Use of a real-time remote monitoring network (RTRM) and shipborne sampling to characterize a dinoflagellate bloom in the Neuse Estuary, North Carolina, USA

The spatial-temporal distribution of a dinoflagellate bloom dominated or co-dominated by Prorocentrum minimum was examined during autumn through early spring in a warm temperate, eutrophic estuary. The developing bloom was first detected from a web-based alert provided by a network of real-time remote monitoring (RTRM) platforms indicating elevated dissolved oxygen and pH levels in upper reaches of the estuary. RTRM data were used to augment shipboard sampling, allowing for an in-depth characterization of bloom initiation, development, movement, and dissipation. Prolonged drought conditions leading to elevated salinities, and relatively high nutrient concentrations from upstream inputs and other sources, likely pre-disposed the upper estuary for bloom development. Over a 7-month period (October 2001–April 2002), the bloom moved toward the northern shore of the mesohaline estuary, intensified under favorable conditions, and finally dissipated after a major storm. Bloom location and transport were influenced by prevailing wind structure and periods of elevated rainfall. Chlorophyll a within bloom areas averaged 106 ± 13 μg L⁻¹ (mean ± 1 S.E.; maximum, 803 μg L⁻¹), in comparison to 20 ± 1 μg L⁻¹ outside the bloom. There were significant positive relationships between dinoflagellate abundance and TN and TP. Ammonium, NO₃⁻, and SRP concentrations did not decrease within the main bloom, suggesting that upstream inputs and other sources provided nutrient-replete conditions. In addition, PAM fluorometric measurements (09:00–13:00 h) of maximal PSII quantum yield (F_v/F_m) were consistently 0.6–0.8 within the bloom until late March, providing little evidence of photo-physiological stress as would have been expected under nutrient-limiting conditions. Nitrogen uptake kinetics were estimated for P. minimum during the period when that species was dominant (October–December 2001), based on literature values for N uptake by an earlier P. minimum bloom (winter 1999) in the Neuse Estuary. The analysis suggests that NH₄⁺ was the major N species that supported the bloom. Considering the chlorophyll a concentrations during October and December and the estimated N uptake rates, phytoplankton biomass was estimated to have doubled once per day. Bloom displacement (January–February) coincided with higher diversity of heterotrophic dinoflagellate species as P. minimum abundance decreased. This research shows the value of RTRM in bloom detection and tracking, and advances understanding of dinoflagellate bloom dynamics in eutrophic estuaries.     

SUPEROXIDE DISMUTASE ACTIVITY IN PERIDINIUM GATUNENSE IN LAKE KINNERET: EFFECT OF LIGHT REGIME AND CARBON DIOXIDE CONCENTRATION1

The activity of superoxide dismutase (EC 1.15.1.1, superoxide: superoxide oxidoreductase) (SOD) was determined in Peridinium gatunense Lemm. under natural and controlled conditions. SOD activity increased toward the end of the spring algal bloom in Lake Kinneret simultaneously with maximal photosynthetic activity and conditions of elevated ambient stress such as high irradiance. Activity staining of native polyacrylamide gel electrophoresis gels of bloom samples showed a similar pattern to the spectrophotometrically measured SOD. Both Mn SOD and CuZn SOD were present, however no Fe SOD was found in Peridinium. One of three isoenzymes of Mn SOD showed marked differential regulation of activity under stress. An increase in the quantity of the 32-kDa Mn SOD polypeptide during the bloom was found to be unrelated to senescence; it was assumed that this polypeptide was induced by stress. Thus, SOD in Peridinium undergoes physiological and molecular acclimation to seasonal environmental changes. When Peridinium was exposed to various O₂ and CO₂ concentrations in culture, CuZn SOD significantly increased under high C0₂ concentrations and normoxic conditions (20% O₂). However, at high irradiances, Peridinium cultures exposed to low and high CO₂ concentrations also had similar CuZn SOD activity. It was concluded that stressful irradiance is the overriding cause of increased SOD activity in both lake samples and in cultures of Peridinium.     

