Carbon isotopic composition of Trichodesmium spp. colonies off Bermuda: effects of colony mass and season

Colonies of Trichodesmium spp. are conspicuous, macroscopiccomponents of the life in tropical and subtropical oceans. Thelarge size and the morphology of the colony raise questionsregarding the mechanism of carbon supply for photosynthesis.Constraints on these mechanisms may be indicated by the stablecarbon isotopic composition (¹³C) that reflects the balancebetween carbon supply and speciation, as well as the growthrate and colony size. The ¹³C of Trichodesmium off Bermuda measuredhere revealed a strong correlation between size of individualcolonies and season. The smallest colonies, 2–7 µgC colony^–1, showed the lightest ¹³C composition (–19),increasing to asymptotic values of –12 above 7 µgC colony^–1. The average ¹³C of the colonies was lightestimmediately after the onset of stratification in the SargassoSea, gradually increasing by 4 to heavier values during thesummer. We propose that the mass effect is due to increaseduse of HCO₃^– by the larger colonies, whereas the seasonalinfluence may be related to changes in irradiance and pCO₂ affectingthe internal carbon cycling.     

Trophic diversity within the planktonic food web of the Elbe Estuary determined on isolated individual species by 13C analysis

The uptake of organic substrates by heterotrophic planktonicorganisms was studied along the freshwater Elbe Estuary in May,July and October 2000 using ¹³C analysis of individually isolateddominant species of copepoda, cladocera, rotifera and ciliata.Non-sedimenting suspended particulate matter (SPM_ns) was separatedfrom sedimenting matter and further analysed for the chemicalcomposition of its different size fractions in order to estimatesubstrate availability. Particles <5 µm accounted for15% of total SPM_ns [40 mg dry weight (DW) L^–1] and containedC:N ratios indicating a predominance of living matter (i.e.mass C:N of phytoplankton). All species under study exhibiteda high capacity for selective feeding with little variationin the diet along the whole freshwater profile. Picoplanktonof 0.2–1.2 µm formed mainly by bacteria had a ¹³Cvalue of –26 in May and July and –29 in October,similar to the ¹³C of the dissolved organic carbon (DOC). Bacteriadid not fractionate isotopically and did not preferentiallyconsume specific subunits of their substrate, i.e. they exhibitedno trophic shift. It appears that phytoplankton exudates werea minor component to total DOC in this estuary. Phytoplanktonwas the exclusive food for all phagotrophic organisms understudy in July, thus only one trophic level was exhibited. DuringMay and October the grazers under study used different substrates,resulting in a planktonic food web of three trophic levels formedby different species of the taxonomic groups under study. Theresults indicate a conditioned behaviour with regard to substrateselection allowing the grazers to produce high abundances evenwhen particles were abundant and competition for phytoplanktonwas high.     

Occurrence of mycosporine-like amino acids in the red-tide dinoflagellate Alexandrium excavatum: UV-photoprotective compounds?

Water extracts of the red-tide dinoflagellate Alexandrium excavatumgrown at ‘high’ light intensity (200 µE m^–2s^–1) show a broad absorbance maximum in the UV regionof the spectrum (310–360 nm). Using TLC and reverse-phaseHPLC a series of mycosporine-like amino acids have been characterized:mycosporine-glycine (_max = 310 nm), palythine (_max = 320 nm),asterina-330 (_max = 330 nm), shinorine (_max = 334 nm), porphyra-334(_max= 334 nm), palythenic acid (_max = 337 nm) and the isomericmixture of usujirene and palythene (_max = 359 nm). From theobserved spectral changes during transference from ‘low’(20 µE m^–2 s^–1) to ‘high’ (200µE m^–2 s^–1) light intensities and vice versa,the series of compounds are supposed to be biogenically relatedto one another. The presence of these compounds in A.excavatumis discussed in relation to their possible role in the photoprotectionto deleterious UV radiation.     

