Hilary E. Glover

High Nitrite Levels off Northern Peru: A Signal of Instability in the Marine Denitrification Rate.

During February and March 1985, nitrite levels along the northern (approximately 7� to 10�S) Peruvian coast were unusually high. These accumulations occurred in oxygen-deficient waters, suggesting intensified denitrification. In a shallow offshore nitrite maximum, concentrations were as high as 23 micromoles per liter (a record high). Causes for the unusual conditions may include a cold anomaly that followed the 1982-83 El Ni�o. The removal of combined nitrogen (approximately 3 to 10 trillion grams of nitrogen per year) within zones of new or enhanced denitrification observed between 7� to 16�S suggests a significant increase in oceanic denitrification.

A nitrate-dependent Synechococcus bloom in surface Sargasso Sea water

Considerable debate exists concerning the magnitude of oceanic primary production, its rate of transfer to other trophic levels and turnover times of carbon and nitrogen1–5. In nitrogen-limited ocean systems, episodic increases in nitrate concentrations can support a significant fraction of annual phytoplankton production5. Yet little information is available regarding the distribution of nitrate in seasonally stratified oceanic surface waters, because concentrations are below the 0.03 μM detection limit of colorimetric methods6. We present the first evidence that high surface productivity in stratified Sargasso Sea water was supported by nanomolar changes in nitrate concentrations. This change was stoichiometrically consistent with the subsequent cellular production of a cyanobacterial (Synechococcus) bloom. Initially, cellular phycoerythrin and chlorophyll pigments increased, after which growth was enhanced to near maximum rates, and grazing was closely coupled to production. These observations suggest that Synechococcus occupies an important trophic position in the transfer of new nitrogen into the oceanic food web.

The effects of light quality and intensity on photosynthesis and growth of marine eukaryotic and prokaryotic phytoplankton clones

Abstract The aim of this work was to assess the relative efficiency of different phytoplankton groups growing under various spectral light fields commonly found in the marine environment. Using neritic and oceanic clones of cyanobacteria (prokaryotic) of the genus Synechococcus and various sized eukaryotic algae representing diverse pigment groups, we compared absorption and fluorescence excitation/emission spectra. Colored filters and neutral density screens were used to simulate oceanic and coastal water-types and rates of photosynthesis and growth were measured under variable conditions of light intensity and quality. Relative photosynthetic efficiencies were determined by comparing light-limited slopes of photosynthesis-irradiance curves in green, blue, and blue-violet light with those in white light. The relative quantum efficiency for photosynthesis was related to both size and pigment composition of the phytoplankter. Independent of light color, smaller algal species were photosynthetically more efficient than larger algae from the same pigment group. In general, the ratio of in vivo cholorophyll intensity fluorescence at the red emission maximum induced by 530 nm excitation to that produced by 470 nm excitation was better than absorption spectra in predicting the ability of organisms from different pigment groups in using various light qualities. Within the ultraplankton size range, algae photosynthesized and grew most efficiently in low intensity blue-violet and blue light, while phycoerythrin-rich Synechococcus clones were most efficient in dim green light. Even though some ultraplankton algal clones, such as the diatom 13−1 and the cryptomonad ID2, contained large quantities of fucoxanthin and phycoerythrin, respectively, their photosynthetic and growth efficiencies in green light were much lower than those of phycoerythrin-rich Synechococcus clones. Moreover, the presence of phycourobilin chromophores in the phycoerythrin of some Synechococcus clones, apparently increased the ability of these cyanobacteria to photosynthesize in low intensity blue light. We conclude that Synechococcus clones containing phycourobilin chromophores could out-compete other Synechococcus clones at depth. However, oceanic ultraplanktonic algae may have a competitive advantage over larger algae and Synechococcus spp. at the base of the photic zone, because these small algae would be more efficient in using the available dim blue-violet light.

