Bull. Fac. Fish. Nagasaki Univ., No. 50, 17,...,26(1981) 17
Red Tides in Nagasaki Bay during Summer Season of 1979
Tengku Dahril and Shoji IIZUKA
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. 5 m in depth at each station with transparent Akryl synthetic resin tubes (18 mm in inner diameter; 1.5 x 3 m 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 108.3 mg m-3 and 5.8 × 107 cells /-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.
Nagasaki Bay is one of the most important fishing ports situated in the western coastal area of Kyushu, Japan. Nagasaki City, of 440,000 people, is located on the coast of the innermost parts of the bay. Area and mean depth of the bay are about 11.03 km2 and 19. 96 m and tidal ranges are 2. 32 m at spring tide and 1.12 m at neap tide. From those values, exchanged volumes during a half tidal period are estimated 11.17 % and 5.61 % to total volume of the bay, respe- ctively. In innermost parts, there are two rivers, Urakami R. and Nakashima R. and the pollutant influx loads by both rivers are 21.15 ppm and 11.88 ppm in BOD with
reference to the published data in 1976 by Department of Environment Protection, Na- gasaki Prefecture. Meanwhile, near the mouth of the Urakami R. there is an urban waste water treatment plant for Nagasaki City which discharges the treated waste water of 35,000 tons a day toward Urakami R.. Concentrations of nitrogen and phospho- rus in the discharged water are about 44.0 pg-atom 1-1 and about 5. 8 pg-atom 1-1, respectively, according to Nagata's personal data. Inflow of such nutritiously rich water may play an important role an eutrophication of Nagasaki Bay. Perhaps, from this reason, almost every year, red tides have occurred
in this bay when warm season comes． Red tides are caused by various kinds of phyto−
plankton． Bay water discolors like coffee because of 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 with exception of
incomplete reports of lizuka and lrie．（1966 and 1968）． ln this paper C the authors dealt with red tide in Nagasaki Bay during the summer season of 1979．
Methods and materials
Survey were conducted in innermost parts of the bay within an area of 3．05 km2．
Survey Stations were distributed in a north−
east direction line reaching from Megami to its opposite coast， Kanzaki． The parts were divided into three areas， Area 1， the nearest to Urakami R．， Area II， the middle parts and Area III， the farthest most part． Five water sampling stations were fixed in each area
1300
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R．
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，｝
Kanzakj．軸軸望1一一ご● Megami
10 、 II ＼ ／ Nagasa，ki 隻1
4 City
・ N ノ コ
v
N o 400m
一
3204i：N
121 052：E
Fig． 1． Survey locations in Nagasaki Bay
（Fig． 1）． Water samplings were done with transparent Akryl synthetig resin tubes （18 mm in inner diameter； 1．5×3 m in length）
which were lowered gradually but vertically until 4．5 m in depth and elevated again to the boat after upper mouth of the tube was fixed tightly by a rubber stopper． By means of this procedure， subsample sea w ater was collected as a water column till 4．5 m in depth at each station． Collected subsample sea water was put in a plastic vessel and mixed with the Qther subsample sea water of the same area． Then， sample sea water of a fixed volume was taken randomly from the mixed subsample sea water． Such sam−
