Primary production and photoadaptation of phytoplankton in relation with tidal mixing in coastal waters

In the eastern English Channel (a coastal and shallow system),photosynthetic parameters of the pbytoplankton population weremeasured during 36 h at four depths, in a neap tide period.The vertical distilbutions of chlorophyll a (chl a), nutrients,and hydrodynamic properties were monitored during the cruise.Despite vertical homogeneity in salinity, chlorophyll a andnutrient profiles,a vertical gradient in both photosyntheticparameters (     

Water-column chlorophyll in an oligotrophic environment: correction for the sampling depths and variations of the vertical structure of density, and observation of a growth period

The chlorophyll content of a water column (WCC), which is commonlyused as an index of the phytoplankton abundance, is affectedby the choice of the sampling depths and by the variations ofthe vertical structure of density. For instance, the thicknessof the water layer, between two sigma-t values, which containsthe deep chlorophyll maximum, can vary with internal waves.The resulting noise often dominates the mesoscale variationsof the observed water-column chlorophyll (OWCC). Sigma-t dependentstatistics (mean, standard deviation) of the chlorophyll concentrationare computed using the observations at 29 casts from a 22-day-longfixed station in an oligotrophic environment at 15•S, 173°E.For each cast, these statistics, the sampling depths, and thewater density at these sampling depths, allow the estimationof a station-dependent ‘expected water-column chlorophyll’(EWCC). The ratio of EWCC to the overall likelihood of WCC duringthe fixed station (i.e. the mean of all OWCC) is a measure ofthe effect of sampling and variable density structure at eachcast. When this effect is removed, the noise in WCC estimatesdecreases significantly. The time variations of WCC during thefixed station then show a trend with relatively high valuesduring the first days, followed by a 12-day-long period withlow values. A regular increase occurred from 1 October, whichwas accompanied by high carbon fixation rates and was mainlydue to an increase of the chlorophyll concentration betweenthe surface and the deep chlorophyll maximum. New productionduring this active phase was estimated to be 535 mgC m^–2day^–1, corresponding to 62% of the total production. Breakingof internal waves which were recorded at the beginning of thegrowth phase and vertical mixing of nutrients can explain theobservation.     

Pigment destruction by Calanus pacificus: impact on the estimation of water column fluxes

Measurements of gut pigment made prior to fecal pellet productionin Calanus pacificus females and CV copepodites suggest that(i) chlorophyll a and/or its pheopigment derivatives are degradedinto molecules that are not detectable by the standard fluorometrictechnique; and (ii) the percentage of ingested chlorophyll awhich degrades into fluorometrically undetected molecules isnot constant. Thus, measurements of chlorophyll and pheopigmenta in the guts of zooplankton can only yield minimum estimatesof in situ grazing rates. Estimates of the vertical flux ofprimary particulates based on chlorophyll and pheopigment abudgets may also be underestimated.     

Appendicularian assemblages in a shelf area and their relationship with temperature

The structure of the community of appendicularians was describedby multivariate analyses throughout a seasonal cycle on thecentral Cantabrian coast. It is shown by correlation and principalcomponents analysis that the appendicularian species may bearranged in a successional sequence in relative abundance thatis closely coupled to a temperature gradient. This sequencestarts with Fritillaria borealis, which exhibits highest relativeabundance during January, being sequentially followed by Oikopleuradioica, Fritillaria pellucida, Oikopleura fusiformis and Oikopleuralongicauda. This species numerically dominated the communityfrom September to December. Sea surface temperature and thetemperature at the depth of the chlorophyll maximum were bothreliable predictors of the species composition of the community.However, only the latter provided an adequate explanation forthe persistence of cryophilic communities in stratified oceanicenvironments and the dominance of thermophilic communities afterthe autumn mixing period. Under stratified conditions, surfacetemperatures are high (up to 21°C), but temperatures atthe depth of the chlorophyll maximum are low (<15°C).These differences disappear after the autumn mixing, when thewater column exhibits a uniform temperature profile (16°C).Critically, however, although there is a sharp decline in surfacetemperature, water at the depth of the chlorophyll maximum iswarmer than during stratification. A simple conceptual modelis proposed to account for these features and predictions aremade regarding the vertical distribution of appendiculariansduring stratification. The relevance of non-anthropomorphictemperature measures, such as the temperature at the depth ofthe chlorophyll maximum, for other zooplankton groups is alsodiscussed.     

