Effect of temperature on growth of the cyanobacterium Aphanizomenon flos-aquae in Lake Biwa and Lake Yogo

The water bloom‐forming cyanobacterium Aphanizomenon flos‐aquae Ralfs ex Bornet et Flahault (Nos‐tocales, Cyanophyceae) appeared in Lake Biwa and Lake Yogo in 1999 for the first time. The morphological characteristics were described using natural samples. In contrast to the other water bloom‐forming cyanobacteria such as Microcystis and Anabaena in Lake Biwa and Lake Yogo, the small summer population of A. flos‐aquae is apt to grow in winter, suggesting the low temperature preference or tolerance of this species. In order to clarify the effect of temperature on the growth, culture experiments were conducted using an axenic strain isolated from Lake Biwa. The strain could grow at above 8°C with an optimum temperature ranging from 23 to 29°C, and survived even at 5°C for at least 25days under low light conditions. Although these results confirmed the ability of the bloom formation during late autumn and winter, it is still unclear why the Aphanizomenon bloom occurred at temperatures of ca 10°C in December and not immediately after the disappearance of Microcystis and/or Anabaena bloom during autumn.     

Phytoplankton in Sardinian reservoirs

Abstract

A picture of the studies carried out in the past 20 years on phytoplankton from the 36 reservoirs and one natural lake in Sardinia is presented. Processing of the 1994 seasonal data shows that the dominant or subdominant algal species in the 36 reservoirs in terms of density belong to only 8 genera, with species of the genus Microcystis in 17 reservoirs, Chlorella in 15, Cyclotella in 12, Ankistrodesmus and Anabaena in 9, Aphanizomenon in 8, Melosira in 7 and Oocystis in 6. Processing of the data from the 16 reservoirs in which annual or plurennial surveys were carried out, shows that on the basis of the biomass the most likely floristic pattern is Microcystis aeruginosa Kg., Microcystis flos-aquae (Wittr.) Kichn., Anabaena flos-aquae (Lyngb.) Bréb., Anabaena planctonica Brunnth., Aphanizomenon flos-aquae (L.) Ralfs., Melosira granulata (E.) Ralfs and Closterium aciculare T. West. In general terms this means that most of these reservoirs are eutrophic. In fact the species are capable of describing an increasing trophic gradient in agreement with the one described using other variables. Specific cases of reservoirs where plurennial surveys have been carried out are considered. From these surveys a great quali-quantitative variability of the phytoplankton is inferred.     

Chemotaxonomy of planktonic cyanobacteria based on non-polar and 3-hydroxy fatty acid composition

Twenty-eight axenio planktonic cyanobacterial strains (10 Microcystis, three Oscillatoria, one Spirulina, one Aphanizomenon, 13 Anabaena) were investigated for their fatty acid composition by measurement of non-polar and hydroxy fatty acids. No 2-hydroxy fatty acids were detected in any strain, but 3-hydroxy fatty acids were detected in minor quantities in 24 strains. The highest portion of total fatty acids were non-polar fatty acids. Qualitative and quantitative analyses of 3-hydroxy fatty acids showed no taxonomic value in these strains, while the type of non-polar fatty acid composition was shown to be consistent within Microcystis and Anabaena strains, distinguishing them as type 4, characterized by the presence of 18:4, and type 2, characterized by 18:3 (α) of the Kenyon-Murata system. Two Oscillatoria agardhii Gomont strains were also included in the type 2 group due to the presence of 18: 3 (α), but the difference in characteristics of 16:2 and 16:3 between O. agardhii and Anabaena further divided type 2 into two subgroups: type 2A for Anabaena and type 2B for O. agardhii. A simplified unweighted pair group method with arithmetic averages (UPGMA) dendrogram demonstrated that the classification of 28 strains (Microcystis spp., Anabaena spp., Aphanizomenon flos-aquae (Lemmermann) Ralfs f. gracile (Lemmermann) Elenkin, O. agardhii and Spirullnasubsalsa Oersted ex Gomont based on numerical analysis of non-polar fatty acids corresponded to morphological species criteria, suggesting that non-polar fatty acid composition is a valuable chemical marker in the taxonomy of planktonic cyanobacteria. However, the fatty acid composition in Oscillatoria raciborskii is similar to that of Microcystis and very different from that of O. agardhii, suggesting its special position in Oscillatoria and the chemical diversity in the genus Oscillatoria.     

