Surveys on harmful algae in the coastal areas of southern Iwate Prefecture

Representative Organization: Tohoku University

2014/04/01 - 2015/03/31
Every one/two month

Ofunato Bay, Okirai Bay

Field survey

Mass culture of shellfish and ascidians has been popular in Sanriku coastal areas maintaining important part of the fisheries there, however paralytic shellfish poisoning (PSP) and diarrhetic shellfish poisoning (DSP) have become great fear against the safe consumption of seafood. PSP and DSP toxins were found to be accumulated to shellfish from the toxic dinoflagellates such as Alexandrium tamarense and Prorocentrum lima respectively. Amnesic shellfish poisoning (ASP) toxin produced by Pseudo-nitzschia multiseries were also found to be the origin of the weekly toxic scallop and blue mussel in Ofunato Bay. Another diatom Nitzschia navis-varingica distributes in brackish areas also has the potential of ASP there. It produces not only domoic acid (DA) but also isodomoic acid B (IB). The Tsunami attacked on March, 2011 along these coastal areas might affect the occurrence of these toxic microalgae. It is important to observe the effect of the disaster on the occurrence of the toxic microalgae for the fisheries there.This study was performed to observe the occurrence of toxic and harmful microalgae and to measure/estimate the PSP, DSP and ASP mainly in Ofunato and Okirai Bay.

Survey on toxic and harmful dinoflagellates 1. Monitoring of PSP and DSP producing dinoflagellates Monitoring on toxic and harmful vegetative harmful algae was performed in Ofunato and Okirai Bay, resulting in confirming the occurrence of A. tamarense and P. lima, a causative dinoflagellate of PSP and DSP respectively. However, in both Bays, they occurred but did not bloom at all. Heterotrophic dinoflagellates seemed to exceed in the occurrence. Benthic dinoflagellate has been reported mainly in tropical or subtropical waters, however 14 species from 5 genera could be confirmed in Nami-ita, Okirai Bay. Among them P. lima which had been reported to produced okadaic acid (OA) was confirmed. However it was newly confirmed that it produces not only OA but also DTX-1. A. tamarense cyst was surveyed in horizontal concentration in the bottom mud of Ofunato Bay, resulted in confirmation that it seemed to decrease in this fiscal year (2014) comparing with those in 2012 or 2013. The concentration decreased much especially in center or back of the Ofunato Bay (eg. decreased to less than 10 % of that of 2012 in some site). Concentration of A. tamarense cyst in the surface of bottom mud at two fixed points was measured in every month. The result showed that there was no remarkable seasonality in its concentration. It might because of the no bloom of A. tamarense in this fiscal year. 2. Monitoring of ASP producing diatom Plankton net samples collected from 4 sites in Ofunato Bay and 5 sites in Okirai Bay showed the DA toxicity of 25-490 pg/L of sea water (June, November, January, Average and SD: 158 and 156 pg/L) and 50-543 pg/L of sea water (May, June, August, Average and SD: 328 and 154 pg/L) respectively. DA concentration of the Ofunato net sample was almost the same average level as that of 2013, on the other hand that of the Okirai net sample showed the four fold higher level than that of 2013. However, fortunately, DA was not detected from cultured scallop nor blue mussel in both bays, showing that no remarkable bloom in both bays occurred, or if they bloomed, no suitable conditions were prepared for their high toxin production. N. navis-varingica has been reported to distribute mainly in brackish water areas. Distribution of N. navis-varingica was newly confirmed at the site one km above the site where it had been confirmed before the 2011 disaster, showing that the brackish area moves up to one km above, because of land subsidence. In this fiscal year, collection of N. navis-varingica was tried from the mud about 5-10 cm depth from the surface. Two strains were isolated showing the toxin profile of a) DA:IB=100:0, and b) 51:49 respectively. The relative toxicity of IB was less than 1/100 of DA, showing that the toxicity of shellfish accumulate the toxin having much IB seemed to be weaker.

FY2014 Studies on the coastal environment and marine resources in the southern part of Iwate Prefecture