Indian Journal of Marine Sciences
Vol. 32(3), September 2003, pp. 222-225
Zooplankton biomass in the Straits of Malacca
*H. Rezai1, F. M. Yusoff1, A. Kawamura2, A. Arshad1 & B. H. R. Othman3
1
Department of Biology, Faculty of Science and Environmental Studies, University Putra Malaysia,
43400 Serdang, Selangor D.E., Malaysia
2
Faculty of Bioresources, Mie University, 1515 Kamihama-cho, Tsu, Mie, 514-8507, Japan
3
School of Environmental and Natural Resource Sciences, National University of Malaysia, 43600 UKM Bangi,
Selangor D.E., Malaysia
*[E-mail: [email protected]]
Received 7 October 2002, revised 25 March 2003
The distribution patterns of zooplankton biomass were studied using samples collected in vertical hauls during four
oceanographic cruises in the Straits of Malacca between November 1998 and August 2000 with 140 µm-mesh and 45-cm
diameter NORPAC net. The average zooplankton biomass during Cruise III (post-SW monsoon) and IV (SW monsoon) was
almost twice that of Cruise I (NE monsoon) with maximum zooplankton biomass occurring during the Cruise IV. Biomass
was generally higher in waters closer to the near-coastal areas than in the neritic areas. Higher zooplankton biomass values
occurred in the central part of the Straits compared to other areas, although spatial and temporal variations of biomass were
not significant. Run off of major rivers and the extensive mangrove forests in the coastal areas might have influenced higher
biomass in the central part of the Straits.
[Key words: Zooplankton biomass, distribution, Straits of Malacca, Malaysia]
Information on zooplankton biomass is important in
evaluating the secondary production and in providing
information on the fishery potential. The Straits of
Malacca is a semi-enclosed, narrow tropical sea that
connects the Indian Ocean to the South China Sea.
Given its importance for the fisheries, only scanty
information exists on the zooplankton distribution and
abundance1-4. The purpose of this study is to describe
the spatial and temporal variation of zooplankton
biomass along the Straits of Malacca from Langkawi
Island in the north to Johor in the south.
Materials and Methods
Zooplankton sampling and general oceanographic
surveys were conducted during four cruises
(November-December 1998, March-April 1999,
August 1999, July-August, 2000) along the Straits of
Malacca (05° 59′ N, 99° 59′ E and 01o 10′ N, 103° 29′ E)
(Fig. 1). The periods of the consecutive cruises
(I, II, III, IV) coincided with NE (northeast) monsoon,
pre-SW (pre-southwest) monsoon, post-SW monsoon
and SW monsoon, respectively. Originally, twentyfour sampling stations were established for this study,
but due to the poor weather conditions, no sampling
was performed at all the stations (cruise I, 17 stations;
cruise II, 19 stations, cruise III, 13 stations and cruise
IV, 20 stations). Details of depth of hauls and
geographic coordinates are shown in Table 1. Two
successive vertical hauls were made at each station
using the NORPAC net (mesh aperture 140 μm with
the net opening, 0.159 m2) from near bottom to the
Fig. 1— Location of sampling stations ( ). Divisions referred to
in the text are: N, north; C, centre and S, south.
Rezai et al.: Zooplankton biomass in the Straits of Malacea
surface. Biomass was estimated from one sample,
while the other was used for quantitative estimation
and for microscopic analysis, and the details of which
have been described elsewhere5. The total zooplankton
biomass (excluding gelatinous zooplankton) was
estimated as dry weight. To simplify data analysis, the
Straits was divided into three sectors based on
geography and hydrography of the region. Multiple
measurements of temperature and salinity were made
from surface to the bottom using Hydrolab Surveyor 3.
Results
Temperature and salinity — Except for a
thermocline in the northern part, there was not much
variation in the temperature of the water column.
Temperature and salinity were homogenous
throughout the study area and the changes were
significant only during periods of heavy rains. At
most of the stations the temperature fluctuated
between 27o and 29o C. Variation in salinity values in
the northern part of the Straits were relatively higher
(ranging between 29 and 35 o/oo) than in the southern
part (ranging from 29 to 33 o/oo). In this shallow
tropical coastal environment vertical gradients in the
temperature and salinity were negligible suggesting
that the water column was well mixed.