Seasonal succession of phytoplankton in Lake Yogo over 2 years: effect of artificial manipulation

We studied the seasonal variation in concentrations of nutrients and phytoplankton in Lake Yogo for 2 years, from May 2000 to May 2002, in order to clarify the seasonal succession of phytoplankton and the effect of various manipulations on it. It was revealed that in spite of the installation of aeration systems and the pumping of mesotrophic water from Lake Biwa during the summer season, the trophic state of Lake Yogo overall has not improved during the past few decades. However, the pumping of water from Lake Biwa did affect the concentrations of nutrients and the periods of cyanobacterial bloom during the summer. The pumping period was different in each year, and the cyanobacterial bloom occurred during the period without pumping in both years. The aeration destratification was not strong enough to prevent cyanobacterial blooms. Cyanobacteria and Bacillariophyceae contributed most to the phytoplankton biomass in both years. Aphanizomenon, Anabaena, and Microcystis were the main genera among cyanobacteria. The bloom of Aphanizomenon or Anabaena occurred early in the summer, and was then replaced by Microcystis. Aphanizomenon was almost always present, and often formed bloom even in winter. The seasonal succession of Bacillariophyceae was almost the same in both years and was well categorized: winter-growing species such as Aulacoseira pusilla (F. Meister) Tuji et Houki and species of Thalassiosiraceae, spring-growing species such as Asterionella formosa Hassall, Fragilaria crotonensis Kitton, and Synedra cf. acus, and fall-growing species such as Aulacoseira ambigua (Grunow) Simonsen, and Aulacoseira granulata (Ehrenb.) Simonsen.     

Effect of cyanobacterial blooms on thermal stratification

Enclosure experiments were performed at Akanoi Bay, Lake Biwa, in 1995 to determine whether the blooms of cyanobacterial algae changed thermal stratification in the lake. We used four rectangular enclosures, each 10 m × 10 m, with a volume of 200 m³, which were open to the sediments. Two enclosures, A and B, were mixed artificially by aquatic pumps from 1000 to 1400 every day, and the other two enclosures, C and D, were controls with no mixing. The experiment was conducted during late summer from August 3 to September 27. Chlorophyll a concentrations were highest in enclosure D, followed by enclosure C, both of which were controls without mixing. Enclosure A had lower concentrations than enclosures C and D, and enclosure B had the lowest concentrations. No large cyanobacterial algae blooms of Anabaena sp. and Microcystis sp. were seen in the mixed enclosures A and B. In enclosures C and D, blooms of Anabaena sp. occurred in the middle of August, and Microcystis sp. later became dominant in enclosure D at the end of August. In enclosure D, the water temperature changed over the diel cycle before August 17, with thermal stratification during the day and complete mixing at night. After August 17, as Anabaena sp. and Microcystis sp. became dominant, the temperature at the bottom of the enclosure did not change clearly over the 24-h cycle. The APE (available potential energy) density (a measure of water column stability) in the enclosures increased by almost 100% when the biovolume of Anabaena sp. + Microcystis sp. exceeded 20 mm³ l⁻¹. These results indicate that blooms of Anabaena sp. and Microcystis sp. can increase the available potential energy in the water column and create more stable stratification for their growth. Received: September 25, 1999 / Accepted: January 6, 2000     

Cyanobacterial toxicity and migration in a mesotrophic lake in western Washington, USA