Zooplankton biomass distribution patterns along the western Antarctic Peninsula (December 2002)

The phytoplankton [chlorophyll a (Chl a)], microzooplankton,mesozooplankton and macrozooplankton biomass and distributionwere studied as part of a multidisciplinary project (Tempano)along the Antarctic Peninsula during December 2002. Even thoughthe summer phytoplankton bloom was not yet developed in thearea, autotrophs dominated the plankton biomass. Phytoplanktonvertical distribution was, in general, homogeneous in the upper40–50 m of the water column, further decreasing with depth.Protozoans showed low biomass; their contribution to the totalplankton being one order of magnitude lower than that of autotrophs.The vertical distribution of protozoans was variable among stationswith marked peaks at depths ranging from 30 to 80 m. Mesozooplankton-integratedbiomass was generally low, although there was a notable increasesouthward near the ice marginal zone. Macrozooplankton distributionwas more variable without any clear zonal distribution pattern.The vertical distribution of meso- and macrozooplankton (>4mm) biomass showed clear peaks of abundance comprising differentspecies depending on the geographical area. Our biomass distributiondata suggest a food-web scenario in which macrozooplankton arepreying on mesozooplankton populations only in the northernerstations, and mesozooplankton are, in their turn, shaping theabundance of the emerging populations of microzooplankton. Phytoplankton,on the other hand, seem to be hardly controlled by grazing activity.     

HPLC analysis of phytoplankton pigments from Lake Kinneret with special reference to the bloom-forming dinoflagellate Peridinium gatunense (Dinophyceae) and chlorophyll degradatio products

Photosynthetic pigments extracted from the paniculate materialof the water column of Lake Kinneret were studied throughoutthe periods of May 1988-June 1989, and November 1993-November1994, by means of HPLC. The temporal and vertical variationof the pigment suite found agreed with the microscopically determinedphytoplankton record. The regression calculations of taxon-specificbiomass with the corresponding signature pigments suggest thatpigment analysis may be a useful tool for the monitoring ofbloom-forming species, e.g. the dinoflagellate Peridinium gatunenseNygaard. The HPLC pigment analysis permitted the identificationand quantification of chlorophyll degradation products, providingfor the first time information about their composition in LakeKinneret. Chlorophyllide a was the major detectable degradationproduct of chlorophyll a, varying between 1 and 9% of the chlorophylla concentration. Other chlorophyll a derivatives appeared mostlyin minor quantities. Pheophytin a was virtually lacking in allthe samples. Removal rates of pigments, measured by sedimentationtraps, indicated that the degradation of chlorophyll a via chlorophyllidea is a dynamic process that continues during the sedimentationof the phytoplankton particles.     

Diel vertical migration of Cryptomonas and Chromatium in the deep chlorophyll maximum of a eutrophic lake

Large populations of the phytoflagellates Cryptomonas rostratiformis,Cryptomonas phaseolus, Cryplomonas undulata and the phototrophicbacterium Chromatium cf. okenii have been observed in the oxic/anoxicboundary layer of the slightly eutrophic, dimictic lake Schlachtenseeduring the summer stratification. Vertical distribution of thesepopulations was studied with the help of a new close-intervalsampler and by in Situ fluorescence measurements with fine spatial(cm to dm) and temporal (h) resolution on 4 days in 1991, 1994and 1995. All populations lived close to the chemo dine butshowed a regular diel vertical migration with daytime ascentand night-time descent and a low migration amplitude. At leastfor one species— C. rostratiformis—the pattern ofmigration suggests that this behaviour has an endogenous origin.As a result of diel vertical migration, the population of C.rostratiformiswas spatially separated from the other dominating populationsduring daytime. Ultimate cause of diel vertical migration wasa better light supply of all populations. Another probable advantagewas the reduction in grazing pressure, as large percentagesof all populations moved into the anoxic, hydrogen sulphidecontaining water layers during night-time. ¹Present address Department of Lowland Rivers and Shallow Lakes,Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm260, D-12587 Berlin, FRG     

Assimilation Rate and Growth of Lolium Populations in the Glasshouse in Contrasting Light Intensities

Using growth-analysis techniques, the variation in relativegrowth-rate (RGR) and its components, net assimilation rate(NAR), and leaf-area ratio (LAR), was examined in 18 populationsof L. perenne, six of L. multiflorum, and two hybrid cultivarsfrom contrasting climatic and agronomic origins, grown at lowand high light intensities in the glasshouse. Significant differences between populations were found for RGR,NAR, and LAR at both light intensities. At both intensitiesthe annual or biennial multiflorum group had a greater LAR anda lower specific leaf weight and chlorophyll content than theperennial perenne group. At the low intensity this was compensatedby a greater NAR in the perenne group, with no resultant differencein RGR. At the high intensity there was no difference betweenthe groups in NAR, and hence a greater RGR in the multiflorumgroup. Within the perenne and multiflorum groups, at both light intensities,the variation between populations in RGR was based on differencesin NAR rather than in LAR. There was no regular correlationof NAR with either specific leaf weight, or chlorophyll contentat either light intensity, though at low light intensity itwas significantly correlated with shoot-root ratio.     

