Dinoflagellate Karenia Mikimotoi Research Articles

Relationships between light environment and subsurface accumulation during the daytime in the red-tide dinoflagellate Karenia mikimotoi

Diurnal vertical migration of the red-tide dinoflagellate Karenia mikimotoi and environmental conditions were measured in Hiroshima Bay and the Yatsushiro Sea in July of 2012 and 2015, respectively. The uppermost daytime depths for K. mikimotoi were 1.3–6.0 m and did not correspond to the pycnocline; most cells reached the bottom each night. Although the incident photosynthetic photon flux density (PPFD) varied among days, average PPFDs at the mean cell distribution depths were similar (59–65 µmol m−2 s−1) between compensation and saturation PPFDs for photosynthesis. Total daily PPFD at the mean depth was between the growth threshold and that for maximum growth rates. Among visible wavelengths, the photon flux density of green and yellow light (500–600 nm) at the mean depth was major (about 61% of the total), and the PFD of blue (400–500 nm) was always relatively minor (about 20%). Laboratory results identified green light as sufficient for K. mikimotoi growth, yielding growth rates equivalent to those under blue light. This study suggests that the vertical cell distribution depth during the daytime is regulated by underwater light transmission and that green light is valuable for growth and photosynthesis of K. mikimotoi.

Detrimental impacts of the dinoflagellate Karenia mikimotoi in Fujian coastal waters on typical marine organisms

Blooms of the toxic dinoflagellate Karenia mikimotoi (K. mikimotoi) have occurred frequently in the East China Sea in recent decades and were responsible for massive mortalities of abalones in Fujian coastal areas in 2012, however, little is known about the effects of these blooms on other marine organisms. In this study, the toxic effects and the possible mechanisms of toxicity of K. mikimotoi from Fujian coastal waters on typical marine organisms at different trophic levels, including zooplankton (Brachionus plicatilis, Artemia salina, Calanus sinicus, and Neomysis awatschensis) and aquaculture species (Penaeus vannamei and Scophthalmus maximus) were investigated. At a bloom density of 3×104cells/mL, the Fujian strain of K. mikimotoi significantly affected the tested organisms, which had mortality rates at 96h of 100, 23, 20, 97, 33, and 53%, respectively. Moreover, the intact cell suspension was toxic to all tested species, whereas cell-free culture and the ruptured cell suspension had no significant effects on the tested organisms. Possible mechanisms for this toxic effect, including reactive oxygen species (ROS) and hemolytic toxins, were evaluated. For K. mikimotoi, 0.014±0.004 OD/(104 cells) superoxide (O2−) and 3.00±0.00nmol/(104 cells) hydrogen peroxide (H2O2) were measured, but hydrogen peroxide did not affect rotifers at that concentration, and rotifers were not protected from the lethal effects of K. mikimotoi when the enzymes superoxide dismutase and catalase were added to counteract the ROS. The lipophilic extract of K. mikimotoi had a hemolytic effect on rabbit erythrocytes but exhibited no significant toxicity. These results suggest that this strain of K. mikimotoi can have detrimental effects on several typical marine organisms and that its toxicity may be associated with intact cells but is not related to ROS or hemolytic toxins.

Individual-based modelling of the development and transport of a Karenia mikimotoi bloom on the North-west European continental shelf

In 2006, a large and prolonged bloom of the dinoflagellate Karenia mikimotoi occurred in Scottish coastal waters, causing extensive mortalities of benthic organisms including annelids and molluscs and some species of fish (Davidson et al., 2009). A coupled hydrodynamic-algal transport model was developed to track the progression of the bloom around the Scottish coast during June–September 2006 and hence investigate the processes controlling the bloom dynamics. Within this individual-based model, cells were capable of growth, mortality and phototaxis and were transported by physical processes of advection and turbulent diffusion, using current velocities extracted from operational simulations of the MRCS ocean circulation model of the North-west European continental shelf. Vertical and horizontal turbulent diffusion of cells are treated using a random walk approach. Comparison of model output with remotely sensed chlorophyll concentrations and cell counts from coastal monitoring stations indicated that it was necessary to include multiple spatially distinct seed populations of K. mikimotoi at separate locations on the shelf edge to capture the qualitative pattern of bloom transport and development. We interpret this as indicating that the source population was being transported northwards by the Hebridean slope current from where colonies of K. mikimotoi were injected onto the continental shelf by eddies or other transient exchange processes. The model was used to investigate the effects on simulated K. mikimotoi transport and dispersal of: (1) the distribution of the initial seed population; (2) algal growth and mortality; (3) water temperature; (4) the vertical movement of particles by diurnal migration and eddy diffusion; (5) the relative role of the shelf edge and coastal currents; (6) the role of wind forcing. The numerical experiments emphasized the requirement for a physiologically based biological model and indicated that improved modelling of future blooms will potentially benefit from better parameterisation of temperature dependence of both growth and mortality and finer spatial and temporal hydrodynamic resolution.

