Summer dynamics of the deep chlorophyll maximum in Lake Tahoe

Vertical profiles of chlorophyll and phytoplankton biomass weremeasured in Lake Tahoe from July 1976 through April 1977. Adeep chlorophyll maximum (DCM) persisted during summer and earlyautumn (July—October) near 100 m, well below the mixedlayer and at the upper surface of the nitracline. The DCM coincidedwith the phytoplankton biomass maximum as determined from cellcounts. In addition, the composition of the phytoplankton assemblagewas highly differentiated with respect to depth. Cyclotellastelligera was the predominant species in the mixed layer whilethe major species in the DCM layer included C. ocellata andseveral green ultraplanktonic species. In situ cell growth playsa substantial role in maintaining the DCM, but sinking of cellsfrom shallower depths and zooplankton grazing above the DCMmay contribute to the maintenance of the DCM. Calculations supportthe interpretation that the summer DCM persists at the boundarybetween an upper, nutrient-limited phytoplankton assemblageand a deeper, light-limited assemblage.     

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.     

Biogeographical structure of the microphytoplankton assemblages in the region of the Subtropical Convergence and across a warm-core eddy during austral winter

The distribution of rnicrophytoplankton in the region of theSubtropical Convergence (STC) and across a warm-core eddy shedfrom the Aguihas Return Current was investigated along two transectsin late austra] winter (June-July) 1993, during the South AfricanAntarctic Marine Eco system Study (SAAMES) III cruise. Samplingwas undertaken for the analysis of nutrients, and for the enumerationand identification of microphytoplankton species. Along bothtransects, chlorophyll con centrations were highest at stationsat the southern boundary of the STC and at the periphery ofthe warm-core eddy. Of the variance associated with chlorophyllconcentration, temperature accounted for 65% of the total. Alongboth transects, a decrease in species richness from north tosouth was observed. The spatial distribution of the numericallydominant diatom species was similar in both tran sects. Themicrophytoplankton assemblage was dominated by the subtropicaldiatom species Chaetoceros constnctus north of the STC, andby Pseudoeunotia doliolus within the eddy and south of the STC.Using cluster and ordination analyses, three significantly differentgroupings of stations were identified along the combined transects.These coincided with stations located north and south of theSTC and with the warm-core eddy proper, confirming that theSTC represents a strong biogeograph ical boundary. The predominanceof the warm-water species P.doliolus and Planktoniella sol inand around the warm-core eddy south of the STC suggests thateddies are important in the transfer of microphytoplankton acrossthis strong biogeographical boundary.     

Pigment gut contents of copepods and deep phytoplankton maximum in the Western Mediterranean

The feeding activity of Centropages typicus in the Western Mediterraneanwas evaluated during the summer stratification period, whena deep phytoplankton and chlorophyll maximum (DCM) develops.The lack of significant day-night differences in gut contentssuggests continuous phytoplankton ingestion, despite nictemeralmigration of this species. Copepods captured in the DCM hadgreater phytoplankton gut contents, both in nocturnal and diurnalsamples. The observed pattern of phytoplankton ingestion andvertical migration implies copepod-mediated upward transportof nutrients, which might contribute to the maintenance of primaryproduction in the photic layers.     