Contribution ofSynechococcus spp. to size-fractioned primary productivity in three water masses in the Northwest Atlantic Ocean

The distribution of phycoerythrin-richSynechococcus spp. relative to eukaryotic algae and the contribution ofSynechococcus spp. toin situ primary production were compared at a neritic front, in warm-core eddy 84-E, and at Wilkinsons Basin, during a cruise to the Northwest Atlantic Ocean in July/August 1984. Immunofluorescence analyses ofSynechococcus strains demonstrated the restricted distribution of the tropical oceanic serogroup to the warm-core eddy, while strains of the neritic serogroup and those labelled by antiserum directed against a motile strain, were abundant in all three water masses. Although the majority ofSynechococcus spp. cells were observed in the 0.6 to 1 μm fraction, an increasing proportion of the totalSynechococcus spp. cells were found in the 1 to 5 μm fraction as nitrate concentrations increased near the base of the thermocline. From immunofluorescence analyses, we determined that the increasing proportion of largerSynechococcus spp. cells at depth was not the result of a change in strain composition, and may therefore be associated with increasing cell volume due to the enhanced nutrient supply. The contribution of the different size fractions to the total standing crop of chlorophyll and thein situ rate of photosynthesis was distincty different for the three water masses. At the neritic front, the larger photoautotrophs of the 1 to 5 μm and >5 μm fractions were the major contributors to chlorophyll concentrations and primary production.Synechococcus spp. appeared to provide only 6% of the dawn-to-duskin situ primary production at the neritic front. In modified Sargasso water in the warm-core eddy,Synechococcus spp. contributed 25% to thein situ rate of integrated primary production. In this warm-core eddy, the 0.2 to 0.6 μm fraction made a major contribution to the standing crop of chlorophyll and primary production that equalled or exceeded that of the larger sze categories. Furthermore, at the bottom of the euphotic layer, eukaryotes numerically dominated the 0.2 to 0.6 μm fraction, which contributed 61% of the primary productivity. At Wilkinsons Basin, theSynechococcus spp.-dominated 0.6 to 1.0 μm fraction made the greatest contribution to the standing crop of chlorophyll an primary production, while smaller photoautotrophs (0.2 to 0.6 μm) accounted for little of the chlorophyll or photosynthetic rates measured over the euphotic layer. Largest numbers ofSynechococcus spp. (2.9x108 cells l-1) occurred at the 18% isolume, coincident with a shoulder in the chlorophyll fluorescence profile and the site of maximumin situ primary productivity. At Wilkinsons Basin,Synechococcus spp. contributed 46% to thein situ photosynthesis integrated over the water-column.

Photosynthetic Characteristics of Picoplankton Compared with Those of Larger Phytoplankton Populations, in Various Water Masses in the Gulf of Maine

AbstractCell numbers of eucaryotes and cyanobacteria in phototrophic picoplankton and ratios of in vivo fluorescence of phycoerythrin: chlorophyll a indicated that chroococcalean cyanobacteria played a more prominent role in phytoplankton communities, at the least productive stations. At stations displaying large vertical density gradients, subsurface maxima of phytoplankton pigments were observed. Ratios of in vivo fluorescence of phycoerythrin: chlorophyll a were always greater at the pigment maximum than at the surface. Cyanobacteria from pigment maxima demonstrated greater phycoerythrin fluorescence intensity and photosynthetic rates than cyanobacteria from the surface. Photosynthetic characteristics of picoplankton ( 3 μm populations. The picoplankton differed from larger phytoplankton, in that (1) their pattern of photosynthetic carbon fixation did not vary significantly with decreasing light intensity, and at optimal intensities ...

Suspended particle and bacterial maxima in Peruvian coastal waters during a cold water anomaly

Simultaneous optical, biological and chemical analyses of coastal waters off Peru were made during a period characterized by anomalously cold surface waters and weak wind-driven coastal upwelling. Particle size distributions and the microbial and chemical nature of the intermediate nepheloid layers provide strong evidence that bacterial growth, settling and offshore transport of particles are major processes controlling the particulate structure of the nearshore waters. The data also support previous suggestions that mid-depth maxima in suspended particles associated with nitrite maxima have a large bacterial component. Further, these results demon- strate the effectiveness of in situ optical methods for detection and quantification of the bacterial component of particle size distributions. While some features were similar to the particulate structures observed previously in Peruvian coastal waters, the data show the region to have significant temporal and spatial variability.