Potential impact of an exceptional bloom of Karenia mikimotoi on dissolved oxygen levels in waters off western Ireland

In the summer of 2005 an exceptional bloom of the dinoflagellate Karenia mikimotoi occurred along Ireland's Atlantic seaboard and was associated with the mass mortality of both benthic and pelagic marine life. Oxygen depletion, cellular toxicity and physical smothering, are considered to be the main factors involved in mortality. In this paper we use a theoretical approach based on stoichiometry (the Anderson ratio) and an average K. mikimotoi cellular carbon content of 329pgCcell−1 (n=20) to calculate the carbonaceous and nitrogenous oxygen demand following bloom collapse. The method was validated against measurements of biochemical oxygen demand and K. mikimotoi cell concentration. The estimated potential oxygen utilisation (POU) was in good agreement with field observations across a range of cell concentrations. The magnitude of POU following bloom collapse, with the exception of three coastal areas, was considered insufficient to cause harm to most marine organisms. This indicates that the widespread occurrence of mortality was primarily due to other factors such as cellular toxicity and/or mucilage production, and not oxygen depletion or related phenomena. In Donegal Bay, Kilkieran Bay and inner Dingle Bay, where cell densities were in the order of 106cellsL−1, estimated POU was sufficient to cause hypoxia. Of the three areas, Donegal Bay is considered to be the most vulnerable due to its hydrographic characteristics (seasonally stratified, weak residual flow) and hypoxic conditions (2.2mgL−1 O2) were directly observed in the Bay post bloom collapse. Here, depending on the time of bloom collapse, depressed DO levels could persist for weeks and continue to have a potentially chronic impact on the Bay.

RNA Sequencing Revealed Numerous Polyketide Synthase Genes in the Harmful Dinoflagellate Karenia mikimotoi.

The dinoflagellate Karenia mikimotoi forms blooms in the coastal waters of temperate regions and occasionally causes massive fish and invertebrate mortality. This study aimed to elucidate the toxic effect of K. mikimotoi on marine organisms by using the genomics approach; RNA-sequence libraries were constructed, and data were analyzed to identify toxin-related genes. Next-generation sequencing produced 153,406 transcript contigs from the axenic culture of K. mikimotoi. BLASTX analysis against all assembled contigs revealed that 208 contigs were polyketide synthase (PKS) sequences. Thus, K. mikimotoi was thought to have several genes encoding PKS metabolites and to likely produce toxin-like polyketide molecules. Of all the sequences, approximately 30 encoded eight PKS genes, which were remarkably similar to those of Karenia brevis. Our phylogenetic analyses showed that these genes belonged to a new group of PKS type-I genes. Phylogenetic and active domain analyses showed that the amino acid sequence of four among eight Karenia PKS genes was not similar to any of the reported PKS genes. These PKS genes might possibly be associated with the synthesis of polyketide toxins produced by Karenia species. Further, a homology search revealed 10 contigs that were similar to a toxin gene responsible for the synthesis of saxitoxin (sxtA) in the toxic dinoflagellate Alexandrium fundyense. These contigs encoded A1–A3 domains of sxtA genes. Thus, this study identified some transcripts in K. mikimotoi that might be associated with several putative toxin-related genes. The findings of this study might help understand the mechanism of toxicity of K. mikimotoi and other dinoflagellates.