Chemical, mechanical and visual cues in the vertical migration behavior of the marine planktonic copepod Acartia hudsonica

Recent experimental evidence in both marine and freshwater systemsindicates that predators can induce vertical migration behaviorin individual zooplankters, yet the specific cues by which zooplankterssense their predators appear to vary. In situ manipulation experimentswere carried out with enclosed populations of the marine planktoniccopepod Acartia hudsonica to re-examine the potential role ofchemical cues in the behavior of A.hudsonica, and to test explicitlyfor the role of mechanical or visual stimuli in triggering verticalmigration behavior in this species. Adult female copepods wereinduced to vertically migrate (descend) when exposed to fishmimics during the day, but no such response occurred when thecopepods were exposed to Fish mimics during the night. Moreover,copepods exhibited no changes in vertical distribution whenexposed to water which, having recently held a natural predator(the threespine stickleback, Gasterosteus aculeatus), was presumedto be laden with predator-produced chemical exudates. Predator-mediatedmechanical or visual cues, or a hierarchy of both, are responsiblefor eliciting vertical migration behavior in adult female A.hudsonica.These results, together with those of other investigations demonstratingthe inducing role of chemical exudates, indicate that the stimulieliciting vertical migration in zooplankton can be expectedto vary between species.     

An attempt to simulate the subsurface chlorophyll maximum using populations of unphased oscillating cells

A model is proposed to represent the vertical distribution ofchlorophyll in tropical waters. It assumes that the phytoplanktonpopulations are composed of cells which oscillate around a meanlevel at a density _t = B (close to the nutricline), with anamplitude A; A and B are normally distributed variables; theoscillations are unphased so that the number of cells in a waterlayer does not vary with the time. This model is tested on datafrom the eastern tropical Atlantic and from the southwesterntropical Pacific. The results agree with the observations whenthe surface mixed layer is nutrient-exhausted. However, themodel seems to account only for a deep population, and is thenconsistent with the hypothesis of a distinct mixed layer floralassociation. The agreement between the results and the observationsis difficult when the surface mixed layer is not nutrient-limited,in areas of upwelling or intense vertical mixing. The modelaccounts for a splitting of the subsurface chlorophyll maximumafter the passage of a front in the Cape Lopez area (GuineaGulf). It also accounts for the relations between the subsurfacechlorophyll maximum, the pycnocline, and the nutricline at 48stations from the cruise PREFIL 2 in the southwestern tropicalPacific. The permanent subsurface chlorophyll maximum of oligotrophicareas seems to be more satisfactorily explained by the unphasedoscillations invoked by the model than by the sinking of thecells. These unphased oscillations have not yet been observed;their possible consequences concerning the primary productionand grazing are postulated.     

Relationship between action spectra for chlorophyll a fluorescence and photosynthetic O2 evolution in algae

Relative excitation spectra of chlorophyll a fluorescence areshown to be very close to relative action spectra of photosystemII O₂ evolution in seven micro- and macro-algae of five phyla.The conditions under which this correspondence should hold,based on theoretical considerations, and the applications ofthis correspondence to interpretation of fluorescence excitationspectra of chlorophyll a from natural populations are discussed.The spectra presented are interpreted in relation to the light-harvestingpigments and their association with the two photosystems.     

Effects of vertical-horizontal coupling on the horizontal distribution of chlorophyll a

The distributions of chlorophyll a and salinity were sampledon successive days along horizontal transects in central LongIsland Sound. Changes in the variance spectra over a periodof three days following a wind event suggest that there wasan input of variance at wave numbers of the order 6 ? 10^–3radians per meter. There was an associated increase in coherencysquared between chlorophyll and salinity. During this periodvertical structure in both chlorophyll and salinity was reestablished.It appears that horizontal structure was generated by the interactionof this vertical structure with a vertical shear in horizontalcurrents at semidiurnal and lower frequencies and possibly byshort period internal waves with frequencies near the V?is?l?frequency.     

