Selective grazing of Temora longicornis in different stages of a Phaeocystis globosa bloom—a mesocosm study

Selective grazing of a calanoid copepod Temora longicornis was measured during different stages of a Phaeocystis globosa bloom, in order to reveal (1) if T. longicornis feeds on single cells and/or colonies of P. globosa in the presence of alternative food sources, (2) if copepod food selection changes during the initiation, maintenance, collapse and decay of a P. globosa bloom and (3) if P. globosa dominated food assemblage provides a good diet for copepod egg production. Our results show low but constant feeding on small colonies of P. globosa, irrespective of the type or concentration of alternative food sources. In contrast, feeding on single cells was never significant, and the total contribution of P. globosa to carbon ingestion of T. longicornis was minor. T. longicornis fed most actively on the decaying colonies, whereas during the peak of the bloom copepods selected against P. globosa. Mostly, T. longicornis fed unselectively on different food particles: before the bloom, the major part of the diet consisted of diatoms, whereas during and after the bloom copepod diet was dominated by dinoflagellates and ciliates. Egg production was highest during the decay of the bloom, coinciding with highest proportional ingestion of heterotrophic organisms, but was not seriously reduced even during the peak of the bloom. We conclude that P. globosa blooms should not threaten survival of copepod populations, but the population recruitment may depend on the type (and concentration) of the dominant heterotrophs present during the blooms. Due to relatively unselective grazing, the impact of T. longicornis to the initiation of a Phaeocystis bloom is considered small, although grazing on decaying colonies may contribute to the faster termination of a bloom.     

A mesocosm study of Phaeocystis globosa (Prymnesiophyceae) population dynamics: II. Significance for the microbial community

The impact of Phaeocystis globosa population decline on the microbial community was studied during a mesocosm experiment, with irradiance regime and inorganic N:P ratios (4, 16, and 44) as controlling factors. Heterotrophic bacterial activity was closely related to enhanced (viral) lysis rates of P. globosa cells and disintegration of the colonies. Up to 85% of the bacterial C demand could be supplied by P. globosa-specific cellular C release. The bacterial populations with high DNA content became dominant (>70% of total). The bacterial community showed a rapid shift in composition to take advantage of the changing conditions during the demise of the P. globosa bloom. Members of the Alphaproteobacteria and the Bacteroidetes group emerged directly upon bloom decay. Multidimensional scaling analysis in conjunction with DGGE fingerprinting implied that clustering was more related to the availability of organic carbon (the collapse of the P. gobosa bloom) than to the nature of the phytoplankton growth-controlling nutrient. Reduced irradiance delayed the development of the P. globosa population and subsequently changes in the bacterial community composition. Disintegration of P. globosa colonies resulted in the formation of transparent exopolymeric particles (TEP) and aggregates, more so under P-depletion than under N-deficient conditions. The colonial matrix transformed into big aggregates under P-depleted conditions but remained largely as ghost colonies under N-depleted conditions. In the mesocosm with initial nitrogen and phosphorus supplied in the Redfield ratio, features intermediate to conditions with either N- or P-depletion were observed. It was hypothesized that TEP affected microbial population dynamics directly through bacterial colonization and indirectly through scavenging of predators and viruses.     

A mesocosm study of Phaeocystis globosa population dynamics: I. Regulatory role of viruses in bloom control

The regulatory role of viruses on population dynamics of the prymnesiophyte Phaeocystis globosa was studied during a mesocosm experiment in relation to growth and loss by microzooplankton grazing and cell lysis. The mesocosms were conducted under varying light conditions (20 and 150 μmol photons m⁻² s⁻¹) and nutrient regime (inorganic nitrogen to phosphorus ratios of 4, 16 and 44). Overall, viruses infecting P. globosa (PgV) were found to be an important cause of cell lysis (30–100% of total lysis) and a significant loss factor (7–67% of total loss). We demonstrate that the morphology of P. globosa cells (solitary versus colonial) differently regulated viral control of P. globosa bloom formation. Reduced irradiance (20 μmol photons m⁻² s⁻¹) was provided for 11 days to select for the solitary cell morphotype. Viruses were able to restrict P. globosa bloom formation even after irradiance became saturating again (150 μmol photons m⁻² s⁻¹). Saturating light conditions from the start of the experiment allowed colony formation and because the colony-morphotype acted as a mechanism reducing viral infection bloom formation succeeded. Nutrient depletion, however, affected specifically the colonies that disintegrated while releasing single cells. Virus infection of these solitary cells resulted in the termination of the bloom. The nature of phytoplankton growth-limiting nutrient (nitrate and/or orthophosphate) did not seem to noticeably affect the level of viral control.     

