An outbreak of food poisoning in Canada during autumn 1987 was traced to cultured blue mussels (Mytilus edulis) from the Cardigan Bay region of eastern Prince Edward Island (P.E.I.). The toxin, identified as domoic acid, had not previously been found in any shellfish and this outbreak represents the first known occurrence of human poisoning by this neurotoxin. A plankton bloom at the time of the outbreak consisted almost entirely of the pennate diatom, Nitzschia pungens f. multiseries, and a positive correlation was found between the number of N. pungens cells and the concentration of domoic acid in the plankton. Nitzschia pungens f. multiseries isolated from Cardigan Bay produced domoic acid in culture at levels (1 to 20 pg∙cell−1) comparable with values estimated for N. pungens in the plankton samples. Isolates of several Cardigan Bay phytoplankton, including the closely related species Nitzschia seriata, failed to produce domoic acid. Other Nitzschia spp. and two Amphora coffeaeformis isolates also failed to produce domoic acid. We conclude that N. pungens was the major source of the domoic acid in toxic mussels in eastern P.E.I. The recurrence, in November 1988, of a monospecific bloom of N. pungens and the presence of domoic acid in plankton and mussels reinforced this conclusion.

In phytoplankton of the eastern tropical Pacific Ocean from 25 to 90 percent of the biomass (measured as chlorophyll a) and 20 to 80 percent of the inorganic carbon fixation were attributable to particles that could pass a screen with a 1-micrometer pore diameter. Evidence is presented that these are indeed autotrophic cells and not cell fragments.

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ABSTRACT:In this study, the performance of the weather research and forecasting (WRF) ARW regional model was evaluated for simulating the regional scale precipitation during Indian summer monsoon (ISM) at 30 km resolution over seven different homogeneous rainfall zones falling under different climatic (perhumid, humid, dry/moist subhumid, dry/moist semiarid, arid) regions of India. Seasonal scale simulations were made for ten summers (JJAS months) over 2000-2009 using the boundary conditions derived from the National Centers for Environmental Prediction (NCEP) reanalysis data. Sensitivity experiments were conducted with three convection schemes (Kain-Fritsch, KF; Betts-Millor-Janjic, BMJ; GrellDevenyi, GD). Simulated regional climate was evaluated by comparison of precipitation with 0.5°India Meteorological Department (IMD) gridded rainfall data over land, Tropical Rainfall Measuring Mission (TRMM) rainfall data over the ocean and atmospheric circulation fields with 1°NCEP global final analysis (FNL). Although all the simulations showed spatio-temporal rainfall patterns, BMJ had least bias towards dryness whereas KF had moist bias and GD had higher dry bias. BMJ could simulate low, moderate and high rainfall reasonably well with relatively higher correlations and threat scores, lower bias and mean absolute errors in most zones as compared to better simulation of heavy precipitation events with KF and low rainfall days alone with GD scheme. The better performance of BMJ scheme is evident owing to better simulation of surface pressure, temperature, and geopotential, lower and upper atmospheric flow fields. Simulations revealed a relatively less intensive heat, weaker low-level westerly winds, weaker north-south geopotential gradients, weaker subtropical easterlies in the El Niño years than in the La Niña years, which indicate the model is able to simulate the interannual variations in monsoon characteristics.

