Blooms of surf-zone diatoms along the coast of the Olympic Peninsula,Washington. IV. Nitrate reductase activity in natural populations and laboratory cultures of Chaetoceros armatum and Asterionella socialis

Nitrate reductase (NR) activity in the surf-zone diatom Chaetoceros armatum T. West was studied in its natural habitat at Copalis Beach, Olympic Peninsula, Washington (USA) over a period of 18 months. Variations of enzyme activity were found, depending on the season and the time of day. General seasonal trends in NR activity were correlated with nitrate concentrations in the surf-zone. The results also indicated that several factors may limit the activity of the enzyme. This is one of the reasons why NR activity could not be correlated with environmental nitrate concentration on the basis of individual measurements at a given point in time. Enzyme inhibition due to the presence of ammonium occurred on several occasions throughout the study period, and could be detected by the NR assay. This phenomenon for the most part masked any pattern of diel periodicity in NR activity that might have been expected to exist in cells in the natural environment. Cultures of C. armatum and Asterionella socialis Lewin and Norris were also studied in the laboratory. A diel fluctuation in NR activity corresponding to the pattern shown in natural phytoplankton by other authors was exhibited in C. armatum under a light-dark regime of 8 h light – 16 h dark and a light intensity of 400 lux.     

Persistent blooms of surf diatoms along the Pacific coast,USA

Productivity was studied in two diatom species, Chaetoceros armatum T. West and Asterionella socialis Lewin and Norris, which form persistent dense blooms in the surf zone along the Pacific coast of Washington and Oregon, USA. Past observations have shown that surf-diatom standing stock usually declines in summer along with concentrations of nitrate and ammonium. Using the ¹⁴C method, photosynthetic rates in natural surf samples were measured monthly for one year (October 1981 through September 1982) at a study site on the Washington coast. Also measured were temperature, salinity, dissolved nutrients, particulate carbon and nitrogen (used as estimates of phytoplankton C and N), and chlorophyll a. Assimilation numbers (P _max) were higher in summer (5 to 8 g C g^-1 chl a h^-1) than in winter (3 to 4gC). Specific carbon incorporation rates (µ_max) showed no obvious seasonality, mostly falling within the range of 0.09 to 0.13 g C g^-1 C(POC) h^-1. The discrepancy between the seasonal trends for chlorophyll-specific and carbon-specific rates reflects a change in the carbon-to-chlorophyll ratio. Because of seasonal differences in daylength and light intensity, daily specific growth rates () are thought to be higher in summer than in winter. Neither ammonium enrichment assays nor particulate carbon-to-nitrogen ratios provided convincing evidence for nitrogen limitation during summer, and the observed changes in diatom abundance cannot be explained on this basis. Both the high diatom concentrations and their seasonal variations probably are due mainly to factors other than growth rates; two factors considered important are diatom flotation and seasonal changes in wind-driven water transport. C. armatum usually dominates the phytoplankton biomass in the surf zone, and evidence suggests that this species is strongly dominant in terms of primary production.Contribution No. 1391 of the School of Oceanography, University of Washington, Seattle, Washington, USA     

Blooms of surf-zone diatoms along the coast of the Olympic Peninsula,Washington. X. Chemical composition of the surf diatom Chaetoceros armatum and its major herbivore,the Pacific razor clam Siliqua patula

The surf diatom Chaetoceros armatum T. West, collected from its natural habitat along the Washington coast (USA), had a large inorganic component in the form of a clay coat (consisting of clay minerals, illite and montmorillonite) surrounding the cell chains: 63% of the dry weight of the natural material collected in November was inorganic. The organic fraction was composed of 67.6% lipid, 29.7% protein, and 1.3% carbohydrate. Culture cells were likewise high in protein and lipid and low in carbohydrate. Traces of chitin found in field samples were probably a contaminant, since chitin was absent from cultured cells. This diatom species serves as a major food source throughout the year for the Pacific razor clam Siliqua patula Dixon, which inhabits these same beaches. Protein constituted 47% and lipid 42% of the dry weight of razor clam tissue. The fatty acid distribution in the diatom lipid resembled that previously reported for other diatom species; similarly, the fatty acid distribution of the clam lipid was similar to that previously reported for other bivalve molluscs. The clam fatty acids differed in chain length and degree of saturation from those extracted from its food source, indicating an active fatty acid metabolism in the clam.Contribution No. 995 from the Department of Oceanography, University of Washington, Seattle, Washington 98195, USA.     

