ECOLOGY OF CALAMUS SINICUS
(COPEPODA，CALANOIDA) IN
OCEANS OF SOUTHERN CHINA
by
LEE KA LUN
Thesis Submitted as Partial Fulfillment
of the Requirements for the Degree of
Master of Philosophy
in
Biology
© The Chinese University of Hong Kong
APRIL, 2003 系硬复® ！^ 0 6 丽 ” li Pv--— - ； UNIVERSITY /_舅 Contents
Pages
Abstract (in English) i
Abstract (in Chinese) iv
. Acknowledgements vi
List of Figures vu
List of Tables xv
Chapter 1 General Introduction 1
Chapter 2 Seasonal population structure, life cycle and body allometry of the planktonic copepod Calanus sinicus
2.1 Literature Review ^
2.1.2 Geographical and seasonal distribution of Calanus sinicus 7
2.1.3 Body length and body weight of Calanus sinicus U 14 2.2 Introduction 2.3 Materials and Methods 17 17 2.3.1 Field sampling 2 3 2 Identification and enumeration of zooplankton 19 1 Q 2.3.3 Body length and weight of Calanus sinicus 上？ 2.4 Results 20 2.4.1 Temperature
2.4.2 Salinity
2.4.3 Ambient Chlorophyll a concentration 22 244 Seasonal occurrence and distribution of Calanus sinicus • • 〜 23 in northern Taiwan
2 4 5 Seasonal occurrence and distribution of Calanus sinicus •‘ 26 in Hong Kong 2.4.6 Life cycle of Calanus sinicus in northern Taiwan 27
2.4.7 Life cycle of Calanus sinicus in Hong Kong 28
2.4.8 Stage ratio index 2.4.9 Seasonal changes in biomass of Calarms sinicus 29
2.4.10 Seasonal changes in the abundances of other copepods
in northern Taiwan 29
2.4.11 Seasonal changes in the abundances of other copepods
in Hong Kong 30
2.4.12 Seasonal changes in biomass of other copepods 31
2.4.13 Seasonal variations in body size 31
2.4.14 Seasonal changes in sex composition in adults 32 2.5 Discussions 32
Chapter 3 Diel vertical migration and gut pigment rhythm of the planktonic copepod Calanus sinicus
3.1 Literature review ..87
3.1.1 Diel vertical migration of Calanus sinicus 87
3.1.2 Diel feeding rhythm of Calanus sinicus 91
3.1.3 Measurement of grazing rate 93 3.2 Introduction 96 3.3 Materials and Methods 98
3.3.1 Zooplankton sampling and physical parameters 98
3.3.2 Identification and enumeration 100
3.3.3 Gut pigment fluorescence 100 3.4 Results 101
3.4.1 Temperature and salinity 101
3.4.2 Ambient chlorophyll a concentration 102
3.4.3 Diel vertical migration 103
3.4.4 Gut pigment content 106 3.5 Discussion 107
Chapter 4 Use of molecular markers in population analysis of Calanus sinicus
4.1 Literature Review 134 4.2 Introduction 138 4.3 Materials and Methods 142
4.3.1 Collection, preservation, and identification of Calansii sinicus samples 142
4.3.2 DNA sequence determination for Calaniis sinicus 143 4.4 Results 1^4 4.5 Discussion 145
Chapter 5 Conclusion 150 Ecology of Calanus sinicus (Copepoda, Calanoida) in
Coastal Oceans of Southern China
by
Lee Ka Lun
Abstract
Copepoda, with over 7,500 described species, are the largest class of small
crustaceans. Calanus sinicus is a dominant copepod in the Yellow Sea, the East
China Sea and the Sea of Japan. A major objective of this thesis is to examine the
seasonal occurrence of C. sinicus in coastal oceans of southern China. Samples were
collected at seven sampling stations in coastal water off northern Taiwan from
November 2000 to March 2002. Outside Port Shelter, Hong Kong, samples were
collected at five sampling stations from February 2001 to April 2002. Population
density of C. sinicus was always higher in Taiwan than in Hong Kong. In Taiwan,
numbers occurred throughout the year and were seasonally abundant. They were
most common in winter months. In Hong Kong, a single peak in abundance
occurred in March, 2001. Sex ratio among adults varied seasonally in Taiwan.
There were usually more females than males. In general，the individuals collected
i during the winter were larger than those collected during the summer.
Diel vertical migration is a widespread phenomenon that is known to exist in
almost all taxa of planktonic organisms. Because phytoplankton is most abundant
near the surface, diel vertical migration is often associated with diel feeding rhythm.
Diel vertical migration and diel feeding rhythm of Calarms sinicus were studied at
two sites located near the northern tip of Taiwan in April and December 2001. The
selective advantage of diel vertical migration in late copepodites and adult female of
C. sinicus in April was the reduction of mortality by predation. In December, the
copepods modified their migration behavior by remaining in the relatively food-rich
surface waters when food availability is low.
Several protocols based on molecular genetic characters have been successfully
applied to marine zooplankton. This thesis also determined if Calarm sinicus
populations in the oceans of southern China are derived from populations in the
Yellow Sea and East China Sea, molecular approach will be used to examine
intraspecific variations in the DNA sequences of C. sinicus specimens collected in
coastal waters outside the Changjiang river mouth and off northern tip of Taiwan.
The result showed that the Zhejiang-Fujian longshore currents carry C sinicus from
the East China Sea into the South China Sea.
ii 南中國沿岸海域大中華哲水蚤生態硏究
李嘉倫
摘要
橈足類是屬於甲穀門下的撓足類綱，已知曉的橈足類大約有七千五百種。
大中華哲水蚤是黃海，東中國海和日本海的優勢種類.本論文對南中國沿岸海
域的大中華哲水蚤的生態進行硏究。自2000年11月至2002年3月在台灣北
部沿岸海域及自2001年2月至2002年4月在香港牛尾海外邊的海域採樣站的結
果表明：大中華哲水蚤的在台灣北部的密度大于在香港的密度，在台灣北部是
全年性發生及具季節性豐度，尤在冬季常見，其在香港海域的紀錄只有2001年3
月。成年的大中華哲水蚤的性別比率同樣帶有季節性，但主要由雌性組成。
結果同時表明其在冬季的體長一般都大於夏季的體長。
曰周性垂直遷移現象常見於淡水及海水的浮游動物。由於浮游植物積
聚在水表層，所以，一般會進行日周性垂直遷移的浮游動物，通常是白天棲息在
較深的水層且不進食，晚上再游到水表層進行攝食行爲。本論文對大中華哲水
蛋在台灣北部沿岸海域的日周性垂直遷移現象和其攝食節律進行探討。在
2001年4月的結果表明，大中華哲水蚤的幼生期和成年雌性的垂直遷移是爲了
躲避以目視法捕食的敵人° 在2001年12月，浮游植物的供應量下降，大部份
的大中華哲水蚤停留在水表層尋找食物。
iv 由於不同的分子遺傳標記已成功應用在海洋的浮游動物，所以，本論文
同時利用分子標記以分析南中國沿岸的大中華哲水蚤是否從黃海和東中國海而
來。硏究利用在長江河口和台灣北部沿岸海域的大中華哲水蚤的標本進行
DNA序列分析。結果表明南中國沿岸的大中華哲水S是跟隨浙江和福建沿岸
流從黃海和東中國海而來。
X Acknowledgements
I am most grateful to my advisor, Prof. Wong Chong Kim for his supervision and
valuable comments during my two years of study. I am also indebted to my thesis
committee members, Profs. Ang Put 0. Jr. and Chu Lee Man for their advice and help.
It is also a pleasure to thank the helpful comments from Prof. Chu Ka Hou. Special
regards are given to Prof. Hwang Jiang-Shiou of the National Taiwan Ocean
University for his willingness to serve as the external examiner of this thesis and to
provide the opportunity for me to work in Taiwan. Thanks are also given to Prof.
Chen Qing Chao of the South China Sea Institute of Oceanology, Academia Science
for his assistance in collecting zooplankton samples outside the Chang]iang River
mouth.
I greatly appreciate the assistance provided by the staff of Marine Science
Laboratory and Department of Biology, the Chinese University of Hong Kong. I
would like to thank Cheung Kwok Chu and Li Chi Pang for their technical advice
during my laboratory work. I also thank Yung Yuk Hay for his help during the two
years of field sampling in Port Shelter, Hong Kong. Thanks are extended to Wan
Chak Lam and Wong Chun Kwan for their support and suggestions in the laboratory.
Special thanks also given to all the staff and students at the National Taiwan Oceanic
vi University who gave me assistance and helped me with the zooplankton samples
collections in Taiwan.
I must also thank all the members of my family here, especially my mother, for
their support.
Finally, a special debt of thanks is due my best friend, Kwan Ning Yan, because
of her continuous encouragement and unconditional support during the past two years.
vii List of Figures
Fig. 1.1: (a) Sequential development of the apparent segmentation of Calarms
sinicus throughout the copepodid stages, CI to CV, male and female,
(b) The fifth pair of legs of swimming Calarms sinicus male and
female.
Fig. 2.1: Map of South China Sea and East China Sea showing location of 利
sampling stations outside Nuclear Power Plant I (NPPI) in coastal
waters off the northern tip of Taiwan.
Fig. 2.2: Map of Port Shelter, Hong Kong showing location of sampling
stations.
Fig. 2.3: Seasonal changes in (a) temperature (oC) and (b) salinity (O/QO) at 4j station B500 off northern Taiwan.
Fig. 2.4: Seasonal changes in (a) temperature (oC) and (b) salinity (O/QO) at ^^
station B1000 off northern Taiwan.
Fig. 2.5: Seasonal changes in (a) temperature (oC) and (b) salinity (O/QO) at ^^
station B2000 off northern Taiwan.
Fig. 2.6: Seasonal changes in (a) temperature (OQ and (b) salinity (O/QO) at 46 station C500 off northern Taiwan.
Fig. 2.7: Seasonal changes in (a) temperature (oC) and (b) salinity (O/QO) at ^^
station CI000 off northern Taiwan.
Fig. 2.8: Seasonal changes in (a) temperature (oQ and (b) salinity (O/QO) at ^^
station C2000 off northern Taiwan.
Fig. 2.9: Seasonal changes in (a) temperature (oC) and (b) salinity (O/QO) at ^^
station C5000 off northern Taiwan.
Fig. 2.10: Seasonal changes in (a) temperature (oC) and (b) salinity (O/QO) at 冗
station I outside Port Shelter, Hong Kong.
viii Fig. 2.11: Seasonal changes in (a) temperature (OQ and (b) salinity (O/QQ) at
station II outside Port Shelter, Hong Kong.
Fig. 2.12: Seasonal changes in (a) temperature (oC) and (b) salinity (o/oo) at
station III outside Port Shelter, Hong Kong.
Fig. 2.13: Seasonal changes in (a) temperature (oC) and (b) salinity (〇/oo) at 。 53 station IV outside Port Shelter, Hong Kong.
Fig. 2.14: Seasonal changes in (a) temperature (oC) and (b) salinity (o/oo) at ^^
station V outside Port Shelter, Hong Kong.
Fig. 2.15: Surface (white), middle (grey) and bottom (black) chlorophyll a ^^
concentration at different stations off northern Taiwan from
November 2000 to March 2002.
Fig. 2.16: Surface (white), middle (grey) and bottom (black) chlorophyll a 56
concentration at different stations outside Port Shelter, Hong Kong,
from February 2001 to April 2002.
Fig. 2.17: Seasonal occurrence of Calanus sinicus (CI to CVI) at different 巧
stations off northern Taiwan.
Fig. 2.18: Seasonal occurrence of different stages of Calanus sinicus at station 58 B500 off northern Taiwan.
Fig. 2.19: Seasonal occurrence of different stages of Calanus sinicus at station ^^
BIOOO off northern Taiwan.
Fig. 2.20: Seasonal occurrence of different stages of Calanus sinicus at station ^^
B2000 off northern Taiwan.
Fig 2.21: Seasonal occurrence of different stages of Calanus sinicus at station ° b丄 C500 off northern Taiwan.
Fig. 2.22: Seasonal occurrence of different stages of Calanus sinicus at station ^^
CI 000 off northern Taiwan.
ix Fig. 2.23: Seasonal occurrence of different stages of Calanus sinicus at station ^ 63 C2000 off northern Taiwan.
Fig. 2.24: Seasonal occurrence of different stages of Calanus sinicus at station ^^
C5000 off northern Taiwan.
Fie. 2.25: Seasonal occurrence of Calanus sinicus (CI to CVI) at different ,产 ^ 65 stations outside Port Shelter, Hong Kong.
Fig. 2.26: Seasonal occurrence of different stages of Calanus sinicus at station 66 I outside Port Shelter, Hong Kong.
Fig. 2.27: Seasonal occurrence of different stages of Calanus sinicus at station 67 II outside Port Shelter, Hong Kong.
Fig. 2.28: Seasonal occurrence of different stages of Calanus sinicus at station 68 III outside Port Shelter, Hong Kong.
Fig. 2.29: Seasonal occurrence of different stages of Calanus sinicus at station 69 IV outside Port Shelter, Hong Kong.
Fig. 2.30: Seasonal occurrence of different stages of Calanus sinicus at station ^^
V outside Port Shelter, Hong Kong.
Fig. 2.31: Seasonal variations in abundance of Calanus sinicus of different ^^
developmental stages (CI to CVI) off northern Taiwan.
Fig. 2.32: Seasonal variations in abundance of Calanus sinicus of different ^^
developmental stages (CI to CVI) outside Port Shelter, Hong Kong.
Fig. 2.33: Seasonal change in copepodite stage ratio index of Calanus sinicus ^^
off northern Taiwan.
Fig. 2.34: Seasonal change in biomass of Calanus sinicus (CI to CVI) at ^^
different stations off northern Taiwan.
Fig. 2.35: Seasonal change in biomass of Calanus sinicus (CI to CVI) at ^^
different stations outside Port Shelter, Hong Kong.
X Fig. 2.36: Seasonal change in abundance of copepods (not including nauplii) at 126 different stations off northern Taiwan.
Fig. 2.37: Seasonal change in abundance of copepods (not including nauplii) at 力
different stations outside Port Shelter, Hong Kong.
Fig. 2.38: Seasonal change in biomass of all copepods (not including nauplii) . 78 at different stations off northern Taiwan.
Fig. 2.39: Seasonal change in biomass of all copepods (not including nauplii) ^^
at different stations outside Port Shelter, Hong Kong.
Fig. 2.40: Seasonal changes in mean prosome length of various copepodite 80 stages and adults of Calarms sinicus collected in coastal water off
northern Taiwan.
Fig. 2.41: Relationship between average water temperature and mean prosome 81 length of various copepodite stages and adults of Calarms sinicus
collected in coastal water off northern Taiwan.
Fig. 2.42: Relationship between prosome length and body dry weight of ^^
various copepodite stages and adults of Calanus sinicus collected in
coastal water off northern Taiwan
Fig. 2.43: Seasonal change in sex ratio among adults of Calanus sinicus in ^^
coastal water off northern Taiwan.
Fig. 3.1: Map of South China Sea and East China Sea showing location of ^^^
sampling stations outside Nuclear Power Plant I (NPPI) in coastal
waters off the northern tip of Taiwan.
Fig. 3.2: Diel variations in vertical distribution of (a) temperature (oC) and ^^^
(b) salinity (O/QO) at station C500 from 1500 h, 10 April to 0900 h，
11 April, 2001.
xi Fig. 3.3: Did variations in vertical distribution of (a) temperature (oC) and
(b) salinity (o/oo) at station C5000 from 1200 h, 10 April to 0600 h,
11 April, 2001.
Fig. 3.4: Diel variations in vertical distribution of (a) temperature (oC) and 116 (b) salinity (o/oo) at station C500 from 0900 h，5 December to 0300
h, 6 December, 2001.
Fig. 3.5: Diel variations in vertical distribution of (a) temperature (oC) and ^^^
(b) salinity (O/QO) at station C5000 from 1200 h, 5 December to
0600 h, 6 December, 2001.
Fig. 3.6: (a) Vertical profiles of chlorophyll a at station C500 from 1500 h, 10 118 April to 0900 h, 11 April, 2001.(b) Vertical profiles of chlorophyll
a at station C5000 from 1200 h, 10 April to 0600 h, 11 April, 2001.
Fig. 3.7: (a) Vertical profiles of chlorophyll a at station C500 from 0900 h, 5 ^^^
December to 0300 h, 6 December, 2001. (b) Vertical profiles of
chlorophyll a at station C5000 from 1200 h, 5 December to 0600 h 6
December, 2001.
Fig. 3.8: Diel variations in the vertical distribution of Calanus sinicus at ^^^
station C500 on 10 & 11 April 2001.
Fig. 3.9: Diel variations in the vertical distribution of Calanus sinicus at ^^^
C5000 on 10 & 11 April 2001.
Fig. 3.10: Diel variations in the vertical distribution of Calanus sinicus at ^^^
station C500 on 5 & 6 December 2001.
Fig. 3.11: Diel variations in the vertical distribution of Calanus sinicus at ^^^
station C5000 on 5 & 6 December 2001.
Fig. 3.12: Gut pigment content of (A) adult and (B) copepodites CIV and CV ^^^
of Calanus sinicus at station C500 on 10 & 11 April, 2001 .
Fig. 3.13: Gut pigment content of (A) adult and (B) copepodites CIV and CV 工乃
of Calanus sinicus at station C5000 on 10 & 11 April, 2001 .
xii Fig. 3.14: Gut pigment content of (A) adult and (B) copepodites CIV and CV 126 of Calanus sinicus at station C500 on 5 & 6 December, 2001 .
Fig. 3.15: Gut pigment content of (A) adult and (B) copepodites CIV and CV
of Calanus sinicus at station C5000 on 5 & 6 December, 2001 .
Fig. 4.1: Gel photo showing PGR products for individual Calanus sinicus. ^^^
Fig. 4.2: Sequence data for a 640 base pair region of the mitochondrial gene • 148
cytochrome oxidase I (COI)] for Calanus sinicus collected in
coastal waters outside the Changjiang River mouth and off northern
tip of Taiwan.
Fig. 4.3: Sequence data for a 474 base pair region of the nuclear gene [first ^卯
internal transcribed space of ribosomal DNA (ITS-1)] for Calanus
sinicus collected in coastal waters outside the Changjiang River
mouth and off northern tip of Taiwan.
xiii List of Tables
Table 2.1: Coordinates of sampling stations in northern Taiwan and Port 84 Shelter, Hong Kong.
Table 2.2: Abundance of all stages of Calanus sinicus (CI to CVI) at different OJ
stations off northern Taiwan and outside Port Shelter, Hong Kong.
Table 2.3: Abundance of copepods (not including nauplli) at different stations 86
off northern Taiwan and outside Port Shelter, Hong Kong.
Table 3.1: Day-night differences in the mean abundance (ind. m'^) and the 12o mean depth (m) of Calanus sinicus at station C500 during April
10-April 11,2001.
Table 3.2: Day-night differences in the mean abundance (ind. m"^) and the ^^^
mean depth (m) of Calanus sinicus at station C5000 during April
10-April 11,2001.
Table 3.3: Day-night differences in the mean abundance (ind. m'') and the ^^^
mean depth (m) of Calanus sinicus at station C500 during
December 5 — December 6, 2001.
Table 3.4: Day-night differences in the mean abundance (ind. m'^) and the ^^^
mean depth (m) of Calanus sinicus at station C5000 during
December 5 - December 6, 2001.
Table 3.5: Gut pigment level (ngChk ind.]) of Calanus sinicus at stations ^^^
C500 and C5000 during April 10-April 11,2001.
Table 3.6: Gut pigment level (ngChk ind ]) of Calanus sinicus at stations
C500 and C5000 during December 5 -December 6, 2001.
XV Chapter 1 General Introduction
Copepoda, with over 7,500 described species, is the largest class of small
crustaceans. Most copepods live in oceans, but there are many estuarine and
freshwater species and some species can be found in moss and soil water films.
Planktonic copepods exist in enormous numbers and are usually the most abundant
and conspicuous components of plankton samples taken from oceans and lakes.
Despite their small size, copepods are of vital importance to the economy of ocean
ecosystems. Planktonic copepods represent some of the most important groups of
herbivorous animals in the world's oceans and provide one of the pivotal links
between algal primary production and the numerous large and small carnivores.
The Copepoda form a subclass of the phylum Crustacea. According to the
classification of Huys and Boxshall (1991), there are ten orders of copepods
containing different number of families, genera and species. The order Calanoida,
excluding the freshwater family Diaptomidae and the freshwater genera of the family
Centropagidae, currently consists of some 41 families, 195 genera and 1800 species.
The gross morphology of the Calanoida is relatively uniform and is markedly
different from groups within other orders of the Copepoda where benthic，commensal
and parasitic life styles have resulted in greatly modified external morphology.
1 Calarms sinicus (Copepoda; Calanoida) (Fig. 1.1) is a dominant zooplankter in
the Yellow Sea, the East China Sea and coastal waters of Japan (Kidachi, 1979a,b).
