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It is difficult to keep a large number of cultured octopuses together in the same holding tank due to the high incidence of cannibalism. Appropriate shelters within which the octopuses can more readily avoid their peers are expected to ameliorate this problem. Shelters can be constructed from square plates assembled with appropriate spacing (gap) between them. The purpose of this study was to ascertain the optimum plate orientation and gap width between plates for shelters to maximize the accommodation of octopuses. It was found that the number of shelter occupants increased with the number of gaps available, such that more than half of the individuals in the experimental tank used the same shelter simultaneously. Octopuses tested singly to determine preferences for shelters placed vertically or horizontally preferred the vertical arrangement. Octopuses of more than 300 g tested singly in aquaria given shelters with different gap widths (20–100 mm) were found to not enter shelters with gap widths of 20 or 40 mm. It is concluded that octopus shelters constructed from square vertical plates spaced with gap widths suitable for octopuses are a useful contribution towards maximizing the number of octopuses that can be maintained in culture conditions.

To clarify the relationship between the quantity of food ingested by and the growth rate of the Japanese egg cockle Fulvia mutica (Reeve), we conducted a laboratory breeding experiment for 2 weeks and estimated the chlorophyll a (chl-a) concentrations in water and the increments in shell length and soft-body weight of this species under five chl-a concentrations. Moreover, we compared the relationship between cockle growth (changes in soft-body weight and shell length) and their feeding environment observed in the laboratory experiment with the results of a field investigation conducted at two sites in the Sea of Japan, Kumihama Bay (35°38′5″ N, 134°54′00″ E) and Kunda Bay (35°33′30″ N, 135°15′4″ E). The changes in soft-body weight were similar in both laboratory and field investigations, but those in shell length were not. We, therefore, considered shell length changes as unsuitable for evaluating the relationship between growth and feeding in F. mutica. Based on the changes in soft-body weight, it was possible to classify the feeding environment of this species into the following three types: (1) a L−1, negative feeding environment for cockle growth; (2) 1.52–5.71 μg chl-a L−1, neutral feeding environment for cockle growth; (3) > 5.71 μg chl-a L−1, positive feeding environment for cockle growth (growth increased with increasing chl-a concentration up to about 11 μg chl-a L−1). These results indicate that maintaining chl-a concentration in the breeding water within 5.71–11 μg chl-a L−1 is desirable for rearing Japanese egg cockle.

The red tide forming heterotrophic dinoflagellate Noctiluca scintillans is common in temperate to tropical waters around the world. Understanding the in situ prey of N. scintillans is essential for elucidating its role in marine microbial food webs. In this study, we applied two polymerase chain reaction (PCR)-based cloning techniques, a predator-specific restriction enzyme, and a blocking primer. The PCR of nuclear 18S rDNA was performed on single N. scintillans cells that were collected from Ishinomaki Bay, Japan, in May 2018. The maximum detection rates of non-Noctiluca sequences were 56% using the restriction enzyme method and 87% with the blocking primer method, representing a broad taxonomic range of organisms, including diatom, dinoflagellate, bolidophyte, haptophyte, euglenophyte, green algae, golden algae, ciliate, heliozoa, copepod, brown seaweed, sponge, bivalve, and polychaete. The diverse DNA was probably ingested by N. scintillans directly or indirectly through secondary predation or ingestion of marine snow or detritus containing many organisms. The application of molecular approaches to various species may reveal undiscovered interactions within the phytoplankton community, including prey-predator, or symbiotic relationships.