Availability of colloidal ferric oxides to coastal marine phytoplankton

Cell growth of a coastal marine diatom, Phaeodactylum tricornutum (stock cultures), and two red tide marine flagellates, Heterosigma akashiwo and Gymnodinium mikimotoi (stock cultures), in the presence of soluble chelated Fe(III)-EDTA (1:2) and of four different phases of ferric oxide colloids were experimentally measured in culture experiments at 20°C under 3000 lux fluorescent light. Soluble Fe(III)-EDTA induced the maximal growth rates and cell yields. The short-term uptake rate of iron by H. akashiwo in Fe(III)-EDTA medium was about eight times faster than that in solid amorphous hydrous ferric oxide (Fe₂O₃·xH₂O) medium. In culture experiments supplied with four different ferric oxide forms, the orders of cell yields are amorphous hydrous ferric oxide>-FeOOH (lepidocrocite)>Fe₅O₇(OH)·4H₂O (hydrated ferric oxyhydroxide polymer >-FeOOH (goethite). The specific growth rates () at logarithmic growth phase in Fe(III)-EDTA, amorphous hydrous ferric oxide and -FeOOH media were significantly greater than those in Fe₅O₇ (OH)·4H₂O and -FeOOH media. The thermodynamically stable forms such as Fe₅O₇(OH)·4H₂O and -FeOOH supported a little or no phytoplankton growth. The iron solublities and/or proton-promoted iron dissolution rates of these colloidal ferric oxides in seawater at 20°C were determined by simple filtration techniques involving -activity measurements of ⁵⁹Fe. The orders of solubilities and estimated dissolution rate constants of these ferric oxides in seawater were consistent with that of cell yields in the culture experiments. These results suggest that the availability of colloidal iron to provide a source of iron for phytoplankton is related to the thermodynamic stability and kinetic lability of the colloidal ferric oxide phases, which probably control the uptake rate of iron by phytoplankton.     

Effect of aging time on the availability of freshly precipitated ferric hydroxide to coastal marine diatoms

Cell growth and iron uptake of the coastal marine diatoms Chaetoceros sociale and Thalassiosira weissflogii were studied in the presence of short-aged amorphous ferric hydroxide (am-Fe(III)) media. These were prepared by aging for 1 day, 3 days, and 3 weeks after adding a small amount of ferric iron acidic stock solution to autoclaved filtered seawater and were experimentally measured in culture experiments at 10°C for C. sociale and 20°C for T. weissflogii. The order of cell yields for both species was: 1-day aged am-Fe(III) >3-day aged am-Fe(III) >> 3-week aged am-Fe(III) media. The iron uptake rates by C. sociale during 0–1 day in 1 day and 3-day aged am-Fe(III) media were about two-thirds and one-fourths, respectively, lower than that in the direct Fe(III) input medium containing C. sociale into which an acidic Fe(III) stock solution was added directly. The longer aging time of am-Fe(III) in media results in reducing the supply of bioavailable iron in the media by the slower dissolution rate of am-Fe(III) with the longer aging time. These results suggest that the chemical and structural changes of freshly precipitated amorphous ferric hydroxide with short aging time affect their ability, such as iron solubility and dissolution rate to supply bioavailable iron for the phytoplankton growth. The chemical and structural conversion of solid iron phases with time is one of the most important processes in changing the supply of available iron to marine phytoplankton in estuarine and coastal waters and in iron fertilization experiments.     

