Journal of Plankton Research Vol.21 no.11 pp.2117–2123, 1999
Carbon content of some common tropical Andaman Sea copepods
Suree Satapoomin
Phuket Marine Biological Center, PO Box 60, Phuket 83000, Thailand and
Marine Biological Laboratory, University of Copenhagen, DK-3000 Helsingør,
Denmark
Abstract. Individual carbon contents of eight common copepod species from the Andaman Sea were
determined. Length–carbon regressions are presented for four calanoids (Acrocalanus gibber,
Centropages furcatus, Temora discaudata and Euchaeta spp.), two cyclopoids (Oncaea spp. and
Corycaeus spp.) and two harpacticoids (Macrosetella gracilis and Microsetella spp.). The copepod
specimens were obtained from different localities and times of the year during 1996–1997. The regression coefficients are good in calanoid and cyclopoid copepods, but poor in the harpacticoids. The slope
values range from 2.3 to 3.8 in the calanoids to 1.2 and 1.6 in the harpacticoids, while the cyclopoids
have slope values of 2.0 and 2.9. The equations derived from this study are expected to be general characteristics, which are applicable for the calculation of copepod biomass and production in tropical areas.
Introduction
The use of regressions of dry weight or carbon (C)–nitrogen (N) contents against
size is an essential tool in studies on zooplankton biomass and production (Uye,
1982). Most studies on copepod body weight or C content have been carried out
in temperate waters (e.g. Durbin and Durbin, 1978; Pearre, 1980; Cohen and
Lough, 1981; Uye, 1982; Christou and Verriopoulos, 1993; Sabatini and Kiørboe,
1994; Tanskanen, 1994). Only a few such studies have been carried out on a
limited number of species in subtropical and tropical areas (Chisholm and Roff,
1990; Webber and Roff, 1995b; McKinnon 1996b).
Tropical seas differ from both temperate and subtropical seas in that temperature and food availability do not change very much over the year. Thus, while the
length–weight C regressions in copepods for a given species in the temperate area
may change over the year, this is not to be expected for tropical seas. Therefore,
values for copepods from temperate seas cannot simply be extrapolated to tropical copepod communities (Webber and Roff, 1995).
The objective of this study was to measure individual C contents of some
common copepods from the Andaman Sea and present their length–C relationships to provide the basic tool for calculation of copepod biomass and productivity.
Method
Eight genera of common copepods (four calanoids, two cyclopoids and two
harpacticoids) were collected from the Andaman Sea waters on several occasions
during 1996–1997 (Figure 1 and Table I). Seasonal variation in surface temperature and salinity is small. However, the vertical range in temperature within the
area investigated was about 16–29ºC and salinity ranged between 31 and 35‰.
Both values were recorded from surface sea water down to 100 m depth. The
depth of stations visited ranged from ~10 to 500 m.
© Oxford University Press 1999
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S.Satapoomin
Fig. 1. Sampling localities of copepod specimens in the Andaman Sea. The numbers of stations on
each transect indicate the working stations during the cruises in 1996–1997 under the SCP programme.
Table I. Sampling occasions for different species of copepods
Copepod species
Sampling occasions
––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––
1
2
3
4
5
PMBC pier Between Phuket Is. SCP-cruise 7-96 SCP-cruise 3-97 Cruise 7-97
and Raja Yai Is.
Calanoids
Acrocalanus gibber x
Centropages furcatus x
Temora discaudata x
Euchaeta spp.
Cyclopoids
Corycaeus spp.
Oncaea spp.
x
Harpacticoids
Macrosetella gracilis
Microsetella spp.
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
Sampling period: 1 and 2, March 1998; 3, August–September 1996; 4, February 1997; 5,
August–September 1997.
Sampling depth: 1, <10 m; 2, 40–50 m; 3–5, 50–100 m.
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Carbon content of common Andaman Sea copepods
The copepods were sampled by several vertical and oblique hauls with 50 and
200 µm nets at depths between 9 and 100 m. Live specimens of the selected
species, copepodites and adults, were sorted out and identified to genera/species.
Cephalothorax length was measured in calanoid and cyclopoid copepods, while
in harpacticoids, where the body is more elongated, total length was measured.
The precision of all measurement was within 20 µm. Specimens were analysed in
April 1997 and during April–June 1998.
Living copepods were placed individually in a small Petri dish, rinsed quickly
about three times with autoclaved GF/C-filtered sea water and finally transferred
to a small pre-combusted foil bowl, ~4 mm in diameter. The copepods were dried
at 60ºC for 3–6 h and kept frozen, at about –20ºC, until analysis.
