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Previously we reported that a significant level of domoic acid, a causative toxin for amnesic shellfish poisoning, was detected in bivalves belonging to a genus Spondylus from various tropical Asian countries. These findings indicate that causative plankton species for domoic acid widely distribute in these areas. In the present study, we monitored seasonal change of domoic acid level of Spondylus versicolor in association with that of plankton samples in Nha Phu Bay, Khanh Hoa, Vietnam from December 2004 to October 2005. The toxicity of S. versicolor showed distinct seasonal variation. During the period when domoic acid level of S. versicolor was increasing, a significant level of domoic acid was detected in the plankton samples, showing the correlation between these two parameters. These findings show that plankton causative for domoic acid occurred in the bay, and S. versicolor accumulate domoic acid during a bloom of the toxic plankton by food web transfer. [ABSTRACT FROM AUTHOR]

Domoic acid was found in bivalves belonging to the genus Spondylus collected randomly from the Philippines, Vietnam, Thailand and Ishigaki Island, Japan. This is the first report of domoic acid accumulating in bivalves from tropical waters. Large differences in domoic acid levels were observed among the Spondylus specimens collected from different areas. The Spondylus specimens from the Philippines and Vietnam showed higher levels of domoic acid whereas the level in Spondylus spp. from Thailand and Japan was low. The highest level of domoic acid—more than four times the safe consumption level of 20 μg/g whole tissue—was found in a specimen from the Philippines. On the other hand, bivalves other than Spondylus collected from the same area at the same time in the Philippines showed very low levels of domoic acid, showing that bivalves belonging to the genus Spondylus accumulate specifically high levels of domoic acid. These results suggest the wide distribution of causative phytoplankton in tropical waters. [ABSTRACT FROM AUTHOR]

Tetrodotoxin (TTX) was detected by HPLC and LC-MS/MS in specimens of the horseshoe crab Carcinoscorpius rotundicauda collected from Tan Hai village, Vung Tau province, Vietnam, where cases of poisoning due to the consumption of horseshoe crab have frequently been reported. The soft tissue from 10 out of the 12 specimens analyzed showed considerable levels of TTX, making them unsafe for human consumption (81.2 ± 50.3 MU/g). Paralytic shellfish poisoning (PSP) toxins were also detected in all of the specimens, but the levels were low. These findings show that the frequency of occurrence of C. rotundicauda specimens with a high level of TTX is significantly high, and that the TTX is responsible for the food poisonings caused by the consumption of C. rotundicauda in this area. [ABSTRACT FROM AUTHOR]

Harmful algal blooms (HABs) occur frequently in the South China Sea (SCS), causing enormous economic losses in aquaculture. We analyzed historical HAB records during the period from 1980 to 2003 in SCS. We found that HABs-affected areas have expanded and the frequency of HABs varied during this period. The seasonal and annual variations, as well as causative algal species of HABs are different among the four regions. Areas with frequent HABs include the Pearl River Estuary (China), the Manila Bay (the Philippines), the Masinloc Bay (the Philippines), and the western coast of Sabah (Malaysia). HABs occurred frequently during March–May in the northern region of SCS, May–July in the eastern region, July in the western region, and year-round in the southern region. Among the species that cause HABs, Noctiluca scintillans dominated in the northern region, and Pyrodinium bahamense in the southern and eastern regions. Causative species also varied in different years for the entire SCS. Both P. bahamense and N. scintillans were the dominant species during 1980–2003. Some species not previously recorded formed blooms during 1991–2003, including Phaeocystis globosa, Scrippsiella trochoidea, Heterosigma akashiwo, and Mesodinium rubrum. Variations in HABs are related to various regional conditions, such as a reversed monsoon wind in the entire SCS, river discharges in the northern area, upwelling in Vietnam coastal waters during southwest winds and near Malaysia coastal waters during northeast winds, and eutrophication from coastal aquaculture in the Pearl River estuary, Manila Bay, and Masinloc Bay. [ABSTRACT FROM AUTHOR]