Temporal and spatial variations in phytoplankton carbon isotopes in a polymictic subtropical lake

Stable carbon isotopes (¹³C) were determined for phytoplanktonand dissolved inorganic carbon (DIC) from Lake Apopka, a shallow,polymictic and hypereutrophic lake in Florida, USA. Bulk planktondominated by pico- and nanqanobacteria were enriched in ¹³(–13.1± 1.1%) as a result of assimilation of extremely ¹³C-richDIC (¹³C = 9.6 ± 3.0%). Diatoms (Aulacoseira spp.) hada ¹³C of –14.3 ± 0.6% that was slightly more negativethan that of small cyanobacteria. Meroplanktonic diatoms hada ¹³C (–13.6 ± 1.8%), similar to their planktoniccounterparts. The ¹³C of a colonial cyanobacterium (Microcystisincerta) was exceptionally heavy (–3.0 ± 1.0%)and attributed to localized carbon limitation. Seasonal variationin ¹³C of bulk plankton was small (4%) relative to reports forother lacustrine systems No difference in the ¹³C of bulk planktonhorn surface water between stratified and non-stratified periodswas found. No measurable changes in ¹³C of bulk plankton wereindicated in light and dark incubation experiments Frequentwind mixing of the water column, high DIC concentration, andconsistently high lake productivity were used to explain thetemporal and spatial isotope consistency of phytoplankton inthis lake.     

Daily vertical migration of dense deep scattering layers related to the shelf-break area along the northwest coast of Baja California, Mexico

Echo signals were collected with a Simrad 200 kHz transduceracross the shelf-break features off the northwest coast of BajaCalifornia (30°05'–30°42'N, 115°50'–116°26'W)during two diel cycles (July 1995) with the objective of describingvertical migrations of two dense deep scattering layers (DSL)found near the shelf break. DSL records were made within anarea ±50 m in the neritic zone, ±200 m at theshelf break and ±1000 m depth in the offshore station.Using an Isaacs-Kidd midwater net and Bongo nets, we inferredthat the DSL were composed mainly of juveniles and adults ofthe euphausiids Nyctiphanes simplex Hansen and Euphausia pacificaHansen. These aggregations have a close interaction with theocean bottom during the daytime and display a vertical migration,rising near to the surface at night where a progressive horizontaldispersion then occurs. The DSL measured 3.5–6.0 km horizontallyduring the night. The ascent and descent migrations of the DSLwere significantly fitted to a polynomial function of the secondorder, suggesting different swimming behavior during these twoprocesses. Vertical migrations of the DSL were between 60 and90 m. During the descent migration, maximum instantaneous speedsreached 0.7 cm s¹, and during the ascent, maximum instantaneousspeeds were 0.3 cm s¹. These coastal euphausiid species, alongwith other macrozooplankton and nektonic organisms, have a dailyclose interaction with the ocean bottom and also with the pelagicenvironment, suggesting that they play an important role providingfood for demersal and pelagic organisms on the slope and shelfbreak in the upwelling region off the northwest coast of BajaCalifornia.     

Temperature and salinity effect on growth and chemical composition of Gyrodinium aureolum Hulburt in culture

A factorial experiment shows highly significant effects of temperature(12 5–22.5°C) and salinity (17.8–34 S) on thegrowth rate of Gyrodinium aureolum, with a significant temperature-salinityinteraction. The maximum growth rate of G aureolum is measuredto 0.61 div. day^–1 at 20°C and 22.3 S. Gyrodiniumaureolum does not grow at temperatures :10 °C or 25°Cand at salinities 12 S. The cellular content of carbon (C) andnitrogen (N) and the elemental ratios N/C, P/C and N/P are significantlyaffected by the temperature The cellular content of phosphorus(P) and the elemental ratios P/C and N/P vary significantlywith salinity Significant temperature-salinity interactionsare found for the cellular content of carbon, nitrogen and phosphorus.Variations in the N/P ratio indicate that G.aureolum has a largestorage capacity for phosphorus It is suggested that temperatureis one important limiting factor in the initiation of bloomsof G.aureolum in north European waters.     