Along the continental shelf waters of China and Japan, the range of C. sinicus extends
from the east and west coasts of Honshu, Japan, in northeast (〜40° N) to the northern
edge of the South China Sea in the south. Along the southeastern coast of China, C.
sinicus has been found in coastal waters of northern Taiwan (Hwang et al., 1998;
Wong et al., 1998). In Hong Kong, C. sinicus has also been recorded from coastal
waters to the east and south during the winter and early spring seasons (Chen, 1980).
In Tolo Harbour, C. sinicus occurs in very low number and its occurrence is restricted
to winter and early spring when the northeast monsoon is prevalent (Wong et al.,
1993). Chen (1980) hypothesized that C. sinicus populations in the coastal waters of
Taiwan and Hong Kong are derived from the northern populations in the Yellow Sea,
the East China Sea and coastal waters of Japan under the influence of the northeast
monsoon in winter. Different populations vary in terms of their breeding season and
number of generations per year. In the northern part of the South China Sea, water
temperature rises rapidly during spring and C. sinicus tends to disappear from the
plankton by early summer when the southwest monsoon becomes dominant.
In addition to its wide geographical distribution, C. sinicus is a prominent
component of planktonic communities in the northern part of the South China Sea
2 because of its large size. Information on the biology and ecology of Calanus sinicus
is primarily based on detailed and extensive studies carried out in Japan (Uye et al.,
1986; Uye, 1990; Huang, 1992). C. sinicus exhibits seasonal occurrence in coastal
waters around Taiwan and Hong Kong (Chen, 1980; Hwang et al., 1998; Wong et al.,
1993; Wong et al., 1998). Its large size and its prevalence in winter when other
species become less abundant suggests that it may be seasonally important and
constitute a major portion of the zooplankton biomass and play an important role in
the energy transfer process of planktonic food web.
The major objective of the research carried out in this thesis was to investigate
the biology and ecology of C. sinicus in coastal oceans in the northern edge of the
South China Sea. This thesis is composed of three separate, but interrelated, studies.
The first study focused on the seasonal occurrence of C. sinicus populations in coastal
waters at the northern tip of Taiwan and at the outer edge of Port Shelter, Hong Kong.
Geographically, these locations marked the southern edge of the C. sinicus
populations in the East China Sea and the southern edge of the range of C. sinicus in
the continental shelf waters of China. Developmental characteristics and body
allometry of different C. sinicus populations were examined by measuring prosome
length and dry weight. The second study examined the diel vertical migration and
diel feeding rhythm of C. sinicus in the coastal waters of northern Taiwan. Diel
J vertical migration of Calanus sinicus was not studied in Port Shelter because densities
encountered during the course of this study were generally too low for detailed
analysis of diel pattern. The third study represented a preliminary attempt to use
molecular markers to determine if C. sinicus populations in the oceans of southern
China are derived from northern populations in the Yellow Sea and the East China
Sea.
4 (a) CI CII cm CIV cv CIV s CVI 半
- � � ‘� � / �� . / \ � ‘‘ i \ / \ I ‘ i 丨，\ / \
L 叫 t ； ； i I / j Cephalosome 4 ^ < r I; I f ^ ‘ .."，..j..i J ； i I I 4 广！… )\ I i \ . ] "' I / ; 丨： ）、— i \ — ‘—.....\ 1 “ " . ‘ I 一 Prosome � ... . -...... 、i~ < \ .r • 、、、....『 >.. •： •：'••K • • ••••• •• : ：.： • J
• , 一 ‘ ...s^ i -vs.,. ？ ；) 、...... … J 、..... •'....I J ：：：i'-N-i. .W.-.-.: .....y.��...... ‘："、.•’ ^ 多： ？ ；1 J > “―• V 。：-...Z-* s. , J S 、，〜.—. 單 L, 、一一〜 …一 Metasome "r i “ , ；： i-.....\ ‘ \.一一.�J: �“ ‘ i I I I „, ‘ \ ； i - c — / •jf:'、 ‘ 一 • * A - ..：^ “； — … 〜 “ > … Urosome (b) “ 、v w.. >� — -. Vv. . _
• ；‘•, 、 ；- , ：：丨. V i 1 mm ‘：、{
CIV $ CVI 罕
Fig. 1.1 (a) Sequential development of the apparent segmentation of Calanus sinicus throughout the copepodid stages, CI to CV, male and female, (b) The fifth pair of legs of swimming Calanus sinicus male and female (modified from 陳淸掉月，章》叔珍 1965; 李松,方金剛1990). Chapter 2 Seasonal population structure, life cycle and body allometry of the planktonic copepod Calanus sinicus
2.1 Literature Review
2.1.1 Taxonomy of Calanidae
There are two conflicting schemes for classification of the Family Calanidae.
Brodsky (1972) considers Calanidae to be composed of the genera Calanus (with four
subgenera), Cathocalanus, Clanoides, and Udinula. In contrast, Bradford and Jillett
(1974) distribute the species in the family among the genera Calanus, Calanoides,
Canthocalanus, Cosmocalanus, Mesocalanus’ Neocalanus and Undinula.
The genus Calanus is characterized by a streamlined torpedo-shaped
cephalosome, five free thoracic segments, and extremely long antennules that bear
three large setae (two backward- and one forward-pointing) at their tips. The
antennules are slightly longer than the entire body. Both the urosome and the
uropods are very short. Each uropod bears long furcal rami.
The genus Calanus comprises 14 species. C hyperboreus, C. simillimus and C
propinquus are morphologically distinctive (Frost, 1974). On the basis of
morphology and geographic distribution, the remaining species have been divided
into two lineages: a C. finmarchicus group and a C. helgolandicus group. The
6 principal characters separating the species are the secondary sexual characteristics.
The first group, whose species are markedly similar in morphology (Frost, 1974),
includes C. finmarchius, C. glacial is, and C marshal lae which are polar and boreal
species of the northern hemisphere. The second group consists of C. helgolandicus,
C. pacificiis, C. australis, C. orientalis, C. sinicus and C. chilensis. The geneus
Calanus also included C. euxins, a Black Sea species (Hulsemann, 1991), and C.
agulhensis, a new species from South African waters (DeDecker et al., 1991). All
these species occur in the mid-latitudes of both hemispheres.
Morphology of C. sinicus has been described by Brodsky (1972). The body
length of female C sinicus ranges from 2.70 to 3.50 mm and that of male is from 2.60
to 3.50 mm (Fig 1.1). The body of C. sinicus is divided into six segments. The
length and the width of the genital somite are the same. The exopods and endopods
of the fifth pair of legs have three segments each. The fifth pair of leg in males is
normally enlarged, especially on the left side.
2.1.2 Geographical and seasonal distribution of Calanus sinicus
C. sinicus is a dominant species in the Yellow Sea, the East China Sea and
coastal waters of Japan (Kidachi, 1979a,b). Along the continental shelf waters of
China and Japan, the range of C. sinicus extends from the east and west coasts of
7 Honshu, Japan, in the northeast (〜40。N) to the northern edge of the South China Sea
in the south. The breeding season and number of generation per year vary
geographically. The distribution and breeding season of Calanus sinicus in China's
northern neritic areas indicate that this species is a temperate species, with distribution
centres in the Yellow Sea and the East China Sea.
The optimal temperature for the occurrence of C. sinicus is about 5-24°C and the
optimal temperature for reproduction is about 10-18。C (Chen, 1992). The specific
growth rate of C. sinicus was also temperature-dependent and highest from CI to CIII,
intermediate from Nil to CI and from CIII to CV, and lowest from CV to CVI. The
growth rates of C‘ sinicus are higher than those of small copepods such as
Paracalarms, Acartia and Microsetella (Uye, 1988).
With the exception of river mouth areas, C. sinicus can be found in most of the
neritic seas along China's east coast. In general, coastal populations are less likely
to be exposed to food limitation than oceanic populations (Huntley and Boyd, 1984).
Food limitation can affect copepods in many ways. It can affect growth in body size,
which in turn influences clutch size and fecundity (Walker and Peterson, 1991). The
quality of food, rather than its quantity, can also affect growth.
The geographical distribution of C sinicus is strongly affected by salinity
(Chen, 1992). Salinity influences the growth and development of estuarine species
8 (Lin and Li, 1984). For most estuarine species, there is an optimal range of salinity
for successful development and growth. The abundance of Calaiis sinicus is highest
in high-salinity waters and decreases in estuarine waters and coastal waters of low
salinity (Chen, 1992).
In the Inland Sea of Japan, C. sinicus occurs throughout the year and is the
second most important species after Paracalanus sp. in terms of biomass and
production (Uye et al., 1986). C, sinicus is most abundant in June-July and least
abundant in October around Kii Channel of the Inland Sea of Japan (Uye et al, 1986).
Reproduction in C. sinicus takes place throughout the year indicating the absence of
diapause phase (Huang et al., 1993).
At the adult stage, females of C. sinicus usually out number males in the Inland
Sea of Japan (Huang et al., 1993). Seasonal change in sex ratio is particularly
common in species with long generation times. Lifespan is usually shorter in males
than in females. In addition, males and females differ in their tendency to
aggregate. The physiological state of the NVI stage influences the later sex
differentiation. High temperature speeds up the development rate of NVI stage and
increases the frequency of males among CI. Lower rates of development, on the
other hand, increase the frequency of females.
In winter, Zhejiang-Fujian longshore currents carrying C. sinicus mix with
9 water masses flowing from northeast to southwest along the eastern coast of
Guangdong under the influence of the NE monsoon. Calanus sinicus is carried into
the northern edge of the South China Sea. C. sinicus has been recorded from coastal
waters near nuclear power plants in northern Taiwan (Hwang et al., 1998; Wong et al.,
1998). In Hong Kong, C. sinicus occurs in coastal waters to the east and south during
the months of winter and early spring (Chen, 1980). C. sinicus has also been
recorded in Tolo Harbour, but only in very low numbers (Wong et al, 1993). In
coastal waters to the south of Fujian and along the coasts of Guangdong and Guangxi,
C. sinicus exhibits seasonal distribution and breeds only during the winter and spring
(Chen, 1980).
Information on the breeding season of copepod can be obtained by examining
seasonal change in the frequency of females carrying eggs and with spermatophores
attached to the urosome (Mauchline, 1994). For Calanus sinicus, breeding season
and number of generation per year tend to vary geographically (Chen, 1992). In the
Bohai and the northern Yellow Sea, there are three breeding peaks and three
generations each year. The first breeding period is from May to June, the second is
in August, and the third is in November when developing copepod larvae will
undergo wintering, and generations would be crossing and overlapping throughout the
year. In the southern part of the Yellow Sea there are also three breeding peaks and
10 three generations. The first breeding peak period is from March to April, one
month earlier than that in the northern Yellow Sea. Early reproduction is probably
related to the higher water temperature in this area. In the East China Sea there are
three breeding periods and three generations per year. The first is in April, the
second is between June and July, and the third is in October. Along the coast of
Fijian, there may also be three breeding periods and three generations per year. The
first is in January, the second is from April to May and the third is from July to
August. A major difference between the East China Sea populations and Fujian
populations, therefore, is that the northern populations tend to start breeding earlier in
the year. Along the coasts of Guangdong and the northern Beibu Gulf, there are
only two breeding periods and two generations per year. The breeding times are
close to those in the Fujian coast. The first is in January and the second is around
April and May.
2.13 Body length and body weight of Calanus sinicus
It is commonly accepted that that the physiological rates of zooplankton are
influenced by their body size with smaller organisms exhibiting higher weight
specific physiological rate (Ikeda, 1974; Lynch, 1977). In this sense, the growth rate
of the large sized Calanus sinicus is expected to be lower than that of other smaller
11 species. However, Uye (1988) noted that the growth rate of Calarms sinicus is
higher than that of smaller species including Paracalarms parous, Acartia clausi and
Microsetella norvegica. These findings agree with those reported for C. pacificus
and a co-occurring small species, Pseiidocalarms sp. in Puget Sound, Washington
(Frost, 1980). This higher growth rate is one of the reasons why C. sinicus is able to
compete with smaller species and dominate in the Inland Sea of Japan (Uye, 1988).
Body length of the adults is a product of the increments at successive moults
during development. The length achieved during an intermoult period, however,
bears some relation to the duration of the stage which is strongly influenced by
temperature. Sabatini (1989) showed that temperature is more important than food
availability in influencing the body length of Acartia tonsa. McLaren (1974) studied
the effects of temperature on the growth of Pseiidocalnus minutus and concluded that
adult females reared from CIII isolated from the field were larger when reared at
lower than at higher temperatures. Body length increment between moults increased
from about 43% at 12。C to about 60% at 6。C. Similarly, Eurytemora herdmani
maintained in the laboratory grew to larger size at lower temperatures (McLaren and
Corkett, 1981).
In some cases, no correlation is found between body size and environmental
temperature at the time of sampling. An adequate supply of suitable food is a
12 prerequisite for development and growth. Klein Breteler and Gonzalez (1982) found
that food concentration influenced body size in several species of copepods and
explained about 80% of the variations in the size of Centropages hamatus in
laboratory cultures. Diel and Klein Breteler (1986) studied populations of Calanus
species in the field and in the laboratory and concluded that development and growth
could be arrested by changes in food quality. Food availability affects development
time and generation time which in turn influence growth in body length. When food
is limited, ingested energy is directed to storage reserves or directly to egg production
rather than to increase in body length. Ohno et al. (1990) also found that the
prosome length of Acartia tsiiensis decreased with increasing culture density. This
was probably the result of decreasing food rations per individual and thus actually
reflected the degree of food limitation.
Calanus sinicus is the largest suspension-feeding copepod (body carbon weight
of adult female: > 50 wg C ind；^) which occurs abundantly in the Inland Sea of Japan
(Uye, 1988). All other quantitatively important genera of suspension-feeding
copepods which co-occur with C. sinicus {Paracalanus, Acartia, Microsetella and
Oithona) are much smaller (< 5 i^g C ind").
The body of a copepod can be conceived as consisting of a structural and a
storage compartments. The storage compartment is usually considered to include the
13 stored lipids or oil sacs. McLaren (1986) suggests that species that do not have
significant quantities of stored lipids exhibit exponential growth in weight, while
species that store marked quantities of lipids tend to show exponential growth only if
the lipid stores are ignored. Body dry weight, like body length, fluctuates seasonally
and is related to environmental temperature. The seasonal change in dry weight
usually, but not always, reflects corresponding seasonal changes in body length.
2.2 Introduction
Calanus sinicus has previously been recorded from coastal waters in northern
Taiwan (Hwang et al., 1998; Wong et al., 1998). Taiwan is located in the southern
edge of the East China Sea and the northern edge of the South China Sea (Fig. 2.1).
The East China Sea longshore current consists mainly of the runoff emptying into the
sea from the Changjiang, Qiantang and Minjiang joining the coastal water to form a
relatively strong low-saline water at the surface layer. The direction of current varies
with the direction of the monsoons. When the northwest and northeast winds are
blowing in the direction roughly parallel to that of the Changjiang runoff in winter,
the longshore current flows southwards with a relatively large velocity and is
relatively stable. Water masses outside northern Taiwan also represent a region
where water along the edge of the Kuroshio Current mixes with water from the
Taiwan Strait and the East China Sea. The Kuroshio Current originates from east of
14 the Philippines and flows northward along the east coast of Taiwan. To the northeast
of Taiwan, the Kuroshio Current runs into the continental shelf-break and forms a
year-round upwelling system. Nutrient-rich water near the western edge of the
upwelling system mixes with waters of the southern East China Sea. Discharge of
heated water from the nuclear power plants into shallow coastal waters can have
harmful effects on aquatic organisms. Warm water from the power plants enhances
algal growth, speeds up the process of eutrophication, and causes changes in species
composition. At the same time, warm temperatures may influence the feeding rates
of herbivorous zooplankton and change the efficiency with which phytoplankton is
harvested.
Port Shelter is a partially enclosed bay in the southeastern part of Hong Kong
(Fig. 2.2). Located near the entrance of Mirs Bay, it is strongly influenced by water
masses of the South China Sea. In winter NE monsoon period, the southwest ward
drift current is dominant and part of the Kuroshio flows along the east coast of Hong
Kong and mixes with the water outside the Port Shelter. Meanwhile, part of the East
China Sea longshore current enters the South China Sea through the Taiwan Strait,
forming a strong south west drift current that flows from north to south in the western
part of the South China Sea. The marine water in Port Shelter is amongst the best
quality in the territory. The Port Shelter Water Control Zone (WCZ) is designated as
15 a secondary contact recreational zone and is very popular for water sport activities.
Major urban developments in the catchment include Sai Kung, Pak Kong, Pak Sha
Wan, Ho Chung, Tai Po Tsai, Silverstrand and Clear Water Bay. These areas, except
Sai Kung town center, basically are dominated by ‘village house' type of development
with relatively low population density. Water quality in the Port Shelter WCZ is
fairly uniform and improves towards the outer part of the bay (EPD，2000). In Hong
Kong, Calanus sinicus is recorded mainly in coastal water in the east and south during
the winter and early spring months (Chen, 1980). Only very small numbers of C.
sinicus have been found in Tolo Harbour, Hong Kong (Wong et al., 1993)。
The populations of C. sinicus in the coastal waters of Taiwan and Hong Kong are
believed to have been derived from the northern populations in the Yellow Sea, the
East China Sea and coastal waters of Japan under the influence of the NE monsoon in
winter. Dense populations of C. sinicus, especially in Port Shelter, are occasionally
recorded during late winter and early spring when the NE monsoon is blowing (per.
comn., Dr. W. X. Wang, HKUST).
The aim of the present study in this chapter was to provide information on the
distribution and seasonal occurence of C. sinicus in the southern edge of the species
range. The life history of C sinicus has been studied in northern part of the species
range in seas around northern China and Japan. Little attention has been given to
16 populations along the coasts of Fujian and Guangdong. The specific objective of
this study was to examine the seasonal occurrence of Calanus sinicus in coastal
oceans of northern Taiwan and Hong Kong. Development characteristics of body
allometry were examined by measuring prosome length and dry weight of C. sinicus.
The study in Taiwan was conducted in waters off the northern tip of Taiwan. This
study was part of the project “Coastal Ecology Survey near the Nuclear Power Plants
I, II and IV at Northern Taiwan“ supported by the Taiwan Power Company. The
Hong Kong study was conducted in coastal waters near the outer edge of Port Shelter.
Life history parameters of C. sinicus at these locations were compared to those of the
northern populations to obtain information on latitudinal patterns in population
structure and life history strategies.
2.3 Materials and Methods
2.3.1 Field sampling
Samples were collected at nearly monthly intervals from November 2000 to
March 2002 from seven sampling stations (Fig. 2.1 and Table 2.1) in coastal waters
off northern Taiwan. Outside Port Shelter, Hong Kong, samples were collected at
five sampling stations (Fig. 2.2 and Table 2.1) at nearly monthly intervals from
February 2001 to April 2002. Duplicate samples were collected in each station.
All zooplankton samples were collected using conical nets with closing mechanism,
17 0.5 m mouth diameter and 125 jim mesh size. In Taiwan, samples were collected
from the upper, middle and lower layers (depend on the water depth) of each sampling
station by towing the net behind the ships for 5 to 10 mins (no duplicate). Most of
the samples were collected during daytime. A calibrated flowmeter was fixed to the
mouth of the net to estimate the volume of water filtered. In Hong Kong, samples
were collected by vertical hauls from 22 m depth to the surface during daytime.
After towing, the net was washed thoroughly, and the catch was preserved in a 4%
formaldehyde-seawater solution in 250 mL plastic bottles. Vertical profiles of
temperature and salinity were measured at each zooplankton sampling site. For the
determination of chlorophyll a, seawater samples collected from the upper, middle
and lower layers of each sampling station by a water sampler were stored in darken
bottles at near freezing temperature (〜0。C). Upon returning to the laboratory, the
water samples were processed immediately. Phytoplankton was concentrated on
0.45 11 m Millipore filters and extracted overnight in 90% acetone (analytical grade) in
a dark refrigerator. Chlorophyll a concentrations of acetone extract were determined
with a Turner Designs fluorometer using the method of Parson et al. (1984). The
concentration of chlorpophyll a was calculated according to the equation ofDagg and
Wyman(1983):
Chi a concentration (mg m’ 二 K(Rb-Ra)v/V
18 where K is the machine calibration constant, Rb and Ra are the fluorescence reading
before and after acidification (5% HCl), v is the volume of acetone extract and V is
the volume of filtered water sample.
2.3.2 Identification and enumeration of Zooplankton
In the laboratory, the volume of zooplankton samples was adjusted to 250 mL
and the number of Calanus sinicus in five 5 mL subsamples was counted. The
developmental stages of C. sinicus (from CI to CVI) were sorted from the samples
and counted under a dissecting microscope. Identification of developmental stages
was based on Chen (1965) and Li (1990). The count of each developmental stage
was converted to individual numbers per unit volume of water. Identification of
males and females was made only for adults. No attempt were made to count the
naupliar stages because of the difficult of identification. An index (stage ratio index)
of the ratio between abundance of copepodite stages [(CVI females - CV)/(CVI
females + CV)] was calculated to describe the stage of development in the
populations of C. sinicus (Melle and Skjodal, 1998).