While cyst germination may be an important factor for the initiation of harmful/toxic blooms, assessments of the fluctuation in phytoplankton cyst germination, from bottom sediments to water columns, are rare in situ due to lack of technology that can detect germinated cells in natural bottom sediments. This study introduces a simple mesocosm method, modeled after previous in situ methods, to measure the germination of plankton resting stage cells. Using this method, seasonal changes in germination fluxes of toxic dinoflagellates resting cysts, specifically Alexandrium fundyense ( A. tamarense species complex Group I) and A. pacificum ( A. tamarense species complex Group IV), were investigated at a fixed station in Kesennuma Bay, northeast Japan, from April 2014 to April 2015. This investigation was conducted in addition to the typical samplings of seawater and bottom sediments to detect the dinoflagellates vegetative cells and resting cysts. Bloom occurrences of A. fundyense were observed June 2014 and February 2015 with maximum cell densities reaching 3.6 × 10 6 cells m −2 and 1.4 × 10 7 cells m −2 , respectively. The maximum germination fluxes of A. fundyense cysts occurred in April 2014 and December 2014 and were 9.3 × 10 3 cells m −2 day −1 and 1.4 × 10 4 cells m −2 day −1 , respectively. For A. pacificum , the highest cell density was 7.3 × 10 7 cells m −2 during the month of August, and the maximum germination fluxes occurred in July and August, reaching 5.8 × 10 2 cells m −2 day −1 . Thus, this study revealed the seasonal dynamics of A. fundyense and A. pacificum cyst germination and their bloom occurrences in the water column. Blooms occurred one to two months after peak germination, which strongly suggests that both the formation of the initial population by cyst germination and its continuous growth in the water column most likely contributed to toxic bloom occurrences of A. fundyense and A. pacificum in the bay.

© The Author(s), 2016. This is the authors version of the work and is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Experimental Marine Biology and Ecology 486 (2017): 368-372, doi:10.1016/j.jembe.2016.11.003. The hypothesis that life cycle of an epibiotic suctorian ciliate Ephelota plana is adapted to the molt cycle of the krill Euphausia pacifica collected in Saanich Inlet, Canada was evaluated. The infestation prevalence of E. plana and the number of individuals attached increased from postmolt stage to premolt stage of E. pacifica, and concurrently cell growth of E. plana was observed. Budding individuals of E. plana first appeared at early premolt stage and increased to 21% at late premolt stage. Thus the life cycle of E. plana seems to be adapted to the molt cycle of E. pacifica. 2018-11-12

This study was performed in order to develop a primer set for mitochondrial cytochrome c oxidase subunit I (COI) in the DHA-rich microalgae of the genus Aurantiochytrium. The performance of the primer set was tested using 12 Aurantiochytrium strains and other thraustochytrid species. There were no genetic polymorphisms in the mitochondrial sequences from the Aurantiochytrium strains, in contrast to the nuclear 18S rRNA gene sequence. This newly developed primer set amplified sequences from Aurantiochytrium and closely related genera, and may be useful for species identification and clarifying the genetic diversity of Aurantiochytrium in the field.

Mesodinium spp. are commonly found in marine and brackish waters, and several species are known to contain red, green, or both plastids that originate from cryptophyte prey. We observed the seasonal succession of Mesodinium spp. in a Japanese brackish lake, and we analysed the origin and diversity of the various coloured plastids within the cells of Mesodinium spp. using a newly developed primer set that specifically targets the cryptophyte nuclear 18S rRNA gene. Mesodinium rubrum isolated from the lake contained only red plastids originating from cryptophyte Teleaulax amphioxeia. We identified novel Mesodinium sp. that contained only green plastids or both red and green plastids originating from cryptophytes Hemiselmis sp. and Teleaulax acuta. Although the morphology of the newly identified Mesodinium sp. was indistinguishable from that of M. rubrum under normal light microscopy, phylogenetic analysis placed this species between the M. rubrum/major species complex and a well-supported lineage of M. chamaeleon and M. coatsi. Close associations were observed in cryptophyte species composition within cells of Mesodinium spp. and in ambient water samples. The appearance of suitable cryptophyte prey is probably a trigger for succession of Mesodinium spp., and the subsequent abundance of Mesodinium spp. appears to be influenced by water temperature and dissolved inorganic nutrients.

It is necessary to monitor shell-associated polydorid worms owing to the risk that they pose to commercially important molluscs. This requires accurate identification, but is often hampered by morphological similarities among species, insufficient type specimens, and abridged species descriptions. Thus morphological characteristics and molecular sequences of the most harmful polydorid species,Polydora uncinatafrom Japan and Australia andPolydora hoplurafrom South Africa were compared to determine whether they represent two morphologically similar, but genetically distinct species, or a single species. A wide range of morphological variation (with respect to size, length of caruncle and pigmentation patterns) was observed in each species and population, and their variations largely overlapped and revealed them to be at the intraspecific level of a single species. This was confirmed by gene sequences of nuclear 18S and 28S rRNA that were completely identical forP. uncinataandP. hoplura. The mitochondrial 16S rRNA andcyt bgene analyses also showed no genetic differences between these two species. The tree topology of the mitochondrialcyt bgene did not reflect geographic differences but instead suggests artificial transportation of the species. We recommend the synonymization ofP. uncinatawithP. hoplura.