plings were carried out principally twice a week from June 12 to August 15 and once a week after August 15 to the end of August．
A total of 21 samples per area were collected for 79 days during the surveys． After measuring water temperature on the boat，
samples were brought to the laboratory to determine chlorophyll−a salinity， inorganic nutrients and to observe species composition of phytoplankton and to count cell numbers．
Cell counting was done three times by O．1 ml of concentrated plankton suspending sea water by naturally dropping a millipore filter
（1．2 pt）． Chlorophyll−a determination was done by fluorometric method （Strickland and Parsons， 1972）． Determination of nutrients followed by mean of the method stated in Kaiyo−kansoku−shishin （1970） published by the Oceanographic Society of Japan．
Results
Changes of temperature and salinity，．
inorganic nutrients， chlorophyll−a and cell number of phytoplankton in each area during the survey are shown in Figs． 2， 3， 4 and 5，
respectively．
Temperature varied from 22．2 O C at the beginning of the survey to．a maximum of 30．3 OC in early August and Salinity ranged from 21．2 to 33．4 ％fi． Variable patterns of
o c 30 28 26 24 22 0／00 32 28 24 20
Bull． Fac． Fish． Nagasaki Univ．， No． 50 （1981）
TEFIPERATURE 一1pg−atom Z 6 4 ， 摘
； i一， 2 ， ：■t寒 ・ひ ミ
02
1
06281
1
﹂マ043210
NO3一 N
︑︑
、
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、
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19
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SALINITY
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2
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CU㎝N 「i ri rl N Qq oつ ▼一11一ζ ．内 N
＞） bi
一1 つ
」 ec
b ＝ く
Changes in temperature and salinity of the strata above 4．5 m in the three areas of Nagasaki Bay， （from June 12 to August 29， 1979）． Area 1 （e）， area II （▲） and area III （圏）．
NO2一 N
｛一一
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NH4一 N
／へ ，べ
，ζ1二訊＼，／二 吹：1、、 ．，．：1； （さ』 鯉 ．．一N一．
、 一冒一 ●
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＼、
u、
が︑︑ヘザ
〃／…
声、 poべP
ノ 、、、
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both elements between each area were almost the same． Maximum， minimum and mean concentration of inorganic nitrogen and phosphorus in each area are shown in table 1． Maximum values of nitrate−N． nitr一
ite−N and ammonia−N in the whole area were 5．52， 1．60 and 15．49 ptg−atom 1−i， and were found concentrically in area 1 on June 22． Occurrences of such high value corre−
sponded with the dropping of salinity caused by heavy rainfall on the preceeding day． lt seems to indicate that inflow of river water plays an important role on supply of nitrogen in this area． Maximum concentration of phosphate−P had been found in area 1 on
や ね げ め ゆ ゆ ね ゆ ゆ の り む め ト む の ね ね の ロ の の
① tS 冨
口 F● コ 5 コ 切 トつ h コ
《
Fig．3． Mean concentrations of inorganic nutrients in the three areas of Nagasaki Bay，（from June 14 to August lo，1979）． Area I（●），
area II （▲） and area III （■）．
June 25 with 3．84 ptg−atom lbi and then，
concentration decreased gradually to O．53 ptg−atom 1−i on July 16． The next highest concentrations were found in area II together with area 1 on July 19． ln general， concen−
trations of inorganic nutrients were high in area I compared with the other two areas．
This fact suggested that nutrients were supplied mainly by river water including waste water discharged from an urban waste water treatment plant．