Inhibition of copepod feeding by exudates and transparent exopolymer particles (TEP) derived from a Phaeocystis globosa dominated phytoplankton community

We investigated if (1) dissolved compounds excreted by Phaeocystis globosa and (2) transparent exopolymer particles (TEP) formed from carbohydrates excreted into the water affect the feeding of nauplii and females of the calanoid copepod Temora longicornis during a P. globosa bloom. Copepod grazing on the diatom Thalassiosira weissflogii in the presence of these possible grazing deterrents was measured during three successive weeks of a mesocosm study, simulating the development of a P. globosa bloom. Our results demonstrate no indication for the presence of feeding deterrents in the dissolved phase, but a strong inhibitory effect of transparent exopolymer particles (TEP) on the consumption of algae by both nauplii and adult copepods. The inhibitory effect of TEP was connected to the accumulation of DOM during the progress of the bloom. We suggest that a reduction in the grazing pressure of zooplankton may increase the survival of the liberated single cells during disruption of colonies and allow seeding populations to persist. Furthermore, P. globosa reduces the trophic efficiency of the food web not only by withdrawal of its colonies from grazing but also by a relaxation of the grazing pressure on co-occurring phytoplankton and by alteration of the food web structure via TEP production.     

Temporal Coherence of Chlorophyll a during a Spring Phytoplankton Bloom in Xiangxi Bay of Three‐Gorges Reservoir,China

Algal bloom phenomenon was defined as “the rapid growth of one or more phytoplankton species which leads to a rapid increase in the biomass of phytoplankton”, yet most estimates of temporal coherence are based on yearly or monthly sampling frequencies and little is known of how synchrony varies among phytoplankton or of the causes of temporal coherence during spring algal bloom. In this study, data of chlorophyll a and related environmental parameters were weekly gathered at 15 sampling sites in Xiangxi Bay of Three‐Gorges Reservoir (TGR, China) to evaluate patterns of temporal coherence for phytoplankton during spring bloom and test if spatial heterogeneity of nutrient and inorganic suspended particles within a single ecosystem influences synchrony of spring phytoplankton dynamics. There is a clear spatial and temporal variation in chlorophyll a across Xiangxi Bay. The degree of temporal coherence for chlorophyll a between pairs of sites located in Xiangxi Bay ranged from –0.367 to 0.952 with mean and median values of 0.349 and 0.321, respectively. Low levels of temporal coherence were often detected among the three stretches of the bay (Down reach, middle reach and upper reach), while high levels of temporal coherence were often found within the same reach of the bay. The relative difference of DIN between pair sites was the strong predictor of temporal coherence for chlorophyll a in down and middle reach of the bay, while the relative difference in Anorganic Suspended Solids was the important factor regulating temporal coherence in middle and upper reach. Contrary to many studies, these results illustrate that, in a small geographic area (a single reservoir bay of approximately 25 km), spatial heterogeneity influence synchrony of phytoplankton dynamics during spring bloom and local processes may override the effects of regional processes or dispersal. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Living in a Phaeocystis colony: a way to be a successful algal species

