Marine Ecosystems under the Global Change in the Northwestern Pacific
Blooms of Pseudo-nitzschia and domoic acid producers from Amursky Bay, the northwestern East/Japan Sea,
2005–2011
Inna V. Stonik
P. calliantha, and P. delicatissima as the dominant species. These species have been associated with domoic acid production in other regions of the world (Bates, Trainer, 2006; Trainer et al., 2008).
An analysis of the samples collected between January 2005 and December 2011, revealed the occurrence of multispecific blooms ofPseudo-nitzschia. The peaks of the Pseudo-nitzschia spp.
density were recorded in summer and in autumn. Abundances of Pseudo-nitzschia were highest in autumn 2005 with up to 1.6·106 cell L−1 (see figure).
The first most intense bloom ofPseudo-nitzschia species was observed in October–November 2005 at a salinity of 31–33.5‰ and a water temperature of 6–12°C. The first peak ofPseudo-nitzschia spp. cell density (with a mean value of 1.4·106 cell L−1), which was recorded in the second half of October after heavy rains, was mainly caused by the massive development of P. multistriata (67% of the total phytoplankton density) and P. calliantha (9%). The second relatively small peak of cell density of Pseudo-nitzschia species (water column average 0.9·105 cell L−1) was recorded at the beginning of November when water temperature decreased to 6°C and salinity slightly increased to 33.5‰. The second cell density peak was also connected with the intense development of P. multi- striata (an average of 60% of total density) and P. calliantha (10%). The field samples collected during this bloom event did not contain detectable and quantifiable domoic acid (DA).
The second bloom occurred in September 2007 at a salinity of 29–30‰ and a water tempera- ture of 18–20°C. It reached cell concentrations of 2·105 cell L−1 consisting of P. calliantha (up to 1.7·105 cell L−1 or 29%) and P. delicatissima (up to 2.6·104 cell L−1 or 4%). The field samples collected in September 2007 were not tested for DA.
The small peaks of cell density of Pseudo-nitzschia species were recorded in October 2009 (up to 2.1·104 cell L−1), in August 2011 (up to 2.4·104 cell L−1) and in September–October 2011 (up to 2.5·104 cell L−1). These events were dominated by P. calliantha with an abundance of 1.9·104 cell L−1, and P. delicatissima with an abundance of 1.2–1.8·104 cell L−1.
Our observations indicate that the peaks of the Pseudo-nitzschia spp. density were recorded in summer and in autumn. High concentrations of P.calliantha, P. multistriata, and P. delicatissima have
Dynamics of the Pseudo-nitzschia spp. densities in relation to salinity and temperature variations during October–November 2005.
Blooms of Pseudo-nitzschia and domoic acid producers
been observed in summer and autumn, with abundances exceeding 1.6·106 cell L−1 and constituting 29–67% of the total density of the phytoplankton assemblage.
DA analysis of unialgal cultures of Pseudo-nitzschia (two isolates) collected from Amursky Bay in October 2011 has been performed. DA was found in stationary-phase P. multistriata culture (days 30–39) at concentrations varying between 334.4 and 1081,8 pg DA ml−1 and DA cell quota varying between 0.017 and 0.024 pg DA per cell, which fall within the lower range reported for other isolates of Pseudo-nitzschia (Thessen, Stoecker, 2008; Alvarez et al., 2009). No DA was detected (<10 pg ml−1) in culture of P. americana from the same locality. Toxicity of a culture of P. multiseries isolated from Amursky Bay has previously been documented (Orlova et al., 2008). Domoic acid was found in stationary-phase (days 20–35) cultures of P. multiseries isolated from Peter the Great Bay at concentrations varying between 180 and 5390 ng ml−1 or 2 to 21 pg cell−1, which is in the range reported for other isolates of P. multiseries. No domoic acid has been detected in cultures of P. calliantha and P. multistriata from the same locality (Orlova et al., 2008).
The relatively low toxicity level of Pseudo-nitzschia cultures isolated from Amursky Bay dur- ing 2005–2011 argues against making Pseudo-nitzschia a monitoring priority; however, having his- torical data on abundance and toxicity could prove valuable in the future. Current conditions in Amursky Bay appear to be unfavorable to highly toxic Pseudo-nitzschia blooms; however, cultural eutrophication and climate change may alter environmental conditions, making them more conduc- tive to DA production. The potential toxicity of Pseudo-nitzschia clones from Amursky Bay suggests that phytoplankton and shellfish toxicity monitoring is warranted in Amursky Bay, where bivalves are commercially harvested for human consumption.
Acknowledgements
This research was supported by grants from the Russian Foundation for Basic Research (no. 10-04-01438_а and 11-04-98557-р_vostok_а), and from Far East Branch of the RAS (12-III-A-06-077, 12-I-P4-02, 12-I-P28-03, 12-I-P30-09).
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Marine Ecosystems under the Global Change in the Northwestern Pacific