Scrippsiella Acuminata Research Articles

The dispersal of dinoflagellate cyst caused by international ships under repair conditions: a potential invasion risk to the Yangtze River Estuary, China.

The foreign dinoflagellate cysts in ships' ballast water tank sediments (BWTS) can be viable for a long time under hostile storage conditions. It is crucial to understand the detailed mechanisms of harmful biological invasions in estuary ecosystems. To study the relationship between the abundance of dinoflagellate cysts and environmental factors, cyst assemblages were analyzed in 7 sediment samples, collected from one international commercial ship that arrived in Shanghai in August 2020. Twenty-three dinoflagellate cyst taxa were identified in 5 groups, including autotrophic (9) and heterotrophic (14) species. Distribution of dinoflagellate cysts in the different ballast water tanks is heterogeneous. Dinoflagellate cysts in BWTS of the repaired ship were dominated by Scrippsiella acuminata, Protoperidinium leonis, Protoperidinium oblongum, Lingulodinium polyedra, Alexandrium tamarense/A. catenella, Protoperidinium pentagonum, and Protoperidinium subinerme. The abundance of the dinoflagellate cysts in each tank ranged from 80.69 to 330.85 cysts g-1 DS (dry sediment). Multivariate statistical analyses revealed that the variation in cysts from different tanks had positive correlations with total nitrogen (TN), total phosphorus (TP), and pH and negative correlations with total organic carbon (TOC) except for sample TK5. For germination of dinoflagellate cysts in BWTS, 12 species were germinated in 40days and cysts of potentially toxic dinoflagellate species were more abundant than those of non-toxic species. Results show that potentially viable and harmful/toxic dinoflagellate cysts are present in BWTS of ships arriving in Shanghai, China. Consequently, knowledge obtained in this study can be valuable for further managing of potential biological invasion of the Yangtze River Estuary.

Effects of dredging activities and seasonal variation on coastal plankton assemblages: results from 10 years of environmental monitoring

Coastal zones support the most productive marine ecosystems, yet they are increasingly threatened by anthropogenic stressors such as dredging. In this study, we investigated how seasonal variation and dredging activities conducted during the construction of a harbor and submarine base (Sepetiba Bay, RJ, Brazil) affected the phytoplankton and zooplankton assemblages. The observed temporal variability at five different sites over 10 years revealed that dredging exceeds the expected influence of dry and rainy seasons on plankton abundance and diversity. In general, the abundance of both groups increased during dredging due to the resuspension of nutrients and benthic organisms. This increase was particularly evident in the dinoflagellate Scrippsiellaa cuminata, the diatoms Thalassiosira rotula and Nitzschia longissima, and the herbivorous zooplankton Acartia clausii and Pseudevadne tergestina. Moreover, season and dredging activities synergistically influenced plankton assemblages, resulting in larger seasonal variations during dredging activities. After the end of the harbor construction, plankton abundance decreased and remained low until the end of the monitoring, which may indicate persistent changes in the biodiversity and ecosystem functioning of impacted areas.

Distribution of Dinoflagellate Cysts in Surface Sediments From the Qingdao Coast, the Yellow Sea, China: The Potential Risk of Harmful Algal Blooms

