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.      

Effect of irradiance and temperature on the growth rate of Thalassiosira curviseriata Takano (Bacillariophyceae), a bloom diatom in Bahia Blanca estuary (Argentina)

Long-term phytoplankton studies in the Bahí Blanca estuary showed a seasonal pattern characterized by a winter-early spring bloom of diatoms dominated by Thalassiosira curviseriata. Laboratory experiments were carried out to elucidate the influence of irradiance, temperature and salinity on the growth rate of T.curviseriata. The maximum daily growth rate was 1.93 divisions at 20C. The compensation point (Ic) varied from approaching zero to 3.08 mol m^-2 s^-1, values were -0.020-0.070 divisions mol^-1, and the calculated Ik (the irradiance at which initial slope line reaches the maximum rate of growth) varied between 32 and 36 mol m^-2 s^-1. Growth became light saturated (when max) between 70 and 80 mol m^-2 s^-1, and was inhibited at -150 mol m^-2 s^-1 at all temperatures (5-20°C). The range of temperatures at which T.curviseriata can grow (5-20°C) coincides with the temperature range over which it is found in the field. In contrast, the thermal optimum for growth, 20°C, was higher than the range of temperatures (between 5 and 10°C) characteristic of the winter-early spring bloom in Bahí Blanca estuary. The mean specific growth rate of T.curviseriata was not affected by salinity over the tested range between 25 and 40 p.p.t. Field observations and experimental data support the characterization of T.curviseriata as a eurythermal and euryhaline species adapted to growth at relatively low light intensity. These characteristics may explain the ability of T.curviseriata to flourish seasonally when light conditions are apparently limiting and its presence almost year round under variable conditions of temperature and salinity.      

Assimilation and release of 14C in a tropical strain of Cryptomonas obovata (Cryptophyceae) exposed to several irradiances

Carbon assimilation (¹⁴C) and dissolved organic carbon (DO¹⁴C) release by a tropical strain of Cryptomonas obovata was studied. Cells were exposed to a range of irradiances (0-2000 mol m^-2 s^-1) using axenic batch cultures in the laboratory (Ek = 180 mol m^-2s^-1). At up to 2000 mol m^-2s^-1, carbon assimilation was not inhibited and an acclimation to low irradiances was observed. DO¹⁴C release was dependent on carbon fixation and no increase was detected under high irradiances. To determine particulate organic carbon (PO¹⁴C) loss and CO¹⁴C release cells acclimated to 350 mol m^-2 s^-1 were incubated during 4 h at 35, 350, 850 and 1900 mol m^-2 s^-1. DO¹⁴C release was responsible for 30% of the PO¹⁴C loss at 1900 mol m^-2s^-1. High- and low-molecular-weight (HMW, LMW) compounds were released by C.obovata under all irradiance conditions. However, increased release with exposure time was observed only for the HMW compounds.      

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.      

Short communication. Determination of generation time and asexual fecundity of doliolids (Tunicata, Thaliacea)

The goal of this study was to provide temporal information on the generation time of Dolioletta gegenbauri and some of the life cycle's components. At 20C and 90 g C l^-1 of ingestible phytoplankton. D.gegenbauri's life cycle is completed in 20.5 days. Phorozooids 5 mm produce on average 11.0 gonozooids day^-1 over a period of 8-18 days. Utilizing field data on the abundance and size distribution of an assemblage of phorozooids and nurses, in conjunction with experimentally obtained rates, indicates that asexual production per cubic meter by phorozooids with that of nurses should result in rapid colonization of a wide shelf by doliolids, as observed during July and August 1981 on the southeastern continental shelf of the USA.      