Structural analysis of winter phytoplankton in the Gulf of Naples

Quantitative and qualitative distribution of surface phytoplankton,as related to hydrographic conditions, was studied in the Gulfof Naples in February 1979. Previous work has shown that the Gulf of Naples is a diversifiedecosystem, due to geographic and hydrographic features as wellas man made eutrophication, that can be subdivided into twomajor parts: a coastal subsystem and an open water one. Hydrographic analysis of the winter situation at the surfacefully confirms this picture, as it identifies two distinct watermasses corresponding respectively to surfaced Tyrrhenian IntermediateWater and to Coastal Surface Water. The structural analysisof phytoplankton reveals three assemblages of species characterizingdifferent water types: 1 - the Ischia and Procida channels affectedby the advection of Volturno river and Cuma outfall plumes;2 - the coastal area of the Gulf proper, namely the bays ofPozzuoli, Naples and Castellammare; 3 - the open waterhemislocated beyond the 100 m isobath. The channel area assemblage is dominated by diatoms, particularlyby fast growing species, such as Asterionella japonica, severalspecies of Chaetoceros and Rhizosolenia hebetata f. semispina.The coastal assemblage is identified, among others, by the diatomsCerataulina bergonii, Hemiaulus sinensis; the dinoflagellatesGlenodinium lenticula, Exuviaella compressa and Porella perforata.The open water assemblage is characterized by the diatoms Coscinodiscuscurvatulus and Hemidiscus cuneiformis, the dinoflagellate Amphidiniumacutissimum and the coccolithophore Coccolithus haeckelii.     

Chlorophyll Content and the Pattern of Yellowing in Senescent Leaves

In senescent leaves of four species, leaf chlorophyll contentwas approximately linearly related to the estimated area ofyellow tissue, but the species differed in the amount of chlorophylllost before yellowing became apparent. Cotoneaster and Vicia leaves and Sinapis cotyledons, which produceddistinct yellowing patterns lost about 40 per cent, whereasSolanumleaves, which yellowed more uniformly lost over 60 percent of the chlorophyll before yellowing was visible. It issuggested that the leaf-cell population of Solanum may senescerather more synchronously than the other species, and that chlorophyllloss before yellowing may be a useful index of synchrony ofsenescence in leaves.     

Spatial distribution of digestive enzyme activities of Calanus finmarchicus and C.hyperboreus in Fram Strait/Greenland Sea

Digestive enzymes of copepodite V (CV) Calanus finmarchicusand C.hyperboreus from two different depths were compared duringMIZEX 1984 (June/July) at stations in the ice and open water.CV of both species from 500–200 m showed reduced enzymeactivity, indicating that they were in a resting stage. In moultingexperiments at the end of June using CV from 100–0 m moultingwas delayed and began only after 3 weeks in C.finmarchicus andafter 3 months in C.hyperboreus. These results suggest thatthe deep CV populations are the seed of the new overwinteringstock. In surface CV C.finmarchicus and C. hyperboreus enzymeactivities were generally much higher than in deep CV. In neitherspecies were enzyme activities correlated with chlorophyll concentrations.Activities in C.finmarchicus reflected overall phytoplanktondistribution and were highest in the marginal ice zone, whereasthey decreased under the ice except for polynya stations onthe East Greenland Shelf. In surface C.hyperboreus digestiveenzymes were not correlated with those of C.finmarchicus, pointingto different diets or regulatory mechanisms. Enzyme activitywas lowest in the marginal ice zone and increased under theice. High activities were found at polynya stations and otherclose pack ice. The utilization of ice algae by C.hyperboreuscould explain these discrepancies in digestive enzyme activitiesof both species.     

Reproduction rates and secondary production of three species of the rotifer genus Synchaeta in the estuarine Potomac River

Rotifers are a relatively well-studied component of lacustrinesystems but their role is only poorly understood in estuaries.Three species of the genus Synchaeta—S. baltica, S. triophthalmaand S.cecilia—dominate the cold-water assemblage of rotifersin Chesapeake Bay. Laboratory experiments were conducted todetermine the temperature dependence of egg development time(EDT) for each species; EDT varied over an approximate rangeof 90–9 h as temperature (T) varied from 2 to 22°C.The EDT/temperature relationships could be closely fitted bya simple polynomial equation of the form log(EDT) = a + b(logT) + c(log T)² for each species. Natural populations of thesethree rotifers were sampled during a cruise in the Potomac River(7–11 March 1983). Estimates of specific reproductiverates (b) were calculated based on the previously defined EDT/temperaturerelationship and the observed ratio of eggs/rotifers for eachspecies. The two most abundant species, S.triophthalma and S.cecilia,showed a clear dependence of b on the observed chlorophyll aconcentrations. Maximum reproductive rates ({small tilde}0.015h^–1) were attained only at relatively high phytoplanktondensities within a bloom of Heterocapsa triquetra where thechlorophyll a concentrations exceeded 10 µg l^–1.Estimates of secondary production suggest that Synchaeta spp.may contribute to the trophic flow of carbon in this systemwith a significance at least similar to that of the planktoniccopepods.     