Isolation by Time During an Arctic Phytoplankton Spring Bloom

The arctic phytoplankton spring bloom, which is often diatom‐dominated, is a key event that provides the high latitude communities with a fundamental flux of organic carbon. During a bloom, phytoplankton may increase its biomass by orders of magnitude within days. Yet, very little is known about phytoplankton bloom dynamics, including for example how blooming affects genetic composition and diversity of a population. Here, we quantified the genetic composition and temporal changes of the diatom Fragilariopsis cylindrus, which is one of the most important primary producers in the Arctic, during the spring bloom in western Greenland, using 13 novel microsatellite markers developed for this study. We found that genetic differentiation (quantified using sample‐specific F_ST) decreased between time points as the bloom progressed, with the most drastic changes in F_ST occurring at the start of the bloom; thus the genetic structure of the bloom is characterized by isolation by time. There was little temporal variation in genetic diversity throughout the bloom (mean H_E = 0.57), despite marked fluctuations in F. cylindrus cell concentrations and the temporal change in sample‐specific F_ST. On the basis of this novel pattern of genetic differentiation, we suggest that blooming behavior may promote genetic diversity of a phytoplankton population.     

Initiation of efficient C4 pathway in response to low ambient CO2 during the bloom period of a marine dinoflagellate

Dinoflagellates are important primary producers and major causative agents of harmful algal blooms in the global ocean. Despite the great ecological significance, the photosynthetic carbon acquisition by dinoflagellates is still poorly understood. The pathways of photosynthetic carbon assimilation in a marine dinoflagellate Prorocentrum donghaiense under both in situ and laboratory-simulated bloom conditions were investigated using a combination of metaproteomics, qPCR, stable carbon isotope and targeted metabolomics approaches. A rapid consumption of dissolved CO₂ to generate high biomass was observed as the bloom proceeded. The carbon assimilation genes and proteins including intracellular carbonic anhydrase 2, phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase and RubisCO as well as their enzyme activities were all highly expressed at the low CO₂ level, indicating that C₄ photosynthetic pathway functioned in the blooming P. donghaiense cells. Furthermore, δ¹³C values and content of C₄ compound (malate) significantly increased with the decreasing CO₂ concentration. The transition from C₃ to C₄ pathway minimizes the internal CO₂ leakage and guarantees efficient carbon fixation at the low CO₂ level. This study demonstrates the existence of C₄ photosynthetic pathway in a marine dinoflagellate and reveals its important complementary role to assist carbon assimilation for cell proliferation during the bloom period.     

A bloom of a brown phototrophic sulfur bacterium in lake kinneret: Hydrochemical aspects

During a bloom of the brown phototrophic sulfur bacteriumChlorobium phaeobacteroides in Lake Kinneret the decisive hydrochemical parameters, pH, pH₂S and pe (p=−log activity) were monitored in situ and related to the phototrophic bacterial bloom. The measured data in dicate a strong influence of the phototrophic bacteria on the metalimnic sulfide concentration and on the prevailing redox conditions. The intensity of theC. phaeobacteroides bloom, which appeared in two distinct peaks, could be related to vertical changes of the thermocline.     