Surface sediments were collected from three sea areas of the Qingdao coast, the Yellow Sea, China, namely, the inner Jiaozhou Bay, the Laoshan coast, and the Amphioxus Reserve area in November to December 2017. Dinoflagellate cysts were observed in the sediments, focusing on the distribution of toxic and harmful species. Contents of biogenic elements were analyzed to reveal their relationships to cysts. A total of 32 cyst taxa were identified, including 23 autotrophic and 9 heterotrophic taxa. Cyst concentrations ranged from 83.3 to 346.5 cysts/g D Wt with an average of 210.7 cysts/g D Wt. Generally, cysts of autotrophic dinoflagellates dominated in sediments from the Qingdao coast with proportions of 41.05%–90.25%. There were no dominant group in cyst assemblages; cysts of Protoperidiniaceae, Suessiales, and Calciodinelloideae showed similar contributions. Cyst assemblages were quite different in the inner Jiaozhou Bay reflected by the lower species richness, diversity, and cyst concentration. Results from the redundancy analysis (RDA) demonstrated the influence of biogenic elements on cyst assemblages, which explained well why the three sea areas with different degrees of human activities showed different dinocyst storages. Notably, 17 harmful algal bloom (HAB) dinoflagellate cysts were identified in this study, including cysts of those producing toxins that may damage human health and marine animals. Some of these cysts occurred widely and dominantly in this study, such as cysts of Gonyaulax spinifera, Azadinium trinitatum, Scrippsiella acuminata, and Biecheleria halophila, suggesting the potential risk of HABs in the Qingdao coastal area.

Inhibitory Effect of Isolated Bacteria from the Phycosphere of Levanderina fissa on the Growth of Different Microalgae

Levanderina fissa (formerly Gyrodinium instriatum) frequently causes blooms in the Pearl River Estuary and has few advantages in interspecific competition with other bloom-forming algal species. Phycosphere bacteria, which closely interact with algal cells, may play an ecologically functional role in the population dynamics and bloom occurrence. To test this hypothesis, we isolated and identified cultivable bacteria coexisting in different growth stages of L. fissa by the gradient dilution method and investigated the characteristics of the bacterial interactions with three diatom species (Chaetoceros curvisetus, Skeletonema dohrnii, and Phaeodactylum tricornutum) and three dinoflagellate species (Scrippsiella acuminata, Karenia mikimotoi, and the host algae) after screening for functional bacteria. One of the isolated bacterial strains, Lf7, which was phylogenetically identified as an Alteromonas species, showed significant inhibitory effects on different algal species except its host. Moreover, all algal species, especially their hosts, showed significant stimulatory effects on bacterial Lf7 growth. These results indicate that the phycosphere bacterium Lf7 may play some ecological roles in the competition between its host alga L. fissa and other phytoplankton. The study also highlights the complicated interactions between phycosphere bacteria and host algae.

Energy metabolism and genetic information processing mark major transitions in the life history of Scrippsiella acuminata (Dinophyceae)

Many dinoflagellates perform sexual reproduction and form cysts as a life history strategy to survive adverse environmental conditions and seed annual harmful algal blooms (HABs). The molecular mechanisms underpinning the life stage transitions can provide clues about how key environmental factors induce encystment and initiation of a HAB but are still poorly understood. Here, we conducted an integrated physiological and transcriptomic study to unravel the mechanisms in Scrippsiella acuminata. We established a culture from a bloom, induced cyst formation, and divided the process into four life stages. Transcriptomic analysis of these stages revealed 19,900 differentially expressed genes (DEGs). The expression of genes related to photosynthesis was significantly up-regulated from vegetative stage to immature cyst stage, consistent with the marked increase in cell contents of energy-storing macromolecules (carbohydrates and lipids). When proceeding to resting cysts, most photosynthesis genes were down-regulated while “genetic information processing” related genes were up-regulated. Comparing germinating cysts with resting cysts revealed 100 DEGs involved in energy metabolism, indicating a high energy requirement of germination. In addition, the transition from germinating cysts to vegetative cells featured up-regulation of photosynthesis. Our results demonstrate that energy storage and consumption play a pivotal role in cyst formation and germination respectively and genetic information processing is crucial in cyst dormancy.

Interspecies competition between Scrippsiella acuminata and three marine diatoms: Growth inhibition and allelopathic effects.