Cyst formation of the noxious red tide flagellate Chattonella marina (Raphidophyceae) in culture

Cyst formation of the noxious red tide flagellate Chattonella marina (Raphidophyceae), cultured from a cyst in sediments of Suo-nada, Japan in 1986, was investigated by culture experiments. Nitrogen limitation was effective in inducing cyst formation. After incubation in N-limited medium at 25°C with 10000 lux on a 14 h light, 10 h dark photo-cycle, cultures were subjected to six different light intensities (0 10000 lux) in order to determine effects of light intensity on cyst formation. Cysts were formed under light intensities of 1000 lux or below, but not at 10000 lux. Cysts formed in culture displayed morphological characteristics quite similar to those natural cysts observed in sediments collected from the Inland Sea of Japan. Observations on nucleus, using diaminidinophenylindole (DAPI)-staining and epifluorescence microscopy, indicated that the majority of cysts formed in culture were uninucleate, a few were binucleate. Germination of cysts was observed under adequate conditions for germination (22°C, 3500 lux with a 14 h light, 10 h dark photo-cycle) even after storage at 11°C in the dark for more than 4 mo.     

Effect of natural and synthetic organic-Fe(III) complexes in an estuarine mixing model on iron uptake and growth of a coastal marine diatom, Chaetoceros sociale

Cell growth of a coastal marine diatom, Chaetoceros sociale, in the presence of different premixed organic-Fe(III) complexes [EDTA-Fe(III) (100:1 and 2:1), citric-Fe(III) (100:1) and fulvic-Fe(III) (0.1, 0.2 and 1 ppm C)] and solid amorphous hydrous ferric oxide [am-Fe(III) or Fe(III) hydroxide] were experimentally measured in culture experiments at 10 °C under 3000 lux fluorescent light. Fulvic-Fe(III) (0.1 and 0.2 ppm C) and citric-Fe(III) (100:1) induced maximal cell yields of C. sociale. The order of cell yields was: fulvic-Fe(III) (0.1 and 0.2 ppm C) ≥ citric-Fe(III) (100:1) > EDTA-Fe(III) (2:1) ≫ solid am-Fe(III) > EDTA-Fe(III) (100:1) ≫ fulvic-Fe(III) (1 ppm C). The short-term iron uptake rates by C. sociale in fulvic-Fe(III) (0.1 and 0.2 ppm C) and citric-Fe(III) (100:1) media were about five to six times faster than those in EDTA-Fe(III) (100:1) and solid am-Fe(III) media. The dissociative precipitation rates of premixed organic-Fe(III) complexes in seawater at 10 °C were determined by simple filtration (0.025 μm) involving γ-activity measurements of ⁵⁹Fe. The order of estimated initial Fe(III) dissociative precipitation rates of these organic-Fe(III) complexes in seawater were nearly consistent with those of cell yields in the culture experiments and short-term iron uptake rates by C. sociale [except for fulvic-Fe(III) (1 ppm C) medium]. In fulvic-Fe(III) (0.1 and 0.2 ppm C), citric-Fe(III) (100:1) and EDTA-Fe(III) (2:1) media, the concentrations of dissolved organic-Fe(III) complexes in initial culture experiments are prone to supersaturate under the culture conditions. The supersaturated dissolved organic-Fe(III) complex in seawater supplies biologically available inorganic Fe(III) species in culture media through its dissociation at high pH and high levels of seawater cations. Therefore, the natural dissolved organic-Fe(III) complexes supplied by riverine input may play an important role in supplying bioavailable iron in estuarine mixing system and coastal waters. Received: 6 September 1998 / Accepted: 8 April 1999     

Binding of manganese by Antarctic Phaeocystis pouchetii and the role of bacteria in its release

The growth of Antarctic Phaeocystis pouchetii and associated bacteria in culture, and the binding and release of manganese were investigated using cultures derived from three clonal isolates collected from Prydz Bay, Antarctica, in November and December 1982. The cultured strains accumulated manganese from the culture medium. The concentration of Mn²⁺ in the alga was up to 58 times that of the medium. The Mn²⁺ apparently binds to the mucilage secreted by the cells and gives the alga its characteristic brown colour. Oxidation or complexing of Mn²⁺ by P. pouchetii was also indicated. Bacterial growth on the mucilage is inhibited in rapidly growing cultures by acrylic acid produced in the mucilage. Once the growth of P. pouchetii and production of ccrylic acid slow, bacterial numbers increase, leading to the solubilization of the mucilage and the release of Mn²⁺. In cool-temperate, subpolar and polar seas where P. pouchetii may form dense blooms, the binding and subsequent release of manganese may have important consequences for competing phytoplankton.     