WINTER PHYTOPLANKTON BLOOMS UNDER ICE ASSOCIATED WITH ELEVATED OXYGEN LEVELS1

Many shallow lakes in north temperate zones experience reduced dissolved oxygen concentration under ice. However, some shallow lakes display supersaturated dissolved oxygen concentrations (>20 mg·L ^{? 1}) in late winter under conditions of maximum ice thickness. During the winters of 1996, 1997, and 1999, we collected phytoplankton samples from Arrowwood Lake near Pingree, North Dakota to determine whether a specific alga was involved in dissolved oxygen supersaturation in this lake. Although dissolved oxygen supersaturation was not observed during this period, we did observe an increase in dissolved oxygen concentration that was associated with a phytoplankton bloom during late February and early March in both 1996 and 1997. In 1996, the bloom was composed of the dinoflagellate, Peridinium aciculiferum (Lemm.) Lemm. and several species of cryptomonads. A similar bloom of P. aciculiferum was followed by a bloom of several species of euglenoids in 1997. In contrast, P. aciculiferum was only a minor component of the winter phytoplankton, dissolved oxygen concentrations remained low, and no bloom event was observed in 1999. Statistical analyses indicated a significant relationship (r_s = 0.57, P = 0.019) between dissolved oxygen levels and the density of the dinoflagellate, P. aciculiferum, but no significant relationship between dissolved oxygen levels and densities of other phytoplankton. These results suggest that the elevated levels of dissolved oxygen are associated with the dinoflagellate, P. aciculiferum. This bloom was most likely the result of an excystment event rather than a general growth response.     

Incorporation of Different N Sources and Light Response Curves of Nitrogenase and Photosynthesis by Cyanobacterial Blooms from Rice Fields

In this work, we estimate the contributions of the different sources of N incorporated by two N₂-fixing cyanobacterial blooms (Anabaena sp. and Microchaete sp.) in the rice fields of Valencia (Spain) during the crop cycles of 1999 and 2000, and evaluate the response of nitrogenase and C assimilation activities to changing irradiances. Our results show that, far from the generally assumed idea that the largest part of the N incorporated by N₂-fixing cyanobacterial blooms in rice fields comes from N₂ fixation, both cyanobacterial blooms incorporated about three times more N from dissolved combined compounds than from N₂ fixation (only about 33–41% of the N incorporated came from N₂ fixation). Our results on the photodependence of C and N₂ fixation indicate that in both cyanobacterial blooms, N₂ fixation showed a steeper initial slope (α) and was saturated with less irradiance than C fixation, suggesting that N₂ fixation was more efficient than photosynthesis under conditions of light limitation. At saturating light, N₂ fixation and C fixation differed depending on the bloom and on the environmental conditions created by rice plant growth. Carbon assimilation but not nitrogenase activity appeared photoinhibited in the Anabaena but not in the Microchaete bloom in August 1999, when the plants were tall and the canopy was important, and there was no limitation of dissolved inorganic carbon. The opposite was found in the Microchaete bloom of June 2000, when plants were small and produced little shade, and dissolved inorganic carbon was very low.     

An unusual bloom of the dinoflagellate Akashiwo sanguinea off the central Oregon, USA, coast in autumn 2009

An algal bloom caused by the dinoflagellate Akashiwo sanguinea was observed in October–November 2009 along the central Oregon coast (44.6°N), off Newport, Oregon, U.S.A. In this paper, the conditions are described which led to the development and demise of this bloom. The bloom was observed for 1 month from 5-October until 4-November with the peak of abundance on 19-October (347,615 cells L⁻¹). The A. sanguinea bloom followed September blooms of the diatoms Pseudo-nitzschia spp, Chaetoceros debilis, and the dinoflagellate Prorocentrum gracile. The bloom occurred when nitrate and silicate concentrations were <2 μM and <8 μM, respectively, and when the water column was stratified. This A. sanguinea dinoflagellate bloom event was closely related to the anomalous upwelling conditions in 2009: upwelling ceased early, at the end of August, whereas a normal upwelling continues into early October. This relaxation extended to near the end of September as a prolonged downwelling event, but then active upwelling reappeared in October and November. The explanation for the occurrence of the A. sanguinea bloom in October may be related to a combination of a prior diatom bloom, a stratified water column with low nutrient concentration in September, and an active upwelling event in October. As for the ultimate source of the cells, the hypothesis is that the seed stock for the A sanguinea bloom off Oregon was southward transport of cells from the Washington coast where a massive bloom of A. sanguinea was first observed in September 2009.     