Several peaks were found in the variation
Table 1． Mean concentrations of inorganic nutrients in the three areas of Nagasaki Bay （from June 14 to August 10， 1979）， and maximum and minimum concentrations of them in the respective areas．
NO3−N NO2−N NH4−N
PO4一 P
AREA I MEAN MAX． MIN．
1 1．63 0．87 5．87 1．97
5．52 1．60 15．49 3．84
O．40 0．35 0．45 0．53
AREA MEAN MAX．
II
MIN．
1．08 0．55 2．64 1：27
4．88 1．20 10．88 3．77
O．04 0．08 0．08 0．05
AREA III MEAN MAX． MIN．
O．81 0．42 2．25 0．90
3．22 0．86 6．56 1．88
o．oo O．07 0．37 0．28
［Unit ： ptg−atom 1−i］
mg m−3
ユ00 80 60 40 20
：1唱1：1葛
t
A︐
ノ@ 、」
・、 ミ 〆昏．
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Ocu寸。。・q o。。。・Φ①，L・tD．。t。，り。r．卜。 Lr）．。、① el H ri cc cu ou 一一rl cu ou cr： rl ri csti N Φ 〉． ぢ
口 一 コ ＝ コ bC h F⊃ コ く
Fig． 4． Mean concentration of chlorophyll−a in the strata above 4．5 m in the three areas of Nagasaki Bay， （from June 12 to August 29， 1979）． Area 1 （e）， area II （A） and area III （一）．
一1 Cells Z lo7 1o6 1o5 1o4 1o3
禽
＼一六一へ／
レ！
、風 《
1，gA．．t b一一7 x，
ゾ 1一 ，ら ノ
i＿＿喧／
At
cq 寸 OO O〕 U「）QG Oつ q）σ）N ⑩（コ） 0つ q） O σつ こ㍉ O Uう eq （D づ ヒイ ね ひユ ふ ヒイ ぶ ぷ り ハ ふ ね
Φ 防 書
ぱ ロ
コ s b−c ト⊃ h） r 曼
Fig．5． Mean cell density of diatoms（●）and dinoflagellates （▲） in the strata above 4．5minthe area I of Nagasaki Bay，
（from June 12 to August 29，1979）．
of chlorophyll−a． The first peak was on June 12 and the values were 108．3 mg m−3 in area 1， 73．7 mg m−3 in area II and 52．2 mg m−3 in area III． Almost the whole area of Nagasaki Bay was covered with a browny−
red colored water． The causative organism
was Olisthodiscus sp． and cell densities were 7．9×106 cells 1−i in area 1． 11．1×106
cells 1−i in area II and 6．1×106 cells 1−i in area III． The second peak was not so high as the first peak， but discoloration appeared also during this time． Causative
Cells lo8
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ほロ リ ノ ノ リ ︑︐呑剛p焔レ藁謝踊翻編梱蹄
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．階隔鵜嵩ひ源．．︑
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や ◎ 、 く ． 亀 ll 亀 む リ ノ た
ハ 1 、、
ご△1 ム 、
！dl l 〜 ll碕＼？一「1奈・、
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㌔ 亀
ノ 翫二。
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1瑞：獄
10．＝ ，ゾ．、、
、謡識講淑
鼎聴
） い
！ x5
／
（Period of red tide）
︑ ︑ ︑ ︑ へ も 込︑ ︑■︑ ヘ ︑ ．︑︑ ︑へ
ム ユ ︑ ＼︑・＼︑．︑︑ ＼︑ ．︑︑︑ ︑△Ob廓＾ ∠ ・︐．．シノ ノ・ら！ ！︐．・／ ノ ！ ︐・．鞠．
m＼
㌧噺岩鳥猿唾
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① 眠 誓
⊆： 一 bD ＝ コ コ ト⊃ 卜「》 くl
Fig．6． Species composition and cell density of phytoplankton in the area I， Nagasaki Bay， from June to August 1979．（△）Sたeletone〃la costatum，（O）01isthodiscus sp．，（□）Prorocentrum minimum，（率）Thala∬iosira sp・，（●）microflagellates，（L）Prorocentrum obtusidens，（「）
Eutrei）tiella sp．，（7） Fibro al）∫αゴaponica，（∠面） ．Mesodiniu〃z rubrerm、（▼） Silicoflagellates，
（■）other diatoms，（▲）other dinoflagellates．
Bull． Fac． Fish． Nagasaki Univ． No． 50 （1981）
organisms were micro一一diatom （Thalassiosira sp．） and Olisthodiscus sp． and the cell densities were 5．6 × 107 cells 1−i and 2．1 × 106 ce11s l−1， respectively． Other species were Prorocentrum obtusidens Schiller （4．1×105 cells 1 i）， Ebria tripartica （Schumann） Le−
Inmerma皿 （5．7×104 cells l−1） and other dinoflagellates （8．3×104 cells 1−i）． The next discoloration continued for 10 days from July 6 to 16． On July 9， chlorophyll−a was 29．25 mg m−3 in area III and was 25．85 mg m−3 in area II on July 16． This causative organism was Skeletonema costatum and the maximum cell density was 4．3×107 cells l i in area 1 on July 9． Then， the population of Skeletonema costatum （Greville） Cleve began to d， ecrease and on the contrary，