Bias in satellite-derived pigment measurements due to coccolithophores and dinoflagellates

Satellite-derived estimates of phytoplankton pigments are thoughtto be affected by the phytoplankton species composition. Measurementsof surface algal chlorophyll and satellite-derived pigment werecompared for waters containing coccolithophores and dinoflagellates.Satellite-derived chlorophyll concentration was underestimatedby a factor of 2–3 in a patch of the large coccolithophore,Umbilicosphaera sibogae, and also in a bloom of the dinoflagellate,Gonyaulax polyedra. Overall abundance and species-specific propertiessuch as light scatter and vertical migration probably causedthese results.     

Phytoplankton pigments at the Weddell-Scotia confluence during the 1993 austral spring

During a 1993 austral spring cruise, a complex biomass was encounterednear South Orkney Island that ranged from a low-biomass, Chaetocerostortissimus assemblage south of the front towards the ice edge,to a high-biomass, Thalassiosira gravida-dominated assemblageat the northern edge. The maximum levels of chlorophyll (Chl)a (up to 6 mg m^–3) were higher than those observed inprevious high-performance liquid chromatography-based studiesof pigments in the pelagic Southern Ocean. The non-photosyntheticpigment chlorophyllide a comprised up to 75% of the chlorophyllouspigments in the southern assemblage, but < 5% in the northernassemblage. Concentrations of the xanthophylls diadinoxanthin(DD) and diatoxanthin (DT), used as indicators of mean irradiance,indicated low-light-adapted populations. Low-light DD + DT/Chla ratios in surface waters indicated that vertical mixing limitedphytoplankton residence time in the near-surface layer, andthus limited exposure to maximum irradiance. Deck incubationsof natural assemblages indicated that the dark epoxidation reaction(i.e. the return of DT to DD) was a two-step reaction with theinitial rate being more rapid (t^1/2 = 9.5 min) than the second(t^1/2 = 55 min). Fucoxanthin, a major diatom pigment, was morestable chemically in the water column than Chl a, and the verticalprofiles of fucoxanthin followed those of chlorophyllide a insome cases. The formation and apparent stability of chlorophyllidea and fucoxanthin are important considerations when estimatingphotosynthetically active biomass over large regions of theocean.     

Impact of Daphnia pulex on a metalimnetic microbial community

A well-structured metalimnetic community, composed mainly ofphototrophic purple bacteria, Cryptomonas, and a few speciesof ciliates and rotifers, was regularly found between 1984 and1991 in Lake Cis. These populations appeared during spring,reached high concentrations and remained in the metalimnionuntil winter mixing. We had previously postulated that thesemetalimnetic populations could persist in such high numbersbecause they were free of efficient predation, since the oxygen-sulfideinterface provided a refuge from predation. In September 1992,an abundant Daphnia pulex population developed in the lake whichresulted in drastic changes in the formerly stable community.The presence of D.pulex induced an extreme clear-water phasein the epilimnion and the metalimnetic populations were severelyreduced. Feeding experiments with Cryptomonas and heterotrophicand phototrophic bacteria as food for D.pulex resulted in clearancerates around 0.7 ml individual^–1 h^–1. The impactwas very high on the microaerophilic populations, whereas theanaerobic populations were least affected, since sulfide limitedthe vertical distribution of ^D.pulex. We conclude from thisevidence that the metalimnetic populations in previous yeanwere mostly food limited (bottom-up control) and that theirhigh abundances were in great part due to a lack of efficientpredation.     

The presence of chlorophyll b and the estimation of phaeopigments in marine phytoplankton

A reverse-phase h.p.l.c. technique was used to estimate theconcentration of chlorophyll b in phytoplankton cultures, fecalpellets of Calanus pacificus, and suspended paniculate matterfrom the Central North Pacific, Oregon coastal waters, and DabobBay (a temperate fjord in Puget Sound, WA, USA). The purposewas to assess the distribution of this pigment in the euphoticzone and its effect on the fluorometnc estimation of phaeopigments.Analyses of natural waters confirm high chlorophyll b concentrations(median mass ratio of b:a > 0.3) at the depth of the chlorophylla maximum in tropical waters while values for temperate planktonare relatively low (median mass ratio of chl b:a = 0.05) andpatchy. Zooplankton fecal pellets showed a significant enrichmentin chlorophyll b, suggesting grazing as a mechanism to explainhigh concentrations of this pigment at the bottom of the euphoticzone. It is estimated that the presence of chlorophyll b couldcause an average overestimation of phaeopigment concentrationby the fluorometnc technique of 38% between 0 and 200 m in theCentral North Pacific. This effect is more pronounced at thelayer of chlorophyll b maximum (120–140 m). ¹Present address: Marine Biology Research Division, A-002, ScrippsInstitution of Oceanography, La Jolla, CA 92093, USA     