Large numbers of swimming and stranding Urechis unicinctus were observed at night during low tide in Sasuhama, Miyagi Prefecture, northeastern Japan, during the periods from January to February in 2012 and 2013. Worms did not drift passively but swam actively, therefore hinting at a certain purpose for such behavior. As trochophore larvae of U. unicinctus were observed to occur simultaneously in the plankton, we infer the possibility that this is an event of reproductive swarming. Anatomical observations of both swimming and stranding U. unicinctus showed that none of the specimens had gametes, which may suggest that these were completely spent after spawning. Urechis unicinctus seemed to begin swimming after dusk and the observed swimming behavior occurred during the evening ebb tide throughout the night low tide during winter time. Stranding U. unicinctus have long been known in Japan and have been attributed to sea storms. The present study shows for the first time the possibility that U. unicinctus swims in order to reproduce at night and that this swimming behavior is closely linked to the stranding of U. unicinctus individuals.

H.,�Sato-Okoshi,�W.,�Nishitani,�G.�andEndo,�Y.�2014.�Verticaldistributionandmigrationofplanktonicpolychaete� larvae in Onagawa Bay, north-eastern Japan. Memoirs of Museum Victoria�71:�1-9. The planktonic larvae of polychaetes are one of the most numerous and diverse groups in coastal zooplankton; however, little is known about their larval dynamics and the factors that affect their vertical distribution. We investigated the vertical distribution and migration of planktonic polychaete larvae in Onagawa Bay, north-eastern Japan, particularly focusingonthedominantspionidlarvae.�Intotal,�14�familiesofplanktonicpolychaetelarvaeand�14�speciesorgeneraof� spionidlarvaewereidentifiedduringourstudy.�Theirdensitygreatlyfluctuatedaccordingtoseasonanddepth,�withthe� polychaetelarvaegenerallydistributedinthelowerlayersofthewatercolumn.�Furthermore,�trendsinverticaldistribution� ofspionidlarvaevariedbetweenspecies.�Inwinterandspring,�larvaeofPolydora onagawaensis were the most prevalent, withawiderangeinverticaldistribution.�Insummerandautumn,�larvaeofPseudopolydora achaeta and Prionospio spp. were the most prevalent spionid larvae and were primarily distributed in the lower layers of the water column. Trends in larval vertical distribution varied as a result of differences in adult habitat; these variations would enable the larvae to efficientlyrecruitintotheirappropriateadulthabitats.�Spionidlarvaedidnotshowdielverticalmigration.�Larvaeoftwo� spionid taxa, Pseudopolydora achaeta and Prionospio spp., exhibited tidal vertical migration, with larvae appearing to avoiddispersalbymovingtoslower-flowingdeeperwaterduringfloodandebbtides.�Althoughmanypreviousstudies� assume that, because of their limited swimming capacity, polychaete larvae are passively dispersed within the water column, this study indicates that polychaete larvae can control their vertical distribution to some extent, and this small- scale vertical migration may be important as a retention mechanism for polychaete larvae.

A new species of spionid polychaete, Polydora onagawaensis, is described from mol- lusk shells in Pacific waters of northeastern Japan. Its nuclear 18S rRNA gene sequence as well as its morphology, reproductive features, life history and infestation characteristics are reported. Polydora onagawaensis sp. nov. belongs to the Polydora ciliata/websteri group and has a moder- ate size and variable black pigmentation on the palps and body. Up to 115 worms were found bor- ing in a single scallop shell from suspended cultures in Onagawa Bay, with significantly higher numbers in the right than in the left valve. Females repeatedly deposited a string of egg capsules from around October to June (seawater temperature was below 15°C). The larvae developed inside the egg capsules for 2 wk (10°C, laboratory conditions), until the 3-chaetiger stage, before being released as planktonic larvae. The main spawning occurred in December, recruitment onto the shells increased after January, and most large worms disappeared between July and October. Thus, the estimated life span is around 1.5 yr after settlement. Details on biology and gene infor- mation not only contribute to distinguishing the species from other polydorids similar in morpho - logy, but also allow control of polydorid infestation in mollusk aquaculture.