In fall 1997, the toxic cyanobacterium Microcystis aeruginosa was documented in Lake Sammamish (western Washington, U.S.A.) for the first time. Cyanobacterial activity and environmental conditions that may promote toxic cyanobacteria were investigated during summer and fall 1999. Development of toxic Microcystis was hypothesized to be due to runoff of nutrients from the watershed (external loading hypothesis) or from vertical migration of dormant cyanobacteria from the nutrient-rich sediments into the water column (cyanobacterial migration hypothesis). Microcystins were detected using an enzyme-linked immunosorbent assay during late August and early September 1999 despite low cyanobacterial abundance. Microcystin concentrations ranged between 0.19–3.8 g l^–1 throughout the lake and at all depths with the exception of the boat launch where concentrations reached 43 g l^–1. Comparison of the conditions associated with the toxic episodes in 1997 and 1999 indicate that Microcystis is associated with a stable water column, increased surface total phosphorus concentrations (> 10 g l^–1), surface temperatures greater than 22°C, high total nitrogen to phosphorus ratios (> 30), and increased water column transparency (up to 5.5 m). Migration of the cyanobacteria, Microcystis and Anabaena, occurred in both the deep and shallow portions of the lake. Microcystis dominated (89–99%) the migrating cyanobacteria with greater migration from the shallow station. External loading of nutrients due to the large rainfall preceding the 1997 toxic episode may have provided the nutrients needed to fuel that bloom. However, toxic Microcystis occurred in 1999 despite the lack of rain and subsequent external runoff. The migration of Microcystis from the nutrient-rich sediments may have been the inoculum for the toxic population detected in 1999.     

Cyanobacteria dynamics in a restored Finnish lake: a long term simulation study

Several explanations have been presented for the formation of lacustrine cyanobacteria blooms. These include elevated water temperature, nutrient enrichment, low N/P ratios, low light energy requirements, high pH and/or low carbon dioxide concentration, selective zooplankton grazing, excretion of compounds which suppress the growth of competing algae, and migration. The impact of the first four were studied in Lake Tuusulanjärvi, a eutrophic Finnish lake, using deterministic simulation. The study, which covered 15 years, included a sequence of cases on the recovery of the lake after the implementation of two restoration measures: aeration of the hypolimnion, and termination of municipal waste discharge, both of which were done during the study period. The focus was on Microcystis and Oscillatoria, and on the N-fixing cyanobacteria, Anabaena and Aphanizomenon. Eukaryotic phytoplankton were also included in the study. Monitoring data were used. The roles of the hypotheses were discussed, from the point of view of the utility of the information in water resources management.     

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     

Comparative adaptations of Aphanizomenon and Anabaena for nitrogen fixation under weak irradiance

1. In situ measurements of nitrogen fixation rates for Aphanizomenon in fertile Colorado lakes with low inorganic nitrogen concentrations demonstrated high efficiency of nitrogen fixation at low irradiance. 2. For study populations, rates of N₂ fixation in darkness and with alternating exposure to light and darkness were a higher percentage of light‐saturated rates for Aphanizomenon than for Anabaena, suggesting storage of reduced metabolites at high irradiance that are used subsequently by Aphanizomenon when cells are forced by mixing into zones of low irradiance. Also, saturation of N₂ fixation occurred over a lower range of irradiance for Aphanizomenon than for Anabaena. 3. High efficiency of N₂ fixation in Aphanizomenon at low or fluctuating irradiance is complementary to its previously demonstrated high efficiency of photosynthesis at low irradiance. Nitrogen fixation rate was also strongly related to DIN concentration; fixation was highest at low DIN (maximum < 5 μg L^?1) but was also most vulnerable to photoinhibition under such conditions. 4. The fixation capabilities of Aphanizomenon under weak or varying irradiance could explain its commonly observed domination over Anabaena when transparency is low and available nitrogen is scarce.     

Bloom formation of Gloeotrichia echinulata and Aphanizomenon flos-aquae in a shallow,eutrophic, Danish lake

Over a period of four years, the seasonal periodicity of dominant phytoplankton species in a shallow, eutrophic Danish lake changed markedly. Cyanophytes prevailed during the summer period of all four years. In the first three years, species of Microcystis, Anabaena and Aphanothece dominated, whereas in the fourth year of investigation, these algae were replaced by Gloeotrichia echinulata (J. E. Smith) Richter and Aphanizomenon flos-aquae (L.) Ralfs. The most striking environmental differences in the fourth year as compared with the previous three years, were an increase in tranparency, from about 0.5 meter in 1989–1991 to more than 2 metres preceding the summer maximum in 1992, and a simultaneous occurrence of low oxygen concentrations. A collapse of the fish population was followed by an increased proportion of large Cladocerans in the zooplankton. Improved light conditions at the bottom and grazing pressure from large Cladocerans favoured growth of the large colony forming blue-green algae, Gloeotrichia echinulata and Aphanizomenon flos-aquae. These species germinate from resting spores in the sediment and are able to sustain some growth there before migration to the lake water. The transfer of algal biomass from the bottom sediment to the water phase was accompanied by a marked increase in concentrations of particulate phosphorus and nitrogen in the entire lake.     