Effects of urea and o-phenanthroline on F-695 emission in chloroplasts

To clarify the nature of the chlorophyll species which fluorescesat about 695 nm in vivo (F-695), effects of the addition ofurea and related compounds and of urea plus o-phenanthrolineon the emission spectra of spinach chloroplast fragments, at77°K, were examined. F-695 emission was partially decreased by the presence of alow concentration (0.1 M) of urea, thiourea, guanidine hydrochloride,methylguanidine hydrochloride, acetamide, N-methylurea, or dimethylurea. The concurrent addition of o-phenanthroline with the reagents(0.1–1 M) caused a marked increase in F-695 emission anda decrease in F-685 emission. Methyl-substituted ureas and acetamide,however, were less effective. The effect was largely dependenton the pH of the sample. These two effects, the decrease and increase in F-695 emission,were reversible and were inhibited by the presence of ethanol. The phenomena are probably due to specific interactions betweenadded reagents and the component(s) in chloroplasts which havean intimate connection with a postulated energy trap; an invivo species of chlorophyll responsible for the fluorescenceemission near 695 nm. (Received August 17, 1971; )     

Mesozooplankton community indicates climate changes in a shelf area of the inner Bay of Biscay throughout 1988 to 1990

The mesozooplankton community was monitored at both coastaland offshore sites of the Basque shelf (inner Bay of Biscay)during 1988–1990 This was considered of interest becausethe local climate change toward dry conditions was found tobe responsible for changes in shelf-water properties. In additionto seasonal changes, interannual variations in mesozooplanktonabundance and composition were evident, and primarily relatedto the year-to-year increase in water temperature and salinity.The increasing trends in copepod dominance, coupled with theincreasing abundance of species with oceanic affinity (e.g.Euchaeta hebes), were presumably a response to the increasein oceanic features in the shelf area. In the same way, thesubstantial year-to-year increase in the abun dance of specieswith summer-autumn development was attributed to the progressivewarming. Among these species, the case of Temora stylifera isdiscussed specifically because this species was very scarcein 1988, but showed unusual high abundances for the study area,and dominated the summer-autumn assemblage in 1990. We thinkthat T.stylifera can be a key species in monitoring climate-oceanologicalchanges affecting the Bay of Biscay. Results are also discussedin the context of the long climate-oceanological series forthe Bay of Biscay, and its biogeographical status.     

Environmental factors influencing diurnal distribution of zooplankton and ichthyoplankton

The diurnal vertical distribution of a large number of speciesof zooplankton, icbthyoplankton and micronekton were determinedin the top 150 m in three locations in the Shelf Water, on theNova Scotia Shelf, and Slope and on Georges Bank during springand fall periods. Species were categorized as to their trophiclevel and their type of diurnal migration behaviour. The influenceof temperature, salinity, and water density on the diurnal verticaldistribution of the species was examined. Temperature was foundto have the greatest influence on the distribution of the largestnumber of species. Diurnal migration behavior of the same speciesin Shelf and Slope water and at different times of the yearwas examined. Results showed that species changed their behaviorin the two water masses, while some species changed their migrationbehavior at different times of the year. During the night inApril the most abundant copepod species, Calanus finmarchicus,making up about 80% of the biomass, was found concentrated abovethe thermocline and the main chlorophyll layer. The majorityof the less abundant species of copepods were found below thethermocline and the chlorophyll layer. At night in August thetwo most abundant copepod species, Centropoger typicus and Paracalanusparvus, making up at least 80% of the zooplankton biomass, werealso concentrated above the thermocline and the main chlorophyllLayer. Three species of copepods were concentrated at the depthof the main chlorophyll layer and two species were concentratedbelow the chlorophyll layer and thermocline. The vertical distributionof other zooplankton and ichthyoplankton species was examinedin relation to the thermocline and chlorophyll layer. Relationshipsbetween concentrations of six species of fish larvae and allspecies of copepods in the same samples showed a general increasein the numbers of larvae m^–3 as the numbers of copepodsm^–3 increased in a range of 500–4000 m^–3.However, the concentration of Merluccius bilinearis decreasedas the concentration of copepods exceeded 4000 m^–3 suggestingthat high concentrations of copepods may not be a favourableenvironment for the larvae.     