Interactions between Scrippsiella acuminata and three diatoms, Chaetoceros curvisetus, Phaeodactylum tricornutum, and Skeletonema dohrnii, were investigated using bi-algal co-cultures and cell-free and sonicated-cell filtrates in this study. Volatile aldehydes in sonicated filtrates of the three diatoms were analyzed by GC/MS. Furthermore, effects of 2E, 4E-decadienal (2,4-D) on the growth and the photosynthetic efficiency of the four microalgal species were studied. The growth of Sc. acuminata was significantly inhibited by the three diatoms in all co-cultures, and the inhibitory effects were higher under nutrient-rich conditions. Both cell-free and sonicated-cell filtrates of the three diatoms showed significant inhibitions on the growth of Sc. acuminata, which highlighted that diatoms produce allelopathic compounds not only to the surrounding environments but also inside the cells. Fifteen aldehydes were detected in the sonicated-cell filtrates of the three diatoms, and 5, 5, and 12 types of aldehydes were detected in C. curvisetus, P. tricornutum, and Sk. dohrnii, respectively. Polyunsaturated aldehydes (PUAs) composition differed among the three diatom species. Phenylglyoxal (C8H6O2) dominated in C. curvisetus, 2,4-D (C10H16O) predominated in P. tricornutum, and high proportions of 2-hexenal (C6H10O), 2E, 4E-heptadienal (C7H10O), and 2,4-D were detected in Sk. dohrnii. 2,4-D showed significantly inhibitory effects on the growth of algal cells including diatoms themselves in a dose-dependent manner, and photosynthetic efficiency was significantly decreased as well. Sc. acuminata was the most sensitive species. The 96h EC50 values of 2,4-D on the growth of the four microalgae were 1.64 μmol/L for Sc. acuminata, 3.09 μmol/L for C. curvisetus, 4.93 μmol/L for P. tricornutum, and 8.54 μmol/L for Sk. dohrnii, respectively. The results suggest that PUAs produced by diatoms may help them to take the competitive advantages in phytoplankton community, and thus to sustain diatom-dominated community structure in nutrient rich coastal waters.

Study on the dinoflagellate cysts in ballast tank sediments of international vessels in Chinese shipyards

The problem of aquatic invasive species caused by discharge of ballast water and sediments from ships’ ballast tanks has become extremely prominent. Seventeen sediment samples taken from ballast tanks of different ships docked in two Chinese shipyards were examined to identify the variety of resting dinoflagellate cysts. Twenty-two dinoflagellate cyst taxa were identified in these samples, including 11 photosynthetic and eleven heterotrophic species. These species represent 10 genera with the dominating assemblages of Alexandrium minutum, Scrippsiella acuminata, Lingulodinium polyedra, Protoperidinium sp. and Protoperidinium conicum. The total abundance of the dinoflagellate cysts ranged from 36 to 448 cysts g−1 dry weight, which demonstrated a wide range of diversity for different ships. It was observed that the number of taxa and concentrations of cysts in ballast tank sediments were slightly greater for ships performing short voyage than ships performing longer voyage. The compositions of dinoflagellate cysts in sediments from ships sailing diverse routes were more variable than those sailing same routes. Sediment moisture content proved to be well correlated to the total cyst abundance (r = 0.7422, P < 0.01). Furthermore, nine toxic and harmful species were observed from all sediment samples, which indicated a wide range of distribution and potential risk of harmful algal blooms if being discharged to Chinese waters. As a result, full attention should be drawn to the studies on dinoflagellate cysts in the ballast tank sediments from ships arriving at China, this is of great significance for preventing introduction of toxic and harmful dinoflagellate cysts and protecting native marine biodiversity.

