Summer nutrient dynamics in the Middle Atlantic Bight: primary production and utilization of phytoplankton carbon

In late summer, production and utilization of carbon in thestratified water of the Middle Atlantic Bight appears to approachsteady-state conditions. In the euphotic zone there is a paniculateorganic carbon (POC) pool of {small tilde}6000 mg Cm^–2.Primary production adds {small tilde}350 mg C m^–2 d^–1,while zooplankton ingestion removes {small tilde}450 mg C m^–2d^–1, of which {small tilde}135 mg C m^–2 d^–1are returned to the POC pool as feces. Sinking of POC averages{small tilde}240 mg C m ^–2 d^–1. Thus, there is anet loss from the euphotic zone of {small tilde}200 mg C m^–2d^–1, which represents a removal rate from the POC poolof {small tilde}3%d^–1. However, sinking losses of phytoplanktoncarbon from the POC pool were small ({small tilde}12 mg C m^–2d^–1), which suggests that most of the primary productionenters the pelagic food chain. This is in sharp contrast tothe conditions in early spring, when the POC pool increasessubstantially, and the main loss is sinking rather than heterotrophicconsumption. ^*This research was supported by the U.S. Department of Energyunder Contract No. DE-AC02-76CH000I6.     

Localization and Characterization of a Novel 20 kDa Polypeptide in the Chloroplast of the Green Alga Dunaliella salina

Recent work with the green alga Dunaliella salina showed thepresence of a {small tilde}20 kDa chloroplast protein that wasrecognized by polyclonal antibodies raised against the isolatedLHC-II [Webb M.R. and Melis A. (1995) Plant Physiol. 107: 885].In this report, a characterization of the {small tilde}20 kDapolypeptide is presented. It is shown that it is localized inthe chloroplast envelope membrane of D. salina. The abundanceof this protein is constant on a per cell basis and independentof the light regime during cell growth. The {small tilde}20kDa polypeptide is easily degraded to a {small tilde}19 kDaproduct during sample preparation. A limited amino acid sequenceof 21 residues from the free N-terminus of the {small tilde}19kDa product was obtained. On the basis of this partial sequence,it was concluded that the {small tilde}20 kDa polypeptide isnot a degradation product of a known LHC-II but rather a novelprotein. The {small tilde}20kDa polypeptide did not cross-reactwith antibodies raised against the Cbr (carotene biosynthesis-related)gene product and showed a different electrophoretic mobilityfrom the latter. Light-shift experiments suggest that the {smalltilde}20 kDa polypeptide is not an ELIP (early light-inducibleprotein). Possible functions of the {small tilde}20 kDa proteinare discussed. ¹Permanent address: Department of Biochemistry, University oflund, PO Box 124, S-221 00 Lund, Sweden     

Diurnal vertical migration of Gymnodinium mikimotoi during a red tide in Hoketsu Bay, Japan

The depth, velocity and timing of the vertical migration ofGymnodinium mikimotoi were examined using fluorometric fieldobservations. Gymnodinium mikimotoi can migrate vertically {smalltilde}20 m daily at velocities of {small tilde}2.2 m h^–1     

In Vitro Phosphorylation of Proteins in IAA-Treated Mesocotyls in Zea mays

Five-mm sections of elongation zones of Zea mesocotyls wereincubated for designated periods with various concentrationsof IAA. In vitro protein phosphorylation in the soluble fraction(85,000 x g supernatant) prepared from the sections was analyzedby sodium dodecyl sulfate-polyacrylamide gel electrophoresis.The phosphorylation of proteins in the soluble fraction thathad been prepared from sections incubated for 20 min in thepresence of 10{small tilde}^s M IAA was greater than that inthe sections incubated for 20 min without IAA. The amount ofphosphorylation of proteins per protein became higher when higherconcentrations increased (10{small tilde}⁸—10{small tilde}⁵M).The growth of sections incubated in the presence of 10{smalltilde}⁸ M IAA or higher concentrations was greater than thatof sections incubated in the absence of IAA. The promotion ofgrowth by IAA was greater at higher concentrations of IAA. Proteinsin the soluble fraction, prepared from sections incubated for20 min in the presence of 10{small tilde}⁵ M IAA, were phosphorylatedin the presence of either 10 fM cAMP, 10 µM cGMP, 100µM W-7, 100 µM W-5, 20 µM H-7 or 20 µMHA1004. The calmodulin antagonist, W-7, and the inhibitor ofprotein kinase C, H-7, inhibited the phosphorylation of proteinsstimulated by incubation with IAA. These results suggest thatIAA promotes cell elongation via protein phosphorylation thatdepends on calmodulin-dependent protein kinase and protein kinaseC. (Received November 29, 1995; Accepted May 20, 1996)     