Abiotic factors influencing cyanobacterial bloom development in the Gulf of Finland (Baltic Sea)

Blooms of cyanobacteria are a recurrent phenomenon in the Baltic Sea, including the Gulf of Finland. The spatial extension, duration, intensity and species composition of these blooms varies widely between years. Alg@line data collected regularly from ferries as well as weather service and marine monitoring data from 1997 to 2005 are analysed to determine the main abiotic factors influencing the intensity and species composition of cyanobacterial blooms in the Gulf of Finland. It is demonstrated that the development of the Nodularia spumigena Mertens bloom is highly dependent on weather conditions such as photosynthetically active radiation and water temperature. Nutrient conditions, especially the surplus of phosphorus (according to Redfield ratio) related to the pre-bloom upwelling events in the Gulf, affect the intensity of Aphanizomenon sp. (L.) Ralfs blooms. Differences in bloom timing and duration indicate that, if the preconditions (like nutrient ratio/concentration and weather conditions) for bloom formation are favourable, then the Aphanizomenon bloom starts earlier, the overall bloom period is longer and the Nodularia peak might appear in a wider time window. Handling editor: K. Martens     

A bloom of Lyngbya majuscula in Shoalwater Bay, Queensland, Australia: An important feeding ground for the green turtle (Chelonia mydas)

Lyngbya majuscula, a toxic cyanobacterium, was observed blooming during June–July (winter) 2002 in Shoalwater Bay, Queensland, Australia, an important feeding area for a large population of green turtles (Chelonia mydas). The bloom was mapped and extensive mats of L. majuscula were observed overgrowing seagrass beds along at least 18 km of coast, and covering a surface area of more than 11 km². Higher than average rainfall preceded the bloom and high water temperatures in the preceding summer may have contributed to the bloom. In bloom samples, lyngbyatoxin A (LA) was found to be present in low concentration (26 μg kg⁻¹_{(dry weight)}), but debromoaplysiatoxin (DAT) was not detected. The diet of 46 green turtles was assessed during the bloom and L. majuscula was found in 51% of the samples, however, overall it contributed only 2% of the animals’ diets. L. majuscula contribution to turtle diet was found to increase as the availability of the cyanobacterium increased. The bloom appeared to have no immediate impact on turtle body condition, however, the presence of a greater proportion of damaged seagrass leaves in diet in conjunction with decreases in plasma concentrations of sodium and glucose could suggest that the turtles may have been exposed to a substandard diet as a result of the bloom. This is the first confirmed report of L. majuscula blooming in winter in Shoalwater Bay, Queensland, Australia and demonstrates that turtles consume the toxic cyanobacterium in the wild, and that they are potentially exposed to tumour promoting compounds produced by this organism.     

Regulation of blue-green algal buoyancy and bloom formation by light,inorganic nitrogen,C02, and trophic level interactions

In highly eutrophic ponds, buoyancy of the gas-vacuolate blue-green alga Anabaenopsis Elenkinii (Miller) was regulated by complex interactions between chemical and physical parameters, as well as by biological interactions between various trophic levels. Algal buoyancy and surface bloom formation were enhanced markedly by decreased light intensity, and to a lesser extent by decreased CO₂ availability and increased availability of inorganic nitrogen. In the absence of dense populations of large-bodied Cladocera, early season blooms of diatoms and green algae reduced light availability in the ponds thus creating conditions favorable for increased buoyancy and bloom formation by A. Elenkinii. The appearance of blue-green algal blooms could be prevented by a reduced density of planktivorous fish, which allowed development of dense cladoceran populations. The cladocerans limited the growth of precursory blooms of diatoms and green algae, and given the resulting clear-water conditions, buoyancy of A. Elenkinii was reduced, and blue-green algal blooms never appeared.     