Biomass — Distribution of zooplankton biomass
fluctuated temporally and spatially (Fig. 2). The
present survey exhibited two localized high biomass
values. Station 14 in particular, showed maximum
value during cruises I, III and IV. While, during
Cruise II, the maximum value was recorded at station
20. During cruises I and IV, biomass was
223
concentrated mainly in near-coastal areas of Port
Klang and Lumut, but during Cruise III, it peaked at
offshore areas of Port Klang. Biomass was generally
higher in waters closer to the near-coastal areas than
in the offshore areas.
There was only a small variation in biomass values
between northern, central and southern parts of the
Straits during the first two cruises (ranging from
25.50 to 87.30 mg dry wt. m-3), whereas there was a
high variation during cruises III and IV (ranging from
84.50 to 252.00 mg dry wt. m-3) (Fig. 3). Biomass was
Table 1 — Sampling stations
Station
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Position
06o00.00′N
06o00.03′N
06o00.09′N
05o30.04′N
05o30.07′N
04o59.97′N
05o00.00′N
04o30.04′N
04o30.13′N
04o30.00′N
04o00.02′N
03o59.98′N
03o29.95′N
03o29.94′N
02o59.94′N
02o29.83′N
02o10.00′N
01o40.66′N
01o29.29′N
01o15.82′N
Fig. 2 — Distribution of zooplankton biomass during the cruises.
99o59.79′E
99o30.05′E
98o59.88′E
99o59.98′E
99o30.00′E
99o58.60′E
99o30.00′E
100o30.03′E
100o00.01′E
99o30.00′E
100o30.02′E
100o00.03′E
100o29.95′E
101o00.11′E
100o59.95′E
101o30.10′E
102o00.10′E
102o38.67′E
103o03.63′E
103o26.34′E
Depth of haul
(m)
31.0
68.0
96.0
37.0
68.0
59.0
60.0
13.0
60.7
50.0
44.8
76.2
64.5
10.5
15.4
68.0
35.0
50.0
38.0
34.6
224
Indian J. Mar. Sci., Vol. 32, No. 3, September 2003
Fig. 3 — Mean estimates of zooplankton biomass in combined stations in different parts of the Straits of Malacca (the vertical bars
represent the standard errors).
maximum (122.59 ± 35.08 mg dry wt. m-3) during
post-SW monsoon (Cruise III) and minimum
(48.50 ± 11.36 mg dry wt. m-3) during NE monsoon
(Cruise I). However, Wilcoxon’s signed-ranks test
showed no significant difference (p> 0.05) in biomass
between the cruises and between geographic locations
within the Straits (P > 0.05).
Discussion
The Straits of Malacca has been classified as a
tropical shallow sea with partially mixed waters and a
circulation pattern that is dominated by monsoon
winds6. The occurrence of high zooplankton biomass
at near-coastal than neritic waters is in close
agreement with previous study4, and may be, partly,
due to the presence of higher amount of nutrients and
chlorophyll a contents in the near-coastal areas7.
Zooplankton biomass might be slightly overestimated in the present study (< 0.5%) due to
contamination of materials such as phytoplanktonoriginated detritus8, re-suspended sediments and
terrestrial runoff 9 in near-coastal waters, especially in
the southern part, near Johor.
The highly localized biomass concentration in the
central part of the Straits may be attributed to the
flushing of nutrients and organic particles by run off
from large rivers such as Klang and Perak, presence
of extensive mangrove forests along the coastal areas
of Klang and Lumut, and the occurrence of upwelling
at One Fathom Bank6,10 and abundant phytoplankton
density in the proximity of Port Klang area.
Differences between geographic locations in the
northern, central and southern parts of the Straits
essentially reflect the differences that exist in
zooplankton densities, particularly copepods5 in those
areas.
On the other hand, the increased zooplankton
biomass during Cruise III might be related to high
nutrient concentrations11 and high phytoplankton
biomass3. But what was the source of nutrients to
initialize the increase of phytoplankton all along the
coast? In the absence of concrete evidence, no
conclusion could be drawn, although the rainfall
might have episodically brought along nutrients into
the coastal environment12.
In accordance with near uniformity of temperature
and salinity, there was no significant spatial variation
in zooplankton biomass between groups of stations in
the northern, central and southern parts of the Straits
and between the cruises.
Acknowledgement
This study was supported by JICA/UPM Technical
Collaborative Project and Malaysian Government
IRPA Research Grant No. 01-02-04-0165.
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