The C content of each copepod specimen was measured, in terms of CO2, by
an Infrared Gas analyser, Model ADC-225 Type MK-3, connected to a tube
furnace, Carbolite MTF 10/25/130, at 600ºC. An integrated value was calculated
using the software IRGA-ana Version 1.06. Empty bowls were measured as
blanks. Standard curves were obtained by measuring different known concentrations of oxalic acid solution.
Values of length (µm) and C content (µg C) were transformed to natural log
values and regression lines were plotted. The length–C relationships were
expressed as ln(W) = b ln(L) + ln(a), where W is weight (µg C) and L is length
(µm), ln (a) is the intercept and b is the slope of the regression line. Regression
lines were, in some cases, tested for differences in regression coefficients, intercept and slope, using the tests of Zar (1984) and Fowler and Cohen (1990).
Results and discussion
The total number of specimens analysed, size range and equations derived from
length–weight regressions of the selected copepod species are summarized in
Table II and Figure 2. The slope of each regression line was significantly different from zero (P < 0.001). The slopes varied from 3.8 to 2.3 in calanoids to 1.6
and 1.2 in harpacticoids, while the values from cyclopoids were 2.9 and 2.0 for
Oncaea and Corycaeus, respectively.
Three species of the calanoid copepods, Acrocalanus gibber, Centropages
furcatus and Temora discaudata, yielded particularly high coefficients of determination (r2 = 0.76–0.92). The lowest coefficient of determination among the
calanoids was found in Euchaeta spp. (r2 = 0.6) in which data were derived from
only 25 specimens, in a small size range, and composed of at least two species.
However, the coefficient of determination for this genus was still relatively high.
Neither of the genera of cyclopoid copepods in this study, Oncaea spp. and
Corycaeus spp., were identified to species level, but the equations still provided
relatively high coefficients of determination: r2 = 0.64 and 0.71, respectively.
Carbon measurements of harpacticoid copepods were carried out for two
genera: Macrosetella and Microsetella. They were found to dominate among the
harpacticoid copepods in the Andaman Sea, from coastal to offshore area
(personal observations from various copepod biomass samples obtained during
1996–1998). The result of the regression analysis gave a fairly good coefficient of
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S.Satapoomin
Table II. Summary of all regressions derived from the measurement and calculation
Size
(µm)
ln a ± SE
––––––––––––––––––––––––
C (µg C)
DW (µg)
b ± SE
RMS
r2
n
380–920
590–1200
340–1280
1640–2280
–13.85 ± 0.77
–24.58 ± 0.98
–22.07 ± 0.61
–25.19 ± 4.89
–13.16 ± 0.77
–23.89 ± 0.98
–21.38 ± 0.61
–24.5 ± 4.89
2.26 ± 0.12
3.82 ± 0.14
3.55 ± 0.09
3.82 ± 0.65
0.075
0.103
0.084
0.101
0.76
0.81
0.92
0.6
114
172
140
25
Cyclopoids
Oncaea spp.
Corycaeus spp.
300–740
–17.5 ± 1.05
280–1000 –12.21 ± 0.79
–16.81 ± 1.05
–11.52 ± 0.79
2.90 ± 0.17
1.99 ± 0.13
0.213
0.096
0.71
0.64
125
143
Harpacticoids
Macrosetella gracilis
Microsetella spp.
Mixed genera
360–1180 –10.92 ± 1.44
240–700
–7.79 ± 1.15
240–1180 –7.07 ± 0.61
–10.23 ± 1.44 1.59 ± 0.21
–7.10 ± 1.15 1.15 ± 0.19
–6.38 ± 0.61 1.03 ± 0.1
0.198
0.157
0.182
0.51
0.26
0.41
55
111
166
Copepod species
Calanoids
Acrocalanus gibber
Centropages furcatus
Temora discaudata
Euchaeta spp.
determination (r2 = 0.51) for the single-species analysis on Macrosetella gracilis,
but a low coefficient for the other genus of presumably mixed species (r2 = 0.26).
The two genera of harpacticoid copepods just overlap in size. In order to
examine whether a common regression line could be produced for tropical
harpacticoid copepods, raw data of both genera were pooled and the regression
line was compared to those obtained from each genus. Statistical testing of the
regression coefficients showed no difference between the regression line of the
mixed harpacticoids and the lines obtained from either M.gracilis or Microsetella
spp.
