The effect of environmental parameters and cyanobacterial blooms on phytoplankton dynamics of a Portuguese temperate Lake

The increasing occurrence of cyanobacterial blooms in freshwaters is of great concern due to the ability of many cyanobacteria to produce cyanotoxins. In the present work, the eutrophied Vela Lake (Central Portugal), used for recreational purposes and as a water source for agriculture, was monitored every fortnight between 2000 and 2001. Phytoplankton diversity and densities were measured and correlated to environmental parameters. A seasonal phytoplanktonic succession was observed and it was mainly correlated with conductivity, temperature, total suspended solids and nutrients availability (particularly phosphorus). Diatoms were dominant during winter months (inferior temperatures and higher nutrients availability) followed by green algae in early spring and then cyanobacteria from late spring until early autumn (less nutrient availability and higher temperatures). A massive cyanobacterial bloom of Aphanizomenon flos-aquae occurred early in May 2001 and was preceded by the lowest nitrogen levels measured in the water during all the study period. At the time of this bloom senescence, dissolved oxygen was severely depleted and a massive death of ichthyofauna was recorded. A Microcystis aeruginosa bloom was also detected in July 2001 and it occurred following a rapid decrease in abundance of green algae and diatoms. By considering not only the environmental parameters but also the occurrence of cyanobacterial blooms as explanatory variables in a canonical correspondence analysis, the variance explained for the phytoplanktonic assemblage during the study period was increased in about 7% achieving a total of 61.0%, indicating a correlation that may be due to the known competitive advantage and/or allelopathy of the bloom-forming cyanobacteria towards microalgae.     

Seasonal and annual variability in the phytoplankton community of the Raunefjord,west coast of Norway from 2001–2006

Changes in phytoplankton community composition potentially affect the entire marine food web. Because of seasonal cycles and inter-annual variations in species composition, long-term monitoring, covering many sequential years, is required to establish a baseline study and to reveal long-term trends. The current study describes the phytoplankton biomass variations and species composition in relation to hydrographic and meteorological conditions in the Raunefjord, western Norway, over a 6-year period from 2001 to 2006. The extent of inflow or upwelling in the fjord varied from year to year and resulted in pronounced differences in water column stability. The annual phytoplankton community succession showed some repeated seasonal patterns, but also high variability between years. Two to four diatom blooms were observed per year, and the spring blooms occurring before water column stratification in March were dominated by Skeletonema marinoi and Chaetoceros socialis, and other Chaetoceros and Thalassiosira spp. Blooms of the haptophytes Phaeocystis pouchetii and Emiliania huxleyi were irregular and in some years totally absent. Although E. huxleyi was present all year round it appeared in bloom concentrations only in 2003, when the summer was warm and the water column characterized by high surface temperatures and pronounced stratification. The annual average abundance of both diatoms and flagellates increased during the six years. Despite the high variation from year to year, our investigation provides valuable knowledge about annual phytoplankton community patterns in the region, and can be used as a reference to detect possible future changes.     

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.     

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     

Phaeocystis globosa and the phytoplankton succession in the East Frisian coastal waters

The phytoplankton succession and related abiotic variables were investigated within the frame of a monitoring programme. Results from 1985 to 1991 are presented. For the prymnesiophytePhaeocystis globosa, an increase in the maximum annual abundance was observed. The appearance of this species in the phytoplankton succession followed an annually recurrent pattern. Among the starting conditions for the bloom, a coincidence with the annual DIN/P maximum was most obvious. Quantitatively, temperature and salinity showed the lowest variability at the onset of the blooms. Nutrient uptake during the increasing phase of the bloom appeared to affect nitrate concentrations more significantly than those of ammonia and phosphate.     