{delta}15N signatures of marine mesozooplankton and seston size fractions in Kiel Fjord, Baltic Sea

The ¹⁵N of marine mesozooplankton species was measured on fouroccasions. Significant differences were found between copepodsand meroplanktonic larvae, yet not between holoplanktonic species.On average, mesozooplankton was enriched by 3.4 ± 0.9relative to selected seston size fractions. Despite suggestingsmall differences (0.5 to 1) in the ¹⁵N of different phytoplanktontaxa on one occasion, the size fractionation procedure generallyproved inadequate in separating major taxonomic groups composingseston. This circumstance, and phase-shifts in the transmissionof rapid changes (>2) in seston ¹⁵N to mesozooplankton complicatethe calculation of mesozooplankton trophic levels.     

Interspecific variability and environmental influence on particulate organic carbon {delta}13C in cultured marine phytoplankton

The stable carbon isotope composition of particulate organicmatter expressed as ¹³C was measured in cultures of 13 speciesof marine microalgae in different phylogenetic groups. The effectsof salinity variations and changes in photoperiod were alsoassayed for three of them (i.e. Skeletonema costatum, Amphidiniumopercularum and Isochrysis galbana); the effect of nature ofnitrogen supply (nitrate. ammonium) was studied for one (S.costatum).These environmental parameters were chosen because of theirvariability in the ocean and their possible effects on ¹³C valuesof phytoplankton organic carbon. Batch culture conditions andsampling time after inoculum were strongly controlled in orderto provide cells in good physiological state which were comparablefrom one culture to the other. In the same way, sampling waslimited to the first 2 days of exponential growth, in orderto avoid a possible dissolved inorganic carbon (DIC) limitation.Carboxylase activities [of the enzyme ribulose 1,5-bisphosphatecarboxylase oxygenase (Rubisco), and the three ß carboxylases:phosphoenolpyruvate carboxylase (PEPC), phosphoenolpyruvatecarboxykinase (PEPCK) and pyruvate carboxylase (PC)] and totalchlorophyll a concentrations were assayed simultaneously. The¹³C values observed were between –30.2 and –12.7i.e. comparable to those observed in the world's oceans. Theisotopic composition of phytoplankton organic carbon was shownto be under the influence of the parameters tested but ¹³C variationsare specific to the species considered. The nature of ßcarboxylase found in each species, or systematic position, couldnot be linked to the isotopic composition of organic carbon.No linear or single correlation between ¹³C variations and environmentalmodifications were observed and there is no evidence for a simpleand universal relation between ¹³C of phytoplankters and theirenvironment. In monospecific cultures as in the field, ¹³C fractionationby Rubisco (and eventually by PEPCK) may be counterbalancedby other mechanisms.     

Response of Gonyaulax tamarensis to the presence of a pycnocline in an artificial water column

In nature, large concentrations of the toxic bloom-forming dinoflagellate,Gonyaulax tamarensis, are frequently observed in the vicinityof the pycnocline. In the absence of a pycnocline the organismis usually recorded near the surface, where light levels aremore advantageous for photosynthesis. In this paper we examinethe swimming behaviour of G.tamarensis when exposed to varyingdegrees of stratification and investigate whether the maintenanceof a subsurface (pycnocline) population is the result of retentionof the algae by a physical barrier or active accumulation ofthe organisms at a density interface. The study indicates thatG.tamarensis cells presented with a halocline of S<{smalltilde}6–7 (occurring over a few centimeters) cross thissalinity barrier and accumulate at the highest available photonflux density ({small tilde}100 µmol m^–2 s^–1).Cells exposed to a gradient of S>{small tilde}7remain atthe halocline (pfd={small tilde}40 µmol m^–2 s^–1).However, when light above the pycnocline is attenuated by theaddition of food colour to the medium, the cells cross a haloclineof S=10 and accumulate at the highest available photon fluxdensity. In the absence of added nutrients (inorganic N andP) the organism fails to exhibit a phototactic response. Thus,the presence of a strong halocline does not represent an inpenetrablephysical barrier for G.tamarensis and the development of pycnoclinepopulations of this organism is a function of density, lightand nutrient climate.     