Length–weight regression of A.gibber obtained in the present study provided
regression lines of lower slope than those obtained by McKinnon (1996), who
carried out field growth experiments of the same species at different temperatures. He found that the slope of the length–weight regressions varied between
2.71 and 3.87 according to season. However, if the slopes were plotted against the
mean temperature, no significant correlation with temperature could be found
(P > 0.2). Anyway, the regression coefficients from these two sets of data could
not be directly comparable since the data of McKinnon were obtained from
pooled specimens, while the present C contents were examined individually.
Length–weight regressions of tropical copepods based on pooled specimen dry
weight analysis (except for Euchaeta marina, where specimens were measured
individually) have previously been presented for nine species of neritic copepods
(Chisholm and Roff, 1990) and 12 genera of oceanic copepods (Webber and Roff,
1995b). These two articles provided data on six copepod genera and, thus, were
comparable to the present study. The neritic species were Centropages velificatus,
Temora turbinata and Corycaeus spp., while the oceanic species were Euchaeta
marina, Oncaea spp. and Macrosetella spp.
In order to make a comparison between their studies and the present one possible, the C weight of each species was converted to dry weight (by assuming a
ratio of 0.5) and regressed. Equations are presented in Table II. For neritic
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Carbon content of common Andaman Sea copepods
Fig. 2. Length–weight regression of some selected copepod species in the Andaman Sea. CL,
cephalothorax length (µm); TL, total length (µm); W, weight (µg C).
copepods, the difference between their values and the ones presented here is
quite small with regard to both the intercept and the slope, varying between 0.6
and 18%. However, the data on oceanic copepods differ more, in the range of
17–57%. Statistical analysis [according to Fowler and Cohen (1990)] of slopes was
employed in order to test the difference between each pair of regression lines. A
significant difference was only found between the slopes of M.gracilis (present
data) and Macrosetella spp. (from Webber and Roff, 1995b) (P < 0.01), while the
other five genera showed no statistical difference at all (P > 0.05).
Data in the present study were pooled from different times of the year, yet the
regressions generally gave quite good coefficients of determination, which
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S.Satapoomin
suggests that seasonal variations in C content are small in the Andaman Sea copepods. This result is in accordance with the findings from the tropical Caribbean
Sea, where the variation in body length of different copepod species did not show
any seasonal pattern, although some variation was found between sampling
periods (Chisholm and Roff, 1990; Webber and Roff, 1995a,b). McKinnon (1996)
demonstrated some variations in C and N content in specimens with a similar
prosome length in adult females of A.gibber covering different times of the year.
However, a strong relationship between temperature and C or N content or with
prosome length of female A.gibber is lacking. Thus, these findings supported the
suggestion of Durbin and Durbin (1978) that short-term weight changes may be
typical for small copepods in general and appear to be due to food availability.
A substantial variation in the C content was found among the harpacticoids in
the present study. This might be explained by their long and slender body shape;
the slopes of the regressions are close to one, which means that variation in C
content is directly proportional to the length of the copepod. In addition to this,
the total length of the body of harpacticoids was measured, not only the
cephalothorax length as in the calanoid and the cyclopoid copepods. Therefore,
only a small difference in width of the specimens with similar body length will
potentially influence their body weight.
As a result, this study provides length–weight regressions for eight common
copepods from the tropical Andaman Sea. A representative regression for each
selected species was obtained by sampling specimens from different times and
places, and all information was pooled into one regression. The equations
obtained from such regressions can be considered representative and applicable
for the further calculations of copepod biomass in tropical areas, especially in the
Andaman Sea.
Acknowledgements
This study was carried out at Phuket Marine Biological Center (PMBC), under
a 5 year Thai–Danish scientific co-operative programme (SCP). Thanks are due
to staff of the Marine Biological Productivity Unit for their assistance in both field
and laboratory work. I acknowledge Mr Ole Schou and Ms Khodeeyoe Pornchai
for their help in sampling and specimen preparation. I am indebted to Dr Thomas
Kiørboe who introduced me to the copepod study. Special gratitude is allocated
to Dr Per Juel Hansen and Dr Torkel Gissel Nielsen for their comments and
suggestions on the manuscript. I appreciate Dr David McKinnon for his advice
on copepod identification and Dr Russell R.Hopcroft for fruitful discussion. This
is contribution no. PMBC 35 of the Phuket Marine Biological Center.
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Received on October 15, 1998; accepted on June 30, 1999
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