Acclimation of bloom‐forming and perennial seaweeds to elevated pCO2 conserved across levels of environmental complexity

Macroalgae contribute approximately 15% of the primary productivity in coastal marine ecosystems, fix up to 27.4 Tg of carbon per year, and provide important structural components for life in coastal waters. Despite this ecological and commercial importance, direct measurements and comparisons of the short‐term responses to elevated pCO₂ in seaweeds with different life‐history strategies are scarce. Here, we cultured several seaweed species (bloom forming/nonbloom forming/perennial/annual) in the laboratory, in tanks in an indoor mesocosm facility, and in coastal mesocosms under pCO₂ levels ranging from 400 to 2,000 μatm. We find that, across all scales of the experimental setup, ephemeral species of the genus Ulva increase their photosynthesis and growth rates in response to elevated pCO₂ the most, whereas longer‐lived perennial species show a smaller increase or a decrease. These differences in short‐term growth and photosynthesis rates are likely to give bloom‐forming green seaweeds a competitive advantage in mixed communities, and our results thus suggest that coastal seaweed assemblages in eutrophic waters may undergo an initial shift toward communities dominated by bloom‐forming, short‐lived seaweeds.     

An association network analysis among microeukaryotes and bacterioplankton reveals algal bloom dynamics

Algal blooms are a worldwide phenomenon and the biological interactions that underlie their regulation are only just beginning to be understood. It is established that algal microorganisms associate with many other ubiquitous, oceanic organisms, but the interactions that lead to the dynamics of bloom formation are currently unknown. To address this gap, we used network approaches to investigate the association patterns among microeukaryotes and bacterioplankton in response to a natural Scrippsiella trochoidea bloom. This is the first study to apply network approaches to bloom dynamics. To this end, terminal restriction fragment (T‐RF) length polymorphism analysis showed dramatic changes in community compositions of microeukaryotes and bacterioplankton over the blooming period. A variance ratio test revealed significant positive overall associations both within and between microeukaryotic and bacterioplankton communities. An association network generated from significant correlations between T‐RFs revealed that S. trochoidea had few connections to other microeukaryotes and bacterioplankton and was placed on the edge. This lack of connectivity allowed for the S. trochoidea sub‐network to break off from the overall network. These results allowed us to propose a conceptual model for explaining how changes in microbial associations regulate the dynamics of an algal bloom. In addition, key T‐RFs were screened by principal components analysis, correlation coefficients, and network analysis. Dominant T‐RFs were then identified through 18S and 16S rRNA gene clone libraries. Results showed that microeukaryotes clustered predominantly with Dinophyceae and Perkinsea while the majority of bacterioplankton identified were Alphaproteobacteria, Gammaproteobacteria, and Bacteroidetes. The ecologi‐cal roles of both were discussed in the context of these findings.     

Long term nutrient loads and chlorophyll dynamics in a large temperate Australian lagoon system affected by recurring blooms of cyanobacteria

While rare globally, blooms of the toxic cyanobacteria Nodularia spumigena are a recurring problem in a few estuaries, such as the Baltic Sea and several southern Australian estuaries. Here, we document recurring Nodularia spumigena Mertens blooms in the Gippsland Lakes, S.E. Australia; a temperate lagoon system with episodic, winter-spring dominated catchment inflows. Physico-chemical conditions exerted a strong influence over bloom development, with blooms consistently occurring at surface water salinities between 9 and 20 (average?=?15), inorganic nitrogen concentrations <0.4?μM, and inorganic nitrogen to reactive phosphorus ratios <5. There was a positive correlation between average annual chlorophyll a and total phosphorus (TP) load in years when there was no Nodularia bloom, but this relationship broke down in Nodularia bloom years, even though there was a strong correlation between in-lake TP and chlorophyll a during these years; this highlights the importance of internal sources of phosphorus to bloom development. Large catchment derived nitrate and nitrite (NO_x) inputs following wildfires and floods in 2007, led to high concentrations of NO_x within the surface waters of the Gippsland Lakes through the second half of 2007 and the start of 2008. We hypothesise that these high NO_x concentrations were a key factor leading to an unprecedented Synechococcus sp. bloom that developed in the austral summer of 2007–2008, despite conditions that would otherwise favour a Nodularia bloom.     

