Repercussions of the Great East Japan Earthquake tsunami on ellipsoidal Alexandrium cysts (Dinophyceae) in Ofunato Bay, Japan

Shellfish aquaculture in Ofunato Bay, Northeast Japan, was seriously damaged by a tsunami generated by the Great East Japan Earthquake, March 11th, 2011, accompanied by paralytic shellfish poisoning (PSP) outbreaks caused by Alexandrium tamarense (Dinophyceae). To understand longer future trends of PSP, an investigation was made of the historical occurrence and causes of Alexandrium outbreaks after the tsunami. Vertical distributions of Alexandrium cysts in two sediment-cores from Ofunato Bay revealed that the sediments above ca. 25 cm were eroded, re-suspended and re-deposited, and they included unusually abundant Alexandrium cysts. This abundance of cysts was due to re-deposition of older sediments by the tsunami. The first Ofunato Bay PSP incident was in 1961 after the Chilean Earthquake tsunami and was probably caused by similar unusual blooms of Alexandrium germinated from older sediments as the Great East Japan tsunami, together with nutrient enrichment because of population increase at the start of shellfish aquaculture

GROWTH RESPONSES OF FIVE NON TOXIC ALEXANDRIUM SPECIES (DINOPHYCEAE) TO TEMPERATURE AND SALINITY

Growth response of five clonal cultures of Alexandrium obtained from tropical and temperate waters were examined. Experiments were carried out in eighteen variable temperature-salinity conditions (temperatures of 15 °C, 20°C, and 25°C; salinities between 5 to 30 psu) under constant illumination of 150 ± 10.0 Amol m-2 s-' at 15:9 light:dark photo-cycle. Our results showed optimum growth of all Alexandrium species at 20 - 25°C. The salinity range for optimum growth however varied among the species. Growth rates of A. eine, A. insuetum, and A. fraterculus (0.28 — 0.37 day') were higher than those of A. leei and A. pseudogoniaulax under the same culture conditions (0.14 —0.22 day-'). The three temperate species showed positive growth at suboptimum temperature, 15°C, but the tropical species did not grow and died off. Salinity tolerance of the five species in decreasing order was A. pseudogoniaulax > A. leei > A. insuetum > A. affine > A. fraterculus. Results of the present study showed vast variations in salinity tolerance among the Alexandrium species regardless the geographical origins. Adaptation of the temperate species at higher temperature indicated that the species might proliferate in warm tropical waters

Autofluorescent bodies in the toxic dinoflagellate Alexandrium tamarense: A potential indicator of the physiological condition of the species

Autofluorescent bodies were examined in cultured and natural cells of Alexandrium tamarense (Lebour) Balech collected from Ofunato Bay, Japan. Three different autofluorescent bodies (pale blue, light blue, and white) and the autofluoresced chloroplast were observed under ultraviolet light excitation. We suggest that the pale-blue and light-blue bodies represent a novel type in dinoflagellates based on their fluorescent properties. We also found that cells with pale-blue and light-blue bodies appeared predominantly in the early and middle to late exponential phases, respectively. A similar pattern was observed in natural populations during a 2-year field survey. Cells with pale-blue bodies were dominant almost one week before the bloom, whereas those with light-blue bodies were mostly apparent during the blooming stage. These results indicate that the observation of autofluorescent bodies could be useful as a physiological indicator for predicting natural population blooms of A. tamarense in Ofunato Bay

In Vitro Acylation of Okadaic Acid in the Presence of Various Bivalves’ Extracts

The dinoflagellate Dinophysis spp. is responsible for diarrhetic shellfish poisoning (DSP). In the bivalves exposed to the toxic bloom of the dinoflagellate, dinophysistoxin 3 (DTX3), the 7-OH acylated form of either okadaic acid (OA) or DTX1, is produced. We demonstrated in vitro acylation of OA with palmitoyl CoA in the presence of protein extract from the digestive gland, but not other tissues of the bivalve Mizuhopecten yessoensis. The yield of 7-O-palmitoyl OA reached its maximum within 2 h, was the highest at 37 °C followed by 28 °C, 16 °C and 4 °C and was the highest at pH 8 in comparison with the yields at pH 6 and pH 4. The transformation also proceeded when the protein extract was prepared from the bivalves Corbicula japonica and Crassostrea gigas. The OA binding protein OABP2 identified in the sponge Halichondria okadai was not detected in the bivalve M. yessoensis, the bivalve Mytilus galloprovincialis and the ascidian Halocynthia roretzi, though they are known to accumulate diarrhetic shellfish poisoning toxins. Since DTX3 does not bind to protein phosphatases 1 and 2A, the physiological target for OA and DTXs in mammalian cells, the acylation of DSP toxins would be related to a detoxification mechanism for the bivalve species

Toxin Profiles of Okadaic Acid Analogues and Other Lipophilic Toxins in <i>Dinophysis</i> from Japanese Coastal Waters

The identification and quantification of okadaic acid (OA)/dinophysistoxin (DTX) analogues and pectenotoxins (PTXs) in Dinophysis samples collected from coastal locations around Japan were evaluated by liquid chromatography mass spectrometry. The species identified and analyzed included Dinophysis fortii, D. acuminata, D. mitra (Phalacroma mitra), D. norvegica, D. infundibulus, D. tripos, D. caudata, D. rotundata (Phalacroma rotundatum), and D. rudgei. The dominant toxin found in D. acuminata was PTX2 although some samples contained DTX1 as a minor toxin. D. acuminata specimens isolated from the southwestern regions (Takada and Hiroshima) showed characteristic toxin profiles, with only OA detected in samples collected from Takada. In contrast, both OA and DTX1, in addition to a larger proportion of PTX2, were detected in D. acuminata from Hiroshima. D. fortii showed a toxin profile dominated by PTX2 although this species had higher levels of DTX1 than D. acuminata. OA was detected as a minor toxin in some D. fortii samples collected from Yakumo, Noheji, and Hakata. PTX2 was also the dominant toxin found among other Dinophysis species analyzed, such as D. norvegica, D. tripos, and D. caudata, although some pooled picked cells of these species contained trace levels of OA or DTX1. The results obtained in this study re-confirm that cellular toxin content and profiles are different even among strains of the same species