Observations on the vertical distribution of zooplankton, including post-larval teleosts, off Plymouth in the presence of a thermocline and a chlorophyll-dense layer

During 1973 – 1977, when Sagitta elegans was returningto dominance over S. setosa in Plymouth waters, there was often,in summer in stratified conditions, a community characterizedby S. setosa in the warm water above the thermocline, and atypical S. elegans community in the colder layer below the thermocline.This vertical separation persisted at night even though somespecies from the S. elegans community migrated up into the warmlayer. Such vertical migration was not stopped by a temperaturediscontinuity of from 3° to 6°C, but fewer individuals,or a lesser proportion of species, took part at the higher temperaturedifference. Only a small part of the zooplankton, comprisingsmall individuals of Limacina retroversa, the appendicularians,and, possibly, post-larvae of Arnoglossus laterna, showed signsof aggregation at the thermocline or the chlorophyll maximumclose to it.     

Fluorescence characteristics of cyanobacteria (blue-green algae)

The fluorescence characteristics of the cyanobacteria Synechocystisaquatilis Sauv., Microcystis firma (Breb. et Lenorm.) Schmidleand Synechococcus leopoliensis (Racib.) Kom. and the green algaScenedesmus quadricauda (Turp.) Breb. were examined. In thethree cyanobacteria, phycocyanin is the main accessory pigment.Phycoerythrin is not present in our investigated strains ofcyanobacteria. The highest excitation of the chlorophyll a (Chla) fluorescence of cyanobacteria resulted from light with wavelengthsof 620–630 nm. A definite ‘Kautsky’ effectis also evident at this wavelength. However, excitation withblue light (420–520 nm) produced only very slight fluorescence.The Kautsky effect is not evident at these wavelengths, evenat high photon flux densities. For Scenedesmus, fluorescencecharacteristics typical of green algae were found. The fluorescenceexcitation of cyanobacteria at 620 nm corresponds to a photosynthesispeak in the action spectrum measured in terms of O₂ production.The results underline the necessity of fluorescence measurementsat several wavelengths whenever mixed populations are involved.Such measurements also present possibilities for more accurateestimation of biomass and potential photosynthetic productionin mixed populations.     

Annual cycle of zooplankton community in the Abra Harbour (Bay of Biscay): abundance, composition and size spectra

The annual cycle of the zooplankton community in a coastal embaymentof the Bay of Biscay was studied from data on zooplankton fractionslarger than 45 and 250 µm Smaller zooplankton and chlorophyllmaxima coincided in summer, while larger zooplankton reachedthe maximum in spring. Copepods dominated in both fractionsmost of the year, being copepod nauplii and postnaupliar stagesof Oithona nana and Paracalanus parvus the main constituentsof the microzooplankton maxima, and older copepodites and adultsof Acartw clausi of the meso-macrozooplankton maxima. Secondarypeaks of abundance due to protozoan blooms of Steno-semellanivalu, in early spring, and Noctiluca santillans, in summer,were also observed in smaller and larger fractions respectively.The collapse of phytoplankton biomass in early autumn was followedby a strong decrease of zooplankton in mid autumn. From thisperiod to winter, chlorophyll and zooplankton abundance showedsmall variations, but noticeable changes in the compositionand size spectra of zooplankton were observed. In winter, valuesof chlorophyll and zooplankton abundance reached minima, A.clausidominated the copepod assemblage and carnivorous zooplankterswere absent or negligible The annual development of the mainpredator populations (Sagitta frideria, Luiopc tetraphylla andanchovies) were found to be synchronized with the variationsin abundance and size spectra of zooplankton in the study area.     

Morphological and Physiological differences between Epilithic and Epiphytic populations of the Lichen Parmelia pastillifera

CO₂ exchanges, morphology and chlorophyll content of epiphyticand epilithic populations of Parmelia pastillifera growing inthe same locality (Bristol, UK) were investigated. Epilithicsamples had reduced net photosynthetic rates and a lower chlorophyllcontent, apparently caused by the high levels of irradianceof the exposed habitat, not completely buffered by the increasedthickness of the upper cortex. These samples also had much moredeveloped rhizinae; this modification is interpreted as a mechanismto increase the water storage capacity of the thallus. Physiologicaldifferences between the two populations seem to be due to themore extreme environmental conditions of the epilithic population.Copyright1995, 1999 Academic Press Chlorophyll content, CO₂-exchange rates, habitat, lichen, morphology, Parmelia pastillifera