Anatoxin-a concentration inAnabaena andAphanizomenon under different environmental conditions and comparison of growth by toxic and non-toxicAnabaena-strains — a laboratory study

Anatoxin-a-concentration in cells ofAnabaena- andAphanizomenon-strains and in their growth media were studied in the laboratory in batch cultures at different temperatures, light fluxes, orthophosphate and nitrate concentrations and with different nitrogen sources for growth. Toxin concentrations were detected by HPLC. Also, the growth of the toxicAnabaena-strains was compared to that of a non-toxic one. The non-toxicAnabaena was never found to produce anatoxin-a. The amount of toxin in the cells of the toxic strains was high, often exceeding 1% of their dry weight. High temperature decreased the amount of the toxin regardless of growth. Growth limiting low and growth inhibiting high light decreased the amount of the toxin in the cells ofAnabaena-strains. The highest light flux studied did not limit the growth or decrease the level of the toxin in the cells ofAphanizomenon. Growth in N-free medium (i.e. N₂ fixation) showed that the cells contained more toxin than growth in N-rich medium. Orthophosphate concentration had no effect on toxin levels, although the lowest concentrations limited the growth of all strains studied. The toxic strains tolerated higher temperatures than the non-toxic one, but the non-toxic strain seemed to be more adjustable to high irradiance than the toxic ones. The yields (dry weight) of non-toxic and toxic strains differed significantly in different phosphate concentrations.     

Seasonal changes in composition of the cyanobacterial community and the occurrence of hepatotoxic blooms in the eastern townships, Quebec, Canada

Four eutrophic lakes in the eastern townships (Québec,Canada) were sampled on a biweekly basis between May and October2001 to examine seasonal changes, and to study the role of taxonomicand environmental factors in cyanobacterial toxin production.Microcystin-LR (MC-LR) equivalent content was determined usinga protein phosphatase inhibition assay on extracts of lyophilizedplankton. Three of the lakes showed a similar pattern of maximumwater column toxicity in late summer, while in the fourth, toxicitywas highest in spring and then declined over the year. Variationsin water toxicity level could be attributed to the abundanceof two potentially toxigenic genera, Microcystis and Anabaena.A multiple regression model explained 75% of the variation inmicrocystin (MC) concentration, based on water column totalnitrogen concentration (TN) and the biomass of these two genera.Microcystis and Anabaena genera appeared to be similarly toxicin all lakes. Increased water column stability, higher lightextinction coefficient and a lack of dissolved nutrients wereall associated with increased total biomass of toxigenic cyanobacterialgenera.     

PCR-based identification of microcystin-producing genotypes of different cyanobacterial genera

Microcystins are harmful hepatotoxins produced by many, but not all strains of the cyanobacterial genera Anabaena, Microcystis, Anabaena, Planktothrix, and Nostoc. Waterbodies have to be monitored for the mass development of toxic cyanobacteria; however, because of the close genetic relationship of microcystin-producing and non-producing strains within a genus, identification of microcystin-producers by morphological criteria is not possible. The genomes of microcystin-producing cells contain mcy genes coding for the microcystin synthetase complex. Based on the sequence information of mcy genes from Microcystis and Planktothrix, a primer pair for PCR amplification of a mcyA gene fragment was designed. PCR with this primer pair is a powerful means to identify microcystin-producing strains of the genera Anabaena, Microcystis, and Planktothrix. Moreover, subsequent RFLP analysis of the PCR products generated genus-specific fragments and allowed the genus of the toxin producer to be identified. The assay can be used with DNA from field samples.Abbreviations RFLP Restriction fragment length polymorphism - MALDI-TOF Matrix-assisted laser desorption/ionization-time of flight spectrometry - HPLC High performance liquid chromatography     

