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

Representative Organization: Tohoku University

2013/04/01 - 2014/03/31
Dinoflagellate survey: Apr. 2013 - Mar. 2014 (every month), Cyst survey: Sep. and Oct. 2013, Diatom survey: Apr. 2013 - Mar. 2014 (every two month)

Okkirai Bay, Ofunato Bay, Otsuchi Bay

Field survey

1. Periodical monitoring on the abundance of harmful microalgae will be conducted at 2 stations in Ofunato Bay and Okkirai Bay, Iwate Prefecture. 2. Horizontal distribution of Alexandrium resting cyst will be surveyed for the sediment of Ofunato Bay. 3. Peridical monitoring of the appearance of ASP toxin-producing pennate diatoms followed by isolation of Pseudo-nitzschia multiseries and measuring the ASPtoxin level of the filtered net sample. 4. Investigation of re-appearance of N. navis-varingica that was once disappeared by the tsunami on March 11, 2011.

1. Survey on toxic or harmful dinoflagellates *Through the monitoring survey, the occurrence of causative dinoflagellate of PSP and DSP was observed in Ofunato Bay and Okkirai Bay, respectively. These occurrnce pattern of them was almost similar to those before the great earthquake in 2011, except for massive abundance of Alexandrium tamarense. *In a survey for horizontal distribution of Alexandrium resting cyst, a decrease of cyst abundance was recognized in the surface sediments of Ofunato bay, between 2013 and 2014. Survey for core sediment sample in Ofunato Bay revealed the influence of the tsunami to disturbance of sediment and cyst distribution. Vertical change of water contents and particle size composition suggest that the re-accumulated layer after the tsunami reached to almost 20-cm depth from surface. Cyst of Alexandrium was observed in this re-accumulaed layer in a high density with four or five peaks of abundance. These results indicate that diffused cysts by tsunami did not accumulated only on the surface of sediment in Ofunato Bay. 2. Survey on ASP toxin producing diatoms *Domoic acid was detected from the plancton net samples (20-170 pg/L sea water in Ofunato Bay) and (8-31 pg/L sea water in Okkirai Bay). Three strains of Pseudo-nitzschia multiseries were isolated from the net sample of Ofunato Bay in October. As a general chacteristic of toxin production of P. multiseries, it is well known that toxin level increases in late stationary growth phase. However, the three isolates showed the characteristic to die before the late stationary growth phase. This might be the reason why the toxin levels of the strains were shown to be rather low in culture experiment (average 0.64 pluses and minuses 0.38pg/cell, DA100%). The toxin levels of scallops (Ofunato Bay, June, September, October, 2013 and February, 2014) and scallops and mussels (Okkirai Bay, November, December, 2013, February, 2014) were below the detection level (0.5 ug/g). It is unknown whether this might depends on the small scale of P. multiseries bloom or the weak characteristic of P. multiseries isolates after the tsunami in 2011 or other reasons. *Many isolates of N. navis-varingica were also established from Otsuchi Estuary where it was isolated last year. In Ofunato Bay, N. navis-varingica was first islated in 2013 from the esturine area 1 km above the site where N. navis-varingica had been isolated before the tsunami. This re-appearance seemed to depend on the movement of esturine area to 1km above because of land subsidence. N. navis-varingica was also isolated from the esturine area in Hitachi and Ichihara where N. navis-varingica disappeared after the 2011 tsunami. Toxin production of theseisolates were confirmed by culture experiments. The origin of the re-appeared N.navis-varingica was seemed to be 1) survived vegitative cells/cysts or 2) newly came vegitative cells from the Tsugaru warm water current.

FY2013 Studies on the coastal environment and marine resources in the southern part of Iwate Prefecture