An Optical Model for Phototactic Orientation in Dictyostelium discoideum Slugs

The optical properties of an enlarged optical model of the tipof a slug (a glass tube filled with sucrose solution) of Dictyosteliumdiscoideum were studied to validate the hypothesis that theorganism orients itself with respect to lateral light usinga lens effect: Light is focussed by refraction onto the distalside of the slug where the higher "signal" compared to the frontside causes a turn toward the light. Light was effectively focusedeven when the model deviated only as little as 10° fromthe light direction. Slugs of D. discoideum strains HO596 and HO813 show bidirectionalphototaxis: They orient themselves at some angle on either sideof the incident light beam. This angle is {small tilde}80°in HO596 and {small tilde}70° in HO813. We suggest thatthis phenomenon can be explained by the optical properties ofthe slug such as absorption and scattering, shape of the tipor location and extension of the light-sensitive zone. The angleof orientation with respect to light is regulated by a balancebetween a turn toward and a turn away from the light direction. (Received October 15, 1985; Accepted February 10, 1986)     

Respiration in eutrophic lakes: the contribution of bacterioplankton and bacterial growth yield

The contribution of bacterioplankton to total plankton respirationwas measured in two eutrophic Danish lakes and in experimentalenclosures treated with planktivorous fish and nutrients. Bacterialrespiration was calculated from measured oxygen uptake ratesin particles passing a 1.0-µm pore size filter, the rateswere then corrected for the size distribution of glucose uptake.During summer the respiration of the planktonic bacteria contributed{small tilde}50% of the community respiration in the two lakes.Prolific phytoplankton growth induced by biomanipulation andnutrient addition created situations where the contributionof the bacteria decreased to 20%. High bacterial contributionsto community respiration were found when the phytoplankton biomassdecreased. Simultaneous measurements of bacterial respirationand production (by means of [³H]thymidine incorporation) allowedan estimation of bacterial growth yield, which ranged from 9to 66%. In the two lakes the growth yield was constant witha mean of 29 ± 5% (±SD, RQ = 1). The variabilityof the growth yield was larger in the enclosures. The wide range(9–66%) was mainly caused by changes in bacterial netproduction without concomitant changes in respiration. The discussionincludes an evaluation of the oxygen uptake method in size fractionatedsamples and the availability of labile organic substrates asa factor controlling bacterial growth yield. Present address: Institute of Biology and Chemistry, Universityof Roskilde, P. Box 260, DK-4000 Roskilde, Denmark     

Nitrate and ammonium uptake by plankton in an Amazon River floodplain lake

Uptake of ammonium and nitrate by plankton was measured in tropicalLake Calado, Brazil. Nitrate uptake was strongly influencedby light and was light saturated at {small tilde}340 µEm^–2 s^–1. In contrast, uptake of ammonium was lessinfluenced by light, and saturated at {small tilde}250 µEm^–2 s^–1. Uptake rates of both forms of nitrogenwere inhibited by up to 80% at light intensities higher thanthose required for saturation. Concentrations of ammonium andnitrate also had a strong influence on uptake rates. Half-saturationconstants (0.3–5 µM) were usually greater than ambientconcentrations (0.1–0.6 µM), indicating that uptakerates at ambient concentrations were less than one-half of thesaturated rates. Ammonium is the more important type of inorganicnitrogen for plankton of Lake Calado because nitrate concentrationsremain low to undetectable except during periodic inputs ofnitrate-rich water from the Amazon River. Using the observeddependence of uptake on concentration and light, maximum uptakerates per unit chlorophyll were computed to be in reasonableagreement with rates derived from P^B_m values for carbon uptake. ¹ Present address: Florida Department of Natural Resources,Marine Research Laboratory, St Petersburg, FL 33701, USA     