The maximum quantum yield of phylopiankton photosynthesis in situ

Light-limited photosynthetic carbon incorportion is expectedto be directly proportional to the scalar quantum irradiance.The proportionality constant is , where _mis the maximum quantum yield (mol C Einstein^–1 absorbed)and $$\stackrel{\&macr;}{{\hbox{ k }}_{\hbox{ c }}}$$ isthe mean spectral absorption coefficient (m² mg^–1 chla). Recent efforts to evaluate of in situphytoplankton photosynthesis are variously flawed. Lack of evidenceof proportionality and lack of correction of cosine to scalarirradiance are common deficiencies. Most data, as we interpretthem, indicate values in the range 0.0003 – 0.0006 mol C m² Einstein1 abs mg1 chl a. New determinationsin lrondequoit Bay, New York, lie in this range. Most estimatesof at depth have been about 0.010 m² mg^–1chl a. Similar values are being obtained for total particulatesfrom lrondequoit Bay; whether detritus contributes significantlyis not yet known. Published data, in our view, all point tovalues of m in situ in the range 0.03–0.07 mol C Einstein^–1abs. Published values >0.10 are almost certainly due to imprecisionor systematic error. ^*This paper is the result of a study made at the Group for AquaticPrimary Productivity (GAP) First International Workshop heldat the Limnological Institute, University of Konstanz, in April1982.     

Feeding and reproduction of Calanus finmarchicus during non-bloom conditions in the Irminger Sea

Simultaneous ingestion and egg production experiments were conductedwith female Calanus finmarchicus in April/May and July/August2002 in the Irminger Sea. Experimental animals were providedwith natural microplankton food assemblages and incubated underin situ conditions for 24 h. The quantity of food consumed wassignificantly related to the concentration of prey cells, withtotal daily ingestion rates ranging from 0.6 to 8.1 µgof carbon female^–1 day^–1, corresponding to carbon-specificrates of 0.6–4.7% day^–1. Egg production rates (EPRs)remained relatively low (0.3–11 eggs female^–1 day^–1)during both periods of investigation and were not influencedby food availability. The data were used to construct energeticbudgets in which the microplankton carbon ingested, includingciliates, was compared with the carbon utilized for egg productionand respiration. These budgets showed that ingestion alone couldnot provide the necessary carbon to sustain the observed demandsfor growth and metabolism. Although ciliates constituted >80%of the total material ingested at times, they were not sufficientto provide the metabolic shortfall. Indeed, the females weretypically lacking 5 µg of carbon each day, 5% of theircarbon biomass. Our study results highlight the possible importanceof internal reserves in sustaining reproduction in C. finmarchicusduring periods of food scarcity.     

Feeding rates of the doliolid, Dolioletta gegenbauri, on diatoms and bacteria

Wild doliolids fed equally efficiently on radiolabelled bacteria>5 µm in size and diatoms >100 µm in size.Feeding by attached asexual buds accounted for 80% of the clearancerates of phorozooids and oozooids     

On filament width in oceanic plankton distributions

A plankton patch deformed by diffusion, straining flow and biologicalgrowth is demonstrated to have a minimum width, /, which ispurely a function of the effective diffusivity, , and the strainrate, .     

Dry Matter Distribution between the Shoot and Storage Root of Carrot (Daucus carota L.): I. Comparison of Varieties