Spatio-temporal variation of the phytoplankton community in a tropical estuarine gradient, under the influence of river damming

The Paraguaçu River is one of the most important rivers in Bahia State, Brazil, and the main tributary of the Todos os Santos Bay, the second largest in that country. We evaluated the spatio-temporal variations in the composition and structure of the phytoplankton community in the Paraguaçu River estuary as influenced by rainfall and fluvial discharge from the Pedra do Cavalo dam. Bi-monthly collections were carried out from May 2018 to March 2019 at 12 sampling stations in the estuary. During this period, phytoplankton samples, water samples to determinate the concentration of dissolved inorganic nutrients and data on salinity, temperature, pH, dissolved oxygen, and water transparency were collected. Data on rainfall and dam discharge were also obtained. Abiotic variables and chlorophyll-a showed significant differences in the estuary zones, and silicate concentrations demonstrated differences between the dam discharge periods. A total of 194 phytoplankton taxa were identified, with diatoms showing the highest densities and diversities throughout the study period. Cyclotella meneghiniana, Nitzschia sp., and Scrippsiella acuminata formed blooms in the dry season, whereas blooms of Planktothrix isothrix occurred in the rainy season and during a period of medium dam discharge in the dry season. The influence of dam discharge was quite evident, with increases in nutrient concentrations in the estuary during the months of higher flow that altered the composition and density of the phytoplankton communities in the different system zones. The formation of blooms in response to increased nutrient availability represents an increase in the primary productivity of the system, although blooms of potentially harmful species (such as Planktothrix isothrix) may represent a risk to human activities in the region.

Dinoflagellate Host Chloroplasts and Mitochondria Remain Functional During Amoebophrya Infection.

Dinoflagellates are major components of phytoplankton that play critical roles in many microbial food webs, many of them being hosts of countless intracellular parasites. The phototrophic dinoflagellate Scrippsiella acuminata (Dinophyceae) can be infected by the microeukaryotic parasitoids Amoebophrya spp. (Syndiniales), some of which primarily target and digest the host nucleus. Early digestion of the nucleus at the beginning of the infection is expected to greatly impact the host metabolism, inducing the knockout of the organellar machineries that highly depend upon nuclear gene expression, such as the mitochondrial OXPHOS pathway and the plastid photosynthetic carbon fixation. However, previous studies have reported that chloroplasts remain functional in swimming host cells infected by Amoebophrya. We report here a multi-approach monitoring study of S. acuminata organelles over a complete infection cycle by nucleus-targeting Amoebophrya sp. strain A120. Our results show sustained and efficient photosystem II activity as a hallmark of functional chloroplast throughout the infection period despite the complete digestion of the host nucleus. We also report the importance played by light on parasite production, i.e., the amount of host biomass converted to parasite infective propagules. Using a differential gene expression analysis, we observed an apparent increase of all 3 mitochondrial and 9 out of the 11 plastidial genes involved in the electron transport chains (ETC) of the respiration pathways during the first stages of the infection. The longer resilience of organellar genes compared to those encoded by the nucleus suggests that both mitochondria and chloroplasts remain functional throughout most of the infection. This extended organelle functionality, along with higher parasite production under light conditions, suggests that host bioenergetic organelles likely benefit the parasite Amoebophrya sp. A120 and improve its fitness during the intracellular infective stage.

Feeding by the newly described heterotrophic dinoflagellate Gyrodinium jinhaense: comparison with G. dominans and G. moestrupii

Heterotrophic dinoflagellates are major grazers of microalgae in marine food webs. The feeding of the newly described heterotrophic dinoflagellate Gyrodinium jinhaense was explored by providing 19 common microalgal prey species and the ciliate Mesodinium rubrum as prey. Furthermore, the specific growth and ingestion rates of G. jinhaense feeding on the chlorophyte Dunaliella salina were determined as a function of prey concentration. Cells of G. jinhaense were able to feed on microalgae of sizes ≤ 26 μm with the exception of the dinoflagellate Karenia mikimotoi. In contrast, G. jinhaense did not feed on microalgae > 26 μm with the exception of the dinoflagellate Lingulodinium polyedra. With increasing mean prey concentration, both the specific growth and ingestion rates of G. jinhaense feeding on D. salina rapidly increased at mean prey concentrations < 504 ng C mL−1 (6300 cells mL−1), but slowly at higher prey concentrations. The maximum growth and ingestion rates of G. jinhaense feeding on D. salina were 0.655 day−1 and 0.82 ng C predator−1 day−1 (10 cells predator−1 day−1), respectively. Gyrodinium dominans and G. moestrupii are able to feed on most microalgal prey species, including the species that G. jinhaense did not feed on. Moreover, these two Gyrodinium species have positive growth rates when feeding on the red-tide dinoflagellates Prorocentrum cordatum and Scrippsiella acuminata, which did not support growth of G. jinhaense. Therefore, G. jinhaense has an ecological niche different from that of G. dominans and G. moestrupii, and this pattern may be the result of evolution among these Gyrodinium species.

