabain and from 3.1 to 4.4 mmHg after addition of 5 µl of 1.42 mM PGF₂ (P > 0.05). In conclusion, we have developed and validated a new in vitro method for studying fluid pressure in loose connective tissue elements with the advantage of allowing reliable and rapid screening of substances that have a potential to modify P_f and studying in more detail specific cell types involved in control of P_f. This study also provides evidence that fibroblasts in the connective tissue can actively modulate P_f. micropuncture; prostaglandin E₁; prostaglandin F₂; ouabain; integrins     

Phytoplankton size fractions in a tropical neritic ecosystem near Kingston, Jamaica

Temporal patterns in phytoplankton size fractions were studiedfor >1 year on the shelf south of Kingston, Jamaica. On average,in the East Channel, total chlorophyll was partitioned as 42%netplankton (>20 µm), 30% nanoplankton (2–20µm) and 28% picoplankton (0.2–2 µm); correspondingaverages for size-fractionated primary production were 27, 30and 43%. Netplankton was more variable than the other size fractions,and it predominated at times of high total chlorophyll concentration.When total chlorophyll was low, picoplankton predominated. Regressionmodels using wind and rainfall parameters could explain up to46% of the variation in chlorophyll concentrations. In theseregression models, the variation accounted for was always greatestfor the net- and least for the picoplankton. A suggested mechanismfor meteorological-phytoplankton coupling is that during periodsof easterly winds (90–150°), offshore water (in whichpicoplankton dominates) is advected onto the shelf, either displacingor diluting the nearshore water. At times of weaker westerlywinds (230–290°) there is a persistence of the phytoplanktoncommunity in nutrient-rich shelf waters and net- and nanoplanktonbiomass increases.     

Ascorbate enhancement of H1 histamine receptor sensitivity coincides with ascorbate oxidation inhibition by histamine receptors

Ascorbate has previously been shown to enhance both ₁- and ₂-adrenergic activity. This activity is mediated by ascorbate binding to the extracellular domain of the adrenergic receptor, which also decreases the oxidation rate of ascorbate. H1 histamine receptors have extracellular agonist or ascorbate binding sites with strong similarities to _1- and ₂-adrenergic receptors. Physiological concentrations of ascorbate (50 µM) significantly enhanced histamine contractions of rabbit aorta on the lower half of the histamine dose-response curve, increasing contractions of 0.1, 0.2, and 0.3 µM histamine by two- to threefold. Increases in ascorbate concentration significantly enhanced 0.2 µM histamine (5–500 µM ascorbate) and 0.3 µM histamine (15–500 µM ascorbate) in a dose-dependent manner. Histamine does not measurably oxidize over 20 h in oxygenated PSS at 37°C. Thus the ascorbate enhancement is independent of ascorbate's antioxidant effects. Ascorbate in solution oxidizes rapidly. Transfected histamine receptor membrane suspension with protein concentration at >3.1 µg/ml (56 nM maximum histamine receptor) decreases the oxidation rate of 392 µM ascorbate, and virtually no ascorbate oxidation occurs at >0.0004 mol histamine receptor/mol ascorbate. Histamine receptor membrane had an initial ascorbate oxidation inhibition rate of 0.094 min·µg protein^–1·ml^–1, compared with rates for transfected ANG II membrane (0.055 min·µg protein^–1·ml^–1), untransfected membrane (0.052 min·µg protein^–1·ml^–1), creatine kinase (0.0082 min·µg protein^–1·ml^–1), keyhole limpet hemocyanin (0.00092 min·µg protein^–1·ml^–1), and osmotically lysed aortic rings (0.00057 min·µg wet weight^–1·ml^–1). Ascorbate enhancement of seven-transmembrane-spanning membrane receptor activity occurs in both adrenergic and histaminergic receptors. These receptors may play a significant role in maintaining extracellular ascorbate in a reduced state. molecular complementarity; vitamin C; seven-transmembrane-spanning membrane receptors     

Measurement of Yield Threshold and Cell Wal Extensibility of Intact Wheat Roots under Different Ionic, Osmotic and Temperature Treatments

