A-335 Akira MIYAZONO
Effects of water temperature and irradiance conditions on the growth of the toxic dinoflagellate isolated from Funka Bay. Alexandrium tamarense
Alexandrium Effects of water temperature, irradiance and day length on the growth of the toxic dinoflagellate isolated from Funka Bay, southeast Hokkaido, were investigated. The strain of e was able tamarense A. tamarens to grow under conditions of 3-5℃, and had a maximum growth rate under 10-18℃. These results are in accordance with the seasonal fluctuations of observed . This indicates that the strain has adapted A. tamarense in situ to the low temperature conditions in Funka Bay. Compensation light intensities were below 5 E m s at 3-18℃. μ -2 -1 Light intensity of the half-saturation constant increased from 13.26 at 3℃to 39.35 E m s at 10℃ and was μ -2 -1 more constant between 32.77-39.35 E m s at 10-18℃. This indicates that the strain is able to grow under μ -2 -1 low irradiance conditions. Growth inhibition under high light intensity was not observed under 600 E m s at μ -2 -1 10-18℃. The growth rate increased as day length become longer under each temperature. Day length mostly affected the growth rate at 10℃. Relative light intensities of underwater irradiance were 0.8-5.2% of the sea surface irradiance at 20m depth, and 0.2-4.1% at 30m depth from January to July at the Yakumo station in 1996-1998.
The compensation light intensities (I :2.37-4.46 E m s ) of the strain of indicate that 0 μ -2 -1 A. tamarense is able to grow between 20 and 30m depth in Funka Bay. A. tamarense
Alexandrium Effects of water temperature, irradiance and day length on the growth of the toxic dinoflagellate isolated from Funka Bay, southeast Hokkaido, were investigated. The strain of e was able tamarense A. tamarens to grow under conditions of 3-5℃, and had a maximum growth rate under 10-18℃. These results are in accordance with the seasonal fluctuations of observed . This indicates that the strain has adapted A. tamarense in situ to the low temperature conditions in Funka Bay. Compensation light intensities were below 5 E m s at 3-18℃. μ -2 -1 Light intensity of the half-saturation constant increased from 13.26 at 3℃to 39.35 E m s at 10℃ and was μ -2 -1 more constant between 32.77-39.35 E m s at 10-18℃. This indicates that the strain is able to grow under μ -2 -1 low irradiance conditions. Growth inhibition under high light intensity was not observed under 600 E m s at μ -2 -1 10-18℃. The growth rate increased as day length become longer under each temperature. Day length mostly affected the growth rate at 10℃. Relative light intensities of underwater irradiance were 0.8-5.2% of the sea surface irradiance at 20m depth, and 0.2-4.1% at 30m depth from January to July at the Yakumo station in 1996-1998.
The compensation light intensities (I :2.37-4.46 E m s ) of the strain of indicate that 0 μ -2 -1 A. tamarense is able to grow between 20 and 30m depth in Funka Bay. A. tamarense
A-336 Akira MIYAZONO
Vertical distribution, germination activity and seasonal density variations of cysts of the toxic dinoflagellate, in Funka Bay. Alexandrium tamarense
Sediment samples were collected monthly off the Yakumo station in Funka Bay, Hokkaido, Japan from April, 1996 to March, 1997. Vertical distribution of cyst, seasonal variation of cyst density and germination activity of were investigated. The cyst densities in each 1cm of 0-15cm core samples changed verticaly, Alexandrium tamarense and two dense layers of cysts, 4-7cm and 12-14cm from the bottom surface, were observed. The two dense layers of cysts suggests that there were two periods when blooms of occurred in Funka Bay. The cyst A. tamarense density was 186-365 in 0-3cm,406-1157 in 3-6cm, 211-736 in 6-9cm, and 90-377 cells per gram sediment wet weight in 9-12cm from the bottom surface.Seasonal variation of the cyst density in each layer was not observed.