Phytoplankton growth rates in the freshwater tidal reaches of the Schelde estuary (Belgium) estimated using a simple light-limited primary production model

During the course of 1996, phytoplankton was monitored in the turbid, freshwater tidal reaches of the Schelde estuary. Using a simple light-limited primary production model, phytoplankton growth rates were estimated to evaluate whether phytoplankton could attain net positive growth rates and whether growth rates were high enough for a bloom to develop. Two phytoplankton blooms were observed in the freshwater tidal reaches. The first bloom occurred in March and was mainly situated in the most upstream reaches of the freshwater tidal zone, suggesting that it was imported from the tributary river Schelde. The second bloom occurred in July and August. This summer bloom was situated more downstream in the freshwater tidal reaches and appeared to have developed within the estuary. A comparison between phytoplankton growth rates estimated using a simple primary production model and flushing rate of the water indicated that no net increase in phytoplankton biomass was possible in March while phytoplankton could theoretically increase its biomass by 20% per day during summer. Chlorophyllaconcentrations at all times decreased strongly at salinities between 5–10 psu. This decline was ascribed to a combination of salinity stress and light limitation. Phytoplankton biomass and estimated annual net production were much higher in the freshwater tidal zone compared to the brackish reaches of the estuary (salinity > 10 psu) despite mixing depth to euphotic depth ratios being similar. Possible reasons for this high production include high nutrient concentrations, low zooplankton grazing pressure and import of phytoplankton blooms from the tributary rivers.     

Phaeocystis colony distribution in the North Atlantic Ocean since 1948, and interpretation of long-term changes in the Phaeocystis hotspot in the North Sea

Monitoring of Phaeocystis since 1948 during the Continuous Plankton Recorder survey indicates that over the last 5.5 decades the distribution of its colonies in the North Atlantic Ocean was not restricted to neritic waters: occurrence was also recorded in the open Atlantic regions sampled, most frequently in the spring. Apparently, environmental conditions in open ocean waters, also those far offshore, are suitable for complete lifecycle development of colonies (the only stage recorded in the survey). In the North Sea the frequency of occurrence was also highest in spring. Its southeastern part was the Phaeocystis abundance hotspot of the whole area covered by the survey. Frequency was especially high before the 1960s and after the 1980s, i.e., in the periods when anthropogenic nutrient enrichment was relatively low. Changes in eutrophication have obviously not been a major cause of long-term Phaeocystis variation in the southeastern North Sea, where total phytoplankton biomass was related significantly to river discharge. Evidence is presented for the suggestion that Phaeocystis abundance in the southern North Sea is to a large extent determined by the amount of Atlantic Ocean water flushed in through the Dover Strait. Since Phaeocystis plays a key role in element fluxes relevant to climate the results presented here have implications for biogeochemical models of cycling of carbon and sulphur. Sea-to-air exchange of CO₂ and dimethyl sulphide (DMS) has been calculated on the basis of measurements during single-year cruises. The considerable annual variation in phytoplankton and in its Phaeocystis component reported here does not warrant extrapolation of such figures.     

The colonization of two Phaeocystis species (Prymnesiophyceae) by pennate diatoms and other protists: a significant contribution to colony biomass

The association of Phaeocystis spp. with small pennate diatoms during three Phaeocystis-dominated spring blooms were investigated in the Eastern English Channel (2003 and 2004) and in coastal waters of Western Norway during a mesocosm experiment (2005). In each of these studies, colonization of the surface of large Phaeocystis spp. colonies by small needle-shaped diatoms (Pseudo-nitzschia spp.) were observed. In the English Channel the diatom Pseudo-nitzschia delicatissima colonized the surface of large (>100 μm) Phaeocystis globosa colonies. The abundance of Pseudo-nitzschia delicatissima reached 130 cells per colony and formed up to 70% of the total carbon associated with Phaeocystis cells during late bloom stages. In Norwegian waters, the surface of large (>250 μm) Phaeocystis pouchetii colonies were colonized by Pseudo-nitzschia cf. granii var. curvata and to a lesser degree by other phytoplankton and protist species, although the abundance of these diatoms was never greater than 40 cells per colony. Based on these observations we suggest that diatoms utilize Phaeocystis colonies not only as habitat, but that they are able to utilize the colonial matrix as a growth substrate. Furthermore, these observations indicate that a considerable fraction of biomass (chlorophyll) associated with Phaeocystis colonies, especially large colonies concerned with intense and prolonged blooms, are due to co-occurring plankton species and not exclusively Phaeocystis cells.     

