Development of compound microsatellite markers in the harmful red tide species Chattonella ovata (Raphidophyceae)

We isolated 12 polymorphic microsatellites from the noxious red‐tide‐causing alga Chattonella ovata. These loci provide a class of highly variable genetic markers, as the number of alleles ranged from four to 12, and the observed and expected heterozygosities ranged from 0.238 to 0.850 and from 0.310 to 0.889, respectively. These loci are useful for revealing the genetic structure of and gene flow among C. ovata populations.     

Development of microsatellite markers for the red tide‐forming harmful species Chattonella antiqua,C. marina,and C. ovata (Raphidophyceae)

We have developed 11 microsatellite markers that are specific to Chattonella antiqua, C. marina, and C. ovata, the red tide‐forming harmful phytoplanktons. The 11 loci were amplified in the three species. The number of alleles per locus ranged from 5 to 16. The three species shared most microsatellite regions, although the genetic differences in specific loci were detected among them. These markers of the Chattonella species will be beneficial for biogeographical, detailed taxonomic, studies.     

Mixotrophy among Dinoflagellates1

Mixotrophy, used herein for the combination of phototrophy and phagotrophy, is widespread among dinoflagellates. It occurs among most, perhaps all, of the extant orders, including the Prorocentrales, Dinophysiales. Gymnodiniales, Noctilucales, Gonyaulacales, Peridiniales, Blastodiniales. Phytodiniales, and Dinamoebales. Many cases of mixotrophy among dinoflagellates are probably undocumented. Primarily photosynthetic dinoflagellates with their “own” plastids can often supplement their nutrition by preying on other cells. Some primarily phagotrophic species are photosynthetic due to the presence of kleptochloroplasts or algal endosymbionts. Some parasitic dinoflagellates have plastids and are probably mixotrophic. For most mixotrophic dinoflagellates, the relative importance of photosynthesis, uptake of dissolved inorganic nutrients, and feeding are unknown. However, it is apparent that mixotrophy has different functions in different physiological types of dinoflagellates. Data on the simultaneous regulation of photosynthesis, assimilation of dissolved inorganic and organic nutrients, and phagotophy by environmental parameters (irradiance. availablity of dissolved nutrients, availability of prey) and by life history events are needed in order to understand the diverse roles of mixotrophy in dinoflagellates.     

Mixotrophy in the phototrophic harmful alga Cochlodinium polykrikoides (Dinophycean): prey species, the effects of prey concentration, and grazing impact

We first reported here that the harmful alga Cochlodinium polykrikoides, which had been previously known as an autotrophic dinoflagellate, was a mixotrophic species. We investigated the kinds of prey species and the effects of the prey concentration on the growth and ingestion rates of C. polykrikoides when feeding on an unidentified cryptophyte species (Equivalent Spherical Diameter, ESD = 5.6 microm). We also calculated grazing coefficients by combining field data on abundances of C. polykrikoides and co-occurring cryptophytes with laboratory data on ingestion rates obtained in the present study. Cocholdinium polykrikoides fed on prey cells by engulfing the prey through the sulcus. Among the phytoplankton prey offered, C. polykrikoides ingested small phytoplankton species that had ESD's < or = 11 microm (e.g. the prymnesiophyte Isochrysis galbana, an unidentified cryptophyte, the cryptophyte Rhodomonas salina, the raphidophyte Heterosigma akashiwo, and the dinoflagellate Amphidinium carterae). It did not feed on larger phytoplankton species that had ESD's > or = 12 microm (e.g. the dinoflagellates Heterocapsa triquetra, Prorocentrum minimum, Scrippsiella sp., Alexandrium tamarense, Prorocentrum micans, Gymnodinium catenatum, Akashiwo sanguinea, and Lingulodinium polyedrum). Specific growth rates of C. polykrikoides on a cryptophyte increased with increasing mean prey concentration, with saturation at a mean prey concentration of approximately 270 ng C ml(-1) (i.e. 15,900 cells ml(-1)). The maximum specific growth rate (mixotrophic growth) of C. polykrikoides on a cryptophyte was 0.324 d(-1), under a 14:10 h light-dark cycle of 50 microE m(-2) s(-1), while its growth rate (phototrophic growth) under the same light conditions without added prey was 0.166 d(-1). Maximum ingestion and clearance rates of C. polykrikoides on a cryptophyte were 0.16 ng C grazer(-1)d(-1) (9.4 cells grazer(-1)d(-1)) and 0.33 microl grazer(-1)h(-1), respectively. Calculated grazing coefficients by C. polykrikoides on cryptophytes were 0.001-0.745 h(-1) (i.e. 0.1-53% of cryptophyte populations were removed by a C. polykrikoides population in 1 h). The results of the present study suggest that C. polykrikoides sometimes has a considerable grazing impact on populations of cryptophytes.     