Drivers and effects of Karenia mikimotoi blooms in the western English Channel

Naturally occurring red tides and harmful algal blooms (HABs) are of increasing importance in the coastal environment and can have dramatic effects on coastal benthic and epipelagic communities worldwide. Such blooms are often unpredictable, irregular or of short duration, and thus determining the underlying driving factors is problematic. The dinoflagellate Karenia mikimotoi is an HAB, commonly found in the western English Channel and thought to be responsible for occasional mass finfish and benthic mortalities. We analysed a 19-year coastal time series of phytoplankton biomass to examine the seasonality and interannual variability of K. mikimotoi in the western English Channel and determine both the primary environmental drivers of these blooms as well as the effects on phytoplankton productivity and oxygen conditions. We observed high variability in timing and magnitude of K. mikimotoi blooms, with abundances reaching >1000cellsmL−1 at 10m depth, inducing up to a 12-fold increase in the phytoplankton carbon content of the water column. No long-term trends in the timing or magnitude of K. mikimotoi abundance were evident from the data. Key driving factors were identified as persistent summertime rainfall and the resultant input of low-salinity high-nutrient river water. The largest bloom in 2009 was associated with highest annual primary production and led to considerable oxygen depletion at depth, most likely as a result of enhanced biological breakdown of bloom material; however, this oxygen depletion may not affect zooplankton. Our data suggests that K. mikimotoi blooms are not only a key and consistent feature of western English Channel productivity, but importantly can potentially be predicted from knowledge of rainfall or river discharge.

The role of hydrographic parameters, measured from a ship of opportunity, in bloom formation of Karenia mikimotoi in the English Channel

Unusually high chlorophyll values (~14mgChlm−3 at 5m depth), recorded on a ship of opportunity (SOO) in July 2010, indicated the occurrence of a potential Harmful Algal Bloom (HAB) in the Western approaches of the English Channel. This bloom, located at 49.7°N, 3.2°W was observed via complementary datasets. These included data from samples collected for microscopic phytoplankton identification, information from satellite maps to follow geographical bloom development and in situ data to identify hydrographic factors related to bloom initiation. The relationships between chlorophyll-fluorescence, temperature, salinity and wind speed were examined. The intense summer bloom predominantly consisted of the dinoflagellate Karenia mikimotoi and followed an increase in sea surface temperature (to 18.5°C). A mid-channel bloom of this magnitude along the SOO route was last seen in 2003. In both years the peak biomass was associated with K. mikimotoi blooms, which occurred at the same location and coincided with the least saline, warmest water and lowest wind speeds. This study demonstrates that ships of opportunity are a useful tool to identify and track HAB events through continuous in situ measurements and for the frequent sampling opportunities that they provide.

Phytoplankton and pigment studies in the Bay of Biscay and English Channel

During the final year (2010) of the MV Pride of Bilbao (PoB) ferry operation between Portsmouth (UK) and Bilbao (Spain) a comprehensive phytoplankton data set was collected based on pigments and taxonomy measurements. The work was in support of the EU project ProTool (http://www.protool-project.eu) that aimed to develop an automated system for measuring primary productivity from ships of opportunity. Not unexpectedly, the biological patterns relate to the hydrographic conditions and in general, pigment distributions are indicative of the taxonomy. A predominately diatom bloom was observed in the Bay of Biscay in April, with a mixed population of diatoms, dinoflagellates and coccolithophores throughout the spring and summer, and a very distinctive bloom, which contained a large proportion of the dinoflagellate Karenia Mikimotoi, to the stratified side of the Ushant Front in mid-July.

Monitoring and trends in harmful algal blooms and red tides in Korean coastal waters, with emphasis on Cochlodinium polykrikoides