2.3.3 Body length and weight of Calanus sinicus
Prosome length (PL) of each copepodite stage was measured under a dissecting
19 microscope fitted with an eye-piece micrometer. Dry weight (DW) of specimens
was determined after placing the preserved specimens in a drying oven (60 °C) until
constant weight. Samples were weighed with a Cahn-3 Microbalance (Model No.
10931-0IF). Two to twenty individuals were measured depending on the abundance
of Calanus sinicus in different months.
2.4 Results
2.4.1 Temperature
Temperature measurements over the 17 months investigation at different stations
off northern Taiwan are presented in Figures 2.3a to 2.9a. Temperatures showed a
cyclical annual pattern with the highest temperature in July to August and the lowest
in January to February. Water temperature off the northern tip of Taiwan ranged
from 17 to 20 °C in the winter. At station C5000, gradual warming of the water
column began in March and a thermocline appeared at the beginning of June (Fig.
2.9). There were stratifications at different depths due to the temperature in June
(around 50 m), July (around 60 m) and August 2001 (around 70 m) at station C5000.
The thermocline began to break down in October when the surface temperature fell to
about 23 °C. No thermoclines appeared in other stations. In addition, no
significant thermal pollution was observed outside the outlet of the nuclear power
20 plant when comparing with the inlet.
Among the five stations outside Port Shelter, Hong Kong, temperature showed
similar seasonal patterns (Fig. 2.10a - 2.14a) over the 15 months study period. At
all of these five stations (station 1- station 5), temperatures recorded between 0 and 20
m depth ranged from an at depth minimum of about 17 C in
surface maximum of about 30 °C in August 2001. Water temperature ranged from
17 to 20 in the winter. The temperature of the water column began to rise in
March and a thermocline appeared at the beginning of June. Summer temperature
ranged from 26 to 32 °C at the surface and dropped to between 23 and 28 °C at the
bottom. The thermocline began to break down in October when the surface
temperature fell to about 26 °C.
2.4.2 Salinity
Salinity measurements over the 17 months investigation at different stations off
northern Taiwan are presented in Figures 2.3b - 2.9b. Because coastal water off the
northern tip of Taiwan is influenced by water masses from the open sea, salinity is
higher and more stable than those in the inner and enclosed harbour. Surface salinity
ranged seasonally from 32.6 to 34.5 %o and was lower and more variable in summer
and fall than in winter and spring. Relatively high surface salinities (>33.5 %o)
21 occurred from December 2000 to March 2001 and from December 2001 to March
2002, and were considered to be derived from the Kuroshio high-saline water. In
other months, less saline water (<33.0 々oo) was recorded in the upper layer, whereas
the bottom water remained virtually unaffected.
The five stations outside Port Shelter, Hong Kong, showed similar seasonal
patterns in salinity (Fig. 2.10b - 2.14b) over the 15 months investigation. Surface
water outside Port Shelter was generally more saline in winter and spring than in the
summer and early autumn rainy season. In rainy season, salinity exhibited
considerable change, from less than 28.0 ^/oo at the surface to more than 32.0 %onear
the bottom. The vertical salinity gradient was magnified after monsoon rains when
surface water over the entire area of Port Shelter showed significant reduction in
salinity, whereas the bottom water remained virtually unaffected.
2.4.3 Ambient Chlorophyll a concentration
Phytoplankton biomass, estimated based on chlorophyll a concentration, showed
a marked seasonality (Fig. 2.15) in coastal water off northern Taiwan. In general,
considerably higher chlorophyll a concentrations (〉1.5 mg m。）were reported from
July 2001 to November 2001. Chlorophyll a concentrations were higher at stations
BIOOO, CI000 and C2000 than at the other stations.
22 Chlorophyll a concentration in the surface water outside Port shelter was high
(Fig. 2.16) and varied very widely from 3.0 to 8.0 mg m'^ at different stations among
different layers outside Port Shelter. Chlorophyll a peaked in May to August 2001
with concentration usually more than 4.0 mg m。in the surface water. The
difference in chlorophyll a concentrations among different stations was not large.
2.4.4 Seasonal occurrence and distribution of Calanus sinicus in
northern Taiwan
Numerical abundance of CI through CVI stages (adults) of Calanus sinicus at
different stations in coastal water off northern Taiwan during the 17-month study
periods are shown in Fig. 2.17. C. sinicus showed clear seasonal pattern of
occurrence off the northern tip of Taiwan. Numbers were highest in winter months
from November to December, and lowest during the summer months from May to
July. Maximum densities of adult males and females were found in December 2000
and 2001 (Fig. 2.31). Numbers of CIV and CV also peaked at these times, while the
densities of all the earlier copepodite stages were higher in summer months (Fig.
2.31).
High abundance was recorded occasionally in station B500. Adult female
concentrations peaked in February and November 2001, reaching densities of,
23 respectively, 3.4 and 1.7 ind. m^, while adult males reached a maximum density of
0.38 ind. m-3 m December 2000 (Fig. 2.18). CI, CII，CIII, CIV and CV reached
maximum densities of 0.24，0.24, 1.9, 4.3 and 8.8 ind. m'^ in December 2001.
The population of Calanus sinicus was quite low in station BIOOO (Fig. 2.17).
CV was numerically the dominant stage in December 2000 and December 2001, with
adults common from February until April (Fig. 2.19). The small peak (1.3 ind. m'^)
in August (Fig. 2.17) was mainly comprised of CIII (Fig. 2.19).
In station B2000, two peaks were found (Fig. 2.17). One in December 2000 and
the other in December 2001, and the populations were least abundant in January in
both these two years (Fig. 2.17). The two December peaks were composed largely
of CV (32 and 16 ind. m'^) with a few adults and CIV (Fig. 2.20). From December
onward, the abundance of CV decreased while another small peak of adults were
observed in February (2.8 ind. m'^ for female, 0.20 ind. m'^ for male) and March 2001
(1.2 ind. m-3 for female, 0.56 ind. m"^ for male). The abundance of younger
copepodite stages CIII peaked in August (1.2 ind. m"^) and December 2001 (1.5 ind.
m-3), but as a whole the proportion of the population comprised of CIII was low.
Only a small number of CII (0.52 ind. m'^) was recorded in July.
C. sinicus were rare or absent during most of the year in station C500. The
maximum abundance of C. sinicus occurred in December 2001 with density of about
24 58 ind. m""' (Fig. 2.17). The December peak was composed largely of CV (41 ind.
m"0 with a few adult females (7.6 ind. m’ and CIV (6.5 ind. m") (Fig. 2.21).
Calanus sinicus was most abundant in the winter months at station CI000 (Fig.
2.17). Four irregular peaks were recorded over the study period in station CI000.
The peak in December 2000 consisted largely of CV (8.4 ind. m'^) with a few CIV
(1.4 ind. m-3). The February peak composed of adult females (6.3 ind. m’ and adult
males (1.3 ind. m'^), the July peak consisted of CIV (2.5 ind. m"^), while the peak
from November to December 2001 comprised of adults, CV and CIV (Fig. 2.22).
Two peaks of C sinicus were found in station C2000, one in December 2000 and
the other in December 2001 (Fig. 2.17). Maximum adult female abundance was 17
ind. m-3 in December 2000 and a pronounced numerical peak (11 ind. m"^) was also
seen in December 2001 (Fig. 2.23). The populations in December 2000 and 2001
were also dominated by CV. The abundances of CV generally fell rapidly after
December. CI, CII, CIII were much rarer, and were recorded in August, as well as
the winter months. Their densities were 0.40, 0.40 and 1.2 ind. m'^ respectively.
Maximum abundance in station C5000 was 100 ind. m'^ in December 2001 (Fig.
2.17) when the population consisted mainly of CIV (39 ind. m'^), CV (39 ind. m"^)
and adult females (15 ind. m"^) (Fig. 2.24). A pronounced numerical peak comprised
of adult females (3.2 ind. m'^), adult males (2.6 ind. m’ and CV (22 ind. m’ was
25 also recorded in December 2000. Abundances of various stages generally fell
rapidly after December, although the abundance of CI, CII, CIII and CIV showed
small secondary peaks in the summer months from June to September. Maximum
abundance of CIII was 11 ind. m"^ in August 2001，while those of CI, CII and CIV
were 1.3, 3.2 and 10 ind. m'^ respectively, in July 2001.
In general, the abundance of Calanus sinicus increased with the distances away
from the Nuclear Power Plant and the number of C. sinicus along each transect was
higher at station C5000, C2000 and B2000 than in the inner stations. During the
17-months study period, mean densities were 21 ind. m"-' at C5000, 13 ind. m'^ at
C2000 and 5.5 ind. m'^ at B2000 (Table 2.2). Mean densities at ClOOO, C500，BIOOO
and B500 were only 4.1，5.8, 2.3 and 2.0 ind. respectively, over the same period
respectively (Table 2.2). C. sinicus was also more abundant outside the outlet of the
Nuclear Power Plant when comparing with the inlet.
2.4.5 Seasonal occurrence and distribution of Calanus sinicus in Hong
Kong
Seasonal variation in the abundance of CI through CVI stages (adults) of C.
sinicus at different stations outside Port shelter over 15-month study period are shown
in Figures 2.26 - 2.30. C sinicus occurred only in January and February 2001 and
26 were absent in all other months during the study period. The January and February
peaks consisted of CV, adult males and adult females. Early copepodite stages were
not found. Densities of Calanus sinicus at different stations did not differ greatly,
but the highest density was lower at station 4 that at the other stations (Table 2.2).
2.4.6 Life cycle of Calanus sinicus in northern Taiwan
Changes in mean abundance of CI through the CVI stages (adults) of C sinicus
over the study period at all the stations in the coastal water off northern Taiwan are
shown in Fig. 2.31. All developmental stages occurred seasonally throughout the
study period. The CIII stage was most abundant from July to September 2001.
The development sequence of this peak was traceable up to the CVI stage. The
disproportionately higher number of older copepodites and adults in winter suggests
that most of the population was derived from populations in the Yellow Sea and the
East China Sea under the influence of the north east monsoon rather than from in situ
reproduction. Maximum abundance of CV occurred in December 2000 and from
November to December 2001. Adults were most abundant during December 2000,
February to March 2001，and November to December 2001. There were three
distinct peaks and three indistinct ones. Seasonal patterns in abundance of females
and males were similar, and males were consistently less abundant than females
27 (female:male = 9:1).
2.4.7 Life cycle of Calanus sinicus in Hong Kong
Seasonal variations in mean abundance of CI through CVI stages (adults) of
Calanus sinicus over the study period at all the stations outside Port shelter are shown
in Fig. 2.32. No younger copepodites (CI to CIII) were recorded outside Port Shelter
over the study period. This observation suggested that C. sinicus does not reproduce
along the east and south coast of Hong Kong. Older copepodites and adults occurred
only in January and February 2001 and were absent in all other months of the study
period. The timing of occurrence of older copepodites and adults outside Port
shelter indicated that C. sinicus were carried by the monsoon drift currents from the
water off the northern tip of Taiwan into the east and south coast of Hong Kong under
the north east monsoon. The abundance of C sinicus in January and February 2002
suggests that the presence of this species in water around Hong Kong is sporadic.
Hong Kong is in the northern edge of the South China Sea where C. sinicus is not a
regular component of the zooplankton.
2.4.8 Stage ratio index
The index of stage ratio increased from -0.84, indicating an abundance of CV, in
28 November 2000 to about 1.00 in January 2001, indicating a population of almost
exclusively adult females (Fig. 2.33). The sharp decline in the stage ratio suggests
that the rate of egg production was high between January and July. In July, the index
was mostly below -0.98, indicating that the population was 99 % CV. The fall in the
ratio when spawning activity was at a high rate could be due to both reduction in the
numbers of CVI females and the development of younger copepodites into CV.
2.4.9 Seasonal changes in biomass of Calanus sinicus
Seasonal variations in average biomass at each station (Fig. 2.34) reflected
changes in numerical abundance (Fig. 2.17). The stage composition affected the
biomass to some extent. Average biomass of Calanus sinicus was higher at stations
in the open ocean, further away from the nuclear power plant, than in the inner
harbour. Average biomass was higher around the outlet of the nuclear power plant
than around the inlet. Biomass of C sinicus did not differ greatly among stations
outside Port Shelter (Fig. 2.35).
2.4.10 Seasonal changes in the abundances of other copepods in
northern Taiwan
Seasonal abundance of copepods at different stations outside the nuclear power
29 plant is presented in Fig. 2.36. A clear seasonal pattern was observed. Density of
copepod was high during July and August 2001 and remained at much lower levels
during the other months. In general, average density was higher at the deeper and
more oceanic waters of stations C5000 (3500 ind. C2000 (3000 ind. m'^) and
B2000 (1900 ind. m'^) decreased progressively towards the inner harbour (Table 2.2).
Mean densities at stations CI000, C500, BIOOO and B500 over the same period were
only 2200, 1600, 1700 and 1600 ind. m\ respectively. The abundances of copepods
were also higher around the inlet of the nuclear power plant than near the outlet.
Common species in summer months included Acrocalamis gracilis, Centropages
orsini, Eucalanus subcrassus, Labidocera acuta, Nannoclanus minor and Temora
turbinate (Wong, 1998)。
2.4.11 Seasonal changes in the abundances of other copepods in Hong
Kong
Density of copepods at different stations along the eastern and southern coasts of
Hong Kong over the study period is shown in Fig. 2.37. A clear seasonal
distribution was also recorded. Higher number of copepods was observed during
July and August 2001 and remained at much lower levels during the other months.
The density of copepods among different stations was similar.
30 2.4.12 Seasonal changes in biomass of other copepods
The seasonal variations in average biomass at each station (Fig. 2.38) reflected
changes in numerical abundance (Fig. 2.36). The species composition affected the
biomass to some extent. The average biomass off the northern tip of Taiwan was
highest at station C5000, followed by C2000 and was lowest at B500 and C500.
Average biomass of copepods did not differ greatly among different stations outside
Port Shelter (Fig. 2.39).
2.4.13 Seasonal variations in body size
Seasonal variations in body size of different developmental stages of Calanus
sinicus in northern Taiwan were measured from November 2000 to March 2002.
Body length ranged from about 0.60-2.20 mm. The largest individuals were found
in the winter months and the smallest ones mainly in summer months, indicating a
possible inverse relationship between prosome length and water temperature (Fig.
2.40). The mean prosome length of each developmental stage was plotted against
the average temperature of occurrence of individuals (Fig. 2.41). Significant
(P<0.05) negative regressions were obtained for CIII，CIV, and adult male. The
mean prosome lengths of these stages {PL, mm) were expressed as a function of
31 temperature (T, °C) as follows:
CIII: = 1.1697-0.00227
CIV: PI = 1.4217-0.00397
CVI $ : PL = 2.0690-0.00417
The mean prosome lengths for CI, CII, CV and adult female were 0.65, 0.84，1.70 and
2.15 mm, respectively. Prosome length (PL, mm) and body dry weight {DW, mg) of
copepodites and adults of Calanus sinicus can be described by the equation (Fig.
2.42):
DW-^ 0.0326 - 0.0744 X + 0.0527PZ?
2.4.14 Seasonal change in sex composition in adults
The sex ratio among adults differed seasonally (Fig. 2.43). Females usually out
numbered males. Females comprised an average of 86.14 % of all adults.
2.5 Discussions
For species with complex life histories, populations are considered to be
regulated, to a large degree, by physical oceanographic processes. Copepods in
other marine ecosystems show life cycles tuned to the physical characteristics of that
system (Conover 1988). The geographical distribution of C sinicus in coastal water
32 off northern Taiwan showed that densities of this species were highest between
November and December. In February, the center of the population seemed to move
to more southern end of the species range in the northern part of the South China Sea.
This geographical shift of the population center may be accounted for by two reasons.
Firstly, the winter NE monsoon period, part of the East China Sea longshore current
enters the South China Sea through the Taiwan Strait, forming a strong southwest drift
current and carrying along with it such species as Calanus sinicus into the South
China Sea. Secondly, the winter comes faster in coastal water off northern Taiwan
than in Hong Kong. The regional, dissimilar occurrence and distribution that are
seen in C. sinicus off northern Taiwan and outside Port Shelter, Hong Kong may be
explained by differences in thermal conditions.
Temperature affects rate of development in copepodites of Calanus spp. (Corket
et al,, 1986) and, thereby length of life cycles and timing of important life history
events such as reproduction. Water temperature off the northern tip of Taiwan
ranged from 17 to 20 °C in winter. The optimal temperature for C sinicus is about
5-24 °C and the optimal temperature for reproduction is about 10-18 °C. Uye (1988)
found that the hatching of C. sinicus eggs is possible between 5 and 23 °C, and Lin
and Li (1986) showed that adult females of this species cannot survive more than 3
days at 24 °C. According to the water temperature, active growth and reproductive
J J of Calanus sinicus in northern Taiwan is confined to only six months of the year,
between November and April when water temperature is below 22 °C. Results
presented here indicate that C sinicus in northern Taiwan spends the winter mainly as
CV, but there is a small proportion of adults. In both winters, younger stages were
either rare or completely absent. C. sinicus decreased in population size rapidly after
reaching an annual abundance peak in December. Small population of CV and
adults were recovered in February to April. From April onward, water temperature
increased gradually and reached the maximum surface temperature of >28。C in July.
The thermal range for the occurrence of this species in northern Taiwan may be
confined to a narrower range. In more open waters (eg. C5000) off northern Taiwan,
the majority of the population might reside in the layer deeper than 60m in summer,
where the temperature is lower. Summer temperature ranged from 24 to 29 °C at the
surface and dropped to between 17 and 28 at the bottom. A gradual increase in
the abundance of younger copepodites from J皿e to September suggests that the
population sank to depths >60m when surface temperature began to increase. In this
sense, average water temperature in layers above 60 m does not represent the habitat
temperature at these stations during the warm seasons. Sharp declines in population
in summer in areas where water depth is shallower than 60 m can be interpreted
chiefly as the result of temperature stress. During the high temperature period, C.
34 sinicus resided in the colder, deeper layers.
Water temperature outside Port shelter in Hong Kong ranged from 17 to 20 °C in
the winter. Summer temperature ranged from 26 to 32 °C at the surface and dropped
to between 23 and 28 °C at the bottom. Since the study sites in Hong Kong are a
shallow coastal area, therefore, population of Calanus sinicus cannot sank to colder,
deeper layer when surface waters began to warm. C sinicus occurred only in
January and February 2001 and were absent in all other months during the study
period. For better understanding of the distribution and occurrence of C. sinicus, the
study area in Hong Kong or northern part of the South China Sea should be expanded
to deeper areas.
The density of C. sinicus was much higher and fluctuated more in coastal water
off northern Taiwan than in Port Shelter, Hong Kong. During the growth season，
between November and April, temperatures are lower in northern Taiwan than in Port
Shelter. In addition, the low temperature condition for C. sinicus tended to last
longer in northern Taiwan (November to April) than in waters around Hong Kong
(December to March).
Estimation of the generation length for C. sinicus is of central importance in
order to justify the multi-generation scenario. From the laboratory data for egg and
naupliar development times obtained in a previous study (Uye, 1988), we attempted to
35 estimate the generation length of Calanus sinicus. Assuming a habitat temperature
of 21 °C (which corresponds to the average water temperature over the study period
off northern Taiwan) and applying the relationship developed by Uye (1988):
Dcvi= 1258(T+0.7)-i.44
where Devi is the time (days) from egg-laying to CVI and T is temperature (°C). An
in situ temperature of 21 °C leads to total development from egg to adults is 15 days
•1258(21+0.7)-1.44 二 15 days]. Because of the 1-month sampling interval of this
study is longer than the estimated generation length of C. sinicus (15 days), it is
difficult to judge whether or not the observed peaks correspond to multiple
generations. Uye (1988) found that the observed generation time of C. sinicus was
much longer in Xiamen Harbor than in the laboratory where calculated development
time from egg to adult was 21.7 days. Three generations were observed to occur
annually in Xiamen Harbor. The observed generation time in Xiamen Harbor, in
comparison, was 2-3 months for the first (from December-January to February-March)
and the second (from February-March to April-May) generations. The longer
development time may be a consequence of the difference in food conditions and
physiological characteristics between geographically-separated populations. Hence,
it is difficult to confirm the generation time of C sinicus off the northern tip of
Taiwan either by the laboratory data or field data. In tracing the development
36 sequence of each cohort, it is evident that a higher abundance of young copepodites
does not necessarily yield a high abundance of adults. During summer, the
abundance of the CV stages and adults was higher than that of CI to CIII stages. This
may be due to introduction of CV and adults from the East China sea and the Yellow
Sea into the northern parts of the South China Sea.
For herbivorous copepods, the abundance of phytoplankton is one of the most
important factors controlling the magnitude of their egg production (Runge 1985;
Hirche and Bohrer, 1987; Peterson, 1988). If food is sufficient, the egg production
rates of copepods are affected by temperature (Uye, 1981; Ambler, 1986). Although
the chlorophyll a concentrations outside Port Shelter in Hong Kong are much higher
than those in northern Taiwan, no younger copepodites were found in Hong Kong.