The Prorocentrum species, which are primarily marine, are distributed worldwide and occur in ocean, neritic, and littoral environments. Prorocentrum is either a planktonic or benthic genus, with some species possibly being both. Until now, about 35 species had been reported including two that are fresh-water. Some species contain toxic substances. As one of many currently active studies, we collected P. vietnamensis sp. nov. from Hon Mé, Gulf of Tongkin, Vietnam. Based on its cell shape, smooth valve surface, arrangement of valves and marginal pores, plus characteristics of the central pyrenoid, we propose that P. vietnamensis is a new species. Its attributes include straight cell sides that are parallel to each other, as well as anterior and posterior areas with rounded ends that form a short, rod-shaped cell that is unique to this species. [ABSTRACT FROM AUTHOR]

Domoic acid production was screened in the Nitzschia-like strains of benthic diatom collected from Ishigaki Island (subtropical area), Tohoku District of Japan (temperate area) and Manila Bay, the Philippines (tropical area). Domoic acid was detected in 88 out of 183 strains collected from these areas. The cellular domoic acid content of these strains ranged from 0.1 to 15.3 pg/cell. All the strains positive for domoic acid production were identified as Nitzschia navis-varingica, a new domoic acid-producing benthic diatom species that was recently found in Vietnam. This species was collected only from brackish water. These results indicate that domoic acid-producing N. navis-varingica is distributed widely in brackish water from tropical to temperate areas. [ABSTRACT FROM AUTHOR]

The seasonal bloom of the toxic dinoflagellate Alexandrium tamarense , with reference to the ambient oceanographic conditions in Hiroshima Bay, Seto Inland Sea, Japan is described. Long-term observations on the vegetative cells of A. tamarense were conducted biweekly to monthly at one fixed station in northern Hiroshima Bay, where recurrent paralytic shellfish poisoning (PSP) incidents have been occurring since 1992. Over the 5-year study period, from April 1994 to December 1998, vegetative cells of A. tamarense were detected each year within the period from January to June. Observed annual maximum cell densities of A. tamarense reached 103 –104 cells/L, and mostly peaked at a depth layer of 5 m at the sampling station in April or May. Oceanographic conditions during the bloom period were as follows: water temperatures ranged from 10.2°C to 20.2°C, and thermal stratification gradually developed around April. Inorganic nutrient concentrations were markedly low throughout the bloom period. Particularly, the annual lowermost concentration of SiO2 -Si was observed each year during this period. These environmental features indicate that the occurrence of vegetative cells of A. tamarense seems to be explained by temperature and nutrient conditions and that the A. tamarense bloom developed subsequently to or concomitantly with the diatom spring bloom. [ABSTRACT FROM AUTHOR]

ABSTRACT: The survey on scallop toxicity in association with causative dinoflagellates was conducted when the cultured scallops Patinopecten yessoensis were found to accumulate paralytic shellfish toxins in late November of 1997 at Otsuchi Bay, Iwate Prefecture, Japan. Alexandrium catenella was observed in high density at the beginning of the survey. The cell density of A. catenella decreased and completely disappeared in early December. The scallop toxicity also decreased with decrease of the cell density of A. catenella. The toxin profile of the scallop was similar to that of natural and cultured cells of A. catenella isolated from the Bay, showing that scallop toxicity is due to A. catenella. This is the first case in which paralytic shellfish toxins were confirmed in scallops during a bloom of A. catenella in Sanriku coast of Iwate Prefecture. [ABSTRACT FROM AUTHOR]

Reports the occurrence of Heterocapsa circularisquama (Dinophyceae) in a coastal area of Hong Kong, South China Sea. Observation of red samples collected in Hong Kong waters; Cell density; Findings of preliminary bioassay; Observation of thecal plate arrangement and fine structure of bioassay using mice and juvenile fishes; Technique used to identify the dinoflagellates; Importance of body scale presentation in the identification of the Heterocapsa species..

Deals with a study which describes the morphology and toxicity of Alexandrium minutum Halim found in northern Vietnam. Prevalence of paralytic shellfish poisoning (PSP) in Southeast Asia; Information on the plankton samples used in the study; Overview of the high-performance liquid chromatography analysis for PSP.