Comparative ecophysiology of the harmful alga Chattonella marina (Raphidophyceae) form South Australian and Japanese waters

The raphidophyte flagellate Chattonella marina was successfully cultured from Boston Bay (South Australia), coincident with mass mortality of farmed bluefin tuna (Thunnus maccoyii) in April 1996. Grown under laboratory conditions at 150 mol m^-2 s^-1 irradiance, optimal growth (>0.5 day^-1) occurred at a temperature of 25C and a salinity of 30 p.s.u., but good growth (>0.3 day^-1) also occurred between a temperature of 10 and 30°C and at a salinity of 15-45 p.s.u. However, cultures grow much faster at an irradiance of 450 mol m^-2 s^-1 (1.08 day^-1). While Australian C.marina had similar temperature and salinity requirements as well-studied Japanese cultures from the Seto Inland Sea, the Australian strains exhibited a light saturation level for growth four times higher than that reported from Japan (150 mol m^-2 s^-1). An adaptation to higher light intensities was reflected in higher concentrations of microsporine-like amino acids in the Australian strains. The different light adaptation phenotypes were still apparent after long-term culturing under similar physiological conditions. Potential growth habitats for this ichthyotoxic flagellate in the Australian region and implications for finfish aquaculture industries are discussed.      

Short communication. The effect of temperature, food concentration and female size on the egg production of the planktonic copepod Acartia bifilosa

Egg production of a brackish water calanoid copepod Acartia bifilosa was measured in the laboratory in different chlorophyll (Chl) a concentrations (0-24 mgr; l^-1) and temperatures 4-24C), and the cephalothorax length and carbon content of females were determined. Egg production was positively correlated both with Chl a concentration and with temperature; highest egg production was obtained with 14-20 g Chl a l^-1 and at 13-18°C. There was also a significant positive correlation between egg production and female length-specific carbon content (g C m^-1). However, no correlation was observed between egg production and cephalothorax length of females. Female carbon content changed during the 3 day experiments; carbon content was positively related to Chl a concentration and negatively related to temperature. We conclude that food availability (Chl a concentration), rather than temperature, limits the egg production of A.bifilosa in the present study area in the northern Baltic Sea. Further, both food concentration and temperature affect egg production not only through the direct effect on the numbers of eggs produced per female, but also through their effect on female carbon content.      

Spatial variability of the photosynthetic parameters and biomass of the Gulf of California phytoplankton

Spatial variability of the central Gulf of California (CGC) phytoplankton biomass and photosynthetic parameters in relation to physical forcing was studied. Sampling was carried out in November, and the surface TC range was 20-27.5°C. Strong tidal mixing in the midrift islands regions injects relatively cool, nutrient-rich waters to the euphotic zone. Some of this water is transported via jets and cool filaments throughout the Gulf. In general, chlorophyll a (Chl) of small phytoplankton (<8 m) (up to >2.5 mg m^-3) was higher than that of large phytoplankton. Highest values of phytoplankton assimilation numbers (P^Bm) [3.17 mg C (mg Chla)^-1 h^-1], and photosynthetic efficiency ^B) [0.23 mg C (mg Chl a)^-1 h^-1 (W m^-2)^-1] were determined for the large phytoplankton cells (>8 m). Our hypothesis that P^Bm values increase from cooler to warmer waters is not supported by the data. We found a 27-fold spatial difference of Chl, compared with a 10-fold difference of P^Bm and a 6-fold difference of ^B. Thus, in our study area, the major source of variability for primary productivity (PP) comes from Chl, and not from P^Bm and ^B. Therefore, we propose that it is possible to estimate late-fall PP for the CGC using average photosynthetic parameters. Average values for P^Bm and ^B of total phytoplankton were 0.72 mg c (mg Chl a)^-1 h^-1 and 0.12 mg C (mg Chl a^-1 h^-1, (W m^-2)^-1, with standard errors of 0.07 and 0.03, respectively.      