Light and temperature demands for growth and reproduction of laminarian gametophytes in southern and central California

The gametophytes of 9 laminarian species (4 from southern California, and 5 from central California, USA) became fertile in the unicellular stage (female gametophytes) or in a few-celled stage (male gametophytes), when appropriate temperatures and a sufficiently high quantum irradiance in the blue part of the spectrum were supplied. Vegetative growth, leading to the formation of filamentous gametophytes was light-saturated at relatively low irradiances (4 W m^-2; equivalent to about 2 nE cm^-2 sec^-1 or an illuminance of 1000 lux), whereas 2 to 3 times this irradiance in continuous fluorescent cool white light was needed to induce the majority of the gametophytes to become fertile. An illuminance of 8300 lux did not inhibit the development of the gametophytes from southern Californian species. Egregia menziesii exhibited an exceptionally low quantum demand for induction of fertility. Gametophytes of species from central and southern California differed in regard to their temperature optimum for growth (12°C in the former, 17°C in the latter) and their upper temperature limit for reproduction (17°C in the former, 20°C in the latter).     

Studies on the growth of some marine unicellular algae under different artificial light sources

Documented evidence of the suitability of various artificial light sources for the culture of unicellular algae is scarce. This paper reports the results of a comparison of the growth rates of 5 species of marine unicellular algae at various light intensities produced by an incandescent filament source or daylight fluorescent tubes. Under light saturating conditions the maximum growth rate achieved by each species was the same under each artificial source. Under sub-optimal intensities, no difference in the growth rates under the 2 sources was detected in the case of Phaeodactylum tricornutum, Chlorella ovalis or Monochrysis lutheri. However, under these conditions both Brachiomonas submarina and Dunaliella primolecta required higher intensities of incident illumination from the fluorescent source than from the incandescent source to maintain a particular relative growth rate.     

Effect of light on apical length growth of Fucus distichus spp. edentatus (Phaeophyta)

The length growth of Fucus distichus L. ssp. edentatus (Pyl.) Powell in continuous light is compared to growth in natural daylight. In continuous light the length growth of vegetative and fertile apices were saturated at 25 to 40 Wm^-2 and 15 to 30 Wm^-2, respectively. In natural daylight vegetative apices reached saturation at about 300 Wm^-2 (in May), while fertile apices were not saturated at 180 Wm^-2 (in March). This shows that saturation levels are dependent on the light regime and that they may be greatly underestimated when continuous light is used. At 20 Wm^-2 vegetative and fertile apices were daylength saturated at 8 and 12 to 16 h, respectively. Maximum growth in vegetative apices occurred in July, but growth rates were high also during wintertime (45% of July maximum in March at 4.0°–4.2°C). This corresponds to the experimental results which indicate that F. d. edentatus grows well at low irradiances and during short photoperiods.     

Change in the uptake and cellular Si:N ratio in diatoms responding to the ambient Si:N ratio and growth phase

A change in the Si:N ratio of diatom cells during growth was examined for Chaetoceros socialis and Thalassiosira sp., with different initial silicate to nitrate (Si:N) ratios in the media. During exponential growth, C. socialis assimilated silicate and nitrate with a molar ratio of 0.5, independent of the ratio in the media, but after the depletion of nitrate, silicate continued to be taken up, and the Si:N ratio in the stationary phase increased to 2 as a function of the Si:N ratios in the media. In contrast, the ratio of silicate to nitrate taken up by Thalassiosira sp. increased with an increase in the Si:N ratio in the media. The Si:N ratio in the cells during the stationary phase increased in response to an increase in this ratio in the media. The Si:chl  a ratio also increased with the increase in the initial Si:N ratio in the media, while the N:chl  a ratio did not change to a great extent, indicating the changes in the cellular Si:N ratio was derived from changes in the Si content of the cells. These results indicated that the cellular Si:N ratio changed with the Si:N ratio in the medium, and the Si:N uptake ratio during the growth phase was different depending on diatom species. Thus, the dominance of different diatom species may affect nutrient composition and dynamics in the ocean.     