Evidence is provided showing that in two species of Phaeocystis (P. globosa and P. pouchetii) the colonial cells possess a much higher growth rate than the single cells when grown under identical conditions. Based on the DNA-cell-cycle method gross growth rate of colony cells exceeded those of co-occurring single cells by a factor 1.5 up to 3.8. The dominance of colonies in blooms of Phaeocystis can therefore be primarily due to their significantly high growth rate allowing a rapid bloom formation.Both Phaeocystis species showed ultradian growth but differed in timing of the initiation of the second DNA replication phase. In both species the first DNA-replication period started at the end of the (local) light period and was completed in the early dark period. In P. globosa this was immediately followed by the second DNA-replication period (first half of the dark period). In P. pouchetii this process was delayed by ca. 12 h until the middle of the light period (local noon).Flow cytometric analysis of the cell size and chlorophyll fluorescence showed little variation in colony and single cells of P. pouchetii. In contrast, colonies of P. globosa showed often the presence of two cell morphs, co-occurring in the same colony. The size of both morphs was identical but they differed in chlorophyll fluorescence up to a factor 4. In general the high chlorophyll cell morph dominated (>70% of the total colony cells). Both colony cell morphs were observed in cultures, mesocosms differing in N/P ratio but also in the field.     

Long-term development of the crustacean plankton in the Saidenbach Reservoir (Germany) – changes,causes, consequences

The rates of development and food intake of the copepod Temora longicornis (Müller) were studied using artificial blooms of Phaeocystis globosa Scherffel under different conditions of nutrient limitation. Mesocosms with 800 l of natural seawater were manipulated by inoculation with cultured P. globosa and by addition of nitrogen and/or phosphorus, to obtain N- or P-limited blooms of P. globosa. During development and ageing of these blooms, water from the mesocosms was used as medium for incubation of nauplii of T. longicornis. Only moderate rates of naupliar development as well as high rates of mortality were observed, irrespective of major differences of nutrient conditions and density of P. globosa. Grazing by the nauplii on P. globosa seemed to be low, suggesting a low food quality of this alga at all physiological conditions studied. The results of this study indicate a low capability of T. longicornis nauplii for control of nuisance algal blooms caused by P. globosa.     

Dynamics of transparent exopolymeric particles (TEP) production by Phaeocystis globosa under N- or P-limitation: a controlling factor of the retention/export balance

The concentration of transparent exopolymeric particles (TEP) was monitored during Phaeocystis globosa blooms that developed in mesocosms under different initial N:P ratios (from N- to P-limited conditions). TEP concentration was measured using the microscopic (TEP_micro, ppm) and the colorimetric (TEP_color, Xanthan equiv. L⁻¹) methods. TEP concentrations varied from 5 to >75 ppm and from 60 to >1500 μg Xanthan equiv. L⁻¹, and were relatively low until the mesocosms reached nutrient (either N or P) depletion and then increased abruptly. From the TEP_micro versus TEP_color concentrations comparison and from their relation to chlorophyll a concentrations, two phases for the dynamics of TEP production were identified: (1) production through active release of precursors during the growth phase of P. globosa — defined as TEP₁ — and their integration into the TEP pool through coagulation processes; (2) release of large TEP from the mucilaginous matrix of P. globosa colonies subsequent to disruption caused by nutrient depletion — defined as TEP₂ — and their direct integration into the TEP pool outside the constraint of coagulation. The formation of a multiorigin TEP pool during P. globosa blooms may have implications for the fate of the blooms, due to difference in TEP bioreactivity according to their source and to difference in timing and intensity of TEP₁ versus TEP₂ production according to N- or P-depletion. For P. globosa blooms developing under N-limiting conditions, the transition from the first source (i.e. TEP₁) to the second one (i.e. TEP₂) was a slow and continuous process. In contrast, the P. globosa bloom developing under P-limiting conditions showed the sudden formation of heavy mucous aggregates when P became depleted, that may have been caused by a massive release of TEP₂. Our study suggests that the nutrient regime may control the export vs. retention balance during P. globosa blooms, via production of a multiorigin TEP pool.     