Regional differences in stratification and its effect on phytoplankton production and biomass in the northwestern Irish Sea

Differences in tidal mixing result in the formation of offshoremixed and stratified regions in the NW Irish Sea during springand summer. Stratification resulted from vertical gradientsin temperature, although vertical gradients in salinity wereimportant during the early stages of stratification. The northerncoastal and offshore mixed regions were characterized and distinguishedfrom the southern coastal and summer stratified regions by thepresence of more saline, cool near-surface water and incompletedepletion of dissolved inorganic nutrients. Distinct regionaldifferences in the production season of phytoplankton were observed.This lasted 6 months with a seasonal production of 155 g C m^–2in the southern coastal region. A shorter season, 4 and 2 months,and lower production of 101 and 96 g C m^–2 occurred inthe summer stratified and northern mixed regions, respectively.The southern mixed region supported the shortest season (<2months) and lowest production (66 g C m^–2). It is estimatedthat a daily light exposure of {small tilde}200 Wh m^–2is required for the onset of the production season and it isconduded that the subsurface light climate as a function ofsolar radiation and surface mixed layer depth, rather than nutrientavailability, controls its duration. The existence of a shortlate production season in the offshore regions is confirmedand this contrast with the season in the North Sea is attributedto differences in the subsurface light climate. Sustained productionin the southern coastal region may play an important role infish recruitment and offset any effect of the short late offshoreproduction season.     

Dynamics of autotrophic picoplankton in Lake Constance

The vertical distribution, biomass concentrations and growthrates of autotrophic picoplankton (APP) were investigated duringthe growing season (March-October) in Lake Constance in differentdepths. Cell numbers determined by epifluorescence microscopyvaried between 1.0 x 10³ and 1.6 times; 10⁵ cells ml^–1depending on season and water depth. Highest concentrationswere recorded above the thermodine in late summer. Numerically,APP consisted almost exclusively of chroococcoid cyanobactena.During lake stratification several peaks of biomass concentrationsoccurred in epilimsietic waters at intervals of 6–8 weeks.In-situ experiments using a dilution technique and dialysisbags revealed that during summer APP population dynamics wereprimarily driven by combined changes of their growth and grazingrates, whereas temperature was less important. Gross growthrates varied between 0.006 and 0.051 h^–1, grazing ratesbetween 0.002 and 0.053 h^–1. On average APP productionwas completely removed by grazing within the microbial community.Ciliates, heterotrophic nanoflagellates and rotifers have beenidentified as the major consumers of APP cells. APP biomassis small compared to larger phytoplankton, ranging from ito5% of total phytoplankton biovolume. Due to its high gross growthrates, which are on the same level as those of free-living pelagicbacteria, APP contributes slightly more to overall primary productionwith maximum percentages of {small tilde}15% in late summer.     

The effects of Cu on the adenylate energy charge of open ocean phytoplankton

The effects of short-term, acute Cu exposure (6 h) on the adenylateenergy charge (EC_A) of open-ocean phytoplankton populations(northeastern equatorial Pacific) were investigated. Energycharge remained at {small tilde}0.77 over the range of Cu additions(0.025 – 5.µg l^–1), even though ¹⁴C uptakeand total adenylate levels (ATP + ADP + AMP) were reduced byas much as 60%. These findings suggest that EC_A alone is nota sensitive indicator of acute sublethal metal effects on phytoplankton. ¹This research was supported by the NSF Biological OceanographyProgram grant #OCE 81-17286.     

Algal respiration and the regulation of phytoplankton biomass in a polymictic tropical lake (Lake Xolotlán,Nicaragua)

Community respiration in tropical Lake Xolotlán, Nicaragua, was assessed seasonally and during diurnal cycles, via oxygen consumption in bottle enclosures. Results were analysed in relation to phytoplankton biomass, mixing depth, depth of photic zone and phytoplankton production. A great part of community respiration was associated with the heterotrophic activity of the phytoplankton biomass or its degradation by bacteria and 80% of the variability in oxygen consumption was explained by the variation of chlorophyll-a. Specific rate of respiration was 1.5 mg O2 mg Chla-1 h-1 during diurnal cycles, which corresponded to less than 5% of the specific rate at optimum depth of production. Still, diurnal water column respiratory losses were always of the same magnitude as the total photosynthetic gains in the photic zone, since the mixing depth exceeded the depth of the photic zone. Total column net growth was zero at a ratio between depth of photic zone and mixing depth of 0.19. Water level variations however altered the mixing depth and affected this ratio and net growth. As a consequence, the phytoplankton biomass either increased or decreased until the ratio was re-established through changes of the photic zone depth, which was governed by the phytoplankton biomass itself through the chlorophyll-a light attenuation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Apparent molar volumes and tastes of molecules with more than one sapophore