Cyanophycean blooms in the reservoir of Val Joly (northern France) and their development in downstream rivers

A study was carried out in 1992 on the Val Joly reservoir and the rivers situated downstream: the River Helpe Majeure and the canalized Sambre into which it flows 40 km below the reservoir. Each year, blooms of blue-green algae occur in the reservoir. They are dominated by species such as Aphanizomenon flos-aquae (L.) Ralfs in 1991 or Pseudanabaena tenuis Koppe and Oscillatoria pseudogeminata G. Schmid in 1992. A typical fluvial composition of the phytoplankton was mostly restored above the confluence with the Sambre. Nevertheless, significant quantities of Oscillatoria and Pseudanabaena have been observed in the River Sambre, just below its confluence with the Helpe Majeure. The environmental conditions in the River Sambre do not allow Aphanizomenon to develop, but could favour Oscillatoria blooms.     

Diel vertical migrations of invertebrate predators (Leptodora kindtii ,Thermocyclops taihokuensis, andMesocyclops sp .) in a shallow, eutrophic lake

We studied vertical distribution patterns of three invertebrate predators – Leptodora kindtii, Mesocyclopssp., and Thermocyclops taihokuensis– in a shallow eutrophic lake, Lake Suwa , Japan. From June to October in 2000 and 2001, we collected samples in the lake center in order to examine the vertical distribution patterns and the densities of the predators in the water column during the day (0900) and at night (2330). We also examined phototactic behavior of Leptodora in the laboratory. The three invertebrate predators showed clear migration patterns. Leptodora and Thermocyclops displayed a typical migration, avoiding the surface and maintaining a high abundance in deeper water during the day, and being distributed uniformly during the night. Mesocyclops, on the other hand, showed no clear vertical distribution pattern in the water column. However, Mesocyclops showed higher densities in the water column during the night than during the day. It suggests that they stayed just above the bottom during the day and migrated upward during the night. Leptodora also showed such a density difference between day and night. In the laboratory, Leptodora showed strong negative phototactic behavior. The observed density changes between day and night in Leptodora and Mesocyclops suggests the possible underestimation of their population density by usual sampling methods, and thus the impact of predation on populations of prey zooplankton species may also be underestimated in shallow water bodies.     

Dynamics and short-term survival of toxic cyanobacteria species in ballast water from NOBOB vessels transiting the Great Lakes—implications for HAB invasions

We measured the presence, viability and potential toxicity of cyanobacteria in ships’ ballast tanks during three domestic voyages through the North American Great Lakes. Using molecular methods, the toxin-producing forms of Microcystis and Anabaena were monitored in ballast water after ships’ ballast tanks were filled at their first port of call, and at subsequent ports as ships transited the Great Lakes. Microcystis was detected in ballast water at intermediate and final ports of call in all three experiments, but the presence of Anabaena was more variable, suggesting low abundance or patchy distribution in ballast tanks. Both species were detected in ballast water up to 11 days old. Detection of the microcystin synthetase gene, mcyE, in ballast tanks indicated entrained cells were capable of producing microcystin, and further analyses of RNA indicated the toxin was being expressed by Microcystis, even after 11 days in dark transit. These data demonstrate within-basin transport and delivery of planktonic harmful algal bloom (HAB) species to distant ports in the world's largest freshwater reservoir, with potential implications for drinking water quality. These implications are discussed with respect to management of microbial invasions and the fate of introduced phytoplankton in their receiving environment.     

冲天湖底泥表层微囊藻休眠体复苏与菌群动态

对频繁暴发微囊藻水华的西洞庭冲天湖表层底泥和上覆水取样,检测和分析了底泥表层微囊藻休眠体丰度和菌浓度、上覆水中微囊藻细胞丰度和菌浓度以及部分理化性质,结合室内模拟试验。结果表明:2—6月份冲天湖底泥表层和上覆水中总菌浓度均显著上升(P0.05),底泥表层总菌浓度显著高于上覆水(P0.05),优势菌群均为微小杆菌属(Exiguobacterium)、假单胞菌属(Pseudomonas)和芽孢杆菌属(Bacillus);4月份底泥表层微囊藻休眠体开始复苏且休眠体丰度下降,6月份休眠体丰度显著低于4—5月份(P0.05),而上覆水中微囊藻细胞丰度上升,6月份显著高于4—5月份(P0.05);复苏优势藻为铜绿微囊藻(Microcystis aeruginosa)、水华微囊藻(Microcystis flos-aqua)和惠氏微囊藻(Microcystis wesenbergii);复苏期间促休眠体复苏优势菌群浓度显著上升、"底泥-上覆水"界面溶解氧浓度与TN/TP比显著下降(P0.05)。说明冲天湖底泥表层和上覆水优势菌群可能通过改变底泥表层理化环境影响微囊藻休眠体复苏。     