Plankton Tracker: A novel integrated system to investigate the dynamic sinking behavior in phytoplankton

Phytoplankton sinking is an important property that can determine community composition, affecting nutrient and light absorption in the photic zone, and influencing biogeochemical cycling via material loss to the deep ocean. To date, the difficulty in exploring the sinking processes is partly due to methodological limitations in measuring phytoplankton sinking rate. However, in the last decade, works have illustrated various methods based on some non-invasive and low perturbing approaches (laser scanner, video-microscopy, fluorescence spectroscopy). In this study, we review the methods for sinking rate estimation and describe the Plankton Tracker, a novel integrated system to investigate in vivo the dynamic sinking behavior of phytoplankton. Plankton Tracker is composed of a long-distance objective and a video-microscopy facility coupled with a specifically developed image analysis system (Plankton Tracker Elements). Diatoms and dinoflagellates were individually-tracked. By processing recorded videos and images, sinking traits (e.g. trajectory length and complexity, sinking velocity, turning angle) were obtained simultaneously with morphological traits (e.g. linear dimensions). We also applied a Biased Correlated Random Walk model to sinking traits. Particularly, we found linear motion in the colony-forming Thalassiosira sp. and sinusoidal reorientation in the dinoflagellate Scrippsiella acuminata. We found complex suspension dynamic of the large Coscinodiscus sp. In this view, the Plankton Tracker approach is likely to provide more insights towards the exploration of dynamic sinking behavior in phytoplankton.

Spatial-temporal distributions of the newly described mixotrophic dinoflagellate Gymnodinium smaydae in Korean coastal waters

Gymnodinium smaydae is a newly described mixotrophic dinoflagellate that feeds on only Heterocapsa spp. and Scrippsiella acuminata among 19 tested algal prey. It is one of the fastest growing dinoflagellates when feeding, but does not grow well without prey. To investigate its spatial-temporal distributions in Korean waters, we quantified its abundance in water samples that were seasonally collected from 28 stations along the Korean Peninsula from April 2015 to October 2018, using quantitative real-time polymerase chain reactions. This dinoflagellate had a wide distribution, as reflected by the detection of G. smaydae cells at 23 of the sampling stations. However, this distribution had a strong seasonality; it was detected at 21 stations in the summer and only one station in winter. The abundance of G. smaydae was significantly and positively correlated with chlorophyll a concentration as well as with water temperature. However, there were no significant correlations between the abundance of G. smaydae and salinity, concentrations of nutrients, or dissolved oxygen concentration. During the study period, G. smaydae was present when water temperatures were 7.6–28.0°C, salinities were 9.6–34.1, concentrations of NO3 were not detectable-106.0 μM, and concentrations of PO4 were not detectable-3.4 μM. The highest abundance of G. smaydae was 18.5 cells mL−1 in the coastal waters of Jinhae in July 2017 when the chlorophyll a concentration was 127 mg m−3 and water temperature was 23.8°C. Therefore, the spatial-temporal distribution of G. smaydae in Korean coastal waters may be affected by chlorophyll a concentration and water temperature. Key words: Gymnodiniaceae; harmful algal bloom; mixotrophy; protist; qPCR; red tide; specific primer; temperature

Scrippsiella acuminata versus Scrippsiella ramonii: A Physiological Comparison.