Feeding by common heterotrophic protists on the mixotrophic alga Gymnodinium smaydae (Dinophyceae), one of the fastest growing dinoflagellates

Gymnodinium smaydae is one of the fastest growing dinoflagellates. However, its population dynamics are affected by both growth and mortality due to predation. Thus, feeding by common heterotrophic dinoflagellates Gyrodinium dominans , Gyrodinium moestrupii , Oblea rotunda , Oxyrrhis marina , and Polykrikos kofoidii , and the naked ciliate Pelagostrobilidium sp. on G. smaydae was investigated in the laboratory. Furthermore, growth and ingestion rates of O. marina , G. dominans , and Pelagostrobilidium sp. on G. smaydae in response to prey concentration were also determined. Oxyrrhis marina , G. dominans , G. moestrupii , and Pelagostrobilidium sp. were able to feed on G. smaydae , but P. kofoidii and O. rotunda did not feed on this dinoflagellate. The maximum growth rate of O. marina on G. smaydae was 0.411 per day. However, G. smaydae did not support the positive growth of Pelagostrobilidium sp. The maximum ingestion rates of O. marina and Pelagostrobilidium sp. on G. smaydae were 0.27 and 6.91 ng C · predator^?1 · d^?1, respectively. At the given mean prey concentrations, the highest growth and ingestion rates of G. dominans on G. smaydae were 0.114 per day and 0.04 ng C · predator^?1 · d^?1, respectively. The maximum growth and ingestion rates of O. marina on G. smaydae are lower than those on most of the other algal prey species. Therefore, O. marina may be an effective predator of G. smaydae , but G. smaydae may not be the preferred prey for supporting high growth of the predator in comparison to other species as inferred from a literature survey.     

Differential feeding by common heterotrophic protists on four Scrippsiella species of similar size

The dinoflagellate genus Scrippsiella is known to cause red tides. Mortality due to predation should be assessed in order to understand the population dynamics of Scrippsiella species. However, predation has been explored only in a few species. In this study, we examined feeding by common heterotrophic dinoflagellates Oxyrrhis marina, Gyrodinium dominans, Polykrikos kofoidii, Oblea rotunda, and Pfiesteria piscicida, and a ciliate Strombidinopsis sp., on four Scrippsiella species, of similar size, namely Scrippsiella acuminata, Scrippsiella donghaiensis, Scrippsiella lachrymosa, and Scrippsiella masanensis. All the heterotrophic protists tested could feed on all the four Scrippsiella species. However, the numerical and functional responses of P. kofoidii to the mean prey concentration were apparently different between the Scrippsiella species. With increasing prey concentration, the growth and ingestion rates of P. kofoidii on S. lachrymosa increased rapidly, and then saturated similar to those on S. acuminata, as previously reported, but those on S. donghaiensis continuously decreased. The cells of S. donghaiensis lysed P. kofoidii cells. In contrast, the growth and ingestion rates of P. kofoidii on S. masanensis were not significantly related to the prey concentration. At similarly high mean prey concentration, the growth and ingestion rates of G. dominans were significantly different between the four Scrippsiella species Therefore, differences in the growth and/or ingestion rates of G. dominans and P. kofoidii on the four Scrippsiella species might result in different ecological niches of both the predator and prey species.     