Effects of different N- and P-loading on primary and secondary production in an experimental marine ecosystem

The effects of nutrient loading on phytoplankton, zooplankton and macrozoobenthos in experimental ecosystems was studied in a 7-month experiment. The mesocosms were designed to mimic the major physical characteristics (irradiance, temperature, mixing) of the Dutch coastal zone in the river Rhine plume. Three different nutrient loading scenarios were used, representing present and future conditions. The level of the spring phytoplankton bloom was determined by phosphorus loading, whereas during summer the nitrogen loading determined phytoplankton biomass. The differences in nutrient loading did not result in shifts in phytoplankton species composition. With exception of the early phase of the spring bloom, diatoms dominated phytoplankton biomass in all nutrient treatments. This was ascribed to microzooplankton grazing on smaller algal species. Microzooplankton biomass showed a positive correlation with primary production, and also significant differences between nutrient treatments. Copepod development was limited, probably due to competition with microzooplankton and predation by benthic fauna. Macrobenthos biomass correlated with primary production, and was lower in the lowest nutrient treatment.     

Responses of Phyto- and Zooplankton Communities to Prymnesium polylepis (Prymnesiales) Bloom in the Baltic Sea

A large bloom of Prymnesium polylepis occurred in the Baltic Sea during the winter 2007 – spring 2008. Based on numerous reports of strong allelopathic effects on phytoplankton exerted by P. polylepis and its toxicity to grazers, we hypothesized that during this period negative correlations will be observed between P. polylepis and (1) main phytoplankton groups contributing to the spring bloom (i.e., diatoms and dinoflagellates), and (2) zooplankton growth and abundance. To test these hypotheses, we analyzed inter-annual variability in phytoplankton and zooplankton dynamics as well as growth indices (RNA∶DNA ratio) in dominant zooplankton in relation to the Prymnesium abundance and biomass. Contrary to the hypothesized relationships, no measurable negative responses to P. polylepis were observed for either the total phytoplankton stocks or the zooplankton community. The only negative response, possibly associated with P. polylepis occurrence, was significantly lower abundance of dinoflagellates both during and after the bloom in 2008. Moreover, contrary to the expected negative effects, there were significantly higher total phytoplankton abundance as well as significantly higher winter abundance and winter-spring RNA∶DNA ratio in dominant zooplankton species in 2008, indicating that P. polylepis bloom coincided with favourable feeding conditions for zooplankton. Thus, primary consumers, and consequently also zooplanktivores (e.g., larval fish and mysids), may benefit from haptophyte blooms, particularly in winter, when phytoplankton is scarce.     

Climate change and the timing, magnitude, and composition of the phytoplankton spring bloom

In this article, we show by mesocosm experiments that winter and spring warming will lead to substantial changes in the spring bloom of phytoplankton. The timing of the spring bloom shows only little response to warming as such, while light appears to play a more important role in its initiation. The daily light dose needed for the start of the phytoplankton spring bloom in our experiments agrees well with a recently published critical light intensity found in a field survey of the North Atlantic (around 1.3 mol photons m^?2 day^?1). Experimental temperature elevation had a strong effect on phytoplankton peak biomass (decreasing with temperature), mean cell size (decreasing with temperature) and on the share of microplankton diatoms (decreasing with temperature). All these changes will lead to poorer feeding conditions for copepod zooplankton and, thus, to a less efficient energy transfer from primary to fish production under a warmer climate.     