The taste qualities of molecules known to generate more thanone type of taste (multisapophoric molecules) or known to containmore than one sapophore (potentially multisapophoric molecules)have been examined by physical methods in an attempt to explaintheir dominant taste response. The physical parameters examinedwere intrinsic viscosity, Huggins constant, apparent molar volumeand apparent specific volume. The apparent specific volume wasfound to discriminate between the four basic tastes (salt <{small tilde}0.33, sour {small tilde}0.33 to {small tilde}0.52,sweet {small tilde}0.52 to {small tilde}0.71 and bitter {smalltilde}0.71 to {small tilde}0.93) when applied to 48 unisapophoricmolecules. The corresponding values for 18 multisapophoric moleculeslie close to the appropriate primary taste interface. The apparentlyanomalous behaviour of six other molecules is discussed. Itis suggested that in order to elicit a particular basic tastea molecule must contain the appropriate sapophore and interactwith water so as to achieve a critical specific volume. Theseresults are consistent with the idea that specific receptorsfor the four taste modalities reside at different layers ofthe taste epithelium.     

The allometry of algal respiration

For 30 years, study after study has shown that respiration ratesincrease as {small tilde}0.75 of body size for organisms rangingfrom protozoans to mammals. However, a number of studies suggestedthat the respiration-size relationship for algae may be a rareexception to this general rule. Algal respiration may be almostproportional to cell size, such that the slope of the respiration-sizerelationship is closer to unity. The present study examinedthe effect of cell size and taxon on phytoplankton respiration,using data collected from the literature. To this end, we collecteda data set of 178 observations of algal respiration and cellsize representing six divisions-chlorophytes. chrysophytes,cyanophytes, euglenophytes, pyrrophytes and rhodophytes. Therelationship between respiration (R, in p1 O₂ cell^–1 h^–1)and cell carbon content (C, in pg C cell^–1) is describedas R = 0.030C^{0 93} and the exponent is significantly >3/4.When we expressed cell size in terms of volume, the exponentdecreased to 0.88 but this is still significantly >3/4. Amongthe six divisions studied, chlorophytes, euglenophytes and rhodophytesseemed to differ significantly in their respiration-size relationshipfrom other taxa. However, euglenophytes and rhodophytes havesuch small size ranges that no meaningful relationships canbe developed for those groups alone. The chlorophyte respiration-sizerelationship has obvious patterns in its residuals which mayindicate that significant sources of error were not controlledin these heterogeneous data. Thus, for the present, the generalmodel seems most appropriate for the prediction of respirationrates of phytoplankton.     

Growth and production of Euphausia lucens in the southern Benguela Current

The growth rate of a population of Euphausia lucens from thewest coast of South Africa was estimated from laboratory studiesand from monthly size-frequency distributions of samples collectedover a 1-year period. Laboratory studies indicated that growthrates ranged from 0.131 (larvae) to 0.047 mm day^–1 (juveniles),while size-frequency distributions suggested a growth rate of{small tilde}0.026 mm day^–1 for the adults. The mean annualbiomass from the inshore, intermediate and offshore regionsranged from 9.75 to 47.29 mg dry wt m^–3 with the highestbiomass being found in the inshore region. Calyptopis larvaewere present for most months of the year, indicating continuousrecrwtment. The relative contribution of flesh, moults and eggsto the total annual production was estimated separately forall three regions. Production due to growth (P_g) was estimatedto be 92.71–185.60 mg dry wt m^–3 year^–1, whileexuviai production (P_e) varied between 60.01 and 281.38 mg drywt m year Production of eggs (P_r) was estimated to range from5.07 to 12.39 mg dry wt m year the lowest value being obtainedin the inshore region. Moult production represented {small tilde}6times the mean biomass in each region, while the P/B ratio forflesh production varied from 3.92 to 8.91, the highest ratiobeing obtained in the offshore region. Total P/B ratios rangedfrom 10.14 to 16.01.     