The distribution of dry matter between shoot and storage rootof a wild variety and cultivars of carrot was investigated ina glasshouse experiment and a field experiment. In both experimentsthe deliberate introduction of variation in plant size revealeda linear relationship between the log weights of these partsat any time throughout growth. In the glasshouse experiment,in which growth was examined from approximately 10–600mg mean dry wt per plant, the slope of the relationship betweenIn shoot and In storage root dry wts decreased markedly duringdevelopment to 100 mg. Subsequently the slope became reasonablyconstant and the intercept progressively more negative. Datafrom the field experiment covered a similar timescale (48–115days) to the glasshouse experiment but the plants grew morequickly and were much heavier (180 mg–6 g dry wt). Therelationship between shoot and storage root for these data wassimilar to that for the plants of comparable size in the glasshouseexperiment. Over the range of development for which the slopeof the relationship was constant, data from both experimentswere described fairly well by the following equations: In shoot = – time+ In storage root where , and are constants. Between cultivars the slope ()and time constant () were similar, but the intercept () increasedwith maturity time of the cultivars. For wild carrot the slopewas larger and the time constant smaller than estimates forthe cultivars. These results on dry matter distribution arediscussed in relation to a model for partitioning assimilatein an individual plant. Daucus carota L., carrot, assimilate distribution, dry matter distribution, storage root, partitioning model     

Spatial heterogeneity and genetic variation in the copepod Neocalanus cristatus along two transects in the North Pacific sampled by the Continuous Plankton Recorder

We present a macrogeographic study of spatial heterogeneityin an important subarctic Pacific copepod and describe the firstgenetic analysis of population structure using Continuous PlanktonRecorder (CPR) samples. Samples of Neocalanus cristatus werecollected at a constant depth of 7 m from two CPR tow-routes,(i) an east–west 6500-km transect from Vancouver Island,Canada to Hokkaido Island, Japan, and (ii) a north–southtransect of 2250 km from Anchorage, Alaska to Tacoma, Washington.Analysis of these samples revealed three features of the biologyof N. cristatus. First, N. cristatus undergoes small-scale dielvertical migration that is larger among stages CV–adult(3–6 times more abundant at 7 m at night), than stagesCI–CIV (only 2–4 times higher at night). Secondly,while there were no regions where N. cristatus did not appear,each transect sampled a few large-scale macrogeographic patches.Thirdly, an analysis of molecular variation, using a partialsequence of the N. cristatus cytochrome oxidase I gene, revealedthat 7.3% (P < 0.0001) of the total genetic variation amongN. cristatus sampled from macrogeographic patches by the CPRcould be explained by spatial heterogeneity. We suggest thatspatial heterogeneity at macrogeographic scales may be importantin plankton evolution.     

Seasonal and spatial distribution of bacterial biomass and the percentage of viable cells in a reservoir of Alabama

Spatial community dynamics of bacterioplankton were evaluatedalong the length of the former stream channel of Elledge Lake,a small reservoir in western Alabama. The reservoir was stronglystratified from April to October with up to a 10°C temperaturedifference across the 1 m deep metalimnion. Bacterial biomasswas highest during late summer, with a general pattern of increasingabundance from the inflowing river (10 µg C l^-1) to thedam (20–30 µg C l^-1). Bacterial numbers also increasedfollowing a >10-fold increase in turbidity associated witha major precipitation event, although only 10% of these cellswere viable. The percentage of viable cells generally increasedthrough the stratified period with 50–70% viable cellsin late summer. Overall, an average of 38% of bacterial cellswere viable, with a range from <20 to 70%. Although thesevalues were similar to those found by others, additional patternswere identified that have not been previously observed: a markeddecline in viable cells was found following turbid storm inflowsand increases in the percentage of viable cells occurred duringspring warming and following autumnal mixing events. Althougha modest increase in abundance occurred along the gradient frominflow down-reservoir to the dam, bacterial abundance did notincrease near the dam in a pattern coincident with the commonlyobserved increased algal biomass in the lacustrine portion ofreservoir ecosystems. The increases observed in bacterial viabilitymoving from the inflowing rivers towards the dam and later instratified periods stress the importance of differences in environmentalconditions in time and space in regulating bacterial biomassand development, as well as of shifts that would be anticipatedaccompanying altered hydrological regimes under climatic change.     