In recent years, several marine heterotrophic nanoflagellates have been reported to feed on diatoms much larger than themselves. However, very little is known about the grazer-prey relationships between heterotrophic nanoflagellates and diatoms in aquatic ecosystems. A diatom-feeding flagellate was discovered in the bottom sediment of OnagawaBay. It fed and proliferated on diatoms, especially Skeletonema costatum sensu lato. This study determined growth and ingestion rates of the flagellate on Skeletonema costatum s.l. under laboratory conditons. Its grazing pressure on the sinking flux of S. costatum s.l. was calculated by combining field data. Specific growth rate of the flagellate increased with increasing prey concentration. The maximum specific growth rate was 0.79 d–1 and maximum ingestion rate of the flagellate was 0.66 ng·C·grazer–1·d–1. Calculated grazing pressure of the flagellate on S. costatum s.l. flux was up to 25.6%. The results imply that the flagellate has a considerable grazing impact on S. costatum s.l. flux at least in a restricted season of the year. Therefore, the present study suggests that this benthic flagellate plays an important role in pelagic-benthic coupling inOnagawaBay.

To determine the process of population expansion and ascertain the origin of the Sea of Japan population, in a noxious red tide forming dinoflagellate Cochlodinium polykrikoides, 13 samples, isolated from 11 different localities in Japanese and Korean coasts, were analysed using 10 polymorphic microsatellites. Analyses by nonmetric multidimensional scaling plots of pairwise F(ST), global amova, and genetic admixture analysis identified three clusters--the Sea of Japan populations, Yatsushiro Sea (Kumamoto Pref.) populations, and other populations--indicating genetic structuring of the 13 samples into three distinct populations. In the proportion of shared alleles by pairwise individuals (P(SAxy)) analyses between the Sea of Japan and the other samples, P(SAxy) was extremely low compared with that among the Sea of Japan or among other samples, indicating that a large genetic barrier has occurred between the populations. No significant relationship of isolation-by-distance patterns and almost no genetic distance were detected between pairwise samples of the Sea of Japan, although there is a maximal distance of600 km between samples. In addition, P(SAxy) data among the samples were extremely high compared with those among other samples, clearly showing that a large-scale transfer from west to east has occurred via the Tushima Warm Current. In the P(SAxy) data of the Seto Inland Sea and Pacific samples, individuals showing relatively high P(SAxy) were concentrated in the three areas of Nagasaki, Harima, and Mie, suggesting that frequent transfer may have occurred by human-assisted dispersal, although Nagasaki and Mie are separated by a distance of approximately 700 km.

S. Nagai, G. Nishitani, Y. Takano, M. Yoshida and H. Takayama. 2009. Encystment and excystment under laboratory conditions of the nontoxic dinoflagellate Alexandrium fraterculus (Dinophyceae) isolated from the Seto Inland Sea, Japan. Phycologia 48: 177–185. DOI: 10.2216/08-43.1. The sexuality (i.e. encystment and excystment) of the nontoxic dinoflagellate Alexandrium fraterculus, isolated from the Seto Inland Sea, Japan, was clarified for the first time under laboratory conditions. Sexual reproduction was by conjugation of isogametes, and plasmogamy was completed in 25–60 min after the conjugation started and produced a planozygote with one transverse and two longitudinal flagella, then a cyst was formed. Cysts were round or elliptical. The cyst size was 37.5–50.0 µm in diameter. The surface of cysts was smooth, and there was no paratabulation. Encystment through sexual reproduction was observed in two of 28 pairs, which included seven self-crossings, by use of seven nonaxenic clonal strains. No ...

We report the successful growth of the toxic dinoflagellate Dinophysis infundibulus under laboratory conditions, when fed the marine ciliate Myrionecta rubra grown with the cryptophyte Teleaulax amphioxeia; this study follows previous studies on D. acuminata, D. caudata, and D. fortii, showing the mixotrophy. We succeeded in maintaining several clonal strains of D. infundibulus for a relatively long period of time (> 8 mol. Growth rates in D. infundibulus ranged from 0.40 to 0.94 divisions d -1 , reaching a maximum concentration of 1.2 to 2.3 x 10 3 cells ml -1 . The rate was 0.36 divisions d -1 when apparently fully expanded cells, resulting from the active ingestion of Myrionecta rubra, were cultivated without the ciliate prey. In contrast, the culture of D. infundibulus was not established in the absence of the ciliate or when provided only with the cryptophyte T. amphioxeia, suggesting that D. infundibulus cannot directly use T. amphioxeia as prey. We also determined the sequences of nuclear small subunit (SSU) rRNA, 5.8S rRNA with internal transcribed spacers (ITS1 and ITS2), and large subunit (LSU) rRNA regions in D. infundibulus. Phylogenetic relationships revealed that they are non-identical with regard to any of the DNA sequence data of Dinophysis deposited in GenBank, and are distinguishable from other Dinophysis species for species identification.