Olisthodisc 浮刀@sp． began to grow， which re−
ached cell density of 1．5×106 cells l−1 0n
21
July 16． lnverse relationship between both species was similar as that of Pratt （1966）
in Narragansett Bay． Next bloom began on July 23 and continued for 7 days． Dominant organisms were Skeletonema costatttm and the other microdiatom （Thalassiosira sp．） and the maximum cell density and chlorophyll−a were 2．0×107 cells ldi and 31．9 mg m−3．
In early August， water temperature increased slowly to 29．7 O C in maximum and salinity wa＄ sustained in 31．0 ％o and the dominant organisms were Prorocentrum minimum （Pa−
villard） Schiller and Glenod（nium sp．． Their cell densities reached， respectively， 2．4 × 106
and 2．2×105 cells 1−i in maximum and chlorophyll−a was 47．6 mg m−3． After heavy rainfall on August 6， salinity decreased and red tide disappeared temporarily but after that， red tide organisms began to growth
一1 Ce1ユ．s Z
lo8
1o7
ユ06
1o5
1o4
i（）3
践︑︑勲測鎌県
一熟新蟹瀞 （Period of
一■一 四■■■■■■鱒■一■■■■ ■■■幽■■■■■■圏一 ■■胴■一■國一一闇国一■一 red tide）
努 タ、
ii ＼
蕪 ハ 2＜価飛 一
：； 4 ・、 や 4 噛、9）・
ロ で の り い ●一・一9
， 、 ll，風 ・ 、｝、
c・ユr・ OD ひ1【O Qc co り。 ひ】o o oつ o O oつ ト。 tn （N O rl r→ ri ou （N cq ¶r ▼r i （N N Cつ H ・一● CL】 c、】
の
Φ λ 塁
トハ 一 r一哩 ），。
コ ゴ コ ト⊃ 卜⊃ く
Fig．7． Species composition and cell density of phytoPlankton．in the area II， Nagasaki Bay，
from ∫une to August 1979．（△） Skeletonema costatum，（○） Olisthodiscus sp．，（口）
Prorocentrum〃〜inimnm，（寧）Thala∬iosira sp．，（●）microflagellates，（L．）Pγoγocθ癬襯 ・伽∫ゴ伽∫，（Y）加・ePti・11αsp．，（7）Fib・・ゆ∫αブαρ・ni・a，（∠）Mes・di・ium・u6・棚，
（▼）Silicoflagellates，（■）other diatoms，（▲）other dinoflagellates．
immediately． This bloom continued from August 10th to 22nd with Skeletonema costatum and micro−diatom （Thalassiosira sp．） as dom−
inant organisms． Maximum chlorophyll−a was
52．7 mg m−3 in are ＝@1 on August．10． ruch
continuous occurrences， like this， of mixed diatom red tide which were mainly composed of Skeletonema costatum． were certified for
about one month from the end of July to the end of August in this bay． This became
s
one of the characteristics of red tide in Nagasaki Bay together with Skeletonema and Olisthodiscus red tides occurrence in the ramy season．
Changes of species composition and cell densities of main organisms in each area shown in Figs． 6， 7 and 8． Changenable patterns were not considerably different between each area．
一1 Cells 7．
lo8
1o7
1o6
ユ．05
ユ．04
1o3
率 続
9 荒
； 茎茎
＝ ll コ ニら
サ ほな
1 、 111嚢
麟▽1
@ @
@逼一塀懲
A＼三密講魂西門増♪病鹸驚
Qi
嚇
tr 一一一一一 一一A Fナノ（■一・一・＿■・、
P．．ズ ＼
購■脳、諸
と 」ギ ㌔i窒堰E！・△
ぴ＼・、．．．却＼プ
（Period of rpd tide）
cuマ， ◎O N lo Oc oつ￠①cu り① ca＜9 0 ce 卜。 ゆ σu ① Hrl rl N cq ou ・r ri rl cq ou oつ ・r H Ct） cq の
望 Φ 〉≧ 一 く ド ロ
壽 ξ ミ
Fig．8． Species composition and cell density of phytoplankton in the area III， Nagasakl Bay，
from June to August 1979．（△）Skeletonema costatum，（○）Olisthodiscus sp．，（口）
Prorocentru〃1〃zinimum，（傘）丁加1α∬iosira sp．，（●）microflagellates，（＼）Prorocentru〃1 0btusidens， （「『） Eutref》tiella sp。， （ρ7） FibrocaPsa ．ノaPonica， （∠） Mesodinit〃2 rubru〃2，
（▼）Silicoflage11ates，（■）other diatoms，（▲）other dinoflagellates．
1）iSCIユssion
1． Dense red tides in Nagasaki Bay
The sampling method accepteq in this survey is C（water−boring method ． By means of this method， fifteen water samples were collected for a short time within one hour in a water column of 4．．5 m，in depth． This