Production of dissolved organic carbon in phyloplankton cultures as measured by high-temperature catalytic oxidation and ultraviolet photo-oxidation methods

The production of dissolved organic carbon (DOC) in culturesof the diatoms Chaetoceros gracilis and Phaeodactylum tricornutum,the flagellate Isochrysis galbana, the dinoflagellate Alexandriumtamarense and a natural algal assemblage from the NorthwestArm, Halifax, Nova Scotia, Canada, was followed using a high-temperaturecatalytic oxidation (HTCO) and a UV photo-oxidation method.Molecular weight fractionation of the DOC was performed fortwo cultures: C.gracilis and I.galbana. While the DOC in theculture medium increased significantly during log-phase growthfor all organisms except the dinoflagellate, this increase wasproportional to the increase in cell numbers; the increase inDOC per cell was either small or zero. In all cultures, maximumrelease took place during stationary and senescent phases, usuallyafter cell numbers had started to decrease. In both C.gracilisand I.galbana, a major portion (>65%) of the organic matterreleased to the medium during log-phase growth had mol. wtsof <10 000 Da. The increase in DOC in the I.galbana culturein stationary and senescent phases was due to the release ofhigh-molecular-weight materials. The differences in extracellularrelease of DOC between species and between different growthstages in the same species suggest that both the species compositionand physiological state of phytoplankton populations must beknown before interpretations and predictions based on fielddata can be made. In order to determine whether the differencesin DOC values found by the HTCO and UV oxidation methods arecaused by the resistance to UV oxidation of some compounds producedby phytoplankton, rather than by less than optimum efficiencyof the UV unit used, standards must be based on naturally occurringcompounds, rather than the pure compounds normally used.     

The Influence of Stress Conditions on Chlorophyll Content of Two Range Grasses with Contrasting Photosynthetic Pathways

The influence of various treatments and temperature regimeson total chlorophylls and on the chlorophyll a:b ratio of westernwheatgrass and blue grama plants was investigated at differenttime intervals during the 120-day growth period. Western wheatgrass,a C₃ species, accumulated greater amounts of chlorophyll thandid blue grama plants, a C₄ species. Maximum concentrations(mg gd wt^–1) of chlorophylls in western wheatgrass andin blue grama were recorded at the lower (13/7°C) and higher(30/18°C) temperature regimes. Nitrogen fertilizer alonedecreased the chlorophyll content in both species. The chlorophylla:b ratio in blue grama ranged from an average of 2·00under irrigated plus fertilized conditions to 3·00 undercontrol and fertilized conditions. On the other hand, the chlorophylla:b ratio in western wheatgrass remained constant at 3·00throughout the growing season under various treatments and temperatureregimes.     

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.     

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.     