Red tides have a long history in Korea with the first record in AD 161, and a total of 38 red tide events reported from AD 161 to 1820. Since the 1980s, the frequency of red tide events has increased and the red tide area has expanded. From 1972 to 2001, 1330 red tide events occurred, and 273 (20.5%) were caused by fish killing dinoflagellates, mostly since the mid 1990s. Overall, the diatom Skeletonema costatum and the dinoflagellate Karenia mikimotoi were dominant HAB species in the 1970s and 1980s. However, the dominant red tide species changed to the dinoflagellates Cochlodinium polykrikoides and Ceratium spp. and the raphidophytes Chattonella spp. in the 1990s and 2000s. In addition, the dinoflagellate Akashiwo sanguinea and Heterosigma akashiwo have been major components during red tides the past four decades. After 1995, when a massive C. polykrikoides bloom occurred, the National Fisheries Research and Development Institute (NFRDI) and local governments began monitoring red tides nationwide. Along with the NFRDI, more than 30 fisheries extension service stations under local governments monitor red tides. The National Maritime Police Agency monitors the movement of red tides using aerial surveillance with helicopters. Paralytic shellfish poisoning events are also monitored by the red tide monitoring network system of NFRDI and local governments. We reviewed here historical records of red tides in Korea, red tide monitoring systems, trends in frequency of occurrence of red tide events, and red tide causative species in Korean waters. Red tide dynamics and physical–environmental factors potentially related to C. polykrikoides red tides are also discussed; red tides caused by C. polykrikoides along Korean coasts have decreased sharply starting from 2008 after achieving a high density bloom annually from 1995 to 2007.

Drag increase and drag reduction found in phytoplankton and bacterial cultures in laminar flow: Are cell surfaces and EPS producing rheological thickening and a Lotus-leaf Effect?

The laminar-flow viscosity of ocean and other natural waters consists of a Newtonian aqueous component contributed by water and salts, and a non-Newtonian one contributed mainly by exopolymeric polymers (EPS) derived largely from planktonic algae and bacteria. Phytoplankton and EPS form thin layers in stratified waters, often associated with density discontinuities. A recent model (Jenkinson and Sun, 2011. J. Plankton Res., 33, 373–383) investigated possible thalassorheological control of pycnocline thickness (PT) by EPS secreted by the harmful dinoflagellate Karenia mikimotoi. The model, based on published measurements of viscosity increase by this species, found that whether it can influence PT depends on the relationship between increased viscosity, deformation rates/stresses and length scale, which the present work has investigated. To do this, flow rate vs. hydrostatic pressure (and hence wall stress) was measured in cultures (relative to that in reference water) in capillaries of 5 radii 0.35–1.5mm, close to oceanic-turbulence Kolmogorov length. We compared cultures of the potentially harmful algae, K. mikimotoi, Alexandrium catenella, Prorocentrum donghaiense, Skeletonema costatum, Phaeodactylum tricornutum and the bacterium Escherichia coli. Drag increase, ascribed to rheological thickening by EPS, occurred in the smallest capillaries, but drag reduction (DR) occurred in the largest ones. Since this occurred at Reynolds numbers Re too small for turbulence (or turbulent DR) to occur, this was laminar-flow DR. It may have been superhydrophobic DR (SDR), associated with the surfaces of the plankton and bacteria. SDR is associated with the self-cleaning Lotus-leaf Effect, in which water and dirt are repelled from surfaces bearing nm- to µm-sized irregularities coated with hydrophobic polymers. Because DR decreased measured viscosity and EPS thickening increased it, we could not validate the model. DR, however, represents hitherto unknown phenomenon in the oceans. Along with rheological thickening, Laminar-Flow DR may represent a new tool for plankton to manage ambient flow fields.

Possible involvement of hemolytic activity in the contact-dependent lethal effects of the dinoflagellate Karenia mikimotoi on the rotifer Brachionus plicatilis

We investigated the effects of two strains (SUO-1 and FUK) of the dinoflagellate Karenia mikimotoi on the rotifer Brachionus plicatilis. The SUO-1 strain was highly toxic to rotifers, whereas the FUK strain was less toxic. After 10-h incubations, the survivorship of rotifers exposed to SUO-1 and FUK was 20% and 95%, respectively. Both the cell-free culture supernatant and the ruptured cell suspension prepared from these strains were not toxic to rotifers. Furthermore, when direct contact between K. mikimotoi and rotifers was interrupted with a cell-impermeable membrane (3-μm pores), the toxicity of both the SUO-1 and FUK strains of K. mikimotoi to rotifers were completely inhibited even after a 24-h exposure. Cell suspensions of SUO-1 showed hemolytic activity toward horse erythrocytes, but the FUK strain did not. The cell-free supernatant and the ruptured cell suspension of SUO-1 showed no significant hemolytic activity. These results suggest that this highly toxic strain of K. mikimotoi causes lethality in rotifers by direct contact in which live cell-mediated hemolytic activity might be a contributing factor.