is a method devised to estimate more accurately the movements of phytoplankton communities containing the motile red tide flagellates which are believed to migrate vertically through the strata of this depth unconcern with sampling time． Another fea−
ture of this sampling method was to mix together subsampling sea water collected in
Bull． Fac． Fish． Nagasaki Univ．， No． 50 （1981）
a vessel． This procedure was effective to deal with numbers of subsamples for count−
ing cell numbers of red tide organisms involved the feeble organisms against fixa−
tion before dark． However． numerals obtained
by this method show only the mixed mean value in intra−area and intra−strata to 4．5 m in depth． This is the reason why chlorophyll−a amounts as well as cell densities were not so high in spite of the dense red tide．
In the present survey， a chlorophyll−a amount over 100 mg m−3 was recorded dnly one time and in many red tides chlo−
rophyll−a amounts were between 40 to 60 mg m−3． lt was also scanty that cell densities over 107 cells 1−i were recorded． Considering that flagellate red tides are biological phe−
nomena which make the cell density concen−
trically increase in superficial strata within one or two meters in depth by floating up and make the water discolored． true values
of superficial strata would be two to four times of previously mentioned values． The−
refore， it was presumed that chlorophyll−a over 100 mg m−3 and cell density reaching 108 cells 1−i would appear often． Cell den−
sities over 108 cells 1−i are maximum status which has been observed in coastal and inbayment waters． Such dense discoloration of Nagasaki Bay， which continued almost every day during midsummer season， is close to that of the highly polluted innermost part of Tokyo Bay and Osaka Bay．
2． Nutritional factors of red tide in Naga−
saki Bay
By the statistical examination， there are no significant differences in cell production among the areas． However， concentrations of ammonia−N and phosphate−P in area I were significantly high compared with the other two areas． lt was supposed that high concentration of such nutrients in this area would be influenced by inflow of river water
23
including treated waste water discharged from an urban waste treatment plant． Nutri−
tional loads of treated waste water are esti−
mated about 22 kg in nitrogen and about 6 kg in phosphorus a day （analytical values were cited from Nagata s personal data）．
The total nitrogen and phosphorus in the whole innermost bay water is about 157 kg and about 32 kg respectively （values were cited from Sato s unpublished annual data）．
It can be understood that influx of such treated waste water towards Urakami R．
has an important effect upon the sea water of Nagasaki Bay．
To understand completely the causative factors of the occurrence of the red tide is difficult． However， it is possible to imagine that high concentration of pollutants might accelerate the growth of red tide organisms．
Growth promoting substances of red tide organisms have been reported by many
authors． For instance， soil extract and river water （Wilson and Collier， 1955）， humic substances in river water． soil and sea mud
（Prakash and Rashid， 1968）， sulfide pulp wastes from a paper−mill （Okaichi and Yagiu，
1969）， decomposed matters of pearls oyster s faeces （under the aerobic condition） （lwasaki，