Growth and Grazing Rates of the Heterotrophic Dinoflagellate Polykrikos kofoidii on Red-Tide and Toxic Dinoflagellates

We investigated growth rates, grazing rates, and prey selection of Polykrikos kofoidii when feeding on several species of red-tide and/or toxic dinoflagellates. Polykrikos kofoidii ingested all prey species used in this study, exhibiting positive growth on Lingulodinium polyedrum, Scrippsiella trochoidea, Ceratium furca, Gymnodinium catenatum, Gyrodinium impudicum, Prorocentrum micans, and the toxic dinoflagellate Amphidinium carterae, but not on P. minimum. Specific growth rates of P. kofoidii increased rapidly with increasing density of L. polyedrum, S. trochoidea, C. furca, and G. catenatum before saturating between 500-2,000 ng C ml(-1). Specific growth rates increased continuously when P. kofoidii was fed the other prey species. Maximum specific growth rates of P. kofoidii on G. catenatum (1.12 d(-1)), S. trochoidea (0.97 d(-1)), and L. polyedrum (0.83 d(-1)) were higher than those on C. furca (0.35 d(-1)), A. carterae (0.10 d(-1)), P. micans (0.06 d(-1)), G. impudicum (0.06 d(-1)), and P. minimum (-0.03 d(-1)). Threshold prey concentrations (where net growth = 0) were 54-288 ng C ml(-1). Maximum ingestion and clearance rates of P. kofoidii on these dinoflagellates were 5-24 ng C pseudocolony(-1) d(-1) and 1.0-5.9 microl pseudocolony(-1) h(-1), respectively. Polykrikos kofoidii strongly selected L. polyedrum over S. trochoidea in prey mixtures. Polykrikos kofoidii exhibited higher maximum growth, ingestion, and clearance rates than previously reported for the mixotrophic dinoflagellate Fragilidium cf. mexicanum or the heterotrophic dinoflagellates Protoperidinium cf. divergens and P. crassipes, when grown on the same prey species. Grazing coefficients calculated by combining field data on abundances of Polykrikos spp. and co-occurring red-tide dinoflagellate prey with laboratory data on ingestion rates obtained in the present study suggest that Polykrikos spp. sometimes have a considerable grazing impact on prey populations.     

Relationships between dynamics of red tide-causing raphidophycean flagellates and algicidal micro-organisms in the coastal sea of Japan

Temporal fluctuations of algicidal micro-organisms against the red tide causing raphidophycean flagellates Chattonella antiqua (Hada) Ono and Heterosigma akashiwo (Hada) Hada ex Hara et Chihara were investigated using the microplate most probable number (MPN) method in northern Hiroshima Bay and Harima-Nada, the Seto Inland Sea, in 1992 and 1993. In Har-ima-Nada, both flagellates appeared at low levels (< 1 cell mL^?1), and killer micro-organisms against the two flagellates (C-killer for C. antiqua and H-killer for H. akashiwo) also appeared at low densities (< 2 mL^?1). In northern Hiroshima Bay, C. antiqua cells were scarce (< 1 cell mL^?1), and C-killers occurred at a low level (≤ 3.4 mL^?1). Conversely, red tides of H. akashiwo occurred there in June of both years. The dynamics of H-killers revealed a close relationship with that of H. akashiwo populations. H-killers followed the increase of H. akashiwo cells, reached a maximum level after the beginning of decline of H. akashiwo, maintained a high level for at least 1 week after the crash of bloom, and then decreased. C-killers consistently remained at low densities during the period of H. akashiwo red tides in both 1992 and 1993. Hence, algicidal micro-organisms specifically associated with the occurrence and crash of H. akashiwo red tides, and presumably contributed to the rapid termination of the red tides in the coastal seas such as northern Hiroshima Bay.     

ALGICIDAL BACTERIA ACTIVE AGAINST GYMNODINIUM BREVE (DINOPHYCEAE). I. BACTERIAL ISOLATION AND CHARACTERIZATION OF KILLING ACTIVITY1,3