Yield stress threshold (Y) and volumetric extensibility () arethe rheological properties that appear to control root growth.In this study they were measured in wheat roots by means ofparallel measurement of the growth rate (r) of intact wheatroots and of the turgor pressures (P) of individual cells withinthe expansion zone. Growth and turgor pressure were manipulatedby immersion in graded osmoticum (mannitol) solutions. Turgorwas measured with a pressure probe and growth rate by visualobservation. The influence of various growth conditions on Yand was investigated; (a) At 27 °C.In 0.5 mol m^–3 CaCl₂ r, P, Y and were20.7±4.6 µm min^–1, 0.77±0.05 MPa,0.07±0.03 MPa and 26±1.9 µm min^–1MPa^–1 (expressed as increase in length), respectively.Following 24 h growth in 10 mol m^–3 KC1 these parametersbecame 12.3±3.5 µm min^–1, 0.72±0.04MPa, 0.13±0.01 MPa and 21±0.7 µm min^–1MPa^–1. After 24 h osmotic adjustment in 150 mol m^–3mannitol/0.5 mol m^–3 CaCl₂ r= 19.6±4.2 µmmin^–1, P = 0.68±0.05 MPa and Y and were 0.07±0.04MPa and 30±0.2 µm min^–1 MPa^–01, respectively.After 24 h growth in 350 mol m^–3 mannitol/0.5 mol m^–3CaCl₂ r= 13.3±4.1 µm min^–1, P= 0.58±0.07MPa, Y=0.12±0.01 MPa and ø 32±0.2 tim min^–1MPa^–1. During osmotic adjustment in 200 mol m^–3mannitol/0.5 mol m^–3 CaCl₂, with or without KCl, the recoveryof growth rate corresponded to turgor pressure recovery (t1/2approximately 3 h). (b) At 15 °C. Lowered temperature dramatically influencedthe growth parameters which became r= 8.3±2.8 um min^–1,P=0.78 MPa, r=<0.2 MPa and =15±0.1 µm min^–1MPa^–1. Therefore, Y and are influenced by 10 mol m^–3 K⁺ ionsand low temperature. In each case the effective pressure forgrowth (P-Y) was large indicating that small fluctuations ofsoil water potential will not stop root elongation. Key words: Yield threshold, cell wall extensibility, wheat root growth, temperature, turgor pressur     

A comparison of estimates of productivity and consumption by zooplankton for planktonic ciliates in Lake Ontario

A multiple regression equation predicting growth rate for ciliatesfrom cell size and temperature was combined with measurementsof biomass to estimate the productivity of ciliates in the epilimnionof Lake Ontario. This method predicts daily production to biomassvalues for ciliates of up to 5 day^–1 and leads to theconclusion that ciliate production could equal half of the carbonfixation by phototrophs. Consumption of ciliates by metazoanzooplankton was estimated by incubating samples passed through44 µm screens, and determining the increase in abundanceof ciliates over 24 h. These rates are much lower, >1 day^–1and often near zero. Production estimates based on these latterrates would be 3–4% of primary production Possible explanationsfor this discrepancy include both predation within the microzooplanktoncommunity and food limitation, as well as bottle effects However,the lower production estimates are still compatible with ciliatesplaying a major role as grazers in this ecosystem     

Copepod grazing impact on the trophic structure of the microbial assemblage of the San Pedro Channel, California

In August 2002 and March 2003 the trophic structure of the microbialassemblage from the San Pedro Channel, California was studiedfollowing the experimental alteration of the number of copepods.Changes in the abundance/biomass of microorganisms <80 µmduring 3-day incubations were monitored in (i) the absence ofmetazoa >80 µm, (ii) the presence of natural abundancesof metazoa and (iii) the presence of an elevated number of copepods.Prokaryotes and small-sized eukaryotes (<4 µm) dominatedplankton biomass during both experimental months. Diatoms numericallydominated the 10–80 µm plankton in August 2002,but ciliate and heterotrophic dinoflagellate biomass generallyexceeded diatom biomass on both dates. Ingestion of protozooplankton(predominantly ciliates) contributed substantially to copepoddaily carbon rations. The adult copepod assemblage removed 4.6and 36% per day of the microzooplankton standing stocks (10–80µm size fraction) in August and March, respectively. Elevatedcopepod grazing pressure on protozooplankton resulted in increasedbiomass of nanoplankton (<5 µm) presumably via a trophiccascade. Accordingly, the copepod–protozoan trophic linkappears to be a key factor structuring the planktonic microbialassemblage in the San Pedro Channel. This paper is one of six on the subject of the role of zooplanktonpredator–prey interactions in structuring plankton communities.     

A PHENOLIC PIGMENT REACTIVE TO L-LACTATE CYTOCHROME C REDUCTASE OF YEAST

1. A phenolic pigment was extracted from baker's yeast. The pigmentis slowly autooxidizable, and rapidly oxidized with Rhus-laccaseor polyphenol oxidase and reduced by dithionite.
2. The pigmentdissolved in ethylether had an absorption peak at258 mµ,shoulders at 289 and 382 mµ and a plateauat 450–500mµ. The difference spectrum between oxidizedand reducedforms of the pigment showed a wide plateau around500 mµ.
3. The pigment supported the oxygen uptake by reconstructed enzymesystem: L-lactate, L-lactate cytochhrome c reductase and Rhuslaccaseor polyphenol oxidase. In its absence, no oxygen uptake tookplace. The pigment was replaced successfully with p-quinone,catechol and menadione, but not with ubiquinone. The sequenceof hydrogen transport can be represented: L-lactate L-lactatecytochrome c reductase "phenolic pigment" oxidase oxygen.