Resting egg production and oviducal cycling in two sympatric species of alpine diaptomids (Copepoda: Calanoida) in relation to temperature and food availability

Resting egg production and oviducal cycling were investigatedfor the calanoid copepods Arctodiaptomus alpinus and Acanthodiaptomusdenticornis both in the laboratory and in a small karstic alpinelake by making a census of the number of eggs produced and theproportion of females in each of four morphologically distinguishedreproductive conditions each day in the laboratory or duringa 2–3 week period in lake enclosures. In the laboratory,individuals were maintained on a mixed diet of natural phytoplanktonat constant temperatures of 4, 10, 15 and 20C, respectively.Both species differed considerably in their temperature requirementsfor reproduction. Lifetime fecundity was highest at 10C in A.alpinusand at 20C in A.denticornis, with up to 327 eggs ^–1 spawnedin the former and up to 582 eggs ^–1 in the latter species.Unfavorable temperatures were further reflected in an increasein egg mortality and the allocation of time spent in a post-reproductivephase, as well as in a decrease of longevity. Increasing temperaturesenhanced egg production rates due to decreasing clutch productionperiods, although clutch size was negatively correlated withtemperature. Maximum rates reached 5.88 and 7.98 eggs ^–1day^–1 in the laboratory, and 0.73 and 0.55 eggs ^–1day^–1 in enclosures in A.alpinus and A.denticornis, respectively.Egg production rates and clutch size were clearly governed bynutritional conditions in the lake, but were less affected byfood supply in the laboratory. Here, rates of egg productionwere adapted to improving food supply by increasing the frequencyof spawning events, rather than the number of eggs per clutch.No correlation was found between female body size and reproductiveparameters in the laboratory. A very low proportion of totalclutch production resulted in clutches composed of subitaneouseggs, i.e. 0.14% in A.denticornis and 1.20% in A.alpinus. Oviducalphase duration allocations indicate that there exists a temperatureoptimum for gamete maturation.     

Potassium Transport Across the Membranes of Chara: II.42K FLUXES AND THE ELECTRICAL CURRENT AS A FUNCTION OF MEMBRANE VOLTAGE

Smith, J. R. 1987. Potassium transport across the membranesof Chara. II. ⁴²K fluxes and the electrical current as a functionof membrane voltage.—J. exp. Bot. 38: 752–777. The current required to clamp the trans-membrane voltage ofinternodal cells of Chara australis at different levels wasmeasured simultaneously with either the ⁴²K influx or efflux.Examination of the voltage-dependence of the ratio of the electricalcurrent to the unidirectional tracer fluxes yielded no evidenceof any amplification of the electrical driving force on theK⁺ ions. There was thus no evidence for the interaction of K⁺ions with themselves or any other species during their passageacross the membrane. These measurements allow the determinationof , the fraction of the electrical current carried by K⁺ ions.When the external [K⁺] = 10 mol m^–3, the average valueof was 0?85 for V_m > –125 mV and 07?5 for V_m <–150 mV. When the external [K⁺] = 0?1 mol m^–3, was 0?6 for V_m < –80 mV and 0?1 for V_m > –250mV. It was also found that the conductance associated with K⁺transport was inhibited by hyperpolarization. Key words: Potassium, conductance, flux-ratio     