Growth and competition of the marine diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana. I. Nutrient effects

Two marine diatoms, Phaeodactylum tricornutum (Bohlin) and Thalassiosira pseudonana (Hasle and Heimdal), were grown both separately and together in batch cultures on a mixture of waste water and seawater enriched with different components of f medium. At 17°C, the maximum division rates of the two species were statistically indistinguishable. The waste water-seawater mixture used proved to have insufficient Si, relative to N and P, for the growth of T. pseudonana, which requires approximately 5x10^-14 g-at Si cell^-1 to divide at a maximum rate. P. tricornutum, on the other hand, although capable of taking up nearly 9x10^-15 g-at Si cell^-1, could sustain maximum rates of division with 4.3x10^-18 g-at Si cell^-1 or less. No allelopathic interaction between the two species could be detected. We conclude that P. tricornutum enjoys a considerable competitive advantage over T. pseudonana in a waste water-seawater-based mariculture system that is not supplemented with Si. Although Si proved necessary for T. pseudonana to complete more successfully with the other diatom, the presence of excess amounts of Si is not necessarily sufficient for the maintenance of T. pseudonana in mixed continuous culture with P. tricornutum: other factors, such as light-related or photoperiod-related growth response, are believed to determine the ultimate outcome of competition between these algae in light-limited continuous culture.Contribution No. 3999, from the Woods Hole Oceanographic Institution.Communicated by M.R. Tripp, Newark     

Distribution and abundance of choanoflagellates (Acanthoecidae) in the coastal cold ocean of Newfoundland, Canada

Water samples from six bays were taken over a 5-year period (1988 to 1992) to determine the distribution and abundance of loricate choanoflagellates in coastal Newfoundland, and to assess the impact that these organisms might have on this cold ocean food web. Scanning electron microscopy was used to study the morphology of these flagellates, allowing us to identify 11 species of loricate choanoflagellates. Parvicorbicula socialis (Meunier) Deflandre was the most abundant species (80 × 10³ cells l⁻¹), particularly during the spring diatom bloom. Single-cell species, such as Bicosta spini fera (Throndsen) Leadbeater and Calliacantha natans (Grontved) Leadbeater, were found more commonly after the spring diatom bloom in the summer months. Many of the single-cell choanoflagellates were attached to bacteria-rich microaggregates and debris in the water column and in unpoisoned sediment traps. The P. socialis cell flux was calculated to be 5.3 × 10⁶ cells m⁻² d⁻¹ in late May sediment traps. P. socialis in the upper 100 m of the water column was removing 0.3% of the standing crop of bacteria each day (April/May), and the equivalent of 7.4% of the daily bacterial production over the water column. Diel studies of P. socialis in Conception Bay suggest that the sharp decline in population numbers observed in midnight samples may be related to the high number of grazing zooplankton observed during the same period. Pelagic tunicate and zooplankton fecal pellets were found to contain large numbers of choanoflagellate costae, thus providing a direct link from the microbial loop to the macrozooplankton. Received: 17 March 1997 / Accepted: 9 May 1997     

Physioecology of zooplankton. I. Effects of phytoplankton concentration,temperature, and body size on the growth rate of Calanus pacificus and Pseudocalanus sp.