Interactions between bacteria and species of harmful and/or toxic algae are potentially important factors affecting both the population dynamics and the toxicity of these algae. Recent reports of bacteria lethal to certain harmful algal bloom (HAB) species, coupled with a rapidly evolving interest in attempting to minimize the adverse effects of HABs through various prevention, control, and mitigation strategies, have focused attention on defining the role of algicidal bacteria in bloom termination. The aim of the present study was to determine whether algicidal bacteria active against Gymnodinium breve Davis, a dinoflagellate responsible for frequent and protracted red tides in the Gulf of Mexico, are present in the waters of the west Florida shelf. To date, we have isolated two bacterial strains from this region lethal to G. breve and have begun to characterize the algicidal activity of one of these strains, 41-DBG2. This bacterium, a yellow-pigmented, gram-negative rod, was isolated from waters containing no detectable G. breve cells, suggesting that such bacteria are part of the ambient microbial community and are not restricted to areas of high G. breve abundance. Strain 41-DBG2 produced a dissolved algicidal compound(s) that was released into the growth medium, and the algicide was effective against the four Gulf of Mexico G. breve isolates tested as well as a closely related HAB species that also occurs in this region, Gymnodinium mikimotoi Miyake et Kominami ex Oda. Nonetheless, data showing that a nontoxic isolate of Gymnodinium sanguineum Hirasaka from Florida Bay was not affected indicate that the algicidal activity of this bacterium does exhibit a degree of taxonomic specificity. Our efforts are currently being directed at resolving several critical issues, including the identity of the algicide(s), the mechanisms regulating its production and ability to discriminate between target algal species, and how the growth rate of 41-DBG2 is affected by the presence of G. breve cells. We have also proposed a conceptual model for interactions between algicidal bacteria and their target species to serve as a testable framework for ensuing field studies.     

Feeding by the newly described, nematocyst-bearing heterotrophic dinoflagellate Gyrodiniellum shiwhaense

We explored the feeding ecology of the newly described, nematocyst-bearing heterotrophic dinoflagellate Gyrodiniellum shiwhaense (GenBank accession number=FR720082). Using several different types of microscopes and high-resolution video-microscopy, we investigated feeding behavior and types of prey species that G. shiwhaense feeds upon. Additionally, we measured its growth and ingestion rates on its optimal algal prey, the cryptophyte Teleaulax sp. and the dinoflagellate Amphidinium carterae, as a function of prey concentration. These rates were measured for other edible prey at single prey concentrations at which the growth and ingestion rates of G. shiwhaense were saturated. After anchoring the prey with a tow filament, G. shiwhaense fed using a peduncle, ingesting small algal species with equivalent spherical diameters (ESDs) of <13 μm. However, it did not feed on larger algal species that had ESDs≥13 μm or the small diatom Skeletonema costatum. The specific growth rates for G. shiwhaense feeding upon Teleaulax sp. and A. carterae increased rapidly with increasing mean prey concentration before saturating at concentrations of ca. 180-430 ng C/ml. The maximum specific growth rate of G. shiwhaense on Teleaulax sp. and A. carterae were 1.05 and 0.82/d, respectively. However, Heterosigma akashiwo did not support positive growth of G. shiwhaense. The maximum ingestion rates of G. shiwhaense on Teleaulax sp. and A. carterae were 0.35 and 0.54 ng C/grazer/d, respectively. The calculated grazing coefficients attributable to G. shiwhaense on co-occurring cryptophytes and Amphidinium spp. were 0.01-1.87/d and 0.08-2.60/d, respectively. Our results suggest that G. shiwhaense can have a considerable grazing impact on algal populations.     