Diurnal patterns in photosynthetic capacity and depth-dependent photosynthesis-irradiance relationships inSynechococcus spp. and larger phytoplankton in three water masses in the Northwest Atlantic Ocean

The photosynthetic characteristics of prokaryotic phycoerythrin-rich populations of cyanobacteriaSynechococcus spp. and larger eukaryotic algae were compared at a neritic frontal station (Pl), in a warm-core eddy (P2), and at Wilkinsons Basin (P3) during a cruise in the Northwest Atlantic Ocean in the summer of 1984.Synechococcus spp. numerically dominated the 0.6 to 1 μm fraction, and to a lesser extent the 1 to 5 μm size fractions, at most depths at all stations. At P2 and P3, all three size categories of phytoplankton (0.6 to 1 μm, 1 to 5 μm, and >5 μm) exhibited similar depth-dependent chages in both the timing and amplitude of diurnal periodicities of chlorophyllbased and cell-based photosynthetic capacity. Midday maxima in photosynthesis were observed in the upper watercolumn which damped-out in all size fractions sampled just below the thermocline. For all size fractions sampled near the bottom of the euphotic zone, the highest photosynthetic capacity was observed at dawn. At all depths, theSynechococcus spp.-dominated size fractions had lower assimilation rates than larger phytoplankton size fractions. This observation takes exception with the view that there is an inverse size-dependency in algal photosynthesis. Results also indicated that the size-specific contribution to potential primary production in surface waters did not vary appreciably over the day. However, estimates of the percent contribution ofSynechococcus spp. to total primary productivity in surface waters at the neritic front were significantly higher when derived from short-term incubator measurements of photosynthetic capacity rather than from dawn-to-duskin situ measurements of carbon fixation. The discrepancy was not due to photoinhibitory effects on photosynthesis, but appeared to reflect increased selective grazing pressure onSynechococcus spp. in dawn-to-dusk samples. Low-light photoadaptation was evident in analyses of the depth-dependency ofP-I parameters (photosynthetic capacity,Pmax; light-limited slope, alpha;Pmax alpha,Ik; light-intensity beyond which photoinhibition occurs,Ib) of the > 0.6 μm communities at all three stations and was attributable to stratification of the water column. There was a decrease in assimilation rates andIk with depth that was associated with increases in light-limited rates of photosynthesis. No midday photoinhibition ofPmax orIb was observed in any surface station. Marked photoinhibition was detected only in the chlorophyll maximum at the neritic front and below the surface mixed-layer at Wilkinsons Basin, where susceptibility to photoinhibition increased with the depth of the collected sample. The 0.6 to 1 μm fraction always had lower light requirements for light-saturated photosynthesis than the > 5 μm size fraction within the same sample. Saturation intensities for the 1 to 5 μm and 0.6 to 1 μm size fractions were more similar whenSynechococcus spp. abundances were high in the 1 to 5 μm fraction. The > 5 μm fraction appeared to be the prime contributor to photoinhibitory features displayed in mixed samples (> 0.6 μm) taken from the chlorophyll maxima. InSynechococcus spp.-dominated 0.6 to 1 and 1 to 5 μm size fractions, cellular chlorophylla content increased 50- to 100-fold with depth and could be related to increases in maximum daytime rates of cellularPmax at the base of the euphotic zone. Furthermore, the 0.6 to 1 μm and > 5 μm fractions sampled at the chlorophyll maximum in the warm-core eddy had lower light requirements for photosynthesis than comparable surface samples from the same station. Results suggest that photoadaptation in natural populations ofSynechococcus spp. is accomplished primarily by changing photosynthetic unit number, occuring in conjuction with other accommodations in the efficiency of photosynthetic light reactions.