The effects of temperature increases on a temperate phytoplankton community — A mesocosm climate change scenario

Prior to the spring bloom in 2003 and 2004, batch temperature experiments of approximately 3 weeks' duration were carried out in land-based mesocosms in at the Espeland field station (Norway), with temperatures on average increased ~ 2.7-3 °C (T1) and ~ 5.2-5.6 °C (T2) above in situ fjord temperature (RM). The development in the chlorophyll concentrations showed an earlier bloom as a response to increased temperatures but the carbon biomass showed that the warmest treatment yielded the lowest biomass. This study indicates that a part of the relationship between temperature and spring bloom timing stems from a temperature-induced change in phytoplankton algal physiology (the efficiency of photosystem II, F_v/F_m, and growth rates, µ_max), i.e. a direct temperature effect. Data analysis performed on microscope identified and quantified species did not show a significant temperature influence on phytoplankton community composition. However, the HPLC data indicated that temperature changes of as little as 3 °C influence the community composition. In particular, these data showed that peridinin-containing dinoflagellates only increased in abundance in the heated mesocosms and that a prasinophycean bloom, which was undetected in the microscope analyses, occurred prior to the blooms of all other phytoplankton classes in all treatments. The microscope analyses did reveal a temperature effect on individual species distribution patterns. Thalassionema nitzschioides was more abundant in the warm treatments and, in the warmest treatment, the spring bloom forming Skeletonema marinoi comprised a smaller proportion of the diatom community than in the other treatments.     

Nutrients and phytoplankton primary production in the marine tidal Oosterschelde estuary (The Netherlands)

In a shallow marine tidal area, the eastern part of Oosterschelde estuary in the S.W. Netherlands, phytoplankton primary production amounted to 176–338 g C.m^?2.y^?1 during the period 1981–1985. The influence of nutrient concentrations on the phytoplankton primary production is discussed. Phosphate and inorganic nitrogen generally were amply available. Import of inorganic nitrogen into the basin was shown and an intense delivery of ammonia by zoobenthos was suggested. Nitrate was considered to be slightly influenced by phytoplankton consumption and mainly by nitrate reduction at the bottom. Silicate may have played a limiting role in phytoplankton primary production. The first phytoplankton bloom in spring (diatom bloom) always terminated when silicate concentration decreased below K_s values. Further on in 1983 and 1984 both primary production and chlorophyll curves showed a dip when silicate was not available. The influence of available light on the primary production was demonstrated during situations with a low extinction coefficient when primary production reached maximum values. Further on during 1985 the spring bloom occurred already in March when winter extinction coefficients were lower than during preceding winters. Long term production studies are necessary to understand the extreme fluctuations of annual production patterns in relation to the prevailing environmental conditions.     

Parasitism as a biological control agent of dinoflagellate blooms in the California Current System

Amoebophrya is a marine parasite recently found to infect and kill bloom-forming dinoflagellates in the California Current System (CCS). However, it is unknown whether parasitism by Amoebophrya can control dinoflagellate blooms in major eastern boundary upwelling systems, such as the CCS. We quantified the abundance of a common bloom-forming species Akashiwo sanguinea and prevalence of its parasite (i.e., % infected cells) in surface water samples collected weekly from August 2005 to December 2008 at the Santa Cruz Wharf (SCW), Monterey Bay, CA. Additionally, we measured physical and chemical properties at the SCW and examined regional patterns of wind forcing and sea surface temperature. Relative abundance of the net phytoplankton species was also analyzed to discern whether or not parasitism influences net phytoplankton community composition. Epidemic infection outbreaks (>20% parasite prevalence in the host species) may have contributed to the end or prevented the occurrence of A. sanguinea blooms, whereas low parasite prevalence was associated with short-term (≤2 weeks) A. sanguinea blooms. The complete absence of parasitism in 2007 was associated with an extreme A. sanguinea bloom. Anomalously strong upwelling conditions were detected in 2007, suggesting that A. sanguinea was able to outgrow Amoebophrya and ‘escape’ parasitism. We conclude that parasitism can strongly influence dinoflagellate bloom dynamics in upwelling systems. Moreover, Amoebophrya may indirectly influence net phytoplankton species composition, as species that dominated the net phytoplankton and developed algal blooms never appeared to be infected.     

大亚湾澳头水域浮游植物群落结构及周年数量动态

对1997年至1998年广东省大亚湾澳头水域的浮游植物群落进行调查和分析。结果发现浮游植物65属198种;硅藻在种类组成和数量上都比甲藻占有优势,存在春季和秋季高峰,主要优势类群依次是角毛藻、骨条藻、拟菱形藻等;甲藻只存在春季高峰,代表种类有裸甲藻、原甲藻等。主要优势种类的生长与调查水域的盐度没有明显关系,但全年水温的季节性变化对优势种类的消长影响显著。Simpson多样性指数、Shannon-Weaver多样性指数、均匀度的年平均值分别是0.611、2.107、0.557,多样性指数没有明显的季节变化规律和水平分布规律。       

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.     