Feeding by the Pfiesteria-like heterotrophic dinoflagellate Luciella masanensis

To explore the feeding ecology of the Pfiesteria-like dinoflagellate (PLD) Luciella masanensis (GenBank Accession no. AM050344, previously Lucy), we investigated the feeding behavior and the kinds of prey species that L. masanensis fed on and determined its growth and ingestion rates of L. masanensis when it fed on the dinoflagellate Amphidinium carterae and an unidentified cryptophyte species (equivalent spherical diam., ESD=5.6 microm), which were the dominant phototrophic species when L. masanensis and similar small heterotrophic dinoflagellates were abundant in Masan Bay, Korea in 2005. Additionally, these parameters were also measured for L. masanensis fed on blood cells of the perch Lateolabrax japonicus and the raphidophyte Heterosigma akashiwo in the laboratory. Luciella masanensis fed on prey cells by using a peduncle after anchoring the prey with tow filament, and was able to feed on diverse prey such as cryptophytes, raphidophytes, diatoms, mixotrophic dinoflagellates, and the blood cells of fish and humans. Among the prey species tested in the present study, perch blood cells were observed to be the optimal prey for L. masanensis. Specific growth rates of L. masanensis feeding on perch blood cells, A. carterae, H. akashiwo, and the cryptophyte, either increased continuously or became saturated with increasing the mean prey concentration. The maximum specific growth rate of L. masanensis feeding on perch blood cells (1.46/day) was much greater than that of A. carterae (0.59/day), the cryptophyte (0.24/day), or H. akashiwo (0.20/day). The maximum ingestion rate of L. masanensis on perch blood cells (2.6 ng C/grazer/day) was also much higher than that of A. carterae (0.32 ng C/grazer/day), the cryptophyte (0.44 ng C/grazer/day), or H. akashiwo (0.16 ng C/grazer/day). The kinds of prey species which L. masanensis is able to feed on were the same as those of Pfiesteria piscicida, but very different from those of another PLD Stoeckeria algicida. However, the maximum growth and ingestion rates of L. masanensis on perch blood cells, A. carterae, H. akashiwo, and the cryptophyte were considerably lower than those of P. piscicida. Therefore, these three dinoflagellates may occupy different ecological niches in marine planktonic communities, even though they have a similar size and shape and the same feeding mechanisms.     

Feeding by Heterotrophic Dinoflagellates and Ciliates on the Free‐living Dinoflagellate Symbiodinium sp. (Clade E)

To investigate heterotrophic protists grazing on Symbiodinium sp., we tested whether the common heterotrophic dinoflagellates Gyrodinium dominans, Gyrodinium moestrupii, Gyrodinium spirale, Oblea rotundata, Oxyrrhis marina, and Polykrikos kofoidii and the ciliates Balanion sp. and Parastrombidinopsis sp. preyed on the free‐living dinoflagellate Symbiodinium sp. (clade E). We measured the growth and ingestion rates of O. marina and G. dominans on Symbiodinium sp. as a function of prey concentration. Furthermore, we compared the results to those obtained for other algal prey species. In addition, we measured the growth and ingestion rates of other predators at single prey concentrations at which these rates of O. marina and G. dominans were saturated. All predators tested in the present study, except Balanion sp., preyed on Symbiodinium sp. The specific growth rates of O. marina and G. dominans on Symbiodinium sp. increased rapidly with increasing mean prey concentration < ca. 740–815 ng C/ml (7,400–8,150 cells/ml), but became saturated at higher concentrations. The maximum growth rates of O. marina and G. dominans on Symbiodinium sp. (0.87 and 0.61/d) were much higher than those of G. moestrupii and P. kofoidii (0.11 and 0.04/d). Symbiodinium sp. did not support positive growth of G. spirale, O. rotundata, and Parastrombidinopsis sp. However, the maximum ingestion rates of P. kofoidii and Parastrombidinopsis sp. (6.7–10.0 ng C/predator/d) were much higher than those of O. marina and G. dominans on Symbiodinium sp. (1.9–2.1 ng C/predator/d). The results of the present study suggest that Symbiodinium sp. may increase or maintain the populations of some predators.     

Response of growth and photosynthesis of marine red tide alga Heterosigma akashiwo to iron and iron stress condition

Heterosigma akashiwo, a red tide alga, was grown in Fe-deficient and Fe-replete batch cultures. Cell final yields and the growth rate were limited when Fe was below 10 nM and alleviated with 100 nM Fe. By comparison with the results under Fe-replete conditions, chlorophyll a-specific and cell-specific light saturated net photosynthetic capacity (P_m ^{chl a} and P_m ^cell), dark respiration rate (R_d ^{chl a} and R_d ^cell) and apparent photosynthetic efficiency (^{chl a} and ^cell) decreased proportionately, whereas the cells became light saturated at higher irradiance under Fe stress (Fe-limited conditions).     