Influence of nutrient ratios on the in vitro extracellular polysaccharide production by marine diatoms from the Adriatic Sea

Three different species of marine diatoms, Nitzschia closterium (Ehr) Smith, Chaetoceros sp. (Ehr) and Skeletonema costatum (Grev) Cleve, were isolated from the Adriatic sea and studied in vitro for the production of extracellular carbohydrates. Variations of the nitrogen (N)/phosphorus (P)/silicon (Si) ratios in the growth medium affect the accumulation and release of carbohydrates. In the N.closterium cultures at high N/P ratio, the rate of extracellular polysaccharide release was higher both in rapidly growing cells (2.14 g per 10⁶ cells day^-1 and in stationary phase (1.0 g per 10⁶ cells day^-1) compared to S.costatum and Chaetoceros sp. Instead, at low N/P ratios, S.costatum and Chaetoceros sp. produced large amounts of extracellular polysaccharides during the logarithmic phase, compared to N.closterium, with values of 10 g per 10⁶ cells day^-1 for S.costatum and 2.8 g per 10⁶ cells day^-1 for Chaetoceros sp., respectively; in particular, only S.costatum was able to produce extracellular carbohydrates (1.2 g per 10⁶ cells day^-1) during the stationary phase of growth. Under Si limitation, any of the three diatom species produce extracellular polysaccharides both in the logarithmic and stationary phase of growth. The potential ecological significance of these findings is discussed.      

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, .     

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.     

{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.     

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     

Effects of UVB radiation on freshwater autotrophic and heterotrophic picoplankton in a subalpine lake

The effects of UVB radiation on the activity of heterotrophic (HPP) and autotrophic (APP) picoplankton (0.2-2 m) and of autotrophic assemblages >2 m has been measured and compared. Under natural UVB irradiance in a large, deep, oligotrophic subalpine lake (Lago Maggiore, 4555N) with mean dissolved organic carbon (DOC) concentrations of 1 mg Cl^-1, the microorganisms of the two size fractions were not significantly photoinhibited in their autotrophic and heterotrophic activities. The vertical attenuation coefficient (Kd) for irradiance at 305 nm ranged from 1.45 to 1.67 during spring and summer. The mixing layer extended to a greater depth than the layer affected by UVB radiation (z1% < zmix), thus enabling the microorganisms living there to photoadapt. As the assimilation numbers of APP and nanoplankton were higher at 2 m depth than near the surface, we suspected that the influence of longer wavelength (UVA, photosynthetically active radiation) could be stronger than UVB in affecting the photosynthetic efficiency of natural populations. The artificial increase in UVB irradiance had a higher detrimental effect on HPP due to their smaller size, less protection and indirect effects through autotrophic cell inhibition. Picocyanobacteria were percentually more affected by UVB than nanoplankton during April due to the presence of diatoms, which are more resistant than other algal groups to solar UVB irradiance. Furthermore, picocyanobacteria had lower assimilation numbers with respect to larger phytoplankton in the quartz tubes during stratification.      

Short communication. Carbon:nitrogen ratios of Baltic Sea copepods-indication of mineral limitation?

The carbon (C) and nitrogen (N) content and the C:N ratio of two common calanoid copepods, Eurytemora affinis and Acartia bifilosa were measured during spring and summer at the SW coast of Finland, northern Baltic Sea. The C:N ratio of both copepod species was slow and stable (4-4.5), irrespective of sampling time, which implies N limitation at least during intermediate to high food concentrations in spring and early summer. In addition, experiments were conducted to reveal whether the diet of copepods affects their C and N content. Adding green algae Brachiomonas submarina in concentrations of 50-500 g C l^-1 to <100-m-filtered sea water did not significantly increase copepod C or N content in 3 day experiments. However, the C and N contents of E.affinis eggs were 2 times higher in high food concentration, which may increase survival of eggs and nauplii.      