Dry Matter Yields and Photosynthetic Rates of Diploid and Hexaploid Triticum Species

The above ground dry matter yields of two wild diploid Triticumspecies averaged 76 per cent of that of two hexaploid breadwheat varieties in field trials carried out over five years.A cultivated diploid species, T. monococcum, gave similar drymatter yields to the bread wheat varieties but had a longergrowth cycle. The flag leaves of wild diploid species had higher rates ofphotosynthesis than those of the bread wheat varieties bothwhen expressed per unit area of leaf or per unit weight of chlorophyll.Photosynthetic rates of other organs, expressed per unit weightof chlorophyll were also greater for the wild diploids thanfor hexaploids. For snoots at the stage when their flag leaveswere fully expanded, the investment in photosynthetic machinery,as measured by chlorophyll concentration, was less in the twowild diploids than in the hexaploids. This compensated for thehigh photosynthetic rate of the former, such that the specificgrowth rates, assessed by carbon-14 fixation per unit shootdry matter, were similar. Triticum spp., wheat, dry matter yield, photosynthesis, carbon-14, ploidy     

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.     

Effects of Daphnia on microzooplankton communities

Intact phytoplankton and microzooplankton communities from eutrophicStar Lake were incubated for 4 days with and without Daphniapulex, Daphnia galeaia mendotae, or a natural assemblage ofDaphnia species. They were sampled at the onset and terminationof the experiment for bacterial, phytoplankton, ciliate, rotifer,copepod and cladoceran densities. The cladocerans had variedeffects on the rotifers, ranging from significant suppressionof most rotifer species (Keratella cochlearis, Polyarthra remata,Keratella crassa) in the D.pulex jars, to the suppression ofone (K.crassa) or no species in the D.galeata mendotae and StarLake Daphnia assemblage jars, respectively. Small ciliates (<30µm, longest dimension), such as Strobilidium sp. and Pseudo-cyclidiumsp., were adversely affected by most of the cladoceran treatments,while several larger ciliates (>81 µm) were unaffectedin all such treatments. Ciliates were not consistently morevulnerable to cladoceran suppression than similarly sized rotifers.The suppression of ciliates and rotifers was attributable toboth direct effects (predation, interference, or both) and indirecteffects (e.g. resource competition) of the cladocerans. ¹Present address: Department of Biology, University of Louisville,Louisville, KY 40292, USA     

Environment Dependent Chlorosis in a Mutant Plant of Festuca pratensis, Huds

The chlorophyll content of the leaf tissue from a chlorotichomozygous recessive mutant plant of Festuca pratensis was affectedby variation in the light and temperature regimes to which theplants were exposed. Chlorophyll content was depressed whenthe plant grew rapidly, but was similar to that of normal greenplants when grown slowly under low-light and low-temperatureregimes. Chlorotic plants showed a reduction in dry weight,percentage dry matter, and plastid number but an increase inthe ratio of chlorophyll a : chlorophyll b compared to normalplants.The chloroplasts of the rapidly grown chlorotic plantsshowed a reduced lamellar structure.     

Pigmented Plant Tissues in Culture: I. Auxins and Pigmentation in Chlorophyllous Tissues

The auxins, I-naphthylacetic acid (NAA) and 2, 4-dichlorophenoxyaceticacid (2, 4-D) are shown to stimulate to varying extents thegrowth of chloro-phyllous tissues of several plant species cultivatedin vitro. Concentrations of 0.1 mg/1 of 2, 4-D or 1.0 mg/1 ofNAA are optimal for Haplopappus gracilis, and concentrationsof 1.0 mg/1 of 2, 4-D or 10.0 mg/1 of NAA are optimal for Hypochaerisradicata, Oxalis dispar, and Acer pseudoplatanus. NAA or 2,4-D in concentrations optimal for growth do not affect pigmentproduction in Hypochaeris, but inhibit in Acer and Oxalis. Inhibitionof chlorophyll formation by 2, 4-D is partial in Acer and completein Oxalis, whereas inhibition by NAA is partial in both species.Inhibition of carotenoid pigments by NAA or 2, 4-D is partialin both these species. NAA stimulates pigment production inHaplopappus and 2, 4-D inhibits; the inhibition of carotenoidsis again partial, whereas the inhibition of chlorophyll is complete. The data are discussed in relation to the development of chloroplastsin tissue cultures.