Hence, it is assumed that the natural Calanus sinicus population was not food limited
but the rate of egg production was determined by water temperature. Since neither
eggs nor nauplii were collected in the present study, the only information available
about the reproduction of C sinicus is the abundance of adult females. Diel and
Tande (1992) suggested that reduction in the copepodite stage ratio between CVI
females and CV immediately after the main spawning could be used as an indicator of
the spawning event in Calanus finmarchicus. In our results, the reduction in the
copepodite stage ratio index that began in February off the northern tip of Taiwan was
37 mostly likely due to reduction in the number of females, assuming that spawning or
spent females have a higher mortality rate. Hence, young copepodites of Calanus
sinicus m our study were most abundant in the summer months. Water temperature
in summer months increased gradually and reached the maximum surface temperature
of >28 °C in July. C. sinicus of younger stages can reside in the colder, deeper layers
during the high temperature period off the northern tip of Taiwan. The absence of
younger stages in Hong Kong may be due to two reasons. Firstly, the population of
younger C. sinicus cannot sank to colder, deeper layer when surface waters
temperature began to increase in summer. Hence, no younger copepodites can
survive. Secondly, the growth season outside Port Shelter is shorter and
temperatures are less suitable for C. sinicus to reproduce. However, this factor is
certainly intermingled with effects of advective transport of oceanic currents.
Compared with the adults, the longer duration for the occurrence of CV may
reflect a longer residence time of the CV, as the mean annual abundance of adults was
less than that of the CV stage. The annual mean abundance of C. sinicus CV was
much greater than those of other copepodite stages, indicating that CV lives longest
among the copepodite stages. Uye (1988) found that the duration of CV of C
sinicus was longest at any temperature in the laboratory.
Although the abundances of C. sinicus were higher outside the inlet of the
38 nuclear power plant when comparing with the outlet, no significant thermal pollution
was observed outside the outlet of the nuclear power plant when comparing with the
inlet. Hence, the mortality of Calanus sinicus is not due to the thermal effects of the
nuclear power plant, but may be due to other reasons.
It is commonly accepted that the physiological rates of zooplankton are governed
by body size, with smaller species having the higher weight specific physiological
rates (Ikeda, 1974; Lynch, 1977). This suggests that smaller species may have
competitive advantages over larger ones. In this sense, the growth rate of C sinicus
is expected to be lower than that of other smaller species. Therefore, it is surprising
to find that the growth rate of C. sinicus is higher than that of smaller species such as
Paracalanus parvus and Acartia clausi (Uye, 1988). This higher growth rate is one
of the reasons why C. sinicus is able to compete with smaller species and dominate in
the coastal water off the northern tip of Taiwan during the winter months. Vidal
(1980) concluded that the effect of food concentration on individual growth became
progressively stronger with increasing age and body weight of copepods. It implies
that the growth of intermediate and large-sized copepods are controlled primarily by
food availability, while that of the smaller ones is more sensitive to changes in
temperature. Hence, the food for C. sinicus off the northern tip of Taiwan was not
limited in the winter months.
39 Seasonal temperature changes have been identified as a primary influence on
body size for a variety of copepod species in estuarine and oceanic environments,
based on both observational (field) and experimental (laboratory) data (e.g. Landry,
1978; McLaren and Corkett，1981; Durbin et al, 1992). Temperature has usually
been found to influence body size in regions with a large annual temperature range
(e.g. Deevey, 1960; McLaren, 1963) or where food is abundant (e.g. Klein Breteler
and Gonzalez, 1988). It has been suggested that, since food is usually seasonally
abundant in regions with a board seasonal temperature range, the availability of food
to the animals is not limiting and therefore has little effect on the ultimate body size
(McLaren, 1963). Regressions of prosome length, for each separate stage and sex,
against temperature were carried out for specimens collected from northern Taiwan.
Previously, such relationships have been reported to be more marked in older stages
(Uye et al., 1982; Ling and Uye, 1996; Liang et al, 1996), and seasonal changes in
prosome length in the current investigations were also greater in many of the older
stages of Calanus sinicus. The present use of specimens preserved in formalin for
DW determinations may not be valid since loss of organic matter could occur during
storage (Hopkins, 1968; Fudge, 1968). Nevertheless, the magnitude of error caused
by formalin preservation is relatively small and unimportant for broad comparisons
between stages of dissimilar species (Gruzov and Alekseyeva, 1970).
40 >1 \ East China Sea
一 C 120。E ^ C5000(^) China \ ^^ B2000 (36 m) 0
^^ BIOOO (26 m)^ • • C2000 (61 m)
—25^ ^ ‘ B500 (16 m) •• • ClOOO (31m)
X / Y C500 (9 m)
if Taiwan / \ •
jfL-AJ Strait / / \ NPPI \ ^ 7 r \l V II
South China Sea \ ^ 園一—一 J
^^ I Pacific Ocean
100 km ^
Fig. 2.1 Map of South China Sea and East China Sea showing location of sampling stations outside Nuclear Power Plant I (NPPI) in coastal waters off the northern tip of Taiwan. Numbers in parentheses refer to water depth. “C’， represents the inlet and “B’ represents the outlet of the nuclear power plant. The numbers next to the letters B and C refer to distance from shore in meter. P ) C J ^ n (20 m) \
Xa •厂 fill (20 m) \ ^ ^lear Water Bay • \ _
\ r c/X O rv (20 m) Kwo Chau ^ 少Tfi m
Fig. 2.2 Map of Port Shelter, Hong Kong showing location of sampling stations. Numbers in parentheses refer to water depth. 2000 2001 2002 Dec Feb Apr Jun Aug Oct Dec Feb
(a) ； ； : ： ！ ^ ！ ： ： ‘ . ： ： ^ V / csi 0 CO 03 G) OvI i ro M CO M IV) CN O CO T C>J qj T T OJ cjg CM •丨 O) cocsj cn ^ cn cn t- � I ！ 1 I . i i ! ' ； ： i : ! : o ！ ！ ！ ; M ； I ‘ ： I D ！ I i ！ I ： ‘ I ： ： i I ; ；; ： I ： • : I: I h I I I ！ ；1 i I I I ； 8 H : I ！ i I ； ^ : I 丨 丨 丨 丨丨I
9 丨 I ！ i I 丨 丨I i £ 1 I 丨 i i i ！ ‘ I i ： I i i ； I I
t 10 1 I 丨H 丨 丨： ：
& i 丨 I丨 丨 I 丨丨 ： Q 丨 I 丨 i i I i I i I I ： I I I i I I M O 1 1 ！ i 1 i 12' i ； ' . ! i '^ : I ' II 1 I I I i i I ！ J I ！ i I I i i ； 丨 ！ I呀 N),丨 I 丨丨 ； 1 备； I i CO 14 ： 串 S $ 5 S SI ^ ^ ^ s K 另平 T II. i I ！ i i 丨 i ： i I I i丨 丨 丨I ： ： I Mi:! I i 1 1 M ; i i ！ I I ‘ 1 I i i I ！ I . I I i —i ： i— 1 1~ � 」_一-一-……丄—
(b) 41 Ty-rp-Tn 1 'I ‘ I ‘ O中 lo 。）o q W P III ^ ^ ^ J,^
6 - T q cn CD CO cp
8 1 I
^ I \ s VJ 12 j .
cp
oo in too w • S 14 - III P.l 彳〒 I I
16 J -LULLi._____
Fig 2.3 Seasonal changes in (a) temperature (�C an) d (b) salinity (义。） at station B500 off northern Taiwan.
43 2000 2001 2002 Dec Feb Apr Jun Aug Oct Dec Feb
5 1 '| I / hi I I In tn—1 (a) fill 丄 I c4 CD CO CD ro 守 roco CO co ^ CN O CO Csi CN T- T- O eg O)中 Csl I I CsJ 10 - _ / I £ 15 - Q- 0) Q ^ 2J0 - L /\ N) ro 25」 ——LJJ '1111 丨 I 11 I^ (b) Txfpxn] 'I I i 10 � 4 I \ 4 ^ E \ 0-5 t CJl ^ V , 1 t 15- II 考罕 1 ^ J S \ I 20 - uO A ： 25」J^lUU —— Fig. 2.4 Seasonal changes in (a) temperature (�C an) d (b) salinity at station B1000 off northern Taiwan. 44 2000 2001 2002 Dec Feb Apr Jun Aug Oct Dec Feb 5 1 -r^ r-h ^ ^ ^I '丨 II ||“——‘f (a) . f 10 - Q cq CN CO OD CD C4 NJ CO 15 - o E £ 20 - S" Q 25 - II cJ CO CD c3 c^ ^r TO c) ^ eg C3 CDO CD 二 CJ ^ T- eg ^ ^ CM C\ CNJ C^J CNCM y CO 30 / \ • T 35」 ——__L—L_LJ_\、U i __L_ (b) 5， CO lo 10 ] ^ I cn \ 15 - ^ 20 1 i，—某 y 》实― J: i •⑴ ± “u ob 〒Y^T Q c)宁C3 O o o T CJI C) 0) I / “ / ^ 25 / T / 3J0 - —— Fig. 2.5 Seasonal changes in (a) temperature (�C an) d (b) salinity (。/。。） at station B2000 off northern Taiwan. 45 2000 2001 2002 Dec Feb Apr Jun Aug Oct Dec Feb 2， T^'I 'I 11 III ‘ ‘ 1^ (a) I Csi CD CO C3 Csi 1 horocjro M M CN O COCO eg C^i 03 Tj- 04 CV4 CN -J^OCJCO CD 4 - E 5 Q. (D O Q o ‘ 7 - gj I liLllll ___LL_ (b) 21 产 I I ‘, ^ 1 ^^^ I ^ 予 4 - i E 5」 a. 0) o Q 6 - W O -7 cri / - O CO 8 SS 1 ^ S 吊 9」 ^ ‘ Fig. 2.5 Seasonal changes in (a) temperature (�C an) d (b) salinity (。/。。） at station B2000of f northern Taiwan. 46 2000 2001 2002 Dec Feb Apr Jun Aug Oct Dec Feb 5 -1 -1 r^ h~“I '| I I I ' I I I I h r^ (a) C4 O CO CO o (N 4rCX0 CO CD ^r c^ Q CO CO C4 CU r- tt- CN CN 中。却 CN CN CN CN Cs| t- tt- + N) . 10- J" rCD Q 20 - I cj c5 o J hJ ro \ ^roJ213 ro S f^ cp。〕 K S T- CO o N)丨 g ^p^n^ cn 千 N) O 干 T ro 30 J -UL±_Ll_lyllLiJ I___——___ LL C __ I L^ ！ S 1 H ‘ (b) ^FTi T f / / 10 - / ^ - ^ i f r 二 o 中 w ocs / \ % 9. CL T en Q) ^ 20 - o / 25 - 力 30 J -J-^LU——LiU___lU L Fig. 2.7 Seasonal changes in (a) temperature (�C an) d (b) salinity (。/。。） at station CI 000 off northern Taiwan. 47 2000 2001 2002 Dec Feb Apr Jun Aug Oct Dec Feb 10 1 r^ 'I ' I^ I r I ^^Y-iu (a) 1 |1 II ' CnI O CO CO O (N N3 CO CM CN r- T- CV4 CN O T 1 _删g 丨1 Ui 50 - T. ？i ？ ？ ^ ^ i JA h s - f T TiV V 60」 ^^ ^ '''''' (b) i� j TjFrm^i n I II11 �I ij j J \ f I “丨 M 5。1 1 I Fig. 2.8 Seasonal fchange s in (a) temperaturIV e_ (� C an) d i(b ) salinity ('/J at statio60n JC200 ^0 off Lnorther n Taiwan. L_L 48 2000 2001 2002 Dec Feb Apr Jun Aug Oct Dec Feb 1 |J IMI '1； III ill O CDCD N) \ CO CO 20 - 7 TM U ^ 1 30 1 I^ i/ Y OW f • 丨 T / IJ • / I 80' ill LA II R^ I ——Li (b) 10 _ urmrrTT"^‘ w ‘ 20」 % 3CH H 丨 \ ± \ f f\ f I 40 i \ ( �… 专 '^25 II S y 另买 J 1J u i f A n 70- M n ^^ / ] 80 J Ji-L^U Fig. 2.9 Seasonal changes in (a) temperature (�C an) d (b) salinity (^/J at station C5000 off northern Taiwan. 49 2001 2002 Mar Jun Aug Oct Dec Feb Apr �� 1 Vlllll II! NJNONJ \ \ CO 5 i \ ‘ .1 h\ ^ 11丨赠 - 15 - I 寸 Ni CD CN -P^' C«4 S K ^^ CV S ^ 04 C4 N 00 另 T— 20」 …丨—— �’TWJT^ ,£ 10 -I 1 •^ “ A � lA ~ ,_ I f^rg cj CD 15 - , cn r) 20 \ ^ Ficr. 2.13 Seasonal changes in (a) temperature (°C) and (b) salinity (^/^J at station IVoutsid e Port Shelter, Hong Kong. 50 2001 2002 Mar Jun Aug Oct Dec Feb Apr 5 - ro Mro \ 00 CO 臂 csi o ct . “ O 1\ CN yCN I M 1115 - 茫 T /hj i M CN -P^ 20 J H H———— (b)� �"WW/ I' (1 ‘ ^ 1 "W 4 ？ ^ vy V �£ 10 J ,A T 丨 ¥ 中 ro Ficr. 2.1230 Seasona- l changes in (a)\ temperature (°C) and (b) salinity (^/^J at station IV outside Port Shelter, Hong Kong. 51 2001 2002 Mar Jun Aug Oct Dec Feb Apr ��� nillV \/lll II il[ N3 Mro \ \ 00 CD CN O fS) N) 00 Q M ^S \J CNCSCVJ CN (N C3 N) 1 � _ 1 00 1 ii。_ h . Q 考 I ， N) ^ C CN 15 - CO O CN N) 00 CO 寸 � NJ CD ^ r- CN CN CN CN CN 04 O C^ C4 20 J i 11 丨—Lliii__U—U—L_L (b)。.丨 M^"WJ/ I E I \ + 1r M\ A 宁I I 气 Tcw J / CO 1 N) \、 ICN OJ Ficr. 2.13 Seasonal changesC O in (a)ro temperature (°C) and (b) salinity (^/^J at statio2n0 IVJ outside Port ShelterU”丨, Hong Kong. 52 2001 2002 Mar Jun Aug Oct Dec Feb Apr 〇- —；'j I ；—V ^ 1 ~‘- ‘~ • ‘ 1 ~ - (a) : 1 Mi \ \ \� i : ； j 1 ro fvJNJM ^Q \ CO C£) V- CN O M M ro 〉 o (NJ^T) \ / (N CM ow O^ CN O rvj ^ . "' 与 I ! ； ‘： ； I ； 1 \ I ： I 1 \ ‘； ： 5— /、\ ：： 丨丨；. 11/ 1 V ：：：；:”： 一 ‘ ^ I ！ i A \ \ I i 、 ^^ 云 I ； i 1 i I S i ： I丨丨丨i [•ml I 丨 M i / \ 丨• I £ 10 ^ I ‘ • ； \ \ : ； Q_ ： " : , i i \ i ‘ O h I； :: :、：1 ” l\\ ！.: i i ! I . . CO _^广 1 ； ^ M I ! ‘ i c J ；�〜 I ； ^ 1” ： ： ： ： I I ； i ‘ ！ ： ！ I ‘, ., i• iI 1 i1 i I i :〇CNI 文� M CO vC TT 04 M o CN M ‘ CO S SJ S ； 丨 S^CMOJCNCNO 彳 CNCNJA 1 ！ CO. ： I i j I I I i ; i i I I j ！'：； I ！ 丨’： 20 j I I ‘ (b) 0 1 一一！; / / 丨 U 11%； / / I r I I ^ - ^ \ \ ": I ‘ .八\\ Ij ^ ：々；‘V ’ , /—” ； /I 9 ‘ ： vy ： n t： /1 一 \ I 11 呈丨A \! s 〜 A - rn / ‘ 15 - ’ . / ‘ CM 20 - Ficr. 2.13 Seasonal changes in (a) temperature (°C) and (b) salinity (^/^J at station IV outside Port Shelter, Hong Kong. 53 2001 2002 Mar Jun Aug Oct Dec Feb Apr �� 1 l/I Nii“ N)\JNJ ^^二 \ CO to ^ CN O M rsj cpsj^i. 巧 W CN CM CN CN CVJ O N； |i�1 /iH � 11 P I 4 C 々 M \ 0 - CN > ro CO CO T T— 20」Mill 丨 ^ (b)� � TWV// I i . 1 力 i 5i k \\ I A �\ JV I . ^^ i -•c -in J ^ n 1？ 15- / 1 - Ficr. 2.13 Seasonal changeUs in知 (a ) temperaturf e (°C) and (b) salinity (^/^J ^ I 1 I at statio20n 」IV outside Port Shelter^ , Hong Kong^ . 54 Station B500 Station C500 3丨 4 - M ..J Station B1000 Station C1000 ^ 6 •； 4 : ‘日” 1 3 1 j I ^ I J 2 1 I 0 iiUiWMWilWUwiA 0 丨隱丨 0 c • station B2000 Station C2000 1 “ 6] I M M g 2 I , 2」 ？ jj ； 2000 2001 2002 station C5000 3 - 1 I M ill I i itouwiuiwyu—II 2000 2001 2002 Fig. 2.15 Surface (white), middle (grey) and bottom (black) chlorophyll a concentration at different stations off northern Taiwan from November 2000 to March 2002. Data missing for middle layer chlorophyll a concentration at stations BIOOO, B2000, CI000，C2000 and C5000 from November 2000 to January 2001 and for all the three layers at stations C500, CI000, C2000 and C5000 in January 2002. 55 Station I Station IV 8 -： 8 - 6 ‘ n 该 6 - . ^ ： ！ ：. 4； J loliMMJUyLiLr[f j 4t- ； I p liiliykliMuilM g I ^ eg i ^ I S I ^ eg i ^ I s r-i i s ^ Station II Station V 1 10 i 8 ] 2 i n n ^ n • 6. nj (D - 謹丨 1』 ：�4.丨‘ f g I i ^ i s i - eg I ^ I o g 2001 2002 Station III 8 I “ 1 巧 I f 4： y I： ；flilliiykyLaiW U ' ‘ ^ f ^ i ^ 1 2001 2002 Fig. 2.16 Surface (white), middle (grey) and bottom (black) chlorophyll a concentration at different stations outside Port Shelter, Hong Kong, from February 2001 to April 2002. 56 Station B500 Station C500 20 -； 80 n 10」 \ 40 -1 \ 5 R - / \ 20 H I \ Station B1000 Station CI000 10 1 - 20 ： C Q -f……：--•——i"..…1-- • r - T “ 「- -「- I •f T—i T ； U • I ^ • 1 I T~ , ^ 11. • 1—^ 1 Station B2000 Station C2000 I 60 - 150 1 I I I I S c? I I I I I I I ^ ^ I ^ I 2000 2001 2002 stat髓 C5000 150「 100 ； 广、\ 50 \ Q J^^rrjb：^ • • -jg-.^.L l—T：^^ - —”~• 2000 2001 2002 Fig. 2.17 Seasonal occurrence of Calanus sinicus (CI to CVI) at different stations off northern Taiwan. 57 c I c w n o o ^ a 5 2 AM/ AMM/ 「—「——「—「—「；• ^ 「 ^///y^WL- I ^ 5 \\\A sf 5 o o 1^0 「—A u z ^ o V. ) 今 5 」 ： o jdld I nf 丁 ：：、 T-I^IAI - I- -- y : : - - --- I- = - : - ,5 s: if &s >02 >02 ；; I \\l 0 rl >o z c J 「 n AM^ _ = o 2 似 go 「 5 11J 了 o I AM 1 uBf 二 (「m r i 力 5 >oz ^ M ；; -- 一 ”. 二 : -- : I 。 .pu)) >02 o c : \v - ass 1 k -n^lAI : -一 /J- 0 4 「—，：1:J—i LIH f f I A/^ ; _ >02 n 3 2 I amv- 7,1 3 2 = 1 「-』 4 o ！ AA uB^ f 含 -- inf 1 li lAI >02 卜 ^ lnr V -- J^I/ M^ 二 _ d3 S >oz ^ 直 「——.——.-- ^ 4 / o c ^ _ / ^ ^ ^ UE「 >oz >oz f g <1 >oz inr m 目 6 4 ^ o ^ f -一 w 2 8 t 8 M d3s 2 对 o Y ^ J y o i ^ 2 o 泡 TO m TO o I 』 o § o ^ ^ 夢 s n 』 2 ，； a o ^ 出 • n 1 B _ T^ ff .廳 w § F ^ riij - i >oz ^ ^ & c I c 43m""I a o 6 4 ch ^/yAn^.a, l . am a 2 「 a >0N -r 力 o j c ::.. “ ；: J inr> + I I : &s I .1 >oz J’ ^l >02 目 I c I II f ”” ^ y A^ ^ ^ In^f 一 OT V V 1 o „ 1 IMM^M/i >。N 如 ——I1f LAxU A^ >0N 一 (〔Im 3f - M = -I .p>ul) - = -T c -I- • >oz V ^////月 ^ J &s 二乏 A/^ \\ >。N ^ ’ SPM c m 4 _—„—!—「—“- 3 J) 2 1 1 ^ o : § UEf = o ^ I c M >oz 、 -- fe .. 2 : - - = 5 i AyJ^ >。N 会乏 — , 2 § 卜 SN • ^ o ro 3 2 ^ 侧 § JHS 1 - rc ^ o I ”： 12 R 「I: 霞』 「l「—i g ^ •爾 膽 ^ “ 2 m ra I _a 一洲 ^ ^ ^ 沉 o 二 V 如 二 【。 , i ^ § c ^ cooooo 1 4 :: 3 5 amm : ^////Aw ^ 2 ^ _n aJ /z 1 o o^ 1 V ^ 一 J == = = = : = ( - - - -I -_ "df= uuf fin -KJAI >o一 z .lulAJ fin >oz ^ aes I c I I 墓 yd3.S 一 月 $ amm IHf J Ar sv ^///^ A///^ I ^ f " 0 1 -I 1 n 「「J ^ n 2 1 o .luIAI ^ 彳 J A/ I : :, : ^/J (〔_m n - 碧 ！ o rK Y ^ -- >oc2u-JlLr^ z CT In^〇f : , I n 尝 直 ) 广 -一 目 lAI - >oz .p>u)n ) f - -II f ^ o c \\v ^ >oz V >oz ^ ///^ 9。UEP>unq v Jdw ^////^ or A 〉 t Jli 「Jl——>i amm^ J 股 Ai 一 J ,1 8 - L V 6 ^ ！ c \v. 1 J 2 -- "i 4 o inf VI ^ - d3S n 2 S >oz ... 2 o ^ >oz ^ S .「It am^ I >02 o >。N cw o w c w 8 t ^ 6 t 「 4 2 g 「— 2「丨^^:::;:-^-,!J- s J g o ^///^ B ^ o s i 2 2 >oz g >oz rf -如 § ra I ^ d • - 恤 n e ^ o 观 F d 肪 s 2:2 2 吼 § 二 m ^ § ^ eg V 「J 1 如 - A^ ro a , 、 o a o \ i • I -一 -I :臺 = -- -- >o-Iz 一一 ” 、v..TT i 1 d3S >0N >oz J c sz 一 c UK f M 二 LiHf inf r Ln^ f -- I書 ！ ^ ^ "V am^ I 臺 一 -- 「——「J 1 -- 3 5 2 _ 一 -- 1 J 一 -- > o 1 >oz (〔_U H I i . if 二 ^///号^T i J J 「 gf c ， f = 1 &s - -j -I o ^ uq in f >oz >O Z - c >02 ！ 2 ^ T n ^ -r/// , O^J i s ^ 1 一 i \ 90U 2 >oz I 乂 inf 川 「 >oz 1 A/ J r 一一 § 幻力 -f 05 i J ‘ >oz in f : imqv >oz 二 一- 一 o -I &s if 十 g c V >oz J ！ .奶 -一 f ^ _ ^ § ra I g ^ 2 T R Inh 2 i 直 8 S 6 「：「i「1 v 一 4 2 2 ^ ^ J Co o J 汀 m A/ o ^ j M 8 - >o §z 2 直 \ . 1 .冗 堪 一 w fe 血 e 沉 肌 股 ^ n o ..加 ^ a c ^ Rw^ ^ g ff ^ ^ 肪 ！ T ^ i ^ 1 2 6 鄉 g .犯 0 c ^ 「 o 「「^^ n8- 6n- 1 —i「1—T: ammm^ 1 8 amm^^i r\/\ 4 6 y/. r\ 2 py- 4 、二 n2- c 1 o V n f uEf 、+ Kf; “ i >〇N - c \ o Al >oz 7y- I! .m ooo>ooz 「— ^ -A/y/L s I 0 fe「8642 o. j 3 ’ 9- £ I In^ f \ 達 \ . c ^///^ -S . 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J -I - ^ T 7 AJ unf d3S I >。N o in f >oz >QN i I c V \、 J- I 2 -r////^^ CT 一 u am^.^ 4 3 2 「丨！" 1 4 3 o A^ ^ : 「 = L、s ( &s 2 ) 」- inf , r— ”！ z >o "f 1 J J c -I t I >oz 〜，. 炉 As J in•-f : J \\ 5 .14 >oz yhnr o c i 碧 V >oz o >0N o 5 「J 11 5 o 2 cooooo o 11 — 0 5^r-:「v : I 2 ——-——「 o d3s I:! 1 I 5 一「f -- 一I — .li o >oz 2 2 ？ 5 -令 ^//y^ 犯 o ^ I § 4 I ！ ^ 3 >oz 2 1 ，「 • ！ "! I- I 如 令。 TO m S 令 s ^ tlbt；：「「l^ k r s X f 1 s 二 ^ g 卞 -I S 職 k a >oz ^ F fT I 謹 § 1 ! ^ = UE f 5 .2 ^ ^ ^ c S 議 Station I Station IV 30 n 10 - « 20 -i / \ / \ 1�/、\ 5 / \ \ ______/ \ _ _ • 〇 丨—•—琴—•—•—•—•—• w • • • " 〇•—：— -：—•—w—•—•—•—•—•—•—•—•—•—• Station II Station V m I 口 40 1 40 - C 3CM 厂 30 - J\ ^ 20 V \ 20:/\ I 10 y \ 10 / \ 力 Q -；-I—「M“•“—•“““~^~~“““ 0 ‘ i—“—“~“ “ • ~““““““““ < 2001 2002 Station III 30] /、 2。/\ 10 i \ ‘ \ 2001 2002 Fig. 2.25 Seasonal occurrence of Calanus sinicus (CI to CVI) at different stations outside Port Shelter, Hong Kong. 65 CI CV 1 ： 6， 0 •••••••••••• 0 ^ ―» ••••••••••• CII cvu 1 ] 10 I , 0.5 j 5 1 • 一 ！ \ 0 •—- • ••琴•琴犀•琴••• 0 •••••••••••• I CIII CVI 罕 I 1 I 10 ] < i I / \ 0.5」 5 y \ 0 »—•• 0 “—^ I ••••••••••••I CIY 2001 2002 6 I 4 i K 2 i 2001 2002 Fig. 2.26 Seasonal occurrence of different stages of Calanus sinicus at station I outside Port Shelter, Hong Kong. 66 CI CV 0.5 I 0.5 」 I • i 0 • •罪琴琴琴• • • • • • 0 • ••••••••••• CII CVI s 1 1 6 I j 4 j h 0.5 ] ： 。2： ^/ / \ ^^ i 1/ \ Q B—lh 琴••琴••蹕••醒•画 Q基—「1—1 琴琴••画••琴 I CIII cvi 竿 5 1 ] 30 丨 0 “ 0 k 遍••••••••••• CIV 2001 2002 6 0 •••••••••••• 2001 2002 Fig. 2.28 Seasonal occurrence of different stages of Calanus sinicus at station III outside Port Shelter, Hong Kong. 67 CI CV 1 : 10 0.5 i 5 / \ i \ 0 丨•••••••••••• 0 -——、••••••••••• CTT CVI $ 丨 4 1八 0.” ” \ ^ ！ y 0 •—* 0 ——• ••••••••••• • I—( I CTTT CVI 早 § 卜 10 ] • 0.5 .: 5 f \ I \ • •••••• •蘭,an Q • • 1 1 • 1 • MII~I~~I~I~I 0 f r ~“ ”i“ ~~ ~”~ ~~ “ s ^ J ' f g s s ^ g^^fS^S^ CiY 2001 2002 6 ： 4 ： 2 i— 2001 2002 Fig. 2.28 Seasonal occurrence of different stages of Calanus sinicus at station III outside Port Shelter, Hong Kong. 68 CI cv 1 ] 6 ] ！ 4 ： f \ 0.5 : 。： / \ I 7 Q I—— I—I—I—I—I—I—I—I—I—1—I—I Q I 「-― 1 •—I—I—I—I—I—•—• • • • CII CVI $ 1 1 -i iI . i 0.5」 0.5 n ！ ^ 丨 ！ 讓• g Q W^ •••••••••••• 0 •••••••••••• • 1—H I CIII CVI 罕 I M 6」 < i 4 1 f\ 0.5 i , ！ / \ I 7 \ CIV 2001 2002 1 ！ ！ 