Reproductive success of soybean (Glycine max L. Merril) cultivars and exotic lines under high daytime temperature

The objectives were to (a) quantify the effects of high daytime temperature (HDT) from gametogenesis to full bloom on photosynthesis and pod set in soybean (Glycine max L. Merril) genotypes and (b) assess the relationships among photosynthesis, cardinal temperatures for pollen germination, in vitro pollen germination percentage, canopy reflectance, and pod‐set percentage. Three field experiments were conducted, and Experiment I had HDT between gametogenesis and full bloom (36.5°C to 38.6°C) compared with Experiments II and III (29.5°C to 31.6°C; optimum temperature). HDT decreased photosynthesis (22%) and pod‐set percent (11%) compared with Experiment III. Cultivars had higher photosynthesis and pod‐set percent than plant introduction (PI) lines. The cultivars (i.e., IA3023 and KS4694) and PI lines (i.e., PI393540 and PI588026A) were HDT tolerant and susceptible, respectively. The decreased pod‐set percentage in susceptible genotypes (PI lines) was associated with pollen characteristics. Significant positive (r² ≥ 0.67) association between photosynthesis, cardinal temperatures for pollen germination (T_opt and T_max) with pod‐set percentage was observed. However, a negative (r² ≥ ?0.43) association between photosynthesis and pod set with canopy reflectance at visible spectrum was observed. In vitro pollen germination and canopy reflectance at visible spectrum can be used as a high‐throughput phenotypic tool for breeding HDT‐tolerant genotypes.     

Ecophysiology of the marine cyanobacterium, Lyngbya majuscula (Oscillatoriaceae) in Moreton Bay, Australia

Large blooms of the marine cyanobacterium Lyngbya majuscula in Moreton Bay, Australia (27°05′S, 153°08′E) have been re-occurring for several years. A bloom was studied in Deception Bay (Northern Moreton Bay) in detail over the period January–March 2000. In situ data loggers and field sampling characterised various environmental parameters before and during the L. majuscula bloom. Various ecophysiological experiments were conducted on L. majuscula collected in the field and transported to the laboratory, including short-term (2 h) ¹⁴C incorporation rates and long-term (7 days) pulse amplitude modulated (PAM) fluorometry assessments of photosynthetic capacity. The effects of L. majuscula on various seagrasses in the bloom region were also assessed with repeated biomass sampling. The bloom commenced in January 2000 following usual December rainfall events, water temperatures in excess of 24 °C and high light conditions. This bloom expanded rapidly from 0 to a maximum extent of 8 km² over 55 days with an average biomass of 210 g_dw⁻¹ m⁻² in late February, followed by a rapid decline in early April. Seagrass biomass, especially Syringodium isoetifolium, was found to decline in areas of dense L. majuscula accumulation. Dissolved and total nutrient concentrations did not differ significantly (P > 0.05) preceding or during the bloom. However, water samples from creeks discharging into the study region indicated elevated concentrations of total iron (2.7–80.6 μM) and dissolved organic carbon (2.5–24.7 mg L⁻¹), associated with low pH values (3.8–6.7). ¹⁴C incorporation rates by L. majuscula were significantly (P < 0.05) elevated by additions of iron (5 μM Fe), an organic chelator, ethylenediaminetetra-acetic acid (5 μM EDTA) and phosphorus (5 μM PO₄⁻³). Photosynthetic capacity measured with PAM fluorometry was also stimulated by various nutrient additions, but not significantly (P > 0.05). These results suggest that the L. majuscula bloom may have been stimulated by bioavailable iron, perhaps complexed by dissolved organic carbon. The rapid bloom expansion observed may then have been sustained by additional inputs of nutrients (N and P) and iron through sediment efflux, stimulated by redox changes due to decomposing L. majuscula mats.     