Scrippsiella is a cosmopolitan dinoflagellate genus that is able to form Harmful Algal Blooms in coastal waters. The large physiological, morphological, and genetic variability that characterizes this genus suggest the existence of cryptic species. In this study, flow cytometric analyses were carried out to compare the cell cycle and life cycle of two Scrippsiella strains from two different species: Scrippsiella ramonii (VGO1053) and Scrippsiella acuminata (S3V). Both species were also investigated by internally transcribed spacer rDNA sequencing and high‐performance liquid chromatography‐based pigment analyses. The reddish‐brown color of S. acuminata and yellowish‐green hue of S. ramonii were consistent with the quantitative differences determined in their pigment profiles. Our results indicate that the cell cycle is light‐controlled and that it differs in the two species. S‐phase was detected during the light period in both, whereas the G2/M phase occurred during the light period in S. ramonii but under dark conditions in S. acuminata. The detection of 4C stages, mobile zygotes (planozygotes), and resting cysts in S. ramonii (nonclonal) provided convincing evidence of sexuality in this species. Sexual related processes were not found in the clonal S. acuminata strain, suggesting its heterothallic behavior (i.e., the need for outcrossing). The differences in the genome size of these species were examined as well. © 2019 The Authors. Cytometry Part A published by Wiley Periodicals, Inc. on behalf of International Society for Advancement of Cytometry.

Comparative Time-Scale Gene Expression Analysis Highlights the Infection Processes of Two Amoebophrya Strains.

Understanding factors that generate, maintain, and constrain host-parasite associations is of major interest to biologists. Although little studied, many extremely virulent micro-eukaryotic parasites infecting microalgae have been reported in the marine plankton. This is the case for Amoebophrya, a diverse and highly widespread group of Syndiniales infecting and potentially controlling dinoflagellate populations. Here, we analyzed the time-scale gene expression of a complete infection cycle of two Amoebophrya strains infecting the same host (the dinoflagellate Scrippsiella acuminata), but diverging by their host range (one infecting a single host, the other infecting more than one species). Over two-thirds of genes showed two-fold differences in expression between at least two sampled stages of the Amoebophrya life cycle. Genes related to carbohydrate metabolism as well as signaling pathways involving proteases and transporters were overexpressed during the free-living stage of the parasitoid. Once inside the host, all genes related to transcription and translation pathways were actively expressed, suggesting the rapid and extensive protein translation needed following host-cell invasion. Finally, genes related to cellular division and components of the flagellum organization were overexpressed during the sporont stage. In order to gain a deeper understanding of the biological basis of the host-parasitoid interaction, we screened proteins involved in host-cell recognition, invasion, and protection against host-defense identified in model apicomplexan parasites. Very few of the genes encoding critical components of the parasitic lifestyle of apicomplexans could be unambiguously identified as highly expressed in Amoebophrya. Genes related to the oxidative stress response were identified as highly expressed in both parasitoid strains. Among them, the correlated expression of superoxide dismutase/ascorbate peroxidase in the specialist parasite was consistent with previous studies on Perkinsus marinus defense. However, this defense process could not be identified in the generalist Amoebophrya strain, suggesting the establishment of different strategies for parasite protection related to host specificity.