1969）， hot extract of bottom mud （Hirayama and Numaguchi， 1972）， cold extract of bottom mud （Uyeno and Nagai， 1973）， suspending matters of bottom mud（Honjo and且anaoka，
1973） and decomposed matters of diatoms
（Prakash et al．， 1973） were summarized by Iwasaki （1978）． Doig and Martin （1974）
described that low concentration of sewage and urban waste water support the growth of Gymnodinium brewe Davis． Therefore，
further study on influence of land， drainage including urban waste water upon the growth of red tide organisms need to be done also in Nagasaki Bay．
3． Causative organisms of red tide in
Nagasaki Bay
In such nutritional environments which have inflow of river water and urban waste water， the sea water of Nagasaki Bay pro−
mote dominantly the growths of Skeletonema costatum and Olisthodiscus sp．． Both species grow well usually in such an eutrophicated bay which has been influenced by river water and high degree of pollution like that of the innermost parts of lse Bay （Adachi and Kawai， 1979）， Osaka Bay （Joh et al．，
1971）， Tokuyama Bay （Otsuka， 1971）， Hakata Bay （Honjo et al．， 1978． and 1978b）， Narra−
gansett Bay （Pratt， 1965） and Nagasaki Bay is no exception from such kinds of bays．
Prorocentrum minimum． Prorocentrum obtusidens
and 一Thalassiosira sp． caused red tides by their growth in this bay but in other times
・they occurred with moderate density in Skeletonema costatum and Olisthodiscus sp． red tides as accompanying organisms． Another species like as Prorocentrum micans Ehrenberg，
Prorocentrum compressum （Ostenfeld） Ab6，
Gonyaulax diacantha （Meunier） Schiller，
Gymnodini襯splendens：Lebour， Gツ〃znodi痂〃z sp． （type 65）， Gymnodinium breve， Ceratium furca （Ehrenberg） Claparede and Lachmann，
Ceratium fusus （Ehrenberg） Dujardin， Noc−
tiluca miliaris Suriray， Fibrocapsa juponica Toriumi and Takano， Eutreptiella sp．， Dic−
tyocha fibula Ehrenberg， Ebria tripartica，
Distephanus sp． of phytoplankton and Mes−
odinium rubrum （Lohmann） Hamburger and Buddenbrock of zooplankton were not causative organisms of red tide but they occurred in moderate densities． Among those organisms， we could not find the specific species which are found only in Nagasaki Bay． No． occurrence of Gymnodinium sp．
（type 65） red tide was the other character−
istics of the red tide in Nagasaki Bay．
Acknowledgements
Authors acknowledge Mr． Toshinobu Na−
gata， Urban Waste Water Treatment Plant of Nagasaki City， and Mr． Tetsushi Sato，
student of Laboratoty of Oceanography，
Faculty of Fisheries， Nagasaki University for permission of using of their data． Thanks are also due to Professor Haruhiko lrie and Dr． Michiro Matsuyama regarding their helpful criticisms of the manuscript and also to Messrs． Shinobu lrie and Takashi Saito for their assistance of the sampling work in Nagasaki Bay． Special thanks are also due to Miss． Lynnette La−Marche for her critical review of， the English of this manu−
script．
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1979年 夏 季 に お け る 長 崎 湾 の 赤 潮
テ ン ク ダハ リル ・飯 塚 昭二
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18㎜,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SkeletonemacostatumとOlisthodiscussp.の 二 種 が 優 占 種 で あ っ た.ほ か に ProrocentrumminimumとProrocentrumobtusidensお よ びThalassiosirasp.な ど が 出 現 し た.最 高 値
は ク ロ ロ フ ィル ーaで108.3mgm一3,細 胞 密 度 は5.8×107Cellsl‑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
と馬、わ れ る.
