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, .     

{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.     

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.     

Influence of salinity and temperature on growth and survival of the planktonic larvae of Marenzelleria viridis (Polychaeta, Spionidae)

In a series of experiments, the planktonic larvae of Marenzelleriaviridis (Verrill, 1873) were exposed to various combinationsof salinity (S = 0.6, 2.5, 5.0, 10 and 20) and temperature (T= 5, 10 and 20C) from the 1-setiger stage to the onset of metamorphosis(16- to 17-setiger stage). One-setiger larvae were unable tocomplete their development to metamorphosis at salinities below5. Metamorphosis was successful at salinities of 10 and 20,when the animals adopted a benthic life mode. Larval developmentwas more rapid at 10 than at 20, and was positively affectedby higher temperatures. Larvae exposed to a salinity of 3.5at the 4- to 5-setiger stage developed and completed metamorphosisto benthic juveniles despite the low salinity. These larvaedeveloped most rapidly at a temperature of 10C. The salinitytolerances (LC₅₀) of M. viridis larvae (t = 48 h), juvenilesand adults (t = 72 h in each case) were determined at 10C.The results showed that all development stages can toleratesalmities <1 The importance of constraints on developmentand tolerance to low salinities for the successful colonizationof oligohaline regions is shown and discussed in connectionwith other brackish-water organisms.     

15N abundance in micronekton in Sagami Bay, Central Japan

The ¹⁵N values of micronekton collected from Sagami Bay rangedfrom 9.4 to 14.2%. The ¹⁵N values of the micronekton, Gonostomagracile, increased with growth (9.4 to 12.6%) and it seems thatmales, before sex reversal, and females consume different foodorganisms.     

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.     

Short communication. Biomass and production characteristics of the first red tide noticed in Kuwait Bay, Arabian Gulf

Observations on the first red tide off Kuwait, Arabian Gulf, yielded high biomass [55.4-262.7 g chlorophyll (Chl) a l^-1] and primary production (507.9-571.2 g C h^-1l^-1), comparable with some of the highest values reported. There were contrasting changes in the carbon assimilation ratios, composition of the phytoplankton and the contribution of nanoplankton (<20 m) between 11 and 12 May. On 11 May, carbon assimilation by nanoplankton was 2.2 g C (g Chl a)^-1 h^-1, but increased to 9.2 g C (g C (g Chl a)^-1 h^-1 the following day. Nanoplankton contributed 56 and 9% of Chl a and production, respectively, on 11 May, while net plankton (>20 m) accounted for >65% of the biomass and primary production on 12 May. Picoplankton (<3 m) contributed <8% of Chl a and <3% of production. Frequent sampling will be necessary to capture such dynamic changes and ephemeral events in these waters.      

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.     

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.     

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.     

Short communication. First record of larval Brama brama (Pisces: Bramidae) and Corphaena hippurus (Pisces: Coryphaenidae) in the Adriatic Sea

The occurrence of early larval stages of Brama brama and Coryphaena hippurus is reported for the first time in Adriatic waters. Two larvae of B.brama between 4.36 and 5.00 mm, and two larvae of C.hippurus between 4.75 and 4.95 mm standard length, were found in ichthyoplankton collections taken off the River Neretva estuary (43010N, 17°250E) and station Stoncica, island Vis (43°000N, 16°20E) (eastern middle Adriatic), respectively. The capture of both species (B.brama) in August 1998; C.hippurus in May 1998) is in agreement with their proposed seasonal life cycle in the Adriatic Sea.      

In situ quantum yield of phytoplankton in a subalpine lake

The percent of light absorbed by algae, estimated from a regressionof attenuation of downwelling photosynthetic photon flux densityon chlorophyll a concentration, was used in conjunction withmeasurements of phytoplankton photosynthesis to estimate quantumyields () of Castle Lake phytoplankton populations during the1980 ice-free season. The maximum values occurred during mid-summerin the deep hypolimnion (<1% of surface photon flux) andwere {small tilde} 78% of the theoretical maximum. However,later in the season (September) the deep-water values decreasedsignificantly to {small tilde}27% of the theoretical maximumin conjunction with a decrease in quantum flux density to thesewaters. The values for epilimnetic phytoplankton populationswere never >15% of the theoretical maximum. The presenceof relatively high concentrations of peridinin and chlorophyllc in the deep-water algae enabled these organisms to absorbthe predominantly green light in this region of the lake which(i) allowed the use of a single extinction value per unit ofchlorophyll (k_c) at all depths when calculating , and (ii) increasedthe of the deep-water algae, relative to those in the near-surfacewaters. These data indicate that the deep-water algae in CastleLake were able to utilize their ambient light field, particularlyin the early summer, and suggest that the deep-chlorophyll layerin this lake is maintained primarily by in situ algal growthrather than sinking and accumulation of organisms from nearsurface waters.     

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.     

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.     

Natural occurrence of phycoerythrocyanin-like pigment in cyanobacterial blooming samples dominated by Microcystis in Lake Kasumigaura

We describe the occurrence of phycocyanin and phycoerythrocyanin-likepigment in natural Microcystis colonies collected in Lake Kasumigaura.For differentiating pigments, the combination of simultaneousdetermination of molecular weights of and ß and subunitsby electrospray ionization mass spectrometry with HPLC separationand fluorescence measurements was used. It was suggested thatthe natural Microcystis colonies may contain the phycoerythrocyanin-likepigment, judged from the excitation and emission spectra. Measuredpigments consisted of different molecular weights of and ßsubunits, but the molecular weights of and ß subunitsin both phycocyanin and phycoerythrocyanin-like pigments werenot always identical.     

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.     

Measurement of photosynthetically available radiation in freshwater: comparative tests of some current instruments used in studies of primary production

Instruments now in common use among biologists for measuringunderwater photosynthetically available radiation (PAR) werecompared as part of the Group on Aquatic Primary Productionworkshop. The effect of differences in spectral response (narrowversus broad wavebands) and collecting properties (cosine versusscalar) on measurements of vertical (diffuse) attenuation coefficient() were tested. As instruments measuring spectral quality canbe expensive a low-cost manual interference-band-filter photometeris described and compared with a scanning spectroradiometer.In Bodensee there was a progressive narrowing of the spectralwaveband with depth, so that by 15 m nearly 75% of the totalquanta were between 525 and 575 nm. Therefore values of forPAR, measured with broad waveband sensors, decreased with depth.With narrow waveband sensors values of were constant with depth.Attenuation was similar with both scalar and cosine instruments.However, comparisons of absolute values were difficult becauseof incorrect calibrations. It is recommended that the calibrationof scalar instruments should be more precisely defined, andthat the intrinsic depth-variability of for PAR should notbe neglected when interpreting measurements. ^*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.     

Modelling interactions between phytoplankton and bacteria under nutrient-regenerating conditions

Two of the algal parameter values in Table II are incorrect.They should read: _a,o minimun algal N:C ratio 0.037 mol N/mol C _a,m maximum algal N:C ratio 0.133 mol N/mol C     

Valerie Andersen (1959 2007)

Valérie Andersen formally began her career in oceanographywith a PhD from the Université de Pierre et Marie Curiein 1985. Her thesis (Andersen, 1985a) was centred on the developmentof numerical models of the pelagic food web. However, it wasfirmly based on her experimental studies of salps (Andersen,1985b, 1986, 1989; Andersen and Nival, 1986) and data she gatheredon cruises in the N.W. Mediterranean Sea (Andersen and