Changes in dry weight and in weight-specific growth rates were measured for copepodite stages of Calanus pacificus Brodsky and Pseudocalanus sp. cultured under various combinations of phytoplankton concentration and temperature. Mean dry weight of early copepodites was relatively unaffected by either food concentration or temperature, but mean dry weight of late stages increased hyperbolically with food concentration and was inversely related to temperature. The food concentration at which maximum body weight was attained increased with increasing temperature and body size, and it was considerably higher for C. pacificus than for Pseudocalanus sp. This suggests that final body size of small species of copepods may be determined primarily by temperature, whereas final body size of large species may be more dependent on food concentration than on temperature. Individual body weight increased sigmoidally with age. The weight-specific growth rate increased hyperbolically with food concentration. The maximum growth rate decreased logarithmically with a linear increase in body weight, and the slope of the lines was proportional to temperature. The critical food concentration for growth increased with body size proportionally more at high than at low temperature, and it was considerably higher for C. pacificus than for Pseudocalanus sp. Because of these interactions, early copepodites optimized growth at high temperature, even at low food concentrations, but under similar food conditions late stages attained higher growth at low temperature. The same growth patterns were found for both species, but the rates were significantly higher for the larger species, C. pacificus, than for the smaller one, Pseudocalanus sp. On the basis of findings in this study and of analyses of relationships between the maximum growth rate, body size, and temperature from other studies it is postulated (1) that the extrapolation of growth rates from one species to another on the basis of similarity in body size is not justified, even for taxonomically related species; (2) that the allometric model is inadequate for describing the relationship between the maximum weight-specific growth rate and body size at the intraspecific level; (3) that the body-size dependence of this rate is strongly influenced by temperature; and (4) that species of zooplankton seem to be geographically and vertically distributed, in relation to body size and food availability, to optimize growth rates at various stages of their life cycles.Contribution No. 1127 from the Department of Oceanography, University of Washington, Seattle, Washington 98195, USA     

Responses of cirripede larvae to light. I. Experiments with white light

The phototactic response of the nauplius larva of Balanus balanoides, B. crenatus and Elminius modestus shows darkadaptation; the response of the cyprid of B. balanoides shows both phototaxis and low photokinesis. The phototactic responses and the orientation of the cyprid to white light at settlement require an intensity of illumination slightly above 10^-5 lux. The ability to select a shaded position by cyprids of R. balanoides requires a higher intensity of 10^-2 to 10^-4 lux; hence a different mechanism may be involved. Barnacle larvae are sufficiently sensitive to be able to respond to light beneath the sea surface, even on cloudy, moonless nights.     

Carbon and nitrogen metabolism by Monochrysis lutheri: Measurement of growth-rate-dependent respiration rates

Dark respiration rates were measured and carbon-excretion rates calculated for a nitrate-limited population of the marine chrysophyte Monochrysis lutheri grown in continuous culture at 20°C on a 12 h light-12 h dark cycle of illumination and over a series of 4 growth rates. A significant (P<0.05) positive correlation was found between dark respiration rate and growth rate. From a simple linear fit to the data, the respiration rate at maximum growth rate was estimated to be roughly 10.5% of the maximum gross-carbon-production rate, and more than three times higher than the extrapolated respiration rate at zero net-growth rate. Carbon-excretion rates showed no significant correlation with growth rate, and averaged less than 5% of the maximum gross-carbon-production rate. Mean cell nitrogen to carbon ratios were correlated in a virtually linear manner (r=0.994) with growth rate, and at a given growth rate were consistently higher than nitrogen to carbon ratios for the same species grown on continuous light. A comparison of carbon and nitrogen quotas as a function of growth rate for M. lutheri and other species suggests that the increase of cellular nitrogen at high growth rates under nitrate-limited growth conditions may be associated with the storage of cellular protein or amino acids rather than the presence of an inorganic nitrogen reservoir. The maximum nitrate uptake rate per cell during the day changed very little over the range of growth rates studied, and was comparable to the maximum uptake rate found for cells grown on continuous light. However, the cell nitrogen quota increased steadily with growth rate, causing a reduction in the maximum specific-uptake rate of nitrate during the day at high growth rates. The dark nitrate-uptake capacity of the population was clearly exceeded by the supply rate at the two higher growth rates, leading to a buildup of nitrate during the night which amounted to as much as 21% of the particulate nitrogen in the growth chamber by morning.Hawaii Institute of Marine Biology Contribution No. 478.     