0.5 -丨 j Q • - •…--•~I~••""”•~•~•••~‘~~•~ “ 2001 2002 Fig. 2.29 Seasonal occurrence of different stages of Calanus sinicus at station IV outside Port Shelter, Hong Kong. 69 CI CV 1 : 1 - 0.5 ^ 0.5 - • M ••琴0 • ••••••••••• CII CVI s 丨—丨 15” 0.5 i 10:/,\ - : 5 i/ \ a 0 • •零蘭麗• ••譯••画 0 “ _••••••••••• • i-H I cm CVI 罕 I 1 i 15 ， PK < 丨 10: / \ 0 “ —• ••••••••• 0 广一 ••••••••••• CIV 2001 2002 4彳6 ：/ \ 2 V \ 0 ^••••••••••• 2001 2002 Fig. 2.28 Seasonal occurrence of different stages of Calanus sinicus at station III outside Port Shelter, Hong Kong. 70 50 45 H 40， 1 — A • adults 2000 2001 肩 2 Fig. 2.31 Seasonal variations in abundance of Calanus sinicus of different developmental stages (CI to CVI) off northern Taiwan. Values represent the average of seven sampling stations. 71 30 i I __^ 25" • I • adult 丨 120； 1 町！ 音 m 國CIV ！ I ‘] • I .cin ^ 101B 口。n 2001 2002 Fig. 2.32 Seasonal variations in abundance of Calanus sinicus of different developmental ‘ stages (CI to CVI) outside Port Shelter, Hong Kong. Each point represents the average of five sampling stations. 72 1.50 1 ：：丨卜、 卜 f -0.50 1 / \ ^ -1.00 ； • -[,50 寸. ！ r ！“- i ！ 1 1 ‘ ‘ 丁 厂—一r—‘；… ‘ 2000 2001 2002 Fig. 2.33 Seasonal change in copepodite stage ratio index of Calanus sinicus off northern Taiwan. No adult females or CV were recorded from August and October 2001. 73 Station B500 Station C500 “ A 4 ： Station B1000 Station C1000 0.6 i 1.” ^ % Station B2000 Station C2000 e — (D Oh 乏 2 —⑴ 2：…乏 2001 2002 station C5000 A 2000 2001 2002 Fig. 2.34 Seasonal change in biomass of Calanus sinicus (CI to CVI) at different stations off northern Taiwan. 74 Station I Station IV i h 。.： vV + Station II Station V fe 4 4” ojo T\ 。： A f 2 \ \ 2 / \ ^ 0 工一厂 0 —「 > Q 2001 2002 Station III 3 - 1 t \ . ... 0 十-n^ > * » ^ t t * » * ' * » 2001 2002 Fig. 2.35 Seasonal change in biomass of Calanus sinicus (CI to CVI) at different stations outside Port Shelter, Hong Kong. 75 Station B500 Station C500 15000 n 8000 - ^ 10000 : A : : �\ 500。： J \ 二 I 一 Station BIOOO Station CI000 15000 -丨 20000 ！ - —•彳 八 ；=彳 八 .5000 I I \ ^ 5000 i ^ J \ § Station B2000 Station C2000 二 < 15000 : 30000 : 10000 -i 八 20000」 5000 : J 10000 ： J \ ⑷ 2001 2⑻2 station C5000 30000 - • 20000 -： A 10000 i / \ • • 2000 2001 2002 Fig. 2.36 Seasonal change in abundance of copepods (not including nauplii) at different stations off northern Taiwan. 76 Station I Station IV 40000 -1 80000 30000 - 八 60000 -； A 20000 - / \ 40000 」 / \ 10000 H / \ yv 20000 ： 」\ station II Station V m I S 60000 -1 40000 1 ……八丨 30000 i A ^ 40000 I 八 20000 1 A 1 I I I I S 5 I I £ ^ I I S I I I ^ 2001 2002 Station III 60000 ~： • 40000 」 A 20000 : y \ 八•—• _••~“ 〇 ！ 興 i “i 「 ^ i ：,!,.! I ^ 5 I ^ - £ ^ 2001 2002 Fig. 2.37 Seasonal change in abundance of copepods (not including nauplii) at different stations outside Port Shelter, Hong Kong. 77 Station B500 Station C500 100 . 150 : ij A :: A � / J ] � ^― , -.J-- .一,— ： - ^^ ( ) •r-*"， —， 一-| 漏 ^^ ” , 1 Station B1000 Station C1000 60 I 100 I ^ Q -i r —丨 [ T 1 1 1 1 1 r i i ‘ i ^ —: (J 1 1 * 1~^ i 1 1 「•-… 1 1 i i 1 I I I I I I ^ c! I I I ^ I I I S I I I I £ z tiO •s Station B2000 Station C2000 Q 150 300 : 100 ^ A 200 i A I I I I S I I I I 臺 I I 臺乏身 。 I I •0 2001 2002 station C5000 800 -丨 600 - A 400 H / \ 2〇CM \ 2000 2001 2002 Fig. 2.38 Seasonal change in biomass of all copepods (not including nauplii) at different stations off northern Taiwan. 78 Station 1 Station 4 200 I • 1000 ： • 100 / \ / \ ^ 500 - \ 。广、：^ y 0 “^：^— (J -1 r 1 T r r——i 1 1 i r 1 i i i U ~ ‘ ^ ‘ ‘ , i , i ！ . . | • Station 2 Station 5 ^^ N m I a ofl 300 I 600 -， 旦 200 彳 A M . 400 -」 A ^ I I I I g I I I I I I I S I £ I ^ 2001 2002 Station 3 600 ] 400 H A M •!— - . ^ ——I 1 1 : ： [ ‘ I "J , I 2001 2002 Fig. 2.39 Seasonal change in biomass of all copepods (not including nauplii) at different stations outside Port Shelter, Hong Kong. 79 2.5 -1 H CVI 罕 I H i H CV § 1.5 - I H H CIV I • * M cm 1.0 - • 5 口 CII • I • CI 0.5 H 1 1 1 1 1 1 ‘ ‘ Dec Feb Apr Jun Aug Oct Dec Feb 2000 2001 2002 Fig. 2.40 Seasonal changes in mean prosome length of various copepodite stages and adults of Calanus sinicus collected in coastal water off northern Taiwan. Each point represents the mean value of the seven sampling stations. Vertical line denotes SD. 80 2.5 1 • ••••••——••• • CVI 罕 百 2.0 O 〇QT-O-O-O 〇~~O~~o CVI $ £ ^ V^ • •——••~•—• * CV _§ 1.5 - E 巧 ^~~ •VV—V ^ CIV 0 1 “——“•""““ “ “ •“ cm 1.0 - •——M——• • cr CII •—•—• ^ ^ CI 0.5 -1 1 1 1 I ‘ 16 18 20 22 24 26 28 Temperature (�C) Fig. 2.41 Relationship between average water temperature and mean prosome length of various copepodite stages and adults of Calanus sinicus collected in coastal water off northern Taiwan. 81 0.16 -1 CVI竿 0.14 - • cvis • g) • • s t —0.10 - 、 吞 • 0 CV • ；0.08 - • # 芒 CIV • t 0 06 _ _ • 0.04 - CIII 今 0.02- CI CII • r 0.00 ^ 1 — ‘ ‘ 0.5 1.0 1.5 2.0 2.5 Prosome length (mm) Fig. 2.42 Relationship between prosome length and body dry weight of various copepodite stages and adults of Calanus sinicus collected in coastal water off northern Taiwan 82 100%� i ia 80% I- cd a I 60% h a B \ o 40% r Q% L - —！ [ 丄- 1——4 •——~‘ ^ • • 2000 2001 2002 Fig. 2.43 Seasonal change in sex ratio among adults of Calanus sinicus in coastal water off northern Taiwan. No adult males or females were recorded from August to October. 83 Table. 2.1 Coordinates of sampling stations in northern Taiwan and Port Shelter, Hong Kong. Station Longitude Latitude Northern Taiwan ^ 121.35.548 E 25.18.045 N BIOOO 121.35.499 E 25.18.232 N B2000 121.36.047 E 25.18.689 N C500 121.35.897 E 25.17.964 N ClOOO 12L36.100 E 25.18.170 N C2000 121.36.458 E • 25.18.733 N C50QQ 121.37.570 E 25.19.882 N Port Shelter I 114.19.161 E 22,16.607 N II 114.19.484 E 22.17.083 N III 114.19.806 E 22.17.559 N IV 114.20.129 E 22.17.976 N V 114.20.387 E 22.18.393 N 84 Table 2.2 Abundance of all stages of Calanus sinicus (CI to CVI) at different stations off northern Taiwan and outside Port Shelter, Hong Kong. Density (ind. m"^) Station Maximum Mean over (Month) study period Northern B^ 16 (Dec 2001) lo Taiwan BIOOO 8.8 (Dec 2001) 2.3 B2000 42 (Dec 2000) 5.5 C500 58 (Dec 2001) 5.8 ClOOO 17 (Dec 2001) 4.1 C2000 100 (Dec 2000) 13 C5Q00 100 (Dec 2001) 21 Port Shelter I 27 (Mar 2001) ^ II 31 (Mar 2001) 2.6 III 27 (Mar 2001) 2.6 IV 9.1 (Mar 2001) 0.65 V 31 (Mar 2001) 2.6 85 Table 2.3 Abundance of copepods (not including nauplli) at different stations off northern Taiwan and outside Port Shelter, Hong Kong. Density (ind. m"^) Station Maximum Mean over (Month) study period Northern 13000 (Jul 2001) Taiwan BIOOO 12000 (Jul 2001) 1700 B2000 9700 (Jul 2001) 1900 C500 7600 (Jul 2001) 1600 CI000 15000 (Jul 2001) 2200 C2000 20000 (Jul 2001) 3000 C5QQQ 28000 (Jun 2001) 3500 Port Shelter I 31000 (Aug 2001) ^ II 38000 (Aug 2001) 6300 III 56000 (Aug 2001) 7500 IV 72000 (Aug 2001) 8200 V 31000 (Aug 2001) 5600 86 Chapter 3 Diel vertical migration and gut pigment rhythm of the planktonic copepod Calanus sinicus 3.1 Literature review 3.1.1 Diel vertical migration of Calanus sinicus Diel vertical migration is a widespread phenomenon which is known to exist in many taxa of zooplankters. Hutchinson (1967) provides a thorough discussion of variations in the vertical movements of copepods. Most species rise to the upper waters at night in a "nocturnal" migration. In some cases, there are two periods of maxima near the surface, the first just after dusk and the second just before dawn. These ubiquitous phenomena puzzle many ecologists since the migrating animals spend energy to put themselves in an unfavorable environment which is cold and food-limited. Light is still considered to be the prime environmental factor controlling the diel vertical migration of copepods and many other planktonic organisms. Tranter et al (1981) successfully caught a variety of shallow water copepods in a light-trap, especially at dusk and dawn or when the moon sets. The behaviour was believed to be caused by movements towards light when light intensities decreased and away from light when light intensities increased. The general description of light control, although widely accepted, is not universal and 87 cannot, for example, apply to reverse migration in which the animals move downward at night and return to the surface in the day. In any case, reverse migration cannot occur unless the ‘normal，light response is overridden by some environmental factors (eg. mechanical or olfactory signs created by predators) or reversed through selection of genotypes with a reverse-phototactic response (Ohman et al., 1983; Fedorenko, 1975). Calanus sinicus performed clear diurnal vertical migration in the Bohai, but their behaviour was somewhat different at different stations (Wang et al., 1998). C sinicus performed more distinct diurnal vertical migrations in stations where the thermocline was well developed. The response to a thermocline varies between species and developmental stage and Gushing (1951) concluded that the migration was really only modified when the temperatures were near those defining the distributional limits of the species concerned. The thermocline is a seasonal phenomenon in middle to higher latitudes and Williams (1985) showed that Calanus finmarchicus and Calanus helgolandicus in the Celtic Sea react differently to the thermocline and halocline. The more northern-living C. finmarchicus is at its southern limit of geographical distribution in this region and consequently the temperature within and above the thermocline present a barrier to its upward migration. The more southern C. helgolandicus may be restricted to water layers 88 above the thermocline because of the lower temperature below it. Several studies on Calanus finmarchicus in various parts of the north Atlantic Ocean (Nicholls, 1933; Farran, 1947) have documented age-specific differences on diel vertical migration behaviour. Uye (1990) studied ontogenetic diel vertical migration of Calanus sinicus in the Inland Sea of Japan in September. Ontogenetic diel vertical migrations occur when the developmental stages of a species within the same water column have distinct bathymetric ranges over the diel cycle. The most common pattern of distribution is for the younger copepodids to live higher in the water column and older ones progressively deeper. Uye (1990) found that the copepodite stages CI to III of C. sinicus were restricted to the upper layer throughout the day and did not undergo diel vertical migration. The studies on C. finmarchicus also indicated that the early copepodite stages (CI and CII) are non-migratory (Nicholls, 1933). However, adult females and males C. sinicus exhibited completely different migration behaviors (Uye, 1990). Females were distributed throughout the water column, and exhibited strong diel vertical migration (Uye, 1990). In contrast, there were no diel vertical migration for males (Uye, 1990). The migratory behavior of C. sinicus is similar to that of C. finmarchicus. The late copepodites migrate, with the CV and CVI stages having the most extensive migrations (Clarke, 1934), The ontogenetic diel vertical migration of C. sinicus was investigated in the 89 Inland Sea of Japan in November and March by Uye (1992). CV and CVI always avoided the surface water in the daytime, aggregated just below the chlorophyll maximum layer in November and stayed within the chlorophyll maximum layer in March. Surface avoidance and daytime depth of aggregation may be a product of compromise between feeding and escape from visual predators. In other words, the benefits of staying in the food-rich layer are balanced by vulnerability to predators. However, the division of factors as either control mechanisms or adaptive significance is probably least useful in the case of food. The importance of food in vertical migrations of zooplankton is often used in evolutionary argument. There is also compelling evidence that food can also act as a proximate cause for migration by influencing the timing of migration as well as the depth distribution of animals. Gauld (1953) proposed that food abundance mediated through hunger or satiation could act as the proximal signal for upward and downward migrations of marine copepods. Many hypotheses have been proposed to explain the adaptive significance of diel vertical migration. Emphasis has been put on avoidance of harmful ultra-violet radiations (Bollens and Frost, 1990), demographic benefits (McLaren, 1974) and energetic advantage (Enright 1977; Enright and Honegger, 1977). However, each of these hypotheses has its own drawbacks. Recent studies have provided data to 90 suggest that predation is a major driving force of diel vertical migration (Fancett and Kimmerer, 1985; Ohman, 1990; Bollens and Frost, 1991; Bollens et al., 1992). The presence of visual predators such as fish, or even fish mimics, has also been shown to induce a downward swimming response in some copepods, possibly by the copepods detecting the shadow of the predator — a shadow response (Bollens and Frost, 1991; Bollens et al., 1992). Forward (1988) discussed this shadow response to predators in some details. The presence of predators may very well reinforce light cues for the downward migration in many species of regularly migrating copepods. Frost (1988), however, examining populations of Calanus pacificus in Dabob Bay, Washington, concluded that predator avoidance is the major selective force for the occurrence of diel migration. Evidence has been obtained in laboratory studies, field studies and manipulated field studies. Unusual reverse diel vertical migration in zooplankton under certain conditions provides convincing support for the predator avoidance hypothesis. 3.1.2 Diel feeding rhythm of Calanus sinicus In a food stratified water body, zooplankton performing diel vertical migration will move from the food-abundant surface layer to the food-scarce deeper layer. Consequently, the migrating zooplankton will inevitably show a diel rhythm in gut 91 content. The appendages of copepod used in feeding are the antennules, antennae, mandibles, maxillules and maxillae. They are most developed in CVs and adult females. Adult males of many species have reduced appendages and do not feed (Marin, 1988; Schnack-Schiel etal., 1991). Two types of diel feeding rhythms have been described: unimodal where a single peak of gut content was found at night and bimodal where gut pigment content peaks at around sunset and sunrise, but were lower at the period in between, suggesting that feeding activity of the zooplankters declines between two active feeding periods. Although unimodal feeding rhythm is most frequently encountered, observation of bimodal feeding rhythm was not uncommon. Diel vertical migrations are considered to be controlled by changing environmental light intensities, the animals migrating towards the surface as dusk approaches, remaining in the surface layers during darkness, and moving downwards at dawn. The adaptative significance for such behavior have been discussed earlier. Although the existence of an endogenous component has been proposed (Duval and Geen, 1976)，external factors like food availability (Huntley and Brooks, 1982) and risk of predation (Bollens and Frost, 1989； Bollens and Sterans, 1992; Bollens et al., 1994) have been considered as potential triggering components of copepod diel feeding rhythms. Feeding implies higher motility, and consequently higher probability of encounter rates (Gerritsen and 92 Strickier, 1977) and increased risk of predation due to the production of hydodynamic signals which can be detected by carnivorous consumers (Tiselius et al” 1995). When food is scarce, zooplankters must spend more time searching for food. When motility increases, so does conspicuousness and predation risk (Piontkovskii and Petipa, 1976; Tiselius, 1992; Saiz, 1994). By the above reasoning, when food is limited, there is a balance between the necessity to feed continuously to obtain the minimum food requirements and the need to reduce the risk of predation. Accordingly, whether unimodal or bimodal feeding rhythm will be observed depends on the food supply of the environment and the food demand of individual species. 3.1.3 Measurement of grazing rate A variety of methods have been used to investigate copepod feeding behavior and to measure grazing rates. Techniques range from microcinematographic observations of feeding in restrained individual animals (Alcaraz et al,, 1980), and incubation experiments with either individual species，stages or communities in vitro (Frost, 1972; Poulet, 1974), to so-called in vivo methods, such as in situ radioactive-labelling experiments (Haney and Hall, 1975; Roman and Rublee, 1981) and gut fluorescence methods (Mackas and Bohrer, 1976; Boyd et al” 1980; Nicolajsen et al., 1983). Each of these methods has some drawbacks. The ability 93 to study diel variations in grazing rate and the grazing impact of copepods on phytoplankton assemblages was limited by methodological problems associated with measuring the rate of removal of particles using electronic particle counters (Roman and Rublee, 1980). Container effects associated with incubation make it difficult to measure diel variations in copepod feeding rates (Roman and Rublee, 1980). Furthermore, it is not feasible to measure the 24 h ingestion or filtration rates of several development stages of each dominant species present in any given copepod assemblage simultaneously. In the laboratory, determination of ingestion rates of even a few different developmental stages of a single copepod species may take months to complete (Paffenhofer, 1971; Paffenhofer, 1984). In the gut fluorescence method, levels of chlorophyll and its phaeopigment breakdown products are measured in copepod guts. Rates of change of gut pigment levels in copepods in vitro have been used as direct measurements of ingestion rate (Dagg, 1983; Dagg and Walser, 1987) and measurements of gut pigment levels from copepods in situ have been widely used to investigate spatial, seasonal and diumal grazing patterns (Mackas and Bohrer, 1976; Boyd et al., 1980; Baars and Oosterhuis, 1984). In order to calculate in vivo ingestion rates from in situ copepod gut pigment levels, gut turnover rates must be known. These have usually been equated with gut clearance rates calculated from the rate of loss of gut pigment in copepods incubated 94 in filtered seawater (Mackas and Borher, 1976; Kiorboe et al., 1982; Head, 1986), which can be described by the following equation dC/dt = -kC, where C is the concentration of gut pigment at time t and k is the defecation, or gut evacuation rate constant. However, several studies have shown that chlorophyll a and its derived phaeopigments cannot be considered as conservative tracers of phytoplankton biomass. Although some authors reported either insignificant pigment losses ranging from 10 to 35% of ingested pigment (Dagg and Walser, 1987; Kiorboe and Tiselius, 1987; Pasternak, 1994; Peterson and Dam, 1996) or zero degradation (Pasternak and Drits, 1988; Peterson et al., 1990), other studies suggested that a significant fraction of phytoplankton chlorophyll could be degraded into non-fluorescent products during gut passage (Conover et al., 1986; Wang and Conover, 1986; Lopez et al., 1988; Penry and Frost, 1991; Head, 1992; Head and Harris, 1992, 1996; Mayzaud and Razouls, 1992). The variability of reported degradation rates has made interpretation of the mechanism of pigment destruction to difficult. In fact, the percentage of pigments lost varies either within or across the species. To explain this variability, it has been suggested that chlorophyll destruction is to some extent related to the feeding history of the animals (Lopez et al., 1988; Penry and Frost, 1991; Head, 1992; Mayzaud and Razouls, 1992). 