Feeding by the harmful phototrophic dinoflagellate Takayama tasmanica (Family Kareniaceae)

The trophic mode of a phototrophic dinoflagellate is a critical factor in the dynamics of its harmful algal bloom. Recent discoveries of the mixotrophic capabilities of phototrophic dinoflagellates have changed the traditional view of bloom dynamics and prediction models. Here, mixotrophy in the harmful phototrophic dinoflagellate Takayama tasmanica was examined. Moreover, growth and ingestion rates of T. tasmanica on each of Alexandrium minutum CCMP1888 and Alexandrium tamarense CCMP1493, suitable prey, were determined as a function of prey concentration. This study reported for the first time that T. tasmanica is a mixotrophic species. Among the phytoplankton species offered as prey, T. tasmanica fed on all prey species whose equivalent spherical diameter (ESD) was greater than 30 μm, but also A. minutum whose ESD was 19 μm. In contrast, T. tasmanica did not feed on the phototrophic dinoflagellates Heterocapsa triquetra, Gymnodinium aureolum, Scrippsiella acuminata (previously S. trochoidea), Cochlodinium polykrikoides, Alexandrium affine, Alexandrium insuetum, and Alexandrium pacificum that its sister species Takayama helix is able to feed on. With increasing mean prey concentration, ingestion rates of T. tasmanica on A. minutum increased, but became saturated at the prey concentrations of >2130 cells mL−1 (1070 ng C mL−1). The maximum ingestion rate (MIR) of T. tasmanica on A. minutum was 0.5 ng C predator−1 d−1 (1.0 cells predator−1 d−1) which is only 64% of the body carbon of a T. tasmanica cell. Growth rates of T. tasmanica on A. minutum were not affected by prey concentrations. Thus, the low maximum ingestion rate is likely to be responsible for the small increases of its growth rate through mixotrophy. In addition, neither growth nor ingestion rates of T. tasmanica feeding on Alexandrium tamarense were affected by prey concentrations. The maximum ingestion rate of T. tasmanica on A. minutum was considerably lower than that of T. helix on the same prey species. Therefore, the mixotrophic ability of T. tasmanica is weaker than that of T. helix, and also T. tasmanica may have an ecological niche different from that of T. helix in marine ecosystems.

Expanding known dinoflagellate distributions: investigations of slurry cultures from Caspian Sea sediment

Abstract To investigate the disparity between plankton and cyst records, sediment slurry cultures were used to isolate the motile stage of dinoflagellates from Caspian Sea sediment. This has resulted in new records for this area of Kryptoperidinium foliaceum, Gymnodinium aureolum and Woloszynskia sp. and for the cyst record, Scrippsiella acuminata. Two Gonyaulax species were isolated, one was identified as Gonyaulax baltica and the other an unknown species. Cultures of Lingulodinium polyedra were also isolated. The approach of using slurries was useful to provide cultures from sediments that were relatively poor in dinoflagellate cysts with contents.

Newly discovered role of the heterotrophic nanoflagellate Katablepharis japonica, a predator of toxic or harmful dinoflagellates and raphidophytes