The relationship between inorganic nitrogen oxidation and organic carbon production in batch and chemostat cultures of marine nitrifying bacteria

Rates of nitrification and organic C production were determined in batch and chemostat cultures of marine nitrifying bacteria; two NH4+-oxidizing species and one NO2−-oxidizing spezies. With increasing age in batch cultures and with decreasing flow rates in chemostats, cellular organic C and N concentrations declined while the intracellular ratio of C:N remained constant. With decreasing flow rates in chemostats, there was a reduction in (a) carboxylating enzyme activity per unit of cellular organic C (the potential for chemoautotrophic CO2 fixation), and (b) the yield of organic C. For both NH4+and NO2−oxidizers, rates of nitrification and C yield were lowest at very slow chemostat growth rates, when compared with optimal growth rates in batch cultures. For both NH4+and NO2−-oxidizing species, the stoichiometric relationship between nitrification and organic C production did not remain constant and appeared to be dependent on the availability of the inorganic N substrate. The organic C yield from NH4+oxidation and hence the free energy efficiency declined with increasing age in batch cultures and with decreasing flow rates in chemostats. The C yield from NO2−oxidation and the free energy efficiency at slow chemostat growth rates was also lower than that at the optimal growth rate in batch culture.

Effects of light intensity and nutrient availability on diel patterns of cell metabolism and growth in populations of Synechococcus spp.

Between July 21 and August 8, 1984, phytoplankton were collected from the surface (2 m) and/or chlorophyll maximum of a neritic front, warm-core eddy 84-E and Wilkinsons Basin in the Northwest Atlantic Ocean and incubated up to 38 h in 200-liter vats. Effects of light intensity and nutrient availability on diel patterns of cell metabolism were analyzed in a 0.6- to 1-μm fraction, where Synechococcus spp. represented 80 to 100% of the total photoautotrophs. Populations held under in situ conditions exhibited daytime peaks in photosynthetic potential (Pmax) that were an order of magnitude higher than nighttime Pmax values. Daytime phasing of Pmax peaks had no relationship to asynchronous fluctuations in cellular activities of ribulose 1,5 bisphosphate carboxylase (RUBPCase) or phosphoenol pyruvate carboxylase (PEPCase), or to variations in chlorophyll content. Daytime Pmax peaks were about 12 h out of phase with nighttime maxima in the frequency of dividing cells (FDC). The phase relationship between Pmax and FDC could be altered by manipulating environmental conditions. High light exposure of depp populations did not affect timing of the Pmax peak, but its magnitude increased and coincided with increased RUBPCase activity and chlorophyll photobleaching. In the eddy population, a major shift in the timing of peak Pmax was induced when increased light intensity was accompanied by nutrient enrichment. This change coincided with major increases in cellular chlorophyll and carboxylating enzyme activity. Lowering irradiance and/or increasing nutrient availability elicited different diel pattern in cellular metabolism in surface populations from the eddy and from Wilkinsons Basin that appeared linked to differences in the nutrient status of the cells. Rates of cell division estimated from the percentage of dividing cells in preserved samples were 0.83 divisions d-1 in surface warm-core eddy populations, supporting the view that carbon and nitrogen turnover rates in oligotrophic waters can be sufficient to promote near optimal growth of Synechococcus spp.

Photosynthetic characteristics of coccoid marine cyanobacteria

Two strains of marine Synechococcus possessed a much greater potential for photorespiration than other marine algae we have studied. This conclusion was based on the following physiological and biochemical characteristics: a) a light-dependent O2 inhibition of photosynthetic CO2 assimilation at atmospheric O2 concentrations. The degree of inhibition was dependent on the relative concentrations of dissolved O2 and CO2, being greatest at 100% O2 with no extra bicarbonate added to the medium; b) actively photosynthesizing cells had high levels of ribulose-1,5-bisphosphate carboxylase compared with phosphoenolpyruvate carboxylase; ribulose-1,5-bisphosphate oxygenase activities were three times greater than ribulose-1,5-bisphosphate carboxylase activities; c) cells photosynthesizing in 21% O2, showed significant 14C-labelling of phosphoglycolate and glycolate and the percentage of total carbon-14 incorporated into these two compounds increased when the O2 concentration was 100%; d) at 100% O2, there was a post-illumination enhanced rate of O2 consumption, which was three times greater than dark respiration, and the rate declined with increasing bicarbonate concentrations.The inhibitory effect of O2 on photosynthesis did not appear to be solely due to photorespiration, since O2 inhibition of photosynthetic O2 evolution was much greater than that of photosynthetic CO2 assimilation. Also, O2 inhibition of photosynthetic O2 evolution declined only slightly with decreasing light intensities, while the inhibition of CO2 assimilation declined rapidly with decreasing light intensity.