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Red Tides in Nagasaki Bay during Summer Season of 1979


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Title: Red Tides in Nagasaki Bay during Summer Season of 1979
Other Titles: 1979年夏季における長崎湾の赤潮
Authors: Dahril, Tengku / Iizuka, Shoji
Authors (alternative): ダハリル, テンク / 飯塚, 昭二
Issue Date: Feb-1981
Publisher: 長崎大学水産学部
Citation: 長崎大学水産学部研究報告, v.50, pp.17-26; 1981
Abstract: Almost every year during the summer season, red tides have occurred in Nagasaki Bay. Red tides are caused by various kind of phytoplankton and bay waters discolor like coffee by the exclusive growth of a single organism or mixed growth of two or three organisms. However, very little is known about red tide in this bay. In this paper the authors dealt with red tides in Nagasaki Bay during the summer season of 1979. The innermost part of this bay was divided into 3 areas. Five water sampling stations were fixed in each area and water samplings were done of a water column 4.5m in depth at each station with transparent Akryl synthetic resin tubes (18mm in inner diameter; 1.5×3m in length). Collected sea water subsample was put in a plastic vessel and mixed with the other sea water subsamples of the same area. Then, sea water sample of a fixed volume was taken randomly from the mixed sea water subsample. These samplings were continued for 79 days from June 12 to August 29 at interval of twice a week, generally, and a total 21 samples per area were collected. The dominant organisms during this season were Skeletonema costatum and Olisthodiscus sp. and the accompanying organisms were Prorocentrum minimum, Prorocentrum obtusidens and Thalassiosira sp.. The concentration of chlorophyll-a and cell density in this layer were 108.3mg m⁻³ and 5.8×10⁷ cells l⁻¹ in maximum, respectively. During the period of survey red tides were observed for about one month and especially, the bay waters were discolored densely every day in August. Those dense discolorations of this bay are close to that of the highly polluted innermost part of Tokyo Bay and Osaka Bay. To understand completely the causative factors of the occurrence of red tide is difficult. However, it is possible to imagine that high concentration of pollutants which were supplied by river water and polluted water discharged from an urban waste treatment plant might accelerate the growth of red tide organisms. / 長崎湾では毎年夏になると赤潮がおこる.赤潮はいろいろの種類によって起こるが,夏季の長崎湾はいつも何かの種か,二つか三つの種の混合した大増殖で湾の海水はコーヒー色に着色する.ここでは1979年夏季の観察から長崎湾の赤潮について報告した.湾奥部(女神から浦上川口まで)を3水域に分け,各区に5点の採水点を設け観察の対象とした.採水は透明アクリル・パイプ(内径18mm,長さ1.5m,3本接続)による水柱採水法で,これにより表面から4.5mの深さの海水を水柱として採取した.採取した海水は各区ごとに一つの容器に入れ,これを各区の標本海水とした.このようなサンプリングを6月12日から8月29日まで夏季の79日間のうち21回行なった.標本海水は顕微鏡下の種別の計数と,クロロフィルーaの測定,塩分および栄養塩類の定量をおこなった.長崎湾の赤潮の原因種はSkeletonema costatumとOlisthodiscus sp.の二種が優占種であった.ほかにProrocentrum minimumとProrocentrum obtusidensおよびThalassiosira sp.などが出現した.最高値はクロロフィルーaで108.3mg m⁻³,細胞密度は5.8×10⁷ Cells l⁻¹ であった.観察期間中1ケ月間以上は赤潮状態であり,8月に入ると毎日のように海水が着色する長崎湾の状況は原因種の類似性においても東京湾,大阪湾と似ている.これは湾奥部に川口をもつ二河川の存在と下水・し尿処理排水など都市排水の流入の影響のためと思われる.このため湾水は強く富養栄化し,これが赤潮発生を促進しているのでないかと思われる.
URI: http://hdl.handle.net/10069/30537
ISSN: 05471427
Type: Departmental Bulletin Paper
Text Version: publisher
Appears in Collections:第50号

Citable URI : http://hdl.handle.net/10069/30537

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