Phytoplankton Spring Bloom Intensity Index for the Baltic Sea Estimated for the years 1992 to 2004

We introduce an index for estimating the annual phytoplankton spring bloom intensity in the Baltic Sea. It is based on chlorophyll a estimates calculated from automatically sampled fluorescence and chlorophyll a measurements on board cargo ships from 1992 to 2004. The intensity is described by an index including information on the chlorophyll a concentration and duration of the spring bloom period. In all of the years studied, the spring bloom was most intense in the Gulf of Finland. In the Gulf of Finland and the Northern Baltic Proper there was a slight tendency for the bloom to start earlier in the spring.     

A Fuzzy Logic Model to Describe the Cyanobacteria Nodularia spumigena Blooms in the Gulf of Finland, Baltic Sea

A fuzzy logic model to describe the seasonal evolution of Nodularia spumigena blooms in the Gulf of Finland was built and calibrated on the basis of monitoring data. The model includes three phosphate sources: excess phosphate after the annual spring bloom and parameterised phosphate transport to the upper mixed layer by turbulent mixing and upwelling events. Surface layer temperature and wind mixing form the physical conditions controlling the growth of N. spumigena. Model simulations revealed that phosphate input caused by turbulent mixing and upwelling have to be taken into account to achieve the best fit with observed data. Testing the fuzzy model for early prediction of maximum N. spumigena biomass about a month before the usual occurrence of blooms, gave good results. The potential use of the model for prediction of bloom risk at a certain location along the Estonian or Finnish coast was tested. The bloom transport velocities used in the fuzzy model were pre-calculated by a 3D numerical circulation model for different wind regimes.     

Increased sea ice melt as a driver of enhanced Arctic phytoplankton blooming

Phytoplankton primary production in the Arctic Ocean has been increasing over the last two decades. In 2019, a record spring bloom occurred in Fram Strait, characterized by a peak in chlorophyll that was reached weeks earlier than in other years and was larger than any previously recorded May bloom. Here, we consider the conditions that led to this event and examine drivers of spring phytoplankton blooms in Fram Strait using in situ, remote sensing, and data assimilation methods. From samples collected during the May 2019 bloom, we observe a direct relationship between sea ice meltwater in the upper water column and chlorophyll a pigment concentrations. We place the 2019 spring dynamics in context of the past 20 years, a period marked by rapid change in climatic conditions. Our findings suggest that increased advection of sea ice into the region and warmer surface temperatures led to a rise in meltwater input and stronger near-surface stratification. Over this time period, we identify large-scale spatial correlations in Fram Strait between increased chlorophyll a concentrations and increased freshwater flux from sea ice melt.     

The influence of environmental conditions on the seasonal variation of <Emphasis Type="Italic">Microcystis</Emphasis> cell density and microcystins concentration in San Francisco Estuary

A bloom of the cyanobacteria Microcystis aeruginosa was sampled over the summer and fall in order to determine if the spatial and temporal patterns in cell density, chlorophyll a (chl a) concentration, total microcystins concentration, and percent microcystins composition varied with environmental conditions in San Francisco Estuary. It was hypothesized that the seasonal variation in Microcystis cell density and microcystin concentration was ecologically important because it could influence the transfer of toxic microcystins into the aquatic food web. Sampling for Microcystis cell density, chl a concentration, total microcystins concentration and a suite of environmental conditions was conducted biweekly at nine stations throughout the freshwater tidal and brackish water regions of the estuary between July and November 2004. Total microcystins in zooplankton and clam tissue was also sampled in August and October. Microcystis cell density, chl a concentration and total microcystins concentration varied by an order of magnitude and peaked during August and September when and α^B were high. Low streamflow and high water temperature were strongly correlated with the seasonal variation of Microcystis cell density, total microcystins concentration (cell)⁻¹ and total microcystins concentration (chl a)⁻¹ in canonical correlation analyses. Nutrient concentrations and ratios were of secondary importance in the analysis and may be of lesser importance to seasonal variation of the bloom in this nutrient rich estuary. The seasonal variation of Microcystis density and biomass was potentially important for the structure and function of the estuarine aquatic food web, because total microcystins concentration was high at the base of the food web in mesozooplankton, amphipod, clam, and worm tissue during the peak of the bloom. Handling editor: D. Hamilton     