Heterotrophic nanoflagellates are ubiquitous and known to be major predators of bacteria. The feeding of free-living heterotrophic nanoflagellates on phytoplankton is poorly understood, although these two components usually co-exist. To investigate the feeding and ecological roles of major heterotrophic nanoflagellates Katablepharis spp., the feeding ability of Katablepharis japonica on bacteria and phytoplankton species and the type of the prey that K. japonica can feed on were explored. Furthermore, the growth and ingestion rates of K. japonica on the dinoflagellate Akashiwo sanguinea—a suitable algal prey item—heterotrophic bacteria, and the cyanobacteria Synechococcus sp., as a function of prey concentration were determined. Among the prey tested, K. japonica ingested heterotrophic bacteria, Synechococcus sp., the prasinophyte Pyramimonas sp., the cryptophytes Rhodomonas salina and Teleaulax sp., the raphidophytes Heterosigma akashiwo and Chattonella ovata, the dinoflagellates Heterocapsa rotundata, Amphidinium carterae, Prorocentrum donghaiense, Alexandrium minutum, Cochlodinium polykrikoides, Gymnodinium catenatum, A. sanguinea, Coolia malayensis, and the ciliate Mesodinium rubrum, however, it did not feed on the dinoflagellates Alexandrium catenella, Gambierdiscus caribaeus, Heterocapsa triquetra, Lingulodinium polyedra, Prorocentrum cordatum, P. micans, and Scrippsiella acuminata and the diatom Skeletonema costatum. Many K. japonica cells attacked and ingested a prey cell together after pecking and rupturing the surface of the prey cell and then uptaking the materials that emerged from the ruptured cell surface. Cells of A. sanguinea supported positive growth of K. japonica, but neither heterotrophic bacteria nor Synechococcus sp. supported growth. The maximum specific growth rate of K. japonica on A. sanguinea was 1.01 d−1. In addition, the maximum ingestion rate of K. japonica for A. sanguinea was 0.13ngC predator−1d−1 (0.06 cells predator−1d−1). The maximum ingestion rate of K. japonica for heterotrophic bacteria was 0.019ngC predator−1d−1 (266 bacteria predator−1d−1), and the highest ingestion rate of K. japonica for Synechococcus sp. at the given prey concentrations of up to ca. 107 cells ml−1 was 0.01ngC predator−1d−1 (48 Synechococcus predator−1d−1). The maximum daily carbon acquisition from A. sanguinea, heterotrophic bacteria, and Synechococcus sp. were 307, 43, and 22%, respectively, of the body carbon of the predator. Thus, low ingestion rates of K. japonica on heterotrophic bacteria and Synechococcus sp. may be responsible for the lack of growth. The results of the present study clearly show that K. japonica is a predator of diverse phytoplankton, including toxic or harmful algae, and may also affect the dynamics of red tides caused by these prey species.

Comparative proteomic studies of a Scrippsiella acuminata bloom with its laboratory-grown culture using a 15N-metabolic labeling approach

Comparative proteomic analysis was carried out using cells isolated from a natural bloom of Scrippsiella acuminata (formerly Scrippsiella trochoidea) in the early bloom (EB) and late bloom (LB) stages as well as with laboratory-grown cultures of cells isolated from the bloom in early growth (EG) and late growth (LG) stages. For quantitative proteomics, LG cells were grown for 20 generations in the presence of 15N as a reference (i.e. common denominator) for all comparison. In comparisons with early growth laboratory grown cells (EG/LG), nearly 64% of proteins identified had similar abundance levels, with the remaining 36% mostly more abundant in EG cells. Calvin cycle, amino acid metabolism, chlorophyll biosynthesis and transcription/translation were among the up-regulated processes. Cells from the early bloom (EB/LG) had a greater abundance of transporters and enzymes related to light harvesting and oxidative phosphorylation, while the abundance of these proteins decreased in late bloom cells (LB/LG). All natural bloom samples showed either constant or lower abundance levels of enzymes involved in sugar synthesis and glycolytic pathways compared to laboratory grown cells. Our results represent the first examination of the proteomic changes in the development of a natural dinoflagellate bloom. Importantly, our results demonstrate that the proteome of cells grown in the laboratory is distinctively different from cells in a natural bloom.

Plankton resting stages in recent sediments of Haifa port, Israel (Eastern Mediterranean) - Distribution, viability and potential environmental consequences

Resting stages of plankton were sampled in the surficial sediments in the port of Haifa, Israel, on the eve of a major port enlargement project. We recorded the structure of the assemblages and examined their relationship with different environments within the port. Our findings reveal a remarkably high diversity coupled with low density and the highest number of oligotrich ciliate cyst types recorded from marine sediments. Near the eutrophic and highly polluted zone of the Kishon estuary ciliates were more abundant than elsewhere in the port, whereas dinoflagellates' abundance was reduced, and these trends held true both for full and empty cysts. Some harmful or potentially toxic species, such as Scrippsiella acuminata, were widespread in the port. The toxigenic species include Alexandrium minutum, Gymnodinium uncatenatum and Lingulodinium polyedrum. Active cells of the unarmoured, bloom-forming Akashiwo sanguinea were identified in the cultures obtained from the incubated sediments.