To elucidate the mechanism of bloom outbreaks of Chattonella ovata (Raphidophyceae), we investigated the cysts of C. ovata and succeeded in finding them from the bottom sediments of Hiroshima Bay. The morphology of the cysts was mostly hemispherical in shape, with a diameter of ca. 30 μm and height of ca. 20 μm. The cysts were usually adhering to solid materials, such as diatom frustules, yellow-greenish in color and had several dark brown grains. The cyst wall was smooth and had no ornamentation. Because the morphological characteristic of the cysts was in general agreement with those of Chattonella antiqua and Chattonella marina, it was difficult to differentiate the cysts of these three species. Germination of the cysts of C. ovata was observed at temperatures from 17.5 to 30 °C, but not at 15 °C or below. The number of the germinated cysts increased with increasing temperature and the optimum temperature for germination was 30 °C. Although cysts of C. antiqua and C. marina germinated at temperatures from 15 to 30 °C, optimum temperature of germination was 22.5 °C. The lower limit and optimum temperatures for germination of C. ovata cysts was higher than for C. antiqua and C. marina. The role of cysts in the population dynamics of C. ovata is discussed.

Recently, Park et al. (2006) succeeded in cultivating the toxic dinoflagellate Dinophysis acuminata and maintaining them by feeding the ciliate Myrionecta rubra grown with a cryptophyte Teleaulax sp. After this report, the present study is the second report of propagation of a Dinophysis species (Dinophysis caudata) under laboratory condi- tions and describes the maintenance of several clonal strains kept at high abundance (� 5,000 cells mL � 1 ) for a rela- tively long period (� 4 months) when fed on M. rubra with the addition of Teleaulax amphioxeia. We confirmed that D. caudata swam actively around its ciliate prey and inserted its peduncle (feeding tube) into the ciliate. Thereafter, the prey became immobile and rounded. Dinophysis caudata actively ingested the cytoplasm of the prey through the pedun- cle. Dinophysis caudata grew at a growth rate of 1.03 divisions day � 1 when supplied with M. rubra as prey, reaching a maximum concentration of ca. 5,000 cell well � 1 (810 mL) during a 9 day growth experiment. In contrast, a culture of D. caudata was not able to be established in the absence of the ciliate or when provided with T. amphioxeia only, suggest- ing that D. caudata can not directly utilize T. amphioxeia as prey.

International audience; In this study, we identified 9 polymorphic compound microsatellite markers in the toxic dinoflagellate Alexandrium catenella, which was isolated from Thau lagoon (France, Mediterranean Sea), using the compound microsatellite marker technique. These new microsatellites were characterized by screening DNA templates from 43 A. catenella clonal strains, which were collected from a seawater sample from Inokushi Bay (Oita Prefecture, Japan). These loci provide one class of highly variable genetic marker: the number of alleles ranged from 3 to 8, and the estimate of gene diversity varied between 0.285 and 0.762. We also analyzed the same 43 DNA samples using microsatellite markers previously identified for A. catenella, comparing the PCR amplification success, the number of alleles and gene diversity. These three parameters were not significantly different, showing that the compound microsatellite markers have the same potential to reveal A. catenella genetic structure. This simple and efficient method reduces the costs for developing SSR markers and for analyzing the genetic structure of populations, therefore, suggesting the effectiveness of applying this method to other species.