Methods used to reveal genetic diversity in the colony-forming prymnesiophytes Phaeocystis antarctica, P. globosa and P. pouchetii—preliminary results

Previous work on the genetic diversity of Phaeocystis used ribosomal DNA and internal transcribed spacer (ITS) sequence analyses to show that there is substantial inter- and intraspecific variation within the genus. First attempts to trace the biogeographical history of strains in Antarctic coastal waters were based on a comparison of ITS sequences. To gain deeper insights into the population structure and bloom dynamics of this microalga it is necessary to quantify the genetic diversity within populations of P. antarctica from different locations (i.e., each of the three major gyres in the Antarctic continental waters) and to calculate the gene flow between them. Here we describe methods to quantify genetic diversity and our preliminary results for P. antarctica in comparison to two other colonial species: P. globosa and P. pouchetii. For this study of genetic diversity, two fingerprinting techniques were used. First, amplified fragment-length polymorphisms (AFLPs) were established as a pre-screening tool to assess clone diversity and to select divergent clones prior to physiological investigations. Second, the more-powerful microsatellite markers were established to assess population structure and biogeography more accurately. Results show differences in the AFLP patterns between isolates of P. antarctica from different regions, and that a wide variety of microsatellite motifs could be obtained from the three Phaeocystis species.     

Different tolerances and responses to low temperature and darkness between waterbloom forming cyanobacterium <Emphasis Type="Italic">Microcystis</Emphasis> and a green alga <Emphasis Type="Italic">Scenedesmus</Emphasis>

The dynamics of planktonic cyanobacteria in eutrophicated freshwaters play an important role in formation of annual summer blooms, yet overwintering mechanisms of these water bloom forming cyanobacteria remain unknown. The responses to darkness and low temperature of three strains (unicellular Microcystis aeruginosa FACHB-905, colonial M. aeruginosa FACHB-938, and a green alga Scenedesmus quadricauda FACHB-45) were investigated in the present study. After a 30-day incubation under darkness and low temperature, cell morphology, cell numbers, chlorophyll a, photosynthetic activity (ETR_max and I _k), and malodialdehyde (MDA) content exhibited significant changes in Scenedesmus. In contrast, Microcystis aeruginosa cells did not change markedly in morphology, chlorophyll a, photosynthetic activity, and MDA content. The stress caused by low temperature and darkness resulted in an increase of the antioxidative enzyme-catalase (CAT) in all three strains. When the three strains re-grew under routine cultivated condition subjected to darkness and low temperature, specific growth rate of Scenedesmus was lower than that of Microcystis. Flow cytometry (FCM) examination indicated that two distinct types of metabolic response to darkness and low temperature existed in the three strains. The results from the present study reveal that the cyanobacterium Microcystis, especially colonial Microcystis, has greater endurance and adaptation ability to the stress of darkness and low temperature than the green alga Scenedesmus. Handling editor: D. Hamilton     

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.     

An extensive Cochlodinium bloom along the western coast of Palawan, Philippines

A massive fish kill and water discoloration were reported off the western coast of Puerto Princesa, Palawan, Philippines in March 2005. Phytoplankton analysis revealed a near monospecific bloom of the dinoflagellate, Cochlodinium polykrikoides, with cell concentrations ranging from 2.5 × 10⁵ to 3.2 × 10⁶ cells per liter. Ground truth data were supplemented by processed satellite images from MODIS Aqua Level 2 data (1 km resolution) from January to April 2005, which revealed high surface chlorophyll-a levels (up to 50 mg/m³) offshore of west and southwest Palawan as early as February 2005. The bloom extended 310 km in length and 80 km in width at its peak in March off the central coast (Puerto Princesa). By April, the bloom declined in intensity, but was still apparent along the northern coast (El Nido). Fluctuations in chlorophyll levels off the western coast of Sabah, Malaysia and Brunei during this time period suggested that the bloom was not limited to the coast of Palawan. Satellite imagery from Sabah in late January revealed a plume of chl-a that is believed to be the source of the C. polykrikoides bloom in Palawan. This plume drifted offshore, advected northward via the basin-wide counterclockwise gyre, and reached nutrient-rich, upwelled waters near Palawan (due to a positive wind stress curl) where the dinoflagellate bloomed and persisted for 2 months from March to April 2005.     