Multi‐wavelength Pulse Amplitude Modulated fluorometry (Phyto‐PAM) reveals differential effects of ultraviolet radiation on the photosynthetic physiology of phytoplankton pigment groups

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Effects of light on nitrogen and carbon uptake during a Prorocentrum minimum bloom

During a 4-week period in late spring 1998 an extensive Prorocentrum minimum (Pavillard) Schiller bloom developed in several tributaries of the Chesapeake Bay. Experiments were carried out in one of these tributaries using ¹³C and ¹⁵N isotopic techniques to characterize C and N uptake as a function of irradiance during the course of this bloom. Uptake rates of N substrates (NO₃⁻, NH₄⁺, urea, and an amino acid mixture) and C substrates (bicarbonate and urea) were measured. For each N substrate, short-term uptake rates (0.5 h) were not substantially different over the irradiance range measured, suggesting that N uptake of this dinoflagellate was not strongly light-dependent over this time scale. Dark uptake rates of all N substrates ranged between 35 and 113% of light uptake rates. Over the duration of the P. minimum bloom, however, total ambient N uptake rates increased with increasing natural irradiance. Uptake of bicarbonate showed typical light-dependent photosynthetic characteristics and the measured photosynthetic parameters suggested that at least on the short time scale (0.5 h), P. minimum cells were adapted to high light. Rates of C uptake from the substrate urea were minimal, <1% of total C uptake from photosynthesis, but doubled over the course of the bloom, and like N uptake, were not strongly light-dependent on the short time scale (0.5 h). Significant N dark uptake by P. minimum was likely to have been important by providing N sources over the daily scale to sustain the bloom.     

Nutrition and growth kinetics in nitrogen- and phosphorus-limited cultures of the novel red tide flagellate Chattonella ovata (Raphidophyceae)

In the summer of 2004, a harmful bloom caused by Chattonella ovata (Raphidophyceae) occurred over almost the entire area of the Seto Inland Sea and caused fishery damages. This incident was the first record of a bloom and damage to the fisheries caused by this species in Japanese waters. In order to elucidate the mechanism of the bloom outbreak, we examined the nutrition and the growth kinetics in nitrogen (N)- and phosphorus (P)-limited semi-continuous cultures of this species. Inorganic N compounds, such as nitrate, nitrite, and ammonium, were found to be good nitrogen sources for the growth of C. ovata, while organic nitrogen (urea and uric acid) was not utilized. This species was capable of using ATP, ADP and inorganic phosphorus compounds, but did not utilize phosphate monoesters as a sole P source. Under both N-limited and P-limited steady state conditions, the growth rate as a function of cell nitrogen and phosphorus quota, respectively, followed the Droop equation. Kinetic parameters μ_m (maximum growth rate) and k_q (minimum cell quota) obtained for N- and P-limited cultures were 0.79 day⁻¹ and 5.5 pmol N cell⁻¹ and 0.86 day⁻¹ and 0.48 pmol P cell⁻¹, respectively. The minimum cell quotas were 23–30% lower than those of C. antiqua. The nutrient availability and kinetic parameters of C. ovata are compared with other harmful algae and the ecological implications of these characteristics discussed.     

Seasonal succession of phytoplankton in a large subarctic river

The factors influencing the abundance of phytoplankton in the Yellowknife River, in the Canadian subarctic, were determined from collections made for 42 consecutive months from June 1975 to November 1978. The spring bloom of plankton occured during April of each year in response to changing light conditions. WhileChlamydomonas lapponica was dominant during this period, it was replaced during the early part of the summer by a rapid succession ofDinobryon species in whichD. cylindricum was followed byD. sociale and in turn byD. bavaricum andD. divergens. Although low nutrient levels permitted the development ofDinobryon during the summer, the abundance of diatoms was greatly limited by the concentrations of SiO₂ (< 0.1 g/m³). Algal densities began to decline in August and reached low overwintering levels by November. The absence of a fall bloom in densities was due to a combination of low temperatures and nutrient levels.P.O. Box 2310, Yellowknife, Northwest Territories, X1A 2P7, Canada