Ten day batch culture examinations of cysts in the 0-3,3-6, 6-9 and 9-12cm layers under a suitable temperature for germination (10℃) were conducted. Over 80% of the cysts in the 0-3cm layer germinated from February to May and below 2% of the cysts germinated from August to December. The same seasonal variations of germination activity were observed in the examination of cysts in the 3-6, 6-9, 9-12cm layers. From these results, it is suggested that cyst germination of the Funka Bay strain is controlled by a circannual internal A. tamarense clock. In batch culture examinations of the cysts under conditions of the bottom temperature, 2-4% of in situ the cysts germinated from February to May and below 0.5% of the cysts germinated from August to December. This indicates that the strain of is able to germinate under 3-5℃ and might play an important role in A. tamarense the occurrence of the winter vegetative population.
Sediment samples were collected monthly off the Yakumo station in Funka Bay, Hokkaido, Japan from April, 1996 to March, 1997. Vertical distribution of cyst, seasonal variation of cyst density and germination activity of were investigated. The cyst densities in each 1cm of 0-15cm core samples changed verticaly, Alexandrium tamarense and two dense layers of cysts, 4-7cm and 12-14cm from the bottom surface, were observed. The two dense layers of cysts suggests that there were two periods when blooms of occurred in Funka Bay. The cyst A. tamarense density was 186-365 in 0-3cm,406-1157 in 3-6cm, 211-736 in 6-9cm, and 90-377 cells per gram sediment wet weight in 9-12cm from the bottom surface.Seasonal variation of the cyst density in each layer was not observed.
Ten day batch culture examinations of cysts in the 0-3,3-6, 6-9 and 9-12cm layers under a suitable temperature for germination (10℃) were conducted. Over 80% of the cysts in the 0-3cm layer germinated from February to May and below 2% of the cysts germinated from August to December. The same seasonal variations of germination activity were observed in the examination of cysts in the 3-6, 6-9, 9-12cm layers. From these results, it is suggested that cyst germination of the Funka Bay strain is controlled by a circannual internal A. tamarense clock. In batch culture examinations of the cysts under conditions of the bottom temperature, 2-4% of in situ the cysts germinated from February to May and below 0.5% of the cysts germinated from August to December. This indicates that the strain of is able to germinate under 3-5℃ and might play an important role in A. tamarense the occurrence of the winter vegetative population.
A-337 Osamu MURAKAMI
Length at maturity and age at maturity of cresthead flounder Pleuronectes schrenki in Saroma Lake, Hokkaido
Assessment of the spawning period, length at maturity and age at maturity are particularly important in order to establish effective resource management policies, such as the regulation of the fishing period and length, management type of SPR(spawning per recruitment) of fisheries. Therefore, using data for the cresthead flounder in Saroma Lake during 1989-1999, the spawning period was examined, and the relationship Pleuronectes schrenki between length and maturity rate,between age and maturity rate were compared using three function models of the maturity curve. It was presumed that the spawning period was between April and May. Based on the results, it seems that maturity depends on length more than age. The length at 50% maturity estimated in October and November was 13.7cm in males,17.1cm in females,and the age at 50% maturity was about 4 years in males,about 5 years in females. In the case of estimating the maturity curve, the period of year which is chosen is most significant, and the simple logistic function model is concluded to be sufficient for practical purposes.
Assessment of the spawning period, length at maturity and age at maturity are particularly important in order to establish effective resource management policies, such as the regulation of the fishing period and length, management type of SPR(spawning per recruitment) of fisheries. Therefore, using data for the cresthead flounder in Saroma Lake during 1989-1999, the spawning period was examined, and the relationship Pleuronectes schrenki between length and maturity rate,between age and maturity rate were compared using three function models of the maturity curve. It was presumed that the spawning period was between April and May. Based on the results, it seems that maturity depends on length more than age. The length at 50% maturity estimated in October and November was 13.7cm in males,17.1cm in females,and the age at 50% maturity was about 4 years in males,about 5 years in females. In the case of estimating the maturity curve, the period of year which is chosen is most significant, and the simple logistic function model is concluded to be sufficient for practical purposes.
A-338 Shoichi AKAIKE , Akio TAKIYA , Fujinori TSUDA , Akira MOTOYA , and Kazuhiro TAKAHASHI
Seasonal occurrence of a kelp-boring amphipod,Ceinima japonica aiong the coasts of Hokkaido from 1997 to 2001.(Short Paper)