Optical spectroscopic studies of light-harvesting by pigment-reconstituted peridinin-chlorophyll-proteins at cryogenic temperatures

Low temperature, steady-state, optical spectroscopic methods were used to study the spectral features of peridinin-chlorophyll-protein (PCP) complexes in which recombinant apoprotein has been refolded in the presence of peridinin and either chlorophyll a (Chl a), chlorophyll b (Chl b), chlorophyll d (Chl d), 3-acetyl-chlorophyll a (3-acetyl-Chl a) or bacteriochlorophyll a (BChl a). Absorption spectra taken at 10 K provide better resolution of the spectroscopic bands than seen at room temperature and reveal specific pigment–protein interactions responsible for the positions of the Q_y bands of the chlorophylls. The study reveals that the functional groups attached to Ring I of the two protein-bound chlorophylls modulate the Q_y and Soret transition energies. Fluorescence excitation spectra were used to compute energy transfer efficiencies of the various complexes at room temperature and these were correlated with previously reported ultrafast, time-resolved optical spectroscopic dynamics data. The results illustrate the robust nature and value of the PCP complex, which maintains a high efficiency of antenna function even in the presence of non-native chlorophyll species, as an effective tool for elucidating the molecular details of photosynthetic light-harvesting.     

Seasonality of North Atlantic phytoplankton from space: impact of environmental forcing on a changing phenology (1998–2012)

Seasonal pulses of phytoplankton drive seasonal cycles of carbon fixation and particle sedimentation, and might condition recruitment success in many exploited species. Taking advantage of long‐term series of remotely sensed chlorophyll a (1998–2012), we analyzed changes in phytoplankton seasonality in the North Atlantic Ocean. Phytoplankton phenology was analyzed based on a probabilistic characterization of bloom incidence. This approach allowed us to detect changes in the prevalence of different seasonal cycles and, at the same time, to estimate bloom timing and magnitude taking into account uncertainty in bloom detection. Deviations between different sensors stressed the importance of a prolonged overlap between successive missions to ensure a correct assessment of phenological changes, as well as the advantage of semi‐analytical chlorophyll algorithms over empirical ones to reduce biases. Earlier and more intense blooms were detected in the subpolar Atlantic, while advanced blooms of less magnitude were common in the Subtropical gyre. In the temperate North Atlantic, spring blooms advanced their timing and decreased in magnitude, whereas fall blooms delayed and increased their intensity. At the same time, the prevalence of locations with a single autumn/winter bloom or with a bimodal seasonal cycle increased, in consonance with a poleward expansion of subtropical conditions. Changes in bloom timing and magnitude presented a clear signature of environmental factors, especially wind forcing, although changes on incident photosynthetically active radiation and sea surface temperature were also important depending on latitude. Trends in bloom magnitude matched changes in mean chlorophyll a during the study period, suggesting that seasonal peaks drive long‐term trends in chlorophyll a concentration. Our results link changes in North Atlantic climate with recent trends in the phenology of phytoplankton, suggesting an intensification of these impacts in the near future.     

棕囊藻北部湾株的18S rDNA分子鉴定

为研究北部湾棕囊藻(Phaeocystis)藻华的成因,采用PCR克隆了棕囊藻北部湾株核糖体18S r DNA序列。结果表明,棕囊藻北部湾株具有游动单细胞与群体结构两种形态;其18S r DNA序列和NCBI基因库中球形棕囊藻(Phaeocystis globosa)的同源性为99%~100%,在系统进化树上与不同海域来源的球形棕囊藻聚在一大分支上,且与球形棕囊藻间的遗传距离均小于其他种。首次从分子生物学上确定棕囊藻北部湾株为球形棕囊藻。