95 Typically, animals collected during the day contain lower gut pigment than animals collected at night. However, it is difficult to conclude whether diel feeding rhythm is related to diel vertical migration. 3.2 Introduction Diel vertical migration of marine zooplankton is well known and has been extensively studied, especially in the genus Calanus (Besiktepe, 1998; Huntley, 1982; Osgood, 1994; Peterson, 1990; Spiridonov, 1997). Diel feeding rhythm has been reported repeatedly among migrating marine copepods. Typically, animals collected during the day contain lower gut pigment content than animals collected at night. However, it is difficult to conclude whether diel feeding rhythm is related to diel vertical migration. Chlorophyll concentration in the sea generally shows a maximum near the surface and decreases with depth. Calanus sinicus constitutes an important component of the zooplankton biomass in continental shelf waters of eastern China (Chen, 1980), but ecological studies on this species are relatively few. Most previous studies on C. sinicus have been confined to description of seasonal occurrence, reproduction and development. In addition, the vertical migratory behavior of C_ sinicus has been examined only in the Inland sea of Japan, and little is known about migratory behavior in other parts of the species range. Uye (1990) first studied ontogenetic diel vertical migration of C. sinicus in the Inland Sea of Japan in 96 September. The onset of prominent diel vertical migration took place in CIV, and the amplitude of vertical migration increased with age, becoming maximal in adult females. Ontogenetic diel vertical migration of Calanus sinicus was recorded in the Inland Sea of Japan again in November and March by Uye (1992). In November, chlorophyll was high at the shallow layer and the majority of C sinicus aggregated in this layer. In March, the vertical distribution of C. sinicus was also closely associated with the layer of high chlorophyll concentration. The diel vertical migration of C. sinicus in the Inland Sea of Japan varies with seasons. This chapter presents results of a study to investigate the diel vertical migration and feeding pattern of C sinicus in the coastal waters near two nuclear power plants in northern Taiwan. The study was part of a survey of plankton ecology around Nuclear Power Plant I and II conducted by scientists at the National Taiwan Ocean University. Previous studies (Ohman et al., 1983; Williams and Conway，1984, 1987; Frost, 1988) have revealed that the pattern of diel vertical migration in copepods tends to vary both temporally and geographically. Since the coastal waters off the northern tip of Taiwan show marked seasonal variations in hydro graphical conditions, it was expected that there would be seasonal variations in the pattern of diel vertical migration and gut pigment rhythm in C. sinicus. This sort of knowledge would provide information not only about the origin and causal mechanisms of diel vertical 97 migration, but also on the seasonal life cycle of Calanus sinicus. Since one of the least understood aspects of vertical migration behavior is how it varies through the life-cycle of a species. In this chapter, the diel vertical migration of C. sinicus was described by means of time series sampling in northern Taiwan. The gut fluorescence technique was used to estimate diel changes in gut pigment content. 3.3 Materials and Methods 3.3.1 Zooplankton sampling and physical parameters Diel vertical migration and gut pigment rhythm were studied at two stations (Fig. 3.1) near the northern tip of Taiwan on the oceanographic vessel “、海硏二號“.These stations were visited twice, on 10-11 April 2001 and on 5-6 December 2001. Station C500 is located about 500 m off the Nuclear Power Plant I and has a depth of 18 m. Station C5000 is located about 5000 m away from the Nuclear Power Plant I and has a maximum depth of 85 m. Water masses outside the nuclear power plant represent a region where water along the edge of the Kuroshio Current mixes with water from the Taiwan Strait and the East China Sea. The water columns at stations C500 and C5000 were divided into 2 and 3 layers, respectively. On each visit, copepods were collected by making duplicate horizontal tows (5-10 mins) with a closing conical net (0.5 m mouth diameter and 125 以 m mesh size). A calibrated flowmeter was fixed in the mouth of the net to 98 determine the volume of water filtered. Copepods collected from the first net haul was preserved in 4% formaldehyde-seawater solution and returned to the laboratory for species identification. Copepods collected from the second haul was concentrated on 0.15 mm sieves, washed with filtered seawater and frozen with liquid nitrogen for later determination of gut pigment fluorescence. Vertical profiles of temperature and salinity were measured at each sampling station with a Seabird CTD. For the determination of chlorophyll a, seawater samples collected at surface, middle and bottom water layers were stored in darken bottles at near freezing temperature (〜0。C). Upon returning to the laboratory, the water samples for chlorophyll a measurement were processed immediately. Phytoplankton was concentrated on 0.45 um Millipore filters and extracted overnight in 90% acetone (analytical grade) in a dark refrigerator. Chlorophyll a concentration of acetone extract was determined fluorometrically with a Turner Designs fluorometer using the method of Parson et al (1984). Chlorpophyll a concentration were calculated according to the equation of Dagg and Wyman (1983): Chla concentration (mg m'^) = K(Rb-Ra)v/V where K is the machine calibration constant，Rb and Ra are the fluorescence reading before and after acidification (5% HCl), v is the volume of acetone extract and V is 99 i. the volume of filtered water sample. 3.3.2 Identification and enumeration In the laboratory, the volume of zooplankton samples was adjusted to 250 mL and the number of Calanus sinicus in five 5 mL subsamples was counted. C. sinicus from CI to CVI were sorted from the samples and counted under a dissecting microscope. The count of each developmental stage was converted to individual numbers per unit volume of water. Identification of males and females was made only for adults. No attempt was made to count naupliar stages because of their scarcity and problems with proper identification. 3.3.3 Gut pigment fluorescence Copepods for gut pigment fluorescence analysis were sorted under a dissecting microscope using low light level to minimize photo-degradation of pigments. Adults of C sinicus were sorted into one group, and CV and CIV copepodites were sorted into another group. Depending on the size of the animals, 5 to 20 animals were placed in a test tube with 90% acetone (analytical grade) and stored overnight in a dark refrigerator. Duplicate samples were used when the number of animals in the net samples was sufficient. Fluorescence of acetone extracts before and after 100 acidification (5% HCl) was measured. The equations of Dagg and Wyman were used to calculate the amount of chlorophyll a and phaeopigment per animal: Chlorophyll a per animal (ng ind") 二 K(Rb-Ra)v/n Phaeopigment per animal (ng ind.'') 二 K(i:Rb-Ra)v/n where K is the machine calibration constant, Rb and Ra are the fluorescence reading before and after acidification (5% HCl), v is the volume of acetone extract, t is the acid ratio and n is the number of individuals in the acetone extract. Phaeopigment values were corrected for pigment destruction assuming an estimated average loss of 33% (Dam and Peterson, 1988). The final gut pigment content is the sum of chlorophylls per animal and phaeopigment per animal after correction and is expressed as ng chlorophyll equivalent per individual (ngChla ind.]). 3.4 Results 3.4.1 Temperature and salinity Vertical profiles of water temperature and salinity at each station are shown in Figures 3.2a 一 3.5a. Vertical profiles of temperature water salinity at sampling stations are presented in Fig. 3.2b - 3.5b. During the late spring (10-11 April, 2001), water temperature at station C500 ranged from 21.8。C at the surface to 21.5 °C at the bottom (Fig. 3.2a). Thermocline was not observed, although surface temperature tended to be slightly higher than that in bottom. Salinity was around 34.3 %o in the 101 whole water column (Fig. 3.2b). The water column was weakly thermally stratified at station C5000 with water temperature at about 22.2 °C at the surface and 20.8 °C at the bottom (Fig. 3.3a). Salinity ranged from 34.2 ^/qoat the surface to 34.4 °/ooat the bottom (Fig. 3.3b). During the early winter (5-6 Dec, 2001)，water temperature was generally lower than that in the late spring. Thermocline was not observed at station C500, although temperature tended to be a little bit higher in the surface than in the bottom. Temperature of the water column ranged from about 20.8 °C at 1800 on 5 December to about 20.2 °C at 0600 on December 6 (Fig. 3.4a). Salinity at station C500 ranged from 33.4 O/oo to 33.6 %o(Fig. 3.4b). At station C5000, the water column was weakly thermally stratified. The mean water temperature was 21.4 °C at the surface and 19.0 °C at the bottom (Fig. 3.5a). Temperature gradually decreased with depth in the upper 30 m. Salinity changed from less than 33.2 at the surface to 34.0 °/oonear the bottom (Fig. 3.5b). 3.4.2 Ambient chlorophyll a concentration Chlorophyll a levels in seawater provides an indirect estimate of phytoplankton biomass in the water (Fig. 3.6 - 3.7). On 10-11 April 2001，chlorophyll a concentrations were distributed almost homogeneneously in the water column at 102 station C500 (Fig. 3.6a). Average concentration was 0.77 mg m'^ at the surface and 0.80 mg m-3 at the bottom. At station C5000, chlorophyll a concentration was 0.65 mg m-3 in the surface and declined to 0.44 mg m'^ near the bottom (Fig. 3.6b). On 5-6 December 2001, chlorophyll a concentrations were also distributed almost homogeneneously in the water column at station C500 (Fig.3.7a). Average concentration was 0.79 mg m'^ at the surface and 0.83 mg m'^ at the bottom. At station C5000，chlorophyll a concentration was 0.37 mg m'^ in the surface and dropped to 0.28 mg m'^ near the bottom (Fig.3.7b). There were no significant difference between the chlorophyll a concentration at station C500 in April and that in December (Student's r-test, P>0.05). However, chlorophyll a concentration at station C5000 was higher in late spring than that in early winter (Student's Mest, P<0.05). 3.4.3 Diel vertical migration During the late spring study on 10-11 April, 2001 at station C500, CIII, CIV, CV, adult females and adult males of Calanus sinicus could be found in nearly the whole water column, the difference in the mean depth between day- time and night-time is not large (Table 3.1). No diel vertical migration was observed for both adults and copepodites stages (Fig. 3.8). Numbers of CI and CII were too low to show any 103 clear distribution pattern. During the late spring study at station C5000, CI was least abundant and the abundance increased progressively with stages among copepodites stages (Table 3.2). Most of CIII were restricted to the upper layer throughout both day and night. CIV were distributed throughout the water column, and did not exhibited strong diel vertical migration (Fig. 3.9). CV were also distributed throughout the whole water column, and showed difference in the mean depth between day (53 m at 1200 h on 10 April) and night (35 m at 0000 h on 11 April) (Table 3.2). Adult females and males exhibited completely different behaviors. Females were distributed throughout the water column, and exhibited strong diel vertical migration. The majority of the female population migrating upward at dusk, remained in the surface layer throughout the night, and then descended to the bottom layer again before dawn (Fig. 3.9). Mean depths of the population were 72 m at 1200 h on 10 April, 52 m at 1800 h on 10 April, 22m at 0000 h on 11 April and 49 m at 0600 h on 11 April (Table 3.2). In contrast, males were distributed below 40 m and the mean depth was 75 m at 1200 h on 10 April and 47 m at 0600 h on 11 April (Table 3.2). No diel vertical migration was observed for males. During the early winter study on 5-6 December, 2001 at station C500, CIV, CV and adult females were distributed homogeneously throughout the water column as in 104 the late spring study at station C500 (Fig. 3.10). No diel vertical migration was observed for both adults and copepodites stages. The abundances of CI, CII, CIII and adult males were too low to observe any distribution pattern (Table 3.3). During the early winter study at station C5000, the populations of CI and CII were also very small (Fig. 3.11). Most of CIII were concentrated on the upper 40 m in the whole day. CIV, CV and adult females occurred in almost the whole of the water column and showed a similar migration pattern (Fig. 3.11). At 1200 h, most of their populations aggregated at the surface layer (mean depth of CIV 二 10 m, CV 二 12 m and adult females 二 24 m) (Table 3.4). At 1800 h, a large number of individuals occurred at the 40 m to show more homogeneous vertical distribution (mean depth of CIV 二 400 m, CV 二 39 m and adult females = 58 m) (Table 3.4). At 0000 h, most of their populations aggregated at depth in 40 m, and fewer individuals occurred at the surface and the bottom layer (mean depth of CIV 二 27 m, CV 二 32 m and adult females 二 39 m) (Table 3.4). After midnight, they began to migrate upward to the phytoplankton rich upper layer again. At 0060 h, the majority of individuals concentrated in the surface layer (mean depth of CIV = 24 m，CV = 23 m and adult females 二 20 m) (Table 3.4). In contrast, males were distributed below 40 m and the mean depth ranged from 74 m at 1200 h on 5 December to 41 m at 0000 h on 6 December (Table 3.4). No diel vertical migration was observed for males. 105 3.4.4 Gut pigment content During the late spring study on 10-11 April, 2001 at station C500, individuals collected at 2100 h and 0300 h tended to contain more gut pigment (Fig. 3.12). Mean gut pigment level of adults of Calanus sinicus was 0.23 ngChk ind.'' and that of copepodites was 0.05 ngChk ind；' at station C500 over 24 h (Table 3.5). The available data showed a substantial increase in gut pigment level after dusk. There were two peaks of gut pigment at station C5000 in both adults and copepodites over 24 h, one peak at 1200 h on April 10 and another peak at 0000 h on April 11 (Fig. 3.13). Mean gut pigment level of adults of C. sinicus was 0.54 ngChla ind."' and that of copepodites was 0.47 ngOikz ind；^ at station C5000 over 24 h (Table 3.5). Mean gut pigment levels were higher in the nighttime than that in the daytime at both station C500 and C5000. In general, individuals collected from upper layers contained more gut pigment than that from bottom layers. During the early winter study on 5-6 December, 2001 at station C500, individuals collected from surface layer at 1500 hrs and surface layer at 2100 h contained much more pigment (Fig. 3.14). Mean gut pigment level of adults of C. sinicus was 0.91 ngChla ind；^ and that of copepodites was 0.66 ngChk ind；^ at station C500 over 24 h (Table 3.6). The differences between mean nighttime value 106 (mean gut pigment values were 1.25 ngChla ind.'^ for adults and 1.08 ngChla ind."' for copepodites) and mean daytime value (mean gut pigment values were 1.08 ngChla ind.-i for adults and 0.84 ngChk ind；^ for copepodites) for both adults and copepodites was not large (Table 3.6). There was one conspicuous peak of gut pigment at station C5000 in both adults and copepodites in the surface water at 1200 h on December 5. Mean gut pigment level of adults of C. sinicus was 0.86 ngChla ind.-i and that of copepodites was 0.77 ngChla ind；^ at station C5000 over 24 h (Fig. 3.15). The differences between mean nighttime value (mean gut pigment values were 0.77 ngChk ind；^ for adults and 0.81 ngChla ind；^ for copepodites) and mean daytime value (mean gut pigment values were 0.95 ngChk ind] for adults and 0.73 ngChla ind ] for copepodites) for both adults and copepodites was not large (Table 3.6). Similar to the pattern observed in the late spring study, individuals collected from upper layers contained more gut pigment than those from bottom layers. 