Influence of temperature on the growth rate of Skeletonema costatum in response to variations in daily light intensity

Daily light intensities (I _o) can vary 10-fold during the winter-spring and late-summer diatom blooms in New England, USA, coastal waters. Laboratory cultures and natural populations incubated in dialysis sacs were examined to determine the time course of growth rate in Skeletonema costatum (Greville) Cleve in response to variations in daily light intensity during two bloom periods in Narragansett Bay, Rhode Island, USA. Log-phase cultures of S. costatum require 2 d to attain maximum growth rates at 2°C following transfer to saturating intensities. At 20°C, only 1 d is required. As temperature increases, Detonula confervacea (Cleve) Gran, Thalassiosira nordenskiöldii Cleve and Ditylum brightwellii (West) Grunow also exhibit rapid increases in mean daily division rates (K) following transfer to saturating light intensities. Thalassiosira pseudonana Hustedt, however, did not alter the time required to achieve maximum K as temperature varied. Natural populations of S. costatum did not show a well-defined relationship between K and light. Throughout a winterspring bloom, K was limited by low temperatures and exhibited no clear response to variations in I _o. A change in K in response to variation in I _o may occur on a daily basis during the summer, when temperatures are near 20°C; this has yet to be verified for in situ populations.     

Inhibitory effect of the iron chelator desferrioxamine (Desferal) on the generation of activated oxygen species by Chattonella marina

Recent studies demonstrated that the toxic red tide phytoplankton Chattonella spp. produce activated oxygen species such as superoxide anion (O ₂ ^- ), hydrogen peroxide (H₂O₂), and hydroxyl radicals (·OH), which may be responsible for the toxicity of this flagellate. However, the mechanism behind the production of these oxygen radicals and H₂O₂ by Chattonella spp. is largely unknown, and the physiological significance of activated oxygen species for Chattonella spp. is also unclear. In the present study, we investigated the involvement of iron in the generation of O ₂ ^- and H₂O₂ by C. marina. The generation of O ₂ ^- by C. marina was related to the growth phase; the highest rate of O ₂ ^- production was observed during the exponential growth phase. However, no such increase during the exponential growth phase was observed in C. marina growing in an iron-deficient medium, even though the growth of C. marina was not significantly affected by iron-deficiency during the first 4 d. In addition, the iron chelator desferrioxamine (Desferal) strongly inhibited the generation of both O ₂ ^- and H₂O₂ by C. marina in a concentration-dependent manner. The growth of C. marina was also inhibited by Desferal. Furthermore, in the presence of 500 M Desferal, C. marina-induced growth inhibition of the marine bacteria Vibrio alginolyticus was almost completely abolished. These results suggest that iron is required for the generation of activated oxygen species by C. marina, as well as for its own growth.     

“Good” and “bad” diatoms: development,growth and juvenile mortality of the copepod <Emphasis Type="Italic">Temora longicornis</Emphasis> on diatom diets

We measured development, growth and juvenile mortality of the common copepod Temora longicornis on 11 different monospecific diatom diets in order to estimate (1) how common the negative effects of diatoms are on the development of this copepod and (2) whether the arrested development is connected to deleterious polyunsaturated aldehydes (PUA) or food nutritional quality. Four diatom species (Thalassiosira weissflogii, Thalassiosira rotula CCMP1647, Leptocylindricus danicus CCPM469 and Skeletonema costatum CCMP1281) supported complete development, whereas development failed in or before metamorphosis on seven diatom species/strains (Chaetoceros affinis CCMP158, C. decipiens CCMP173, C. socialis, T. rotula CCMP1018, Thalassiosira pseudonana CCMP1010 and CCMP1335). However, four out of these seven species were not ingested by nauplii, either due to morphology (Chaetoceros spp.) or large size (T. pseudonana CCMP1010). The growth rate did not correlate with the ingestion rate of PUA, neither with ingestion of food mineral (nitrogen) nor with biochemical (polyunsaturated fatty acids, sterols) components. We show that, although some diatoms are of inferior food quality, this is unlikely to be connected to toxicity or due to a direct limitation by a single food nutritional compound.