Corrigendum

Due to an apparent fault in the telex system, a number of mistakeswere not corrected in this paper. The corrected lines are givenbelow p. 539: line 17In vivo fluorescence action spectra of chl a p. 541: Figure 2 legend, line 92.5 µW cm^–2 at 550nm (0.12 µE m^–2 s^–1 p. 542: Figure 3 legend, line 5( 89 µE m^–2 s^–1).Monochromatic beam intensity was 6 µW cm^–2 at 550nm (–0.28 µE m^–2 s^–1), Figure 3 legend, lines 8 and 9with intensity of 3 mW cm^–2( 179 µE m^–2 s^–1) Monochromatic beam intensitywas 7 5 µW cm^–2 at 550 nm (0.35 µE m^–2s^–1). line 6tivity. The match between the spectra of chl a fluorescenceand PSII O₂ evolution is lines 23–25fluorescence increasingly deviate from thoseof PSII O2 evolution. We attribute this discrepancy to selectivelight scattering by the algae. This scattering increases substantiallywith decreasing wavelength at that region when using a standardspectrofluorometer p. 543: Figure 4 legend, lines 3 and 4as in Chroomonas, withintensity of 2 mW cm^–2 ( 120 µE m^–2 s^–1).Monochromatic beam intensity was 15 µW cm^–2 at 550nm ( 0.7 µE m^–2 s^–1). line 7:ment types in the oceans. While all photoautotrophicorganisms have chl a (the bulk lines 12 and 13:and Barrett (1983). Our spectral data reflectthe great variability in pigment composition and functionalassociation in the major groups of algae. lines 25 and 26:Hiller, 1983). However, blue-violet and redPSII activity is much lower in cryptomonads than might be expectedfrom their absorption spectra (Haxo and Fork, 1958; Haxo, 1960), p. 544: Table I, column 3, entry 6:R-phycocyanin Table 1 legend, lines 1 and 2:^aHaxo and Blinks (1950); ^bFork(1961); ^cHaxo et al. (1955); ^dO'Carra and O'hEocha (1976); ^cresemblesDelesseria decipiens, Haxo and Blinks (1950, Figure 20); ^fHaxoand Fork (1969), like lines 1 and 2:I) indicates that these pigments are affiliatedwith PSII, perhaps exclusively, as in the red algae. In Rhodomonas,the peak of activity at 465 nm may be due to chl c absorp- p. 545: line 2:xanthophyll (fucoxanthin in diatoms, peridininin dinoflagellates and chl c. The ac line 7:shown to be similar to those of the much-studied Chlorella(Vidaver, 1966; Ried, 1972). line 14:tivity of PSII in algae. Spectrofluorometers, with theirsuperior sensitivity and stability, line 34:of natural populations, making these spectra more similarto the PSII photosynthesis lines 36 and 37:Large differences between the values of FIIfor different components within the algal population can distortfluorescence spectra, if they do not correspond with dif lines 41 and 42:different components are not similar to eachother. The necessary handling procedures of natural samples,such as filtration (Yentsch and Yentsch, 1979; Neori et al.,1984), p. 546: lines 20 and 21:DOE contract DE-AT03-82ER60031, anda grant to A.N., O.H.H. and F.T.H. from the Foundation for OceanResearch. Travel to the IInd GAP workshop was facilitated by lines 25 and 26:the culture of Chroomonas, J.Lance for helpwith cultures, J. and E.Yguerabide for the use of their spectrofluorometer,C.R.Booth, Y.Blatt and L.Petrosian for technical line 28:This study was in partial fulfilment for a Ph.D. degreeby A.N. line 42:Dutton.H.J., Manning.W.M. and Duggar.B.M. (1943) Chlorophyllfluorescence and energy transfer in the     

Factors controlling primary production in a hypertrophic lake (Hartbeespoort Dam, South Africa)

The physical factors controlling algal primary production weredemonstrated from data collected for a hypertrophic lake. A_maxranged between 12.4 and 5916 mg C m^–3 h^–1. Arealrates (A) varied between 46.9 and 3381 mg C m^–2 h^–1.The factors permitting and controlling production were subjectivelyseparated into two categories. In category 1, nutrients (N +P), which were in overabundance, permitted large standing cropsof Microcystis aeruginosa to develop (>1000 µg chla 1^–1). Wind patterns determined the dramatic spatialand temporal changes in algal standing crop which could dropto 2.7 µg chl a 1^–1. In category 2 were the factorswhich affected the rate processes. The buoyancy mechanism ofMicrocystis usually kept the alga in the euphotic zone. A powerrelationship (r = 0.92, n = 54) between A and A_max/_min showedthat with increasing phytoplankton vertical stratification,A_max was increasingly important in the integral. The saturationparameter I_K and photosynthetic capacity were temperature dependent.Variations of A were significantly related to changes in watercolumn stability (g cm cm^–2) because both axes of thephotosynthesis depth-profile were affected by stability changes.