Microzooplankton, vertical mixing and advection in a larval fish patch

A large ({small tilde}30 ? 75 km) patch of larval walleye pollock,Theragra chalcogramma, was located south of the Alaska Peninsuladuring May 1986. A drifter deployed in this patch followed ananticyclonic path consistent with dynamic topography. Changesin community composition and vertical distribution of microzooplankton>40 µm were sampled for 4 days alongside this drifterto examine feeding conditions for larvae. Biological and physicalchanges during the first 2 calm days revealed substantial small-scalevariability within the larger circulation pattern. Changes duringthe last 2 days were dominated by vertical mixing due to strongwinds. Despite mixing, prey concentrations remained adequatefor feeding by larval pollock as determined by laboratory studies.A satellite-tracked drifter replaced the first drifter and wasstill located within the patch 6 days later. Overall distributionsof larvae and movements of the drifters show a net translationof 7.8 km day^–1 south-westward, but details of the studyreveal complex interactions between coastal waters and a coastalcurrent. During the 10-day period there was an increase in standardlength of the larval fish population of 0.13 mm day^–1and a decline in abundance of {small tilde}7.6% day^–1.Both calculated rates must be underestimates due to continuingrecruitment of small larvae from hatching eggs.     

Environmental control of phytoplankton productivity in turbulent turbid systems

Factors affecting phytoplankton productivity are analysed in turbid systems, such as shallow lakes and rivers. When resuspension from the sediment or loading from the catchment significantly increases inorganic (non-algal) turbidity and hence light attenuation potentials for high production are not realised. Energy available for phytoplankton growth is strongly regulated by underwater light availability which depends on the critical mixing depth, fluctuating light intensities and algal circulation patterns. Higher production rates in shallow waters are often compensated by greater algal respiration due to higher water temperatures when compared to deeper lakes.Total daily integral production of turbulent, turbid environments can be predicted from a combination of easily measured variables such as maximum photosynthetic rates, algal biomass, surface irradiance and some measure of underwater light attenuation.     

Red tide assemblage formation in an estuarine upwelling ecosystem: Ria de Vigo

Red tides are conspicuous in the upwelling system of Galicia(NW Iberian Peninsula). At present, there are conflicting hypothesesabout the generation site of these phytoplankton assemblages.It is interesting to know whether the rias can be sites of redtide formation or if they act only as accumulation sites ofpopulations advected from shelf waters. A study in the Ra deVigo, carried out during late September 1990, showed the developmentof a red tide assemblage, composed of Alexandrium affinis, Ceraiiumfusus and Gymnodinium catenaium, during a 2 week upwelling-downwellingcycle. Growth occurred at the bottom of the thermocline-topof the nutricline. Above this assemblage, a diatom assemblage(large diatoms) was blooming. Prior to the formation of thered tide, a subsurface chlorophyll maximum made up of smalldiatoms (Nilzschia f. seriaia, Chaeloceros socialis), smallflagellates (<30 µm) and small gymnodinid forms (<30µm) was observed. In the nutrient-depleted upper layer,several autotrophic and large heterotrophic dinoflagellatesdominated. It is suggested that the ratio between the velocityof upward water movement and the depth of the stratified upperlayer (flushing rate, day^–1) is the critical parameterwhich triggers active phytoplankton growth. It can be concludedthat upward water velocities of {small tilde}2.5 m day^–1and a stratified upper layer of 10 m depth (flushing rate 0.25day^–1) are the main physical constraints for red tidedevelopment.     

The annual cycle of Mesodinium rubrum in the waters surrounding the Isles of Shoals, Gulf of Maine

Mesodinium rubrum was collected in Kemmerer bottles, fixed inBouin's solution and protargol stained. Cell volume showed aseasonal change of over an order of magnitude, being largest(3.25x10⁴ µm³) in the early spring and smallest in thesummer. Cell abundance was highest in the spring and lowestin the summer. Biomass followed a similar trend ranging from{small tilde}1 to 147 J m^–3 Production, estimated by amultiple regression that incorporated ambient temperature andcell volume, was 2.5 kJ m^–3 day^–1 This is {smalltilde}0.3% of the primary production.