The influence of integral solar radiation on the spring bloom of phytoplankton in the Ucha Reservoir

The results of the study of the quantitative relationships between solar radiation (integral radiation and PAR), the content of nutrients, and the spring bloom parameters in the Ucha Reservoir are presented. Positive significant correlations between the date of peak bloom and the sum of light intensity over the period from the 35the to the 40th days (the upper reaches of the reservoir, station Pestovo) and the period from the 44th to the 49th days (the lower reaches of the reservoir, station Listvyanka) were determined on the basis of a retrospective analysis of the data from the period of 1993–2003. Regression equations were derived, which permit forecasting the start of phytoplankton growth in spring according to the results of solar radiation measurements. The sum of light intensity over the course of 50 calendar days in each years correlate positively with the phytoplankton abundance in spring (the highest daily number of algae and integral estimation of algae number in spring).     

Annual microplankton cycles in Villefranche Bay, Ligurian Sea, NW Mediterranean

Abundance and composition of microplankton were studied overa period of 2 years at two depths in Villefranche Bay (LigurianSea, NW Mediterranean Sea). Diatoms dominated the microplanktonin late spring and autumn, whereas dinoflagellates composedthe major part of the microplankton in summer. The silicoflagellateDictyocha fibula and the diatom Thalassionema frauenfeldii dominatedin winter. Ciliates showed low variability throughout the yearwith the lowest abundance in February and an increase whichcoincided with the diatom maxima during autumn in both years.In 1998, the spring bloom (in May) was mainly composed of dinoflagellatesnear the surface and of diatoms in deeper layers. Subsurfacediatom maxima were observed in August–September and November.In 1999, diatoms peaked in May both at the surface and at thedepth of 50 m. They showed a strong maximum in October. Dinoflagellatesand tintinnids showed maxima in early November. Comparisonswith previous studies reveal that (i) changes in species compositionhave not been significant, (ii) the silicoflagellate’sabundance is lower during the present study, (iii) the sequentialspring bloom is composed of a pico-nanoplankton bloom in Marchand microphytoplankton in May, whereas in other western Mediterraneanareas the spring microphytoplankton bloom is reported in Februaryand March, (iv) high water transport through the Corsica channelcoinciding with low or negative winter values of North AtlanticOscillation (NAO) index are associated with the anomalous strongdevelopment of the spring diatom blooms in the Bay of Villefranche,whereas the usual trend is the lack of or weak development ofthe spring diatom bloom. This feature may determine the natureand the fate of primary production and the interannual variabilityin the relative importance of the microbial food web versusthe microbial loop.     

Fortnightly periodicity in the abundance of diatom and dinoflagellate taxa at a coastal study site

From 3 July to 15 September 2000, plankton samples were collected roughly every 2 days at three stations within 1.5 km from shore at Sunset Bay, OR. In these samples we enumerated Coscinodiscus-like diatoms, Protoperidinium spp., and the potentially toxic phytoplankter, Pseudo-nitzschia spp. Using time series analysis, the abundance of these phytoplankters was compared to wind stress, tidal range, and sea surface temperature (SST). SST was significantly cross-correlated with wind stress (lower SST occurred during upwelling favorable winds) and maximum daily tidal range (cold and warm anomalies in SST occurred around the neap and spring tides, respectively). We found no significant cross-correlations between wind stress (upwelling vs. downwelling winds) and the abundance of any of the taxa. Significant cross-correlations were found between phytoplankton abundances and the maximum daily tidal range (peak concentrations occurred between the neap and spring tides) and SST (peak concentrations occurred during periods of warmer SST). We hypothesize that this pattern of abundance may be caused by shoreward transport of offshore phytoplankton populations by internal tidal waves.