(Received August 11, 1967; )     

Microzooplankton herbivory and bacterivory in Newfoundland coastal waters during spring, summer and winter

Grazing by microzooplankton on autotrophic and heterotrophicpicoplankton as well as >0.7 µm phytoplankton (as measuredby chlorophyll a) was quantified during July, August, October,January and April in the surface layer of Logy Bay, Newfoundland(47°38'14'N, 52°39'36'W). Rates of growth and grazingmortality of bacteria, Synechococcus and >0.7 µm phytoplanktonwere measured using the sea water dilution technique. Microzooplanktoningested 83–184, 96–366 and 64–118% of bacterial,Synechococcus and >0.7 µm phytoplankton daily potentialproduction, respectively and 34–111, 25–30 and 16–131%of bacterial, Synechococcus and >0.7 µm phytoplanktonstanding stocks, respectively. The trends in prey net growthrates followed the seasonal cycles of prey biomass, suggestingthat microzooplankton are important grazers in Newfoundlandcoastal waters. Ingestion was lowest during January and October(~2 µg C l^–1 day^–1) and highest in August(~20 µg C l^–1 day^–1). Aside from April when>0.7 µm phytoplankton represented the majority (~80%)of carbon ingested, bacterioplankton and <1 µm phytoplanktonrepresented most of the carbon ingested (~40–100%). Althoughmicrozooplankton have here-to-fore been unrecognized as an importantgrazer population in Newfoundland coastal waters, these resultssuggest that they play an important role in carbon flow withinthe pelagic food web, even at low temperatures in Logy Bay.     

Heterotrophic protozoa and small metazoa: feeding rates and prey-consumer interactions

A common approach to divide zooplankton into groups has beenby size or size fractionation (micro-, meso- and macrozooplankton).Whereas almost all zooplankton retained by 200 µm meshare metazoa, those not retained are proto- and metazoa. Evenso, the variability of major taxa among those retained by 200µm mesh can range widely between samples, that of passing200 pm can vary even more when considering the grazing impact.If heavily weighted towards protozoa, the <200 µm communityfeeding rate on small phytoplankton could be several times therate when most animals would be metazoa. Also, the interactionbetween proto- and metazooplankton passing 200 µm meshought to be considered, as should be that among protozoa. Usingpublished data from the North Atlantic Ocean, the potentialimpact of small metazooplankton on the chlorophyll standingstock and primary productivity as well as on protozooplanktonwas evaluated. It was found that metazoo plankton passing <200µm mesh removed a much larger part of the primary productivitythan those retained by 200 µm mesh. Although the biomassof the 200 µm mesh metazoa was close to that of protozoapassing the same mesh, their ration was only a relatively smallpart of the primary productivity ingested by the latter. Yet,due to their unusually high abundance in these oceanic waters,the overall metazooplankton appeared to come close to controllingprotozooplankton >50 µm³ in volume, i.e. those whichcould be actively perceived. It is hypothesized that in theabsence of control by meta zooplankton, protozoa control theirown abundance by predation/cannibalism.     

Mitochondrial regular arrangement in muscle cells: a "crystal-like" pattern

The aim of this work was to characterize quantitatively the arrangement of mitochondria in heart and skeletal muscles. We studied confocal images of mitochondria in nonfixed cardiomyocytes and fibers from soleus and white gastrocnemius muscles of adult rats. The arrangement of intermyofibrillar mitochondria was analyzed by estimating the densities of distribution of mitochondrial centers relative to each other (probability density function). In cardiomyocytes (1,820 mitochondrial centers marked), neighboring mitochondria are aligned along a rectangle, with distance between the centers equal to 1.97 ± 0.43 and 1.43 ± 0.43 µm in the longitudinal and transverse directions, respectively. In soleus (1,659 mitochondrial centers marked) and white gastrocnemius (621 pairs of mitochondria marked), mitochondria are mainly organized in pairs at the I-band level. Because of this organization, there are two distances characterizing mitochondrial distribution in the longitudinal direction in these muscles. The distance between mitochondrial centers in the longitudinal direction within the same I band is 0.91 ± 0.11 and 0.61 ± 0.07 µm in soleus and white gastrocnemius, respectively. The distance between mitochondrial centers in different I bands is 3.7 and 3.3 µm in soleus and gastrocnemius, respectively. In the transverse direction, the mitochondria are packed considerably closer to each other in soleus than in white gastrocnemius, with the distance equal to 0.75 ± 0.22 µm in soleus and 1.09 ± 0.41 µm in gastrocnemius. Our results show that intermyofibrillar mitochondria are arranged in a highly ordered crystal-like pattern in a muscle-specific manner with relatively small deviation in the distances between neighboring mitochondria. This is consistent with the concept of the unitary nature of the organization of the muscle energy metabolism. confocal microscopy; quantitative analysis; cardiac and skeletal muscles; probability density function; unitary structure of cells