Abundance and biogeography of tintinnids (Ciliophora) and associated microzooplankton in the Southwestern Atlantic Ocean

Absolute abundances of foraminifers, polycystine and phaeodarian radiolarians, tintinnids, pteropods and early crustacean larvae and moults were assessed in a collection of 57 vertically stratified (0-100 m) net microplankton samples from 22 stations located between 34 and 58S (along 51-56°W), covered on 8-16 November 1994. Tintinnids were identified to species and measured in order to estimate their biomass from biovolume to carbon conversions. The distribution of the microzooplanktonic groups assessed was irregular and patchy, both geographically and vertically, and their abundances were characteristic of oceanic low to medium productivity environments. Tintinnid biomass was also generally low (0.05-0.40 g Cl^-1). With the exception of the tintinnids, associations between microzooplanktonic numbers and chlorophyll a were generally loose. Eighty-eight tintinnid taxa were recorded, yet only five accounted for 53% of the specimens identified. Multivariate (cluster) analysis of tintinnid specific distribution patterns clearly showed several distinct zones. From north to south, these are: Transition Zone (TZ), with three subzones, TZ north (34°S-38°S), TZ central (39°44S-44°S) and TZ south (46°S); Subantarctic Zone (SZ; 48-55°S); Polar Front Zone (55°30S); Antarctic Zone (AZ; 58-59°36S). Each of these was characterized by distinct tintinnid assemblages, abundance and biomass. With few exceptions, tintinnid cells were fairly evenly distributed throughout the upper 50 m. Taxonomic composition usually changed little with depth. Mean population depths were calculated for a subset of 35 tintinnids; 29 of these dwell preferably above 40 m. The spatial distribution of tintinnid species richness showed a more or less gradual decrease from north to south. Specific diversity and equitability generally increased with depth, and were higher in antarctic waters than the southern transitional and subantarctic ones; this trend is tentatively attributed to higher water column vertical stability south of the Polar Front.      

Mastoparan analogues stimulate phospholipase C- and phospholipase D-activity in Chlamydomonas: a comparative study

The G-protein activator mastoparan and its analogues are becoming popular tools for studying signalling in plants. Therefore the abilities of mastoparan, mas7, mas8, and mas17 to activate phospholipase C (PLC), PLD and to induce the deflagellation response in Chlamydomonas moewusii Gerloff were compared. The aim was to test whether their relative potencies in a plant system resemble those reported for bovine brain Go and Gi, as is generally assumed, and to determine at which concentrations cells become permeabilized, a known effect of higher concentrations. The concentrations at which 50% deflagellation was induced, were 2.0 M mastoparan, 3.0 M mas8, 3.6 M mas7, and 5.8 M mas17. Similar activities were found for the production of phosphatidic acid, which is the result of the combined activities of PLD and PLC (together with diacylglycerol kinase). PLD activity alone was measured in vivo by its ability to phosphatidylate n-butanol. Surprisingly, the concentrations that stimulated maximum activity were about 10-fold lower (1 M) than those that stimulated maximum PLC activity (10 M). Mas17 was an exception with both maxima above 10 M. All the compounds except mas17 permeabilized C. moewusii cells. The concentrations at which 50% of the cells were permeabilized to Evan's blue were 7.4 M mas8, 16.0 M mas7 and 22.4 M mastoparan. In conclusion, only mastoparan itself and the least active analogue mas17 induced maximum deflagellation, PLC and PLD activities without permeabilizing the cells.Keywords: Chlamydomonas, deflagellation, mastoparan, phospholipases C and D, phospholipid metabolism      

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.     

Short communication. A steep Ca2[IMAGE]-dependence of a K[IMAGE] channel in a unicellular green alga

An increase of cytosolic Ca² in the unicellular green alga Eremosphaera viridis activities Ca²-dependent K channels causing a hyperpolarization of the plasma membrane. Data from parallel calcium, and potential measurements were combined with I/V relationships. This yielded a steep Ca²-dependence of K channels with a co-operativity of 4 and an affinity of 300 nM.Key words: Eremosphaera viridis, plasma membrane, Ca²-dependent K channel, co-operative binding.