The raphidophyte Chattonella antiqua is a single-celled alga that forms 'red tides' in coastal areas. C. antiqua produces superoxide anions (O2-), the excessive production of which has been associated with fish mortality. It is suggested that putative NADPH oxidase in the outer membrane oxidizes intracellular NADPH to produce O2- and secrete it externally. Earlier studies revealed that photosynthetic electron transport, a major producer of NADPH in photosynthetic organisms, is involved in the production of O2- in C. antiqua but the details of the O2- production mechanism have yet to be elucidated. Since nutrient deficiency adversely affects the formation of blooms of C. antiqua, in this study, we examined the effects of nutrient deficiency on O2- production in C. antiqua. When cells were grown under nitrogen (N)- or phosphorus (P)-deficient conditions, the production of O2- was stimulated. In particular, the extracellular levels of O2- under N- or P-deficient conditions were high during the dark period when photosynthetic activities in terms of actual quantum efficiency and photochemical quenching were low. The extracellular levels of O2- under the nutrient-deficient conditions were unaffected by the presence of 3-(3,4-dichlorophenyl)-1,1‑dimethylurea (DCMU), an inhibitor of photosynthetic electron transport, but decreased when the nutrients were present. LXG6403 clinical trial Furthermore, the intracellular ratio of NADPH to NADP+ under N- or P-deficient conditions was higher than that under nutrient-replete conditions. These observations suggest that another metabolic pathway, independent of photosynthesis, provides NADPH for the production of O2- under nutrient deficiency.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.In July 2009, an unusually intense bloom of the toxic dinoflagellate Alexandrium catenella occurred in the Gulf of Maine. The bloom reached high concentrations (from hundreds of thousands to one million cells L-1) that discolored the water and exceeded normal bloom concentrations by a factor of 1000. Using Medium Resolution Imaging Spectrometer (MERIS) imagery processed to target chlorophyll concentrations (>2 µg L-1), patches of intense A. catenella concentration were identified that were consistent with the highly localized cell concentrations observed from ship surveys. The bloom patches were generally aligned with the edge of coastal waters with high-absorption. Dense bloom patches moved onshore in response to a downwelling event, persisted for approximately one week, then dispersed rapidly over a few days and did not reappear. Coupled physical-biological model simulations showed that wind forcing was an important factor in transporting cells onshore. Upward swimming behavior facilitated the horizontal cell aggregation, increasing the simulated maximum depth-integrated cell concentration by up to a factor of 40. Vertical convergence of cells, due to active swimming of A. catenella from the subsurface to the top layer, could explain the additional 25-fold intensification (25 × 40=1000-fold) needed to reach the bloom concentrations that discolored the water. A model simulation that considered upward swimming overestimated cell concentrations downstream of the intense aggregation. This discrepancy between model and observed concentrations suggested a loss of cells from the water column at a time that corresponded to the start of encystment. These results indicated that the joint effect of upward swimming, horizontal convergence, and wind-driven flow contributed to the red water event, which might have promoted the sexual reproduction event that preceded the encystment process.Multiple dinoflagellate species from the genus Karlodinium have been well known to form massive and toxic blooms that consequently cause fish kills in many coastal waters around the world. Karlodinium australe is a mixotrophic and potentially ichthyotoxic species associated with fish kills. Here, we investigated phagotrophy of K. australe (isolate KaJb05) established from a bloom event in the West Johor Strait, Malaysia, using several prey species (phytoplankton, zooplankton, and larval fish). The results showed that K. australe ingested relatively small prey cells of co-occurring microalgae by direct engulfment, while it fed on larger prey cells of microalgae by tube feeding. The results of animal exposure bioassays using rotifer (Brachionus plicatilis), brine shrimp (Artemia salina), and larval fish (Oryzias melastigma) demonstrated that phagotrophy (in terms of the trophic mode of the dinoflagellate), or micropredation (in terms of the mechanism of lethal effects on prey), played a more important role thanh as species of Karlodinium and of HAB events in general.The Tasmanian abalone fishery represents the largest wild abalone resource in the world, supplying close to 25% of the annual wild-caught global harvest. Prompted by the need to manage Paralytic Shellfish Toxin (PST) contamination of Blacklip Abalone (Haliotis rubra rubra) from east coast Tasmania, the uptake of toxins by this species is investigated in a land-based, controlled aquaculture setting. Abalone were exposed to either live Alexandrium catenella microalgal cultures or PST contaminated feed pellets during a 28 day exposure period and toxins quantified in viscera, foot muscle and epipodium tissues. PST profiles of abalone foot tissues were dominated by saxitoxin and neosaxitoxin, whilst viscera more closely resembled those of the toxin source (A. catenella cells rich in gonyautoxin 1&4 and 2&3 or feed pellets containing A. catenella extracts rich in these analogues). This indicates direct uptake of PST in the viscera via browsing/grazing on the pellet and /or sedimented microalgal cells. After exposure to A.