3.5 Discussion Two common hypotheses can be used to explain the selective forces behind diel vertical migration of zooplankton. Under the energetic hypothesis, migrating zooplankton can gain energetic benefit by feeding in warm, phytoplankton rich surface layer and then convert energy to growth in the cold bottom layer. However, 107 this hypothesis cannot be applicable to the vertical migration of late copepodites and adult females of Calanus sinicus at station C5000 in April, which experienced only a small temperature differences of 2 between surface and bottom layer. Moreover, this hypothesis does not explain why younger development stages or adult males do not undergo diel vertical migration. The second hypothesis puts emphasis on predation avoidance. It is assumed that low light conditions at night can provide protection for some zooplankton from fish predators. Early copepodites are less vulnerable to fish predation in the daytime because of their small size. In addition, the co-occurrence of other copepod species may decrease the risk of young C. sinicus copepodites. Therefore, CI, CII and CIII can stay in the phytoplankton-rich upper layer throughout both day and night. For late copepodites and adult females of C sinicus, the advantage of diel vertical migration at C5000 in April is the minimization of mortality by fish predation. No diel vertical migration was observed for both adults and copepodites stages at station C500 in April. The trade-off between feeding and predator avoidance is generally believed to be an important factor in the evolution of vertical migration behaviour (Clark and Levy, 1988). In December, C. sinicus did not avoid the surface water in the daytime, but they aggregated apparently within the chlorophyll maximum layer. Therefore, surface avoidance and daytime depth of aggregation may be the result of compromise 108 between escape from visual predators and feeding. In view of all these, the vulnerability to predators of staying in the upper layer in the daytime is compensated by the benefits of staying in the high food layer. A copepod migrating down in the absence of fish may experience retarded development and growth (Frost, 1988), but its survival is not evidently threatened. In contrast, not migrating down in the presence of fish could mean death. An innate, evasive response to foraging predators has obvious survival value. This is not the first time that food and feeding activity have been suggested as regulatory factors in vertical migration. Indeed, previous study (Bollens and Frost, 1991) hypothesized that the time spent at the surface by migratory herbivores might be inversely proportional to food availability, because satiated animals would descend. A logical corollary to this hypothesis is that unsatiated animals would stay longer in the surface waters, either by ascending earlier or by descending later than usual. In the extreme case, zooplankters may remain at the surface continuously. Because many invertebrate predators do not depend on light for hunting, deep dark habitats do not provide an absolute refuge for Calanus. Chaetognaths are believed to be important predators on copepods (Feigenbaum and Maris, 1984), with a diet often reflecting the zooplankton available (Pearre, 1973; Sullivan, 1980). Since the chlorophyll a concentration at station C5000 was higher in April than that in December (Student's r-statistic, P<0.05), it is 109 reasonable to assume that most of the Calanus sinicus population must spend most of time in the phytoplankton-rich upper layer at station C5000 in December. In summary, we suggest that diel vertical migration behavior in C. sinicus off the northern tip of Taiwan is a conditional response to two levels of stimuli. The primary stimulus appears to be hunger. When food availability is low, the copepods modify their migration behavior by remaining in the relatively food-rich surface waters to feed. The secondary stimulus, which operates under conditions of high food availability and low competition for food, appears to have regular, circadian periodicity. When the copepods are able to satisfy their nutritional requirements by nocturnal feeding alone, they respond to the secondary stimulus and perform regular diel migrations. As development of Calanus pacificiis progressed through the copepodite stages, the night depths remained approximately the same (i.e., within the food-rich surface waters) but day depths became deeper, becoming maximal in the late copepodite stages (Huntley and Brooks, 1982). In my study, clear diel vertical migration in late copepodites and adult Calanus sinicus female in April may be due to the enhanced swimming ability of these stages. When comparing with adult females, the distribution of adult C. sinicus males was limited to the deeper layer and did not exhibit diel vertical migration. Males do not necessarily undergo migration for 110 feeding because males are weak feeders. In addition, males are physiological less tolerant than females (Uye et al., 1990), and hence must avoided high temperature surface waters and remained in cool deeper waters throughout the whole day. Diel variations in feeding were found for all copepod species, whether they migrated vertically at night or not (Baars and Oosterhuis, 1984). Taxa that did perform diel vertical migrations are considered to show diel feeding rhythms. Like diel vertical migration, diel feeding rhythms are probably controlled by diel changes in the light field. For those taxa that did perform diel vertical migrations, the increase in gut pigment content which began at dusk is probably due to feeding by relatively hungry individuals who have just ascended into the food-rich layer. So, the observed increase in gut pigment content at night could have been due to both increased feeding by individuals who were present in the euphotic zone during the day, as well as feeding by starved migrants. Diel variations in the pigment content of copepods have been reported by many others. The common pattern is that gut pigment content begins to increase at s皿set, and after a 2 to 3 h period, reaches a value 2-10 times greater than mean daytime values. Following this initial 2-3 h burst in feeding activity, gut pigment content decreases, then levels off and remains constant throughout the night. A substantial increase in gut pigment level was first observed at 1200 h at station C5000 in April even though significant upward 111 migration was not detectable until mid-night. This result suggested that changes in gut pigment level in copepods was not relate to vertical migration. Since some animals were always present in the surface water at station C5000 in April，the significant increase in gut pigment levels at 0000 h in this layer could be the result of both increased feeding by individuals who were present in this layer during the day, as well as feeding by starved migrants. Although ambient chlorophyll a concentration was lower during the winter than during the summer, mean gut pigment levels of Calanus sinicus over 24 h were higher during the winter. This suggested that C. sinicus was not limited by food during the winter and chlorophyll a concentrations encountered during the summer were probably in excess of the food requirement of C. sinicus. Diel feeding rhythm has been related to visual predation, but the level of visual predation pressure at stations C5000 and C500 had not been evaluated in this study. Mean gut pigment levels were much higher for adults than for the smaller sized copepodites. In general, C. sinicus collected from upper layers tended to contain more gut pigments because feeding took place in the surface layers where ambient chlorophyll a concentration was higher. 112 『imrwiiwmnrrrrr"麵™ I East China Sea I Chma V 她 1 / ^^ C5000 (85 m) • —25^1 Jp~— 厂 " C500 (18—22m) ！y Taiwan 广 \ • I Strait / /\ NPPI ^ 'y H \| V I South China Sea \ ？ """"""" 丨丨'' 丨丨卩丨 Pacific Ocean 100 km xi Fig. 3.1 Map of South China Sea and East China Sea showing location of sampling stations outside Nuclear Power Plant I (NPPI) in coastal waters off the northern tip of Taiwan. Numbers in parentheses refer to water depth. “C” represents the inlet and “B，represents the outlet of the nuclear power plant. The numbers next to the letters B and C refer to distance from shore in meter. 10 April 11 April 1500 2100 0300 0900 (a) j I I I 4 - lo ro ^ / onJ 'cn ^ ^， 百 8 - fS 10 - j \ 12 - 14 - CJi CT) 16 J [ (b) 2 厂 I I I I I III 4 - 8 ^ ^ I / ^ - f J 1 ] \ / 1 6 - ^ ^ I： J V Q 1U - 12 - Fig. 3.2 Diel variations in vertical distribution of (a) temperature and - �� ！ ^？ ^ (b) salinity (。/。。）at station C50I0 from 1500 h, 10 April to 0900 h, 11 April，2001. White bar means day time, black bar means night time. J�^^^U^^I114 —— 10 April 11 April 1200 1800 2400 0600 (a) ‘ 22.4-^=*"™™ J 10 - 2。_、^^入 乂y • \ \ 21.8 21.8 40 - \ 广 21.6 g- 50 - >4.4�^ ^ \ H救:_ 80 - ^ \、% \ 90� ibipPF；^ 1；4。/ n ) S � 广从"、\ 60 - 二\ … j ] 7。^Sll^ ’ \ 30 f 拟.4、 么•沾\ \ 1 90� Fig. 3.3 Diel variations in vertical distribution of (a) temperature (°C) and (b) salinity (；。/。。）at station C5000 from 1200 h，10 April to 0600 h, 11 April, 2001. White bar means day time, black bar means night time. 115 5 December 6 December 0900 1500 2100 0300 J 1 1 I ！巧 I 2 I i J 1 “ f f ( iJ 10 - I / L/ ‘ Q 、 20 - \ \ Y ^ f h h i ^ T - i 2 I 25 - J ^\ (b) 丨 I \ \ 1 11 r 5 - ( I ] \ \ ^ I t \ / / /厂^兑明 I T \ [ {[[ ；i Q { 1 20 - 乂 \ L m - a ^ ？S S " 急 25�丨 M I I I I� Fig. 3.4 Diel variations in vertical distribution of (a) temperature (�C an) d (b) salinity at station C500 from 0900 h, 5 December to 0300 h， 6 December, 2001. White bar means day time, black bar means night time. 116 5 December 6 December 1200 1800 2400 0600 (a) io'j \、^2.4——1，.”7_T I ^^ -21.2— r 20 - ) 30 - ^ 广 , 80 J (b) J / i 30 - 々 60 - V� y y V 70 _ ^^33.^；：：^^ 80 “ Fig. 3.5 Diel variations in vertical distribution of (a) temperature (�C an) d (b) salinity (。/。。）at station C5000 from 1200 h, 5 December to 0600 h, 6 December, 2001. White bar means day time, black bar means night time. 117 Chlorophyll a concentration mg m'^ 0.0 0.2 0.4 0.6 0.8 1.0 I I L 1 1 1 0 n 丨卞 5 - �^ Q 15 - 丄 20 - Fig. 3.6a Vertical profiles of chlorophyll a at station C500 from 1500 h，10 April to 0900 h, 11 April, 2001. Chlorophyll a value presented are averages of values recorded at 1500 h and 2100 h on 10 April and 0300 h and 0900 on 11 April, 2001. Horizontal line denotes SD. Chlorophyll a concentration (mg 0.0 0.2 0.4 0.6 0.8 1.0 - — ‘ 0 - 卞 20 -： T/ ？ 4。） 亡 1 6。丨 / 80 ： , L, 100丨 Fig. 3.6b Vertical profiles of chlorophyll a at station C5000 from 1200 h, 10 April to 0600 h, 11 April, 2001. Chlorophyll a value presented are averages of values recorded at 1200 h and 1800 h on 10 April and 0000 h and 0600 on 11 April, 2001. Horizontal line denotes SD. 118 Chlorophyll a concentration mg m'^ 0,0 0.2 0.4 0.6 0.8 1.0 1.2 门 \ - —^― -— I 6 1。丨 Q 15丨 I 20 I : 1^ ； jI 25丨 Fig. 3.7a Vertical profiles of chlorophyll a at station C500 from 0900 h, 5 December to 0300 h, 6 December, 2001. Chlorophyll a value presented are averages of values recorded at 0900 h, 1500 h and 2100 h on 5 December and 0300 h on 6 December, 2001. Horizontal line denotes SD. Chlorophyll a concentration mg nr) 0,0 0.2 0.4 0.6 0.8 i 20 i ^ 1 a I 1 40 -j I— — ^ • • “ • I / & i / Q 60 1 / 80 i 「-“」 丨100」 Fig. 3.7b Vertical profiles of chlorophyll a at station C5000 from 1200 h, 5 December to 0600 h 6 December, 2001. Chlorophyll a value presented are averages of values recorded at 1200 h and 1800 h on 5 December and 0000 h and 0600 h on 6 December, 2001. Horizontal line denotes SD. 119 A 1500 2100 0300 0900 B 1500 2100 0300 0900 ^ 1500 2100 0300 0900 m丽m D 1500 2100 0300 0900 ^ ^^qq 2IOO 0300 0900 ^ 1500 2100 0300 0900 ^ 1500 2100 0300 0900 § I —— I I •_••••_ I II ••••— I I I I I I I I I I 16j • • • • 16] • • • 16] 16] Fig. 3.8 Diel variations in the vertical distribution of Calanus sinicus at station C500 on 10 & ~ 3 II April 2001 . (A) adult female, (B) adult male, (C) CV, (D) CIV, (E) CIII, (F) CII and (G) CI. 2 md. m White bar means day time, black bar means night time. A 1200 1800 0000 0600 ^ i200 1800 0000 0600 ^ 1200 1800 0000 0600 I T 1 I MM— I I TZl t o 1 III I �I • ill I I I :lii! lOQj 100】 100 j 一 D 1200 1800 0000 0600 ^ 1200 1800 0000 0600 ^ 1200 1800 0000 0600 ^ 1200 1800 0000 0600 5 I ——CZZI I —I I — 1 I H——•CHID 1。 I 1 0丨 I 1 0丨 I I 20 20 I 20 I 40 40 40 I 60 60 60 1 80 80 80 100] 100' 100 100丨 WhitFig11 .Apri 3.e 9bal Die200r meanl 1variation . s(A da) adulys time int thfemale, eblac verticak, ba(Bl)r distributioadulmeant smale nighn , ot(C f timeCalanus) CV. , (D )sinicus CIV, (E a) tCill C500, (F0) oCIn I 1an0 d& (G) CI. ^~ ind. m ^ A 0900 1500 2100 0300 B 0900 15OO 2100 0300 090Q 1500 2100 0300 I 10 10 I m I 15 15 15 I I 20 20 20 丨胃 25 j •釀 25 25 D 0900 1500 2100 0300 ^ 0900 1500 2100 0300 ^ 0900 1500 2100 0300 ^ 0900 1500 21QQ 0300 S I MMM— I —— I JMBM—• I —— 0 I 1 • 0 0 0 I 5 • 5 5 5 10 I • 10 10 10 15 •丽 15 15 15 20 M I 20 20 20 25 25 I 25 1 25 Fig. 3.10 Diel variations in the vertical distribution of Calanus sinicus at station C500 on 5 & 3 6 December 2001 . (A) adult female. (B) adult male. (C) CV, (D) CIV, (E) CIII. (F) CII and (G) CI. md. m White bar means day time, dark bar means night time. � A 1200 1800 0000 0600 B |200 1800 0000 0600 ^ 1200 1800 0000 0600 I •iiiiiiw I I ——ZIZ： I ——• I t 40 i A 1 40 40 I I if I� I w I � 。•！ W I :J I •丨：• :J I I T 1 —D 1200 1800 0000 0600 ^ 1200 1800 0000 0600 ^ 1200 1800 0000 0600 ^ 1200 1800 0000 0600 。 I •—•• I I I ——IZZD I ———CIIZ] l 。1 。1 f I 20 20 20 40 I 40 40 40 60 I 60 60 60 80 I 80 80 80 100 100 J lOo' 100 Fig. 3.11 Diel variations in the vertical distribution of Calanus sinicus at station C5000 on 5 & 6 December 2001 . (A) adult female, (B) adult male, (C) CV, (D) CIV, (E) CIII. (F) CM and (G) CI. 50 ind. m ^ White bar means day time, black bar means night time. B A 1500 2100 0300 0900 1500 2100 0300 0900 0 1 •••• mmm •• 0 n m 4 4 - 口 B t 8 8 - (U Q 12 12 - 16 " L L 16」 L L Fig. 3.12 Gut pigment content of (A) adult and (B) copepodites CIV and CV of Calanus sinicus at •••••• station C500 on 10 & 11 April, 2001. White bar means day time and black bar means night time. 0.5 ngChla ind-丨 A B 1200 1800 0000 0600 1200 1800 0000 0600 0 mmmmmmmm 0 mmm wmmmmm 20 20 口 B U 40 n II mmmm 40 -• mam (D Q 60 60 80 * ” 80 * Fig. 3.13 Gut pigment content of (A) adult and (B) copepodites CIV and CV of Calanus sinicus at ••‘•• station C5000 on 10 & 11 April, 2001 . White bar means day time and black bar means night time. 1 ngChk ind-i A B 0900 1500 2100 0300 0900 1500 2100 . 0300 0 "P •••••i •^••••1 0 P !••••• [•••••••• 5 5 to g CTn W t 10' 10- CD Q 15 15 20 L mmmm L L 20 ^ “ “ Fig. 3.14 Gut pigment content of (A) adult and (B) copepodites CIV and CV of Calanus sinicus at • station C500 on 5 & 6 December, 2001. Whit bar means day time and black bar means night time. 1 ngChlo ind"^ A B 1200 1800 0000 0600 1200 1800 0000 0600 0 -mmmmmm p ••••• • 0 iwmm • PH P 20 20 - t 40 - • • • 40 • • • 60 60 80 ]• L L 80 ” ” • Fig. 3.15 Gut pigment content of (A) adult and (B) copepodites CIV and CV of Calanus sinicus at • station C5000 on 5 & 6 December, 2001. White bar means day time and black bar means night time. 1 ngChk/ ind'' Table 3.1 Day-night differences in the mean abundance (ind. m'^) and the mean depth (m) of Calanus sinicus at station C500 during April 10 - April 11,2001. Time 1500 2100 Q3QQ 0900 mean mean mean mean mean mean mean mean ^ abundance depth abundance depth abundance depth abundance depth a - 0^00 - ^ : CII 0.00 - 0.00 - 0.00 - 0.00 - cm 0.36 16 0.94 5.8 0.17 1.0 0.33 16 CIV 0.36 16 0.74 10 0.74 11 0.91 10 CV 0.64 14 2.1 9.8 0.70 6.2 0.54 11 Adult male 0.00 - 0.31 8.5\ 0.22 16 0.00 - Adult female 0.52 13 0.95 16 0.91 8.9 1.08 12 Table 3.2 Day-night differences in the mean abundance (ind. m'^) and the mean depth (m) Calanus sinicus at station C5000 during April 10 - April 11,2001. Time 1800 mean mean mean mean mean mean mean mean G abundance depth abundance depth abundance depth abundance depth ^ 0^00 - 1.0 ^ - oTo To CII 0.00 - 0.31 1.0 0.10 1.0 0.00 - CIII 0.15 1.0 0.31 1.0 0.31 16 0.11 40 CIV 1.2 27 0.45 13 0.72 34 0.31 15 CV 2.3 53 0.98 52 2.5 35 0.33 43 Adult male 0.59 75 0.00 - 0.1 1.0 0.23 47 Adult female 1.5 12_ 0^96 52 1^5 ^ 49 Table 3.3 Day-night differences in the mean abundance (ind. m"^) and the mean depth (m) of Calanus sinicus at station C500 during December 5 - December 6, 2001. Time 0900 1500 2100 0300 mean mean mean mean mean mean mean mean I~^ o abundance depth abundance depth abundance depth abundance depth a ^ - - ^ - ^ - CII 0.00 - 0.00 - 0.00 - 0.00 - cm 0.36 20 0.00 - 0.00 - 0.00 - CIV 4.7 20 9.7 1.3 1.3 4.2 0.00 - CV 12 19 17 6.2 0.41 1.0 1.1 18 Adult male 0.36 20 0.00 - 0.00 - 0.00 - Adult female O 20 2.2 5.0 OM 0.23 18 Table 3.4 Day-night differences in the mean abundance (ind. m'^) and the mean depth (m) of Calanus sinicus at station C5000 during December 5 一 December 6, 2001. Time Ts^o mean mean mean mean mean mean mean mean ^ abundance depth abundance depth abundance depth abundance depth CI ^ To ^"To - 0.17 1.0 CII 0.00 - 0.30 1.0 0.17 1.0 0.17 1.0 CIII 0.00 - 0.77 18 1.5 40 0.00 - CIV 10 10 7.7 40 9.8 27 5.5 24 CV 24 12 19 39 31 32 20 23 Adult male 0.14 74 0.66 60 2.4 41 0.46 52 Adult female 9.0 24 8.9 58 21 39 8.4 20 Table 3.5 Gut pigment level (ngChk ind.]) of Calanus sinicus at stations C500 and C5000 during April 10-April 11,2001. C500 Overall mean gut Mean gut pigment pigment Day Night Adults ^ ^ CV + CIV ^ 0.10 C5QQ0 Overall mean gut Mean gut pigment pigment Day Night Adults ^ ^ ^ CV + CIV ^ ^ 132 Table 3.6 Gut pigment level (ngChk ind.'^) of Calanus sinicus at stations C500 and C5000 during December 5 - December 6, 2001. C500 Overall mean gut Mean gut pigment pigment Day Night Adults ^ im ris CV + CIV ^ 1.08 C500Q Overall mean gut Mean gut pigment pigment Day Night Adults ^ ^ CV + CIV • ^ OM Ijj Chapter 4 Use of molecular markers in population analysis of Calanus sinicus 4.1 Literature Review Ocean circulation patterns play a major role in determining the patterns of biological productivity in coastal and oceanic waters (Cooksey, 1988). Prediction of the spatial patterns of secondary production in the ocean is difficult because dispersal of zooplankton is a function of both passive transport and active swimming by zooplankton, which may exhibit highly variable behavioral responses to water movement (Cooksey, 1988). Quantitative estimates of dispersal are particularly difficult to obtain for marine zooplankton。The difficulty of direct observation of dispersal processes is magnified by the small size and numerical abundance of planktonic organisms and by the vast distances their dispersal traverse. Dispersal is one of the most important processes determining the distribution and abundance of marine planktonic populations (Cooksey, 1988). By investigating dispersal processes, we can identify regions that have sufficient secondary production to function as source populations for recmitment to other regions (Cooksey, 1988). In addition, we can estimate how much of the export from these source regions is lost, by being transported to areas where the zooplankton cannot reproduce. For species with wide geographical distribution, we can determine whether individual populations 134 are genetically cohesive or partitioned by the formation of geographic races and subspecies. Population subdivision can be attributed to geographic isolation and the subsequent cessation of gene flow (Endler, 1977). Population subdivision is relatively common in species with or without a life history conductive to high dispersal rates (Avise et al,, 1987). In the marine environment, population abundances are often determined by dispersal rates rather than in situ reproduction and mortality (Avise et al,, 1988). In order to understand the nature and causes of population fluctuations in marine planktonic species, ocean circulation patterns and mixing processes should be considered to be primary drivers. Patterns of secondary production in the oceans may be governed primarily by dispersal processes driven by ocean circulation (Cooksey, 1988). In addition, behavioral limits to dispersal and natural selection can lead to population structures in marine animals that have comparatively larger effective population sizes and extensive geographic ranges (Avise, 1994; Burton and Lee, 1994; Palumbi, 1994). One effective method of tracking and predicting spatial patterns of dispersal among zooplankton species is through molecular analysis of gene flow patterns. Analysis of gene flow involves the assay of genetically variable traits of individuals. The frequencies of the variants in each population may then be used to infer patterns 135 of gene flow across the species' geographic range. Electrophoretic separation of allelic variants of enzymes (allozymes) has been used to study the population genetics for many years (Boileau and Hebert, 1988a; Burton and Lee, 1994). More recently, genetic variation at the molecular level (i.e., structural traits of nucleic acids such as DNA) has been used in population genetic studies of a wide variety of species (Boileau, 1988; Bucklin and Kocher, 1996; Bucklin and LaJeunesse, 1994; Bucklin et al., 1992; Caudill, 1995). Recent advances have made it possible to rapidly assess molecular variation at the highest level of detail (i.e. that of the nucleotide base sequence of the DNA molecule). The freshwater calanoid copepod, Diaptomis leptopus, collected from six temporary and permanent lakes and ponds have been sequenced for a 300 bp region of the mitochondrial gene, cytochrome oxidase I (COI) (Boileau and Hebert, 1988b). Genetic differences among D. leptopus populations from different ponds, or even neighboring ponds, were large, with all but one haplotype restricted to a single pond (Boileau and Hebert, 1988b). This suggests that permanent lakes and ponds may accumulate and maintain greater genetic diversity, since multiple colonizations will occur over longer time periods. Thirteen haplotypes were identified among Acartia tonsa individuals collected from four estuaries on the east coast of the USA (Caudill, 1995). Levels of 136 molecular diversity were generally high and tended to vary significantly among populations from in different estuaries (Caudill, 1995). The observed patterns suggests that gene flow among estuarine populations of A. tonsa may be highly restricted. Individuals of the copepod Calanus finmarchiciis collected from the Norwegian Sea and the Labrador Current, Gulf of St Lawerence, Gulf of Maine, and Georges Bank of the NW Atlantic Ocean were sequenced for a 350 bp portion of the mitochondrial 16S rRNA (Bucklin et al‘, 1996). The estuary of the St Lawerence River appeared to be a source region supplying individuals to Georges Bank to initiate the population increase in the next spring (Plourde and Runge, 1993). The lack of significant population structure within the NW Atlantic was also consistent with the physical pattern of circulation in the region (Herman et al., 1991), indicating that zooplankton dispersal across this region may be extensive and rapid. In contrast, the significant differences between populations on either side of the North Atlantic suggested that zooplankton dispersal across the ocean basin may be highly restricted. Marine copepods, such as Calanus, are among the most numerous animals on earth. These organisms provide population geneticists with an opportunity to study abundant and highly dispersive species in a wide range of environments. Comparison among a number of such species in different environments may lead to 137 more powerful conclusions about the effect of life history and environment on population genetic diversity and structure. 