Okadaic acid (OA) and OA binding protein 2 (OABP2) were previously isolated from the marine sponge Halichondria okadai. Because the amino acid sequence of OABP2 is completely different from that of protein phosphatase 2A, a well-known target of OA, we have been investigating the production and function of OABP2. In the present study, we hypothesized that OABP2 plays a role in the detoxification of OA in H. okadai and that the OA concentrations are in proportional to the OABP2 concentrations in the sponge specimens. Based on the OA concentrations and the OABP2 concentrations in the sponge specimens collected in various places and in different seasons, however, we could not determine a positive correlation between OA and OABP2. We then attempted to determine distribution of OA and OABP2 in the sponge specimen. When the mixture of dissociated sponge cells and symbiotic species were separated with various pore-sized nylon meshes, most of the OA and OABP2 was detected from the same 0-10 μm fraction. Next, when sponge cell clusters were prepared from a mixture of dissociated sponge cells and symbiotic species in the presence of penicillin and streptomycin, we identified the 18S rDNA of H. okadai and the gene of OABP2 in the analysis of genomic DNA but could not detect OA by LC-MS/MS. We thus concluded that the sponge cells express OABP2, and that OA was not apparently present in the sponge cells but could be colocalized with OABP2 in the sponge cells at a concentration less than the limit of detection.

Fluctuations of the genus Dinophysis, which contained several toxic species of diarrhetic shellfish poisoning (DSP), were investigated during blooms in Hiroshima Bay, Mutsu Bay and Ise Bay, Japan. The co-occurrences of small phytoplanktons (cryptophytes, other nanophytoplanktons, cyanobacteria and eukaryotic picophytoplanktons) were investigated to search for relationships with mixotrophic Dinophysis. Cryptophytes were divided into three size-groups based on length of their chloroplasts (>10, 5–10 and

Coccoid picophytoplankton cells (1–2 μm in diameter) were observed to attach to the cell surface of the toxic dinoflagellates Dinophysis acuminata and D. fortii in water samples collected in Maizuru Bay, Japan, in spring of 1998. A relatively large number of picophytoplankton cells were noticed in the cingulum near the flagellar-pore region in D. fortii. These picophytoplankton cells were not cyanobacteria. Food vacuolate cells of D. fortii were observed. In view of the existence of a tongue-like structure (food ingestion organelle), the size of the aperture of the flagellar pore (cytostome) of about 1.5 μm, and the finding of picophytoplankton cells attached to the Dinophysis cell surface, we suggest that the food microorganisms for mixotrophic D. acuminata and D. fortii are picophytoplankton. The food picophytoplankton may be composed of different species, and some of them may contain diarrhetic shellfish poisoning toxins and/or their precursors. We suggest that Dinophysis species such as D. acuminata and D. fortii may originally be nontoxic and may only become toxic secondarily, through the ingestion of toxic picophytoplankton. This working hypothesis could reasonably explain the marked fluctuations observed in the toxicity of D. acuminata and D. fortii.

We isolated 24 polymorphic microsatellite markers from the toxic dinoflagellate A. tamiyavanichii. These loci provide a class of highly variable genetic markers, as the number of alleles ranged from 2 to 6, and the estimate of gene diversity was from 0.269 to 0.739 across the 24 microsatellites. We consider that these loci have a potentially to reveal the genetic structure and gene flow among A. tamiyavanichii populations.

The marine phytoplankton, Karenia mikimotoi, causes severe red tides which are associated with mass mortality of marine fish, and have expanded their distributions in the coastal waters of western Japan. To assess the dispersal mechanism, a population genetic study using highly polymorphic genetic markers is one of the crucial approaches. Here we developed 12 polymorphic microsatellite markers from K. mikimotoi. These loci provide a class of highly variable genetic markers, as the number of alleles ranged from 5 to 23, and the estimate of gene diversity was from 0.551 to 0.933 across the 12 microsatellites. We consider these loci potentially useful for detailing the genetic structure and gene flow among K. mikimotoi populations.

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.

We isolated 15 polymorphic microsatellites from one of the most noxious red tide-causing dinoflagellate species, Heterocapsa circularisquama . These loci provide one class of highly variable genetic markers, as the number of alleles ranged from two to six, and the estimate of gene diversity was from 0.205 to 0.684 across the 15 microsatellites. These loci have the potential to reveal genetic structure and gene flow among H. circularisquama populations.

We isolated 15 polymorphic microsatellites from Cochlodinium polykrikoides. These loci provide a class of highly variable genetic markers, as the number of alleles ranged from two to 15, and the estimate of gene diversity was from 0.083 to 0.880 across the 15 microsatellites. We consider that these loci have a potential to reveal the genetic structure and gene flow among C. polykrikoides populations.