The Ecological Roles of Heterotrophic Dinoflagellates in Marine Planktonic Community1

Heterotrophic dinoflagellates are ubiquitous and often abundant protists in marine environments. Recently, several novel predator-prey relationships between heterotrophic dinoflagellates and other planktonic organisms have been discovered and shown to have diverse ecological roles. Heterotrophic dinoflagellates are predators on a wide array of prey items, including phytoplankton, copepod eggs, and early naupliar stages. They are in turn important prey for some metazoa. Some heterotrophic dinoflagellates are predators of and simultaneously prey for other dinoflagellates. These newly discovered predator-prey relationships may influence our conventional view of energy flow and carbon cycling in the marine planktonic community.     

Florida red tide knowledge and risk perception: Is there a need for tailored messaging

Harmful algal blooms of the toxic dinoflagellate, Karenia brevis, occur throughout the Gulf of Mexico. Recent research efforts sponsored by the National Institute of Environmental Health Sciences (NIEHS) and others found that Florida red tide causes both acute and possibly chronic health effects from the toxic aerosols. Florida red tide also demonstrated significant social and economic impacts to both coastal residents and visitors. In conjunction with the research, persistent outreach efforts were conducted over the 11-year period. The goal of this project was to assess potential needs for tailored messaging needed among different red tide information user groups. Survey participants included 303 local residents, both with asthma and without, and ‘snowbirds (seasonal residents that reside in the Sarasota area for more than 3 months but less than 6 months/year), also both with asthma and without. The questionnaire assessed Florida red tide knowledge and risk perception regarding Florida red tide using items drawn from two previously published surveys to allow comparison. Our results reveal that overall knowledge of Florida red tide has not changed. We found that knowledge was consistent across our selected groups and also did not vary by age, gender and education level. However, knowledge regarding consumption of seafood during Florida red tide has declined. Risk perception increased significantly for people who have asthma. Individuals responsible for public health communication regarding Florida red tide and human health concerns need to continue to pursue more effective outreach messages and delivery methods.     

中国赤潮的发生趋势和研究进展

通过对中国沿海赤潮发生历史的回顾以及主要赤潮事件的分析,阐明了中国沿海赤潮发生所呈现的趋势,即频率增加,规模扩大,新的赤潮藻种不断出现,有毒赤潮种比例上升,以及有害赤潮危害程度日益增加,且初步分析了赤潮频发的内因和外因,综述了我国科学家在赤潮生消过程监测,赤潮灌的培养生物学和分类学,赤潮藻类的营养动力学及生理生态学特性,赤潮藻类的生活史,赤潮藻类毒素,赤潮的模型和赤潮防治及国际合作等方面工作的进展,指出了研究还存在的不足之处,并对未来赤潮研究和管理提出了建议。     

Occurrence of the polyamines caldopentamine and homocaldopentamine in axenic cultures of the red tide flagellates Chattonella antiqua and Heterosigma akashiwo (Raphidophyceae)

The polyamines caldopentamine and homocaldopentamine were detected in axenic strains of Chattonella antiqua and Heterosigma akashiwo ( Raphidophyceae ), respectively, as well as spermidine, the most abundant polyamine in both phytoplankton species. Trace amounts of putrescine, diaminopropane and norspermine were also detected in both species. Spermine was detected only from C. antiqua . These long linear polyamines are characteristic components of thermophilic bacteria. The detection from two species of Raphidophyceae indicates that the occurrence of long linear polyamines is not restricted to thermophilic microorganisms.     

Florida red tide and brevetoxins: Association and exposure in live resident bottlenose dolphins (Tursiops truncatus) in the eastern Gulf of Mexico,U.S.A.

Bottlenose dolphins (Tursiops truncatus) along the Gulf of Mexico are frequently exposed to blooms of the toxic alga, Karenia brevis, and brevetoxins associated with these blooms have been implicated in several dolphin mortality events. Studies on brevetoxin accumulation in dolphins have typically focused on analyses of carcasses from large‐scale die‐offs; however, data are scarce for brevetoxin loads in live individuals frequently exposed to K. brevis blooms. This study investigated in vivo brevetoxin exposure in free‐ranging bottlenose dolphins resident to Sarasota Bay, Florida, utilizing samples collected during health assessments performed during multiple K. brevis blooms occurring from 2003 to 2005. Brevetoxins were detected by ELISA and LC‐MS in 63% of bottlenose dolphins sampled (n= 30) concurrently with a K. brevis bloom. Brevetoxins were present in urine and gastric samples at concentrations ranging from 2 to 9 ng PbTx‐3 eq/g, and in feces at concentrations ranging from 45 to 231 ng PbTx‐3 eq/g. Samples from individuals (n= 12) sampled during nonbloom conditions (≤1,000 cells/L) were negative for brevetoxin activity. Brevetoxin accumulation data from this study complement dolphin carcass and prey fish data from the same study area, and aid in evaluating impacts of harmful algal blooms on sentinel marine animal species along the west Florida coast.     