4.2 Introduction Calanoid coppeods of the genus Calanus are dominant members of the zooplankton in most temperate oceans (Bucklin et al., 1992). The genus is an important component of the marine food chains because of its relative abundance and ^ role in fisheries productivity (Bucklin et al., 1992). The distribution and breeding season of Calanus sinicus in China's northern neritic areas indicate that it is a temperate species with distribution centres in the Yellow Sea and the East China Sea. Coastal waters along the Chinese coast to the south of Fujian represent a seasonal distributional zone where breeding occurs in winter and spring. From the distribution zone, populations are carried by the Zhejiang-Fujian longshore current into the northern parts of the South China Sea in winter. The Yellow Sea, located between China mainland and the Korea Peninsula, is a semi-enclosed shallow sea. It links with the Bohai in the north and the East China Sea in the south. According to Chen (1992)，the Yellow Sea longshore current is a low-salinity current which is strong in winter but weak in summer. In the north it connects with the longshore current from the Bohai and flows east along the north 138 coast of the Shandong Peninsula. At the Chengshan Cape of the Shandong Peninsula, it joins the north-flowing branch of the Yellow Sea warm current, then mostly bypasses the Cape and flows south. When reaching the area to the north of the Changjiang mouth, it turns southeast, crossing over the Changjiang Bank, and enters the East China sea. The East China Sea borders the China mainland on the west and links with the Yellow Sea in the north. The southern edge of the East China Sea is marked by a line linking Dongshan of Fujian Province and Maopi Tou at the southern tip of Taiwan. According to Chen (1992), the East China Sea longshore current consists of coastal waters and runoff from the Changjiang, Qiantang and Minjiang. It forms a relatively strong layer of low-saline water and its direction tends to vary with the monsoons. In winter the prevailing NW and NE winds push longshore currents southwards with relatively high velocity and stability. In areas to the north of Zhejiang, this longshore current is called the Jiangsu-Zhejiang longshore current, while in areas to the south of Zhejiang it is called the Zhejiang-Fujian longshore current. In the South China Sea, monsoon drift currents are well developed. In NE monsoon period during the winter, part of the East China Sea longshore current enters the South China Sea through the Taiwan Strait, forming a strong SW drift current and flowing from north to south in the western part of the South China Sea. It is believed that the Zhejiang-Fujian longshore currents link with 139 currents which flow along the coast of eastern Guangdong from NE to SW in winter. Along with these current systems, species such as Calanus sinicus enters into the South China Sea from the Yellow Sea and the East China Sea. This chapter reports preliminary attempts to use molecular markers to determine if C. sinicus populations in the oceans of southern China are derived from populations in the Yellow Sea and the East China Sea. The choice of genetic markers for analysis of population genetic structure and gene flow has important implications for the results obtained. Mitochondrial DNA (mtDNA) is useful in molecular population genetic analysis of zooplanktons (Bucklin et al., 1992; Bucklin and Kocher, 1996; Bucklin et al, 2000; Schizas et al, 1999). For lineages that have diverged relatively recently, mtDNA may be the best means to demonstrate significant divergence. MtDNA has a number of advantages as an indicator of the evolutionary history and dynamics of species and populations. First, the gene structure of mtDNA and the functions and functional constraints of the component genes are well known. The compact animal mitochondrial genome lacks introns or intergenic spacer regions, so that mechanisms of sequence change are more easily inferred. The clonal pattern of inheritance is also an advantage because it allows discrimination and identification of maternal lineages within a species, and elucidating population structures better than nuclear markers that experience 140 recombination each generation (Birky et al., 1989). The asexual pattern of inheritance of mtDNA greatly hastens the differentiation of mitochondrial traits over nuclear traits of the newly founded populations and slows their homogenization (Birky et al., 1989). Maternal inheritance may make mtDNA traits better indicators of population structure for marine plankton than nuclear markers because genetically identical mothers and offspring can be more easily recognized even if they are dispersed by periodic ocean mixing. Using mitochondrial cytochrome oxidase I (COI) sequence variation, Bucklin ef al. (2000), revealed significant differences among individuals of Calanus finmarchicus collected in Atlantic and Arctic waters surrounding Iceland. PGR amplification of the internal transcribed spacer (ITS) region of ribosomal DNA has become a popular method for phylogenetic analysis of closely related species and populations (Chen and Miller, 1996; Sajdak and Philips, 1994; Schlotterer et al, 1994). Because the internal transcribed spacers are flanked by highly conserved regions, it is possible to design primers for the amplification of the first internal transcribed spacer region (ITS-1) by examination of known sequences of the 18S and 5.8S coding regions. Both direct sequencing and cloning of PGR products can be used for ITS analysis. Their deployment depends on the hierarchical scale of the question. Direct sequencing generates a consensus sequence for phylogenetic 141 analysis. For population questions, additional profit is gained from information among single repeat units. Hence, PGR products need to be cloned and sequenced. Schizas (1999) suggested that molecular marker (ITS-1) yielded genetic differentiation among populations of estuaries, harpacticoid copepod {Microarthridion littorale) from the southeastern Atlantic and northern Gulf of Mexico coasts of the USA. In this study, intraspecific variations between Calanus sinicus populations from coastal waters outside Changjiang and off the northern tip of Taiwan were estimated using sequence data from a mitochondrial gene (cytochrome oxidase I, COI) and a nuclear gene (first internal transcribed space, ITS-1). The aim was to test if C. sinicus populations in coastal oceans of southern China are derived from populations in the Yellow Sea and the East China Sea. 4.3 Materials and Methods 4.3.1 Collection, preservation, and identification of Calansu sinicus samples C sinicus was collected from coastal waters outside the mouth of the Changjiang oand from coastal waters off the northern tip of Taiwan by making horizontal tows with a plankton net. All samples were preserved in 95% ethanol. In the laboratory, 142 adult females were sorted under a stereomicroscope. 4.3.2 DNA sequence determination for Calanus sinicus Adult females of Calanus sinicus were prepared for molecular analysis by boiling in distilled water for 10-15 min to evaporate the alcohol. The QIAamp DNA Mini Kit (QIAGEN Cat. No. 51304) was used for DNA extraction. Amplification of the COI and ITS-1 gene was performed on single, preserved individuals without prior purification of the DNA. The amplification primers of COI used were LCO-1490 (5,-GGT CAA CAA ATC ATA AAG ATA TTG G-3') and HCO-2198 (5，-TAA ACT TCA GGG TGA CCA AAA AAT CA-3'). The primers of ITS-1 used were SP-1-5'138 (5'CAC ACC GCC CGT CGC-3') and SP-lo' (5'-ATT TAG CTG CGG TCT TCA TC-3'). Amplification was carried out in a Programmable Thermal Controller (Model: PTC-100, MJ Research Inc.). The cycling parameters included: 90 seconds at 94 45 cycles of 5 mins at 96 2 mins at 45 °C and 3 mins at 72 °C, and finally stored at until use. 5 ul aliquots of the amplification products were aiialvzed bv agarose sel electrophoresis (1.5%) and electrophorsed at 70-80 V for 25-30 min to check amplification efficiency. The QIAamp Gel extraction Kit (QIAGEN Cat. No. 28704) was used for purification of PGR products. Purified double-strand PGR products were sequenced using DyeTermionator Cycle 143 Sequencing Ready Reaction Kit (ABI PRISM, Perkin-Elmer. Part. No. 402079) and analyzed on an ABI 310 Genetic Analyser. Two cycle-sequencing reactions, one for each primer, were done for each template, so that DNA was sequenced from both direction for each individual. Raw sequences taken from ABI PRISM 310 Genetic Analyzer were subjected to appropriate treatment. This included alignment of the complementary strands of the gene from the same individual and eye inspection of the chromatograms with the aid of software (ABI SeqEd v. 1.0.3) to edit those apparently miscalled bases. 4.4 Results PGR results were determined by electrophoresis of the amplification products on a 1.5 % agarose gel (Fig. 4.1). Direct sequencing of PGR products was done for 3 individuals from each population collected in coastal water outside the Changjiang mouth and off northern Taiwan. The COI sequence obtained from sequencing of PCR products from individuals collected in coastal water outside the Changjiang mouth and off northern Taiwan are given in Fig. 4.2. A total of 590 bp of COI were obtained. There were no differences in nucleotide base sequences between the populations of Calanus sinicus from Changjiang mouth and northern Taiwan. The result constituted a 100% sequence identity for this gene. The sequences between 144 individuals from the same location are also 100% identical. Nucleotide base sequences for a 474 bp region of the ITS-1 were also determined for the populations of Calanus sinicus from the two studied arrears (Fig. 4.3). Complete ITS-1 sequence identity was found between the two populations. Similar to COI, there was also no within sample variation (i.e. no base differences among the three individuals sequenced for each location). 4.5 Discussion Questions concerning genetic partitioning of widely distributed planktonic species are interesting and important for biological oceanographers. Genetic differentiation may result from reproductive isolation. For both COI and ITS-1, there were no differences in nucleotide base sequences between populations of Calami sinicus, indicating a 100% sequence identity for this gene. The result means that the species range does not exceed the dispersal capabilities of the average individual and populations of C. sinicus may not be reproductively isolated by distance. In winter，the Zhejiang-Fujian longshore currents flow along the Guangdong and Fujian coast from NE to SW, carrying species as C. sinicus from the East China Sea and the Yellow Sea into the South China Sea. Genetic exchange may occur between adjacent populations. C. sinicus populations in the oceans of 145 southern China are probably derived form populations in the Yellow Sea and the East China Sea. Mitochondrial genes, which are clonally (matrilineally) inherited, may be useful descriptors of population genetic structure of plankton, since both ocean mixing and recombination during sexual reproduction may erase evidence of structure based on frequently differences of nuclear markers. To solve questions about genetic partitioning of widely distributed planktonic species, sequencing of additional, more variable portions of the geneome may be required. 146 M 3 4 6 7 • 600 bp ~~• 100 bp ~~• Fig. 4.1 Gel photo showing PGR products for individual Calanus sinicus. Lane M : 100-bp molecular marker; lane 3 二 PGR products of COI collected outside the Chang]iang River mouth; lane 4 二 PCR products of COI collected off northern Taiwan; lane 6 = PGR products of ITS-1 collected outside the Changjiang River mouth; lane 7 = PCR products ofITS-1 collected from northern Taiwan. PCR products of COI for Calanus sinicus are larger and migrate less far compared to products of ITS-1. 147 Ca/aA7«^_Changjiang GGGCATATTC TGGAATAATC GGAACGGGGT TGAGTATAAT TATTCGATTA Ca/(3/7W5_Tai wan Ca/a/2i/^_Chang)iang GAGTTAGGTC AAGCTGGCTC TCTAATTGGA GATGATCAGA TTTATAATGT Taiwan Ca/a^7i/^_Chanaiang GGTAGTCACT GCTCACGCCT TCATTATAAT TTTTTTTATA GTTATACCTA Ca/a/7W5_Taiwan Ca/anw5_Changjiang TTCTGATTGG AGGGTTCGGT AACTGATTAG TGCCTTTAAT ATTGGGGGCG Ca/a77W5_Taiwan Ca/a«w5_Changjiang GCAGATATGG TGCCTTTAAT ATTGGGGGCG GCAGATATGG CATTCCCCCG Ca/(3nw5_Taiwan Ca/anu5_Chanaiang TATAAACAAT ATAAGCTTTT TGTCAAGGTC TTTAGTGGAG GGGGGAGCGG Ca/a«w^_Taiwan Ca/a 仰 s—Changjiang GCACGGGTTG AACGGTGTAC CCGCCCCTCT CAAGTAATAT TGCCCATGCT Ca/a«w^_Taiwan Ca/ani^j—Chan^iang GGGGCTTCAG TGGATTTTGC AATTTTCTCC CTACATTTGG CCGGGGTTAG Ca/<3«wjr_Taiwan Ca/a/mS-Cha 咽 iang TTCAATTTTA GGTGCGGTGA ATTTCATCAG CACTTTAGGT AATTTACGAG Ca/anw5_Taiwan Ca/fl 仰•s_Chanaiang TATTTGGAAT ATTACTAGAC CGGATACCCC TATTTGCCTG GTCGGTATTA Ca/a«w^_Taiwan Ca—uj_Changjiang ATTACCGCAG CAGGGGCCAT TACAATACTA TTAACAGATC GTAACCTGAA Calanus JldAVjon Calanus_Ch^ng^x2.ng CACCACATTT TATGATGTGG GGGGAGGAGG AGATCCTATT Ca/anwj_Taiwan Fig. 4.2 Sequence data for a 640 base pair region of the mitochondrial gene [cytochrome oxidase I (COI)] for Calanus sinicus collected in coastal waters outside the Changjiang River mouth and off northern tip of Taiwan. 148 Chapter 5 Conclusion Calanus sinicus showed clear seasonal pattern of occurrence off the northern tip of Taiwan and outside the Port Shelter in Hong Kong. C.sinicus was most abundant in the winter months from November to December, and rare during the summer months from May to July in waters to the north of Taiwan. Maximum densities of adult males and females were found in December 2000 and 2001. The numbers of CIV and CV also peaked at these times, while the densities of all the earlier copepodite stages peaked in the summer months. C. sinicus occurred only in January and February 2001 in Port shelter, Hong Kong, and were absent in the other parts of the year. The January and February peaks were composed of CV, adult males and adult females only. Younger copepodite stages were not recorded. In more open waters (eg. C5000) to the north of Taiwan, the majority of the population resided in layers deeper than 60m in summer, where water temperature was low. Since the study sites in Hong Kong are limited to shallow areas, therefore, population of C. sinicus could not sink to colder, deeper layer when surface waters began to warm. In February, the center of the C. sinicus population seemed to move to the more southern end of the species range in the northern part of the South China Sea. It is because in the winter NE monsoon period, part of the East China Sea longshore 150 current enters the South China Sea through the Taiwan Strait. In addition, the winter comes earlier in coastal waters off northern Taiwan than in Hong Kong. The largest individuals of Calanus sinicus were found in the winter months and the smallest ones were collected mainly in the summer months, indicating an inverse relationship between prosome length and water temperature. Since the coastal waters off the northern tip of Taiwan had greater seasonal variations in environmental conditions, there were seasonal variations in the diel vertical migration and gut pigment rhythm in C. sinicus. No diel vertical migration was observed for both adults and copepodites stages at station C500 in April. During the April study at station C5000, CI was least abundant and the abundance increased progressively with stages among copepodites stages. Most of CIII were restricted to the upper layers throughout both day and night. CIV were distributed throughout the water column, and did not exhibit strong diel vertical migration. CV were also distributed throughout the whole water column but exhibited diel vertical migration. Adult females and males exhibited completely different behaviors. Females were distributed throughout the water column, and exhibited strong diel vertical migration. In contrast, no diel vertical migration was observed for males. The selective advantage of diel vertical migration in late copepodites and adult females of C. sinicus in April is the reduction of mortality by predation. There were 151 two peaks of gut pigment at station C5000 in both adults and copepodites over 24 h. One peak was observed at 1200 hrs on April 10 and another peak was recorded at 0000 hrs on April 11. In December, no diel vertical migration was observed for both adults and copepodites stages at station C500. During the December study at station C5000, the populations of CI and CII were also very small. Most of CIII were concentrated in the upper 40 m during the whole day. CIV, CV and adult females occurred in the phytoplankton rich upper layer. It appears that when food availability is low and competition for food is high, the copepods may modify their migration behavior by remaining in the relatively food-rich surface waters. No diel vertical migration was observed for males. At station C5000, adults and copepodites exhibited one gut pigment peak over 24 h, in the surface water at 1200 hrs on December 5. Complete COI and ITS-1 sequence identity was found between the populations of Calanus sinicus in coastal water outside the Changjiang River mouth and off northern Taiwan. 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