Kleptoplastidy is the retention of plastids obtained from ingested algal prey, which may remain temporarily functional and be used for photosynthesis by the predator. We showed that the marine dinoflagellate Dinophysis mitra has great kleptoplastid diversity. We obtained 308 plastid rbc L sequences by gene cloning from 14 D. mitra cells and 102 operational taxonomic units (OTUs). Most sequences were new in the genetic database and positioned within Haptophyceae (227 sequences [73.7%], 80 OTUs [78.4%]), particularly within the genus Chrysochromulina . Others were closely related to Prasinophyceae (16 sequences [5.2%], 5 OTUs [4.9%]), Dictyochophyceae (14 sequences [4.5%], 5 OTUs [4.9%]), Pelagophyceae (14 sequences [4.5%], 1 OTU [1.0%]), Bolidophyceae (3 sequences [1.0%], 1 OTU [1.0%]), and Bacillariophyceae (1 sequence [0.3%], 1 OTU [1.0%]); however, 33 sequences (10.8%) as 9 OTUs (8.8%) were not closely clustered with any particular group. Only six sequences were identical to those of Chrysochromulina simplex , Chrysochromulina hirta , Chrysochromulina sp. TKB8936, Micromonas pusilla NEPCC29, Micromonas pusilla CCMP491, and an unidentified diatom. Thus, we detected >100 different plastid sequences from 14 D. mitra cells, strongly suggesting kleptoplastidy and the need for mixotrophic prey such as Laboea , Tontonia , and Strombidium -like ciliates, which retain numerous symbiotic plastids from different origins, for propagation and plastid sequestration.

We analyzed cryptophyte nucleomorph 18S rRNA gene sequences retained in natural Myrionecta rubra cells and plastid 16S rRNA gene and psbA sequences retained in natural cells of several Dinophysis species collected from Japanese coastal waters. A total of 715 nucleomorph sequences obtained from 134 M. rubra cells and 564 plastid 16S rRNA gene and 355 psbA sequences from 71 Dinophysis cells were determined. Almost all sequences in M. rubra and Dinophysis spp. were identical to those of Teleaulax amphioxeia , suggesting that M. rubra in Japanese coastal waters preferentially ingest T . amphioxeia . The remaining sequences were closely related to those of Geminigera cryophila and Teleaulax acuta . Interestingly, 37 plastid 16S rRNA gene sequences, which were different from T. amphioxeia and amplified from Dinophysis acuminata and Dinophysis norvegica cells, were identical to the sequence of a D. acuminata cell found in the Greenland Sea, suggesting that a widely distributed and unknown cryptophyte species is also preyed upon by M. rubra and subsequently sequestered by Dinophysis . To confirm the reliability of molecular identification of the cryptophyte Teleaulax species detected from M. rubra and Dinophysis cells, the nucleomorph and plastid genes of Teleaulax species isolated from seawaters were also analyzed. Of 19 isolates, 16 and 3 clonal strains were identified as T. amphioxeia and T. acuta , respectively, and no sequence variation was confirmed within species. T. amphioxeia is probably the primary source of prey for M. rubra in Japanese coastal waters. An unknown cryptophyte may serve as an additional source, depending on localities and seasons.

Monitorings were conducted on DSP toxins in mid-gut gland of scallop (mouse assay), cell numbers of toxic dinoflagellate species of Dinophysis, and diarrhetic shellfish poisoning (DSP) toxins in small-sized (0.7-5 microm) plankton fraction of seawater collected from surface (0 m) and 20 m depth at a station in Mutsu Bay, Aomori Prefecture, Japan, in 2000. A specific enzyme-linked immunosorbent assay (ELISA) was employed for the analysis of DSP toxins in small-sized plankton fraction using a mouse monoclonal anti-okadaic acid antibody which recognizes okadaic acid, dinophysistoxin-1, and dinophysistoxin-3. DSP toxins were detected twice in the mid-gut gland of scallops at 1.1-2.3 MU (mouse units) g(-1) on 26 June and at 0.6-1.2 MU g(-1) on 3 July, respectively. Relatively high cell densities of D. fortii were observed on 26 June and 11 September, and may only contribute to the bivalve toxicity during late June to early July. D. acuminata did not appear to be responsible for the toxicity of scallops in Mutsu Bay in 2000. ELISA monitoring of small-sized plankton fraction in seawater could detect DSP toxins two weeks before the detection of the toxin in scallops, and could do so two weeks after the loss of the bivalve toxicity by mouse assay. On 17 July, toxic D. fortii was detected at only small number