ABSTRACT. Dornoic acid (DA) production by Pseudo-nitzschia multiseries (Hasle) was studied at various silicate concentrations and under silicate perturbation. Both slowly dividing and non-dividing population~ produced DA, and the production rates were inversely correlated with the ambient silicate concentrations. Production of DA was significantly enhanced when overall cell metabolism (i.e growth rate) declined as a result of silicate stress. Following silicate starvation, cultures supplemented with silicate registered uptake, but suspended DA production. Results suggest that luxury uptake of Si by P. multisenes may happen only in phys~ologically active populations, i.e, the exponential phase, but not in the stationary phase. There were 2 stages of DA production The first stage corresponded to a decline in growth caused by moderately low lcvels of remaining s~licate in the medium, wh.ile the second stage was caused by severe silicate limitation. The production rate during the second stage (13.67 to 30.20 fg DA cell-' d-') was about an order of magnitude higher than during the first stage (0.97 to 4.98 fg DA cell-' d-l). Increases and decreases in cellular DA content corresponded to decreases and increases in growth rates.KEY WORDS: Domoic acid . Pseudo-nitzschia multiseries . Silicate limitation . Batch culture INTRODUCTIONPseudo-nitzschia multiseries, formerly known as Pseudonitzschia pungens f. multiseries (Hasle, 1995), produces domoic acid (DA), which has caused amnesic shellfish poisoning (ASP) in Atlantic Canada (Addison & Stewart 1989). The ASP problem has now been observed on both the Atlantic and Pacific coasts of North America (Fritz et al. 1992, Garrison et al. 1992. Studies on DA production have shown it to occur only during the stationary phase, coinciding with low levels of silicate in the medium (Subba Rao et al. 1990, Bates et al. 1991, Pan et al. 1991). These observations suggest a possible relationship between silicate limitation and DA production. However, direct linkage between DA production and silicon depletion is unlikely, as silicate is neither a component of DA nor apparently involved in its synthesis.The magnitude of a diatom bloom is often directly related to the availability of silicon in sea water. Silicon regulates the growth and frustule formation of diatoms. Decreases in silicate concentrations to low or undetectable levels in marine and freshwater habitats during diatom blooms have been well documented (Paasche 1973a, Sommer & Stabel 1983, Egge & Aksnes 1992, Harrison et al. 1993.In cultures, silicate concentrations in the medium may regulate the yield of diatom cells (Taguchi et al. 1987). Cessation of cell division, which may be due to cessation of DNA synthesis (Darley & Volcani 1969, Sullivan & Volcani 1973, was found to accompany depletion of silicon in the culture medium (Lewin 1955, Lewin & Chen 1968, Vaulot et al. 1987, Brzezinski et al. 1990. Bates et al. (1991) first showed a connection between silicate limitation and DA production. Two of their 5 treatments with low s...

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Production of domoic acid (DA), a neurotoxin, by the diatom Pseudo‐nitzschia multiseries (previously Nitzschia pungens f. multiseries) Hasle and its cellular chemical composition were studied in phosphate‐limited chemostat continuous cultures and in subsequent batch cultures. Under steady‐state chemostat conditions, DA production increased from 0.01 to 0.26 pg DA · cell−1· d−1 as the growth rate decreased. When the nutrient supply was discontinued (to produce a batch culture), DA production was enhanced by a factor of ca. 3. DA production was temporarily suspended upon addition of phosphate to the batch cultures but resumed 1 d later at a higher rate coincident with the decline of phosphate uptake. In both steady‐state continuous culture and batch culture, more DA was produced when alkaline phosphatase activity (APA) was high. The association of high DA production with high levels of APA and high cellular N:P ratios strongly suggests that phosphate limitation enhances DA production. Also, DA production was high when other primary metabolism (e.g. uptake of carbon, nitrogen, phosphorus and silicon, and cell division) was low, but chlorophyll a and adenosine triphosphate were generally high. This suggests that the synthesis of DA requires a substantial amount of biogenic energy.

[1] The NCEP/NCAR reanalysis data during the period 1958 -1998 show a positive trend in the 100 hPa zonal wind, decrease in the strength of Tropical Easterly Jet (TEJ) during the summer monsoon period of June through September. This is confirmed by the Radiosonde data. The number of observed Tropical Cyclonic Systems (TCS) over Bay of Bengal during the same period shows a decreasing trend. There is a strong negative correlation (À0.549 for the period 1958 -1998, 41 years, significant at 99.9% level by a two sided student t test) between the strength of TEJ and the number of Bay of Bengal TCS. This result has potential for long-range prediction of TCS, which is vital for the prediction of monsoon rainfall.