Detection and quantification of Karenia mikimotoi using real-time nucleic acid sequence-based amplification with internal control RNA (IC-NASBA)

Nucleic acid sequence-based amplification (NASBA) is an isothermal method used to amplify RNA and has been used for clinical, environmental, and food testing applications. Quantification of RNA by real-time NASBA occurs by comparing time to positive (TTP) fluorescence values, similar to threshold cycle (Ct) values in PCR, of unknown samples to a standard curve of known RNA titers. Incorporation of an internal control RNA molecule (IC-RNA) has been used to increase precision and accuracy of real-time NASBA and also serves as an indicator of NASBA inhibition. A real-time IC-NASBA assay was developed targeting the ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO) large-subunit gene ( rbcL) of the harmful algal bloom (HAB) causing dinoflagellate Karenia mikimotoi. This assay is sensitive to one K. mikimotoi cell and 1 × 10 3 copies of in vitro transcript with a high degree of specificity against closely related organisms. Enumeration of K. mikimotoi from environmental samples by IC-NASBA was not significantly different from microscopic cell counts ( P = 0.156, α = 0.05) performed by the Fish and Wildlife Research Institute (FWRI, a division of the Fish and Wildlife Conservation Commission, St. Petersburg, FL), the agency responsible for monitoring red tide status throughout the state. In addition, the IC-NASBA enumeration had a good linear relationship ( r 2 = 0.887) with FWRI microscopic cell counts. IC-NASBA is an alternative method for the rapid and reliable detection and quantification of K. mikimotoi from marine waters.

Complexation of iron by microbial siderophores and effects of iron chelates on the growth of marine microalgae causing red tides

SUMMARYThe growth rates of 13 species of abundant red tide algae in media with different iron species complexed with microbial siderophores (Ferrichrome and Ferrioxamine) and Fe‐Catechol were investigated. Our study demonstrated that the Fe‐chelates (at molar ratios = 1:1) were bioavailable to some red tide species. In Fe‐Catechol medium, growth was observed for the raphidophyte Heterosigma akashiwo, the dinoflagellates Heterocapsa circularisquama and Heterocapsa triquetra, the diatom Ditylum brightwellii, the cryptophyte Rhodomonas ovalis, the chlorophyte Oltmannsiellopsis viridis, and the haptophyte Cricosphaera roscoffensis. In Ferrioxamine medium, we found the growth of the dinoflagellate Karenia mikimotoi, the diatom Ditylum brightwellii, and the cryptophyte Rhodomonas ovalis. But, the existence of higher ligand concentrations (molar ratios ≥ 1:10) decreased the growth rates of most red tide species that were examined. Furthermore, all red tide species examined were not able to grow in Ferrichrome medium. In particular, the Chattonella species examined did not grow in the presence of Fe‐chelates. These results suggest that bioavailability of iron depends not only on ligand species, but also on the concentration of the ligands; moreover, microbial siderophores may play an important role in controlling the uptake of iron complexed with organic materials that exist in coastal water and the formation of red tides in coastal areas.

Production of Superoxide Anion and Hydrogen Peroxide by the Red Tide Dinoflagellate Karenia mikimotoi

We found that the red tide dinoflagellate Karenia mikimotoi ( Gymnodinium mikimotoi ) generates reactive oxygen species (ROS). In chemiluminescence analysis using an O 2 − specific probe, a slightly lower but significant level of O 2 − was detected in a K. mikimotoi cell suspension as compared to one containing Chattonella marina , a well-known ROS-producing red tide phytoplankton. Interestingly, the chemiluminescence response pattern caused by K. mikimotoi was different from that of C. marina , although both responses were almost completely abolished in the presence of superoxide dismutase (SOD). By fluorescence spectrophotometric analysis, H 2 O 2 was also detected in the K. mikimotoi cell suspension, but the level of H 2 O 2 was approximately 10% of that in the C. marina suspension based on the cell number. No significant increase in O 2 − generation by K. mikimotoi was observed in the presence of lectins such as concanavalin A (Con A) and wheat germ agglutinin (WGA) or fish mucus substances prepared from the skin and gills of yellowtail, whereas C. marina generated an increased level of O 2 − in response to these stimuli. Furthermore, O 2 − production in C. marina , but not in K. mikimotoi , was inhibited by treatment with proteinase K.