Effects of temperature, and availability of nitrogen and phosphorus on the abundance of Anabaena and Microcystis in Lake Biwa, Japan: an experimental approach

Under optimal nutrient conditions, both Microcystis sp. and Anabaena sp. isolated from Lake Biwa grew optimally at 28–32°C but differed in maximal growth rates, phosphate uptake kinetics, maximal phosphorus quotas, and growth responses to nitrogen and phosphorus limitation. The maximal growth rates of Microcystis and Anabaena were 1.6 and 1.25 divisions day⁻¹, respectively. With phosphate and nitrate in the growth-limiting range, the growth of Microcystis was optimal at an N : P ratio of 100 : 1 (by weight) and declined at lower (nitrogen limitation) and higher (phosphorus limitation) ratios. In contrast, Anabaena growth rates did not change at N : P ratios from 1000 : 1 to 10 : 1. Starting with cells containing the maximal phosphorus quota, Microcystis growth in minus-phosphorus medium ceased in 7–9 days, compared with 12–13 days for Anabaena. The phosphate turnover time in cultures starved to their minimum cell quotas was 7.9 min for Microcystis and 0.6 min for Anabaena. Microcystis had a higher K _s (0.12 μg P l⁻¹ 10⁻⁶ cells) and lower V _max (9.63 μg P l⁻¹ h⁻¹ 10⁻⁶ cells), than Anabaena (K _s 0.02 μg P l⁻¹ h⁻¹ 10⁻⁶ cells; V _max 46.25 63 μg P l⁻¹ h⁻¹ 10⁻⁶ cells), suggesting that Microcystis would not be able to grow well in phosphorus-limited waters. We conclude that in spite of the higher growth rate under ideal conditions, Microcystis does not usually bloom in the North Basin because of low availability of phosphorus and nitrogen. Although Anabaena has an efficient phosphorus-uptake system, its main strategy for growth in low-phosphorus environments may depend on storage of phosphorus during periods of abundant phosphorus supply, which are rare in the North Basin. Received: July 31, 2000 / Accepted: October 18, 2000     

Seasonal variations of Microcystis populations in sediments of Lake Biwa, Japan

Seasonal variations of colony numbers of Microcystis aeruginosa(Kütz.) Kütz. and M. wesenbergii(Komárek) Komárek in N. V. Kondrat. in sediments of Lake Biwa were investigated over a period of 1 year. At two stations located in the shallow South Basin of Lake Biwa (ca. 4 m water depth), the colony number of Microcystisfluctuated seasonally. The number had a tendency to gradually decrease from winter to early summer, while it increased through mid-summer and autumn. Since the Microcystispopulation in sediment was rather small, intensive growth and accumulation in the water column should be important for the formation of Microcystisblooms in Lake Biwa. Microcystiscolonies in the sediment samples after June were observed to be floating in a counting chamber under a microscope. The observation suggests that the recruitment of Microcystis colonies into the water column mostly occurs in early summer. The number of Microcystiscolonies in the deep North Basin of Lake Biwa (70 – 90 m water depth) was larger than in the South Basin. Because the seasonal variation of colony numbers was not observed in the North Basin, and Microcystiscells do not have gas vesicles, these colonies will not return into the water column. The colonies isolated from the sediment of the North Basin were able to grow in cultured conditions, in the same way as those from the sediment of the South Basin. Therefore, Microcystiscolonies may survive for a long time under stable conditions of low temperature (ca. 8 °C) and darkness, in the sediment of the deep North Basin, accumulating gradually each year.