Mixotrophy in the phototrophic dinoflagellate Takayama helix (family Kareniaceae): Predator of diverse toxic and harmful dinoflagellates

Takayama spp. are phototrophic dinoflagellates belonging to the family Kareniaceae and have caused fish kills in several countries. Understanding their trophic mode and interactions with co-occurring phytoplankton species are critical steps in comprehending their ecological roles in marine ecosystems, bloom dynamics, and dinoflagellate evolution. To investigate the trophic mode and interactions of Takayama spp., the ability of Takayama helix to feed on diverse algal species was examined, and the mechanisms of prey ingestion were determined. Furthermore, growth and ingestion rates of T. helix feeding on the dinoflagellates Alexandrium lusitanicum and Alexandrium tamarense, which are two optimal prey items, were determined as a function of prey concentration. T. helix ingested large dinoflagellates ≥15 μm in size, except for the dinoflagellates Karenia mikimotoi, Akashiwo sanguinea, and Prorocentrum micans (i.e., it fed on Alexandrium minutum, A. lusitanicum, A. tamarense, A. pacificum, A. insuetum, Cochlodinium polykrikoides, Coolia canariensis, Coolia malayensis, Gambierdiscus caribaeus, Gymnodinium aureolum, Gymnodinium catenatum, Gymnodinium instriatum, Heterocapsa triquetra, Lingulodinium polyedrum, and Scrippsiella trochoidea). All these edible prey items are dinoflagellates that have diverse eco-physiology such as toxic and non-toxic, single and chain forming, and planktonic and benthic forms. However, T. helix did not feed on small flagellates and dinoflagellates <13 μm in size (i.e., the prymnesiophyte Isochrysis galbana; the cryptophytes Teleaulax sp., Storeatula major, and Rhodomonas salina; the raphidophyte Heterosigma akashiwo; the dinoflagellates Heterocapsa rotundata, Amphidinium carterae, Prorocentrum minimum; or the small diatom Skeletonema costatum). T. helix ingested Heterocapsa triquetra by direct engulfment, but sucked materials from the rest of the edible prey species through the intercingular region of the sulcus. With increasing mean prey concentration, the specific growth rates of T. helix on A. lusitanicum and A. tamarense increased continuously before saturating at prey concentrations of 336–620 ng C mL⁻¹. The maximum specific growth rates (mixotrophic growth) of T. helix on A. lusitanicum and A. tamarense were 0.272 and 0.268 d⁻¹, respectively, at 20 °C under a 14:10 h light/dark cycle of 20 μE m⁻² s⁻¹ illumination, while its growth rates (phototrophic growth) under the same light conditions without added prey were 0.152 and 0.094 d⁻¹, respectively. The maximum ingestion rates of T. helix on A. lusitanicum and A. tamarense were 1.23 and 0.48 ng C predator⁻¹d⁻¹, respectively. The results of the present study suggest that T. helix is a mixotrophic dinoflagellate that is able to feed on a diverse range of toxic species and, thus, its mixotrophic ability should be considered when studying red tide dynamics, food webs, and dinoflagellate evolution.     

Development of microsatellite markers in the noxious red tide‐causing algae Heterosigma akashiwo (Raphidophyceae)

We isolated 13 polymorphic microsatellites from the noxious red tide‐causing algae, Heterosigma akashiwo. These loci provide a class of highly variable genetic markers as the number of alleles ranged from three to 12 and the observed and expected heterozygosities ranged from 0.286 to 0.926 and from 0.314 to 0.888, respectively. We consider these loci potentially useful for detailing the genetic structure and gene flow among H. akashiwo populations.