Spatial Distribution of Copepods along the Salinity Gradient of Perai River Estuary, Penang, Malaysia
W.O. Wan Maznah,
M.K. Abu Hena
Investigation on copepod communities in Perai river estuary was conducted from November 2005 to May 2006. Five stations were established for monthly sampling and were located from the river mouth to the upper reaches of the river. Copepod samples were collected from vertical tows using a standard zooplankton net. The Perai river estuary was slightly stratified and salinity decreases significantly from the mouth of the river towards the upper reaches of the river. A total of 28 species of copepods were recorded and comprised of 14 families, Paracalanidae, Oithonidae, Corycaeidae, Acartiidae, Calanidae, Centropagidae, Eucalanidae, Pontellidae, Pseudodiaptomidae, Tortanidae, Ectinosomatidae, Euterpinidae, Clausidiidae and Cyclopidae. A total of 10 species showed high positive affiliation towards salinity (R>0.60), Acartia spinicauda, Euterpina acutifrons, Microsetella norvegica, Oithona nana, Oithona simplex, Paracalanus crassirostris, Paracalanus elegans, Paracalanus parvus, Pseudodiaptomus sp. and Hemicyclops sp. The copepod species Pseudodiaptomus dauglishi were negatively affiliated towards salinity (R = -0.71). The copepod assemblages classified into two distinct groups according to salinity regimes, euryhaline-polyhaline group (25 marine affiliated species) and oligohaline-mesohaline group (3 freshwater affiliated species).
Received: October 05, 2012;
Accepted: October 10, 2012;
Published: January 23, 2013
Estuaries are highly productive ecosystems, many of its functions as breeding,
feeding and nursery grounds for many aquatic organisms including fish and shrimp
species. Zooplankton plays an important key role in the aquatic food webs as
primary grazers of phytoplankton and as food to higher trophic organisms. According
to Nasser et al. (1998), salinity is the most
important factor controlling species composition and distribution of a tropical
estuary. Zooplankton composition varies throughout the salinity gradient thus
giving rise to diverse population of zooplankton (Jayasinghe
et al., 2003). In addition, estuarine zooplankton can be divided
into three main groups viz., (1) high saline or marine species concentrated
at the river mouth (2) medium saline or brackish-water species at the middle
and (3) low saline or freshwater species at the upper reaches of the estuary
(Jayasinghe et al., 2003).
The Perai river estuary opens into the northern and southern Penang Straits
through its river mouth. The river is deepest at the river mouth and the sides
of the river banks are filled with mud deposits of sand and silt particles caused
by the tidal currents. The river meanders into the interior in the northeast
direction cutting across wide area of urban, industrial and agricultural areas.
The river exhibited a diverse assemblages of riparian plants from mangrove dominated
(river mouth) to weed dominated (upper sections) (Abdul-Rahman
et al., 2010). Studies on zooplankton in Malaysian waters
were more focused towards the marine environment (Rezai
et al., 2004; Johan et al., 2002).
In addition, the information on diversity and distribution of zooplankton especially
of copepods in the coastal and oceanic waters of Malacca Straits is quite extensive
and updated. However, there is very limited records and information on the zooplankton
of estuaries in Malaysia (Chua, 1970, 1973;
Sewell, 1933). This study analyzes the relationship
between the spatial distribution of copepod assemblages with salinity regimes
in the Perai river estuary, Penang, Malaysia.
MATERIALS AND METHODS
Five sampling stations (ST1-ST5) were established along the Perai river estuary
and represented various section of the river system (Fig. 1).
Sampling was carried out monthly from November 2005 to May 2006. Salinity was
measured at different depths using SCT Meter YSI Model 33. Copepod was collected
using a plankton net (mesh size: 150 μm, diameter 25 cm). The net was towed
vertically from the bottom. The volume of water filtered by the net was derived
from the line-length and net opening (Kuipers et al.,
1993). Copepod samples were preserved in a bottle containing 4% of neutralized
formalin diluted with seawater (Omori and Ikeda, 1984).
In the laboratory, the copepod specimens were identified and enumerated under
the stereo microscope and compound microscope. Identification were based on
taxonomic descriptions (Boxshall and Hasley, 2004; Matsuo
and Masaaki, 1997; Huys et al., 1996; Heron
and Bradford-Grieve, 1995; Bradford-Grieve, 1994;
Zhong, 1989; Yamaji, 1986; Boxshall,
Copepod absence/presence data were used for correlation analysis and cluster
analysis. One-way analysis of variance was used to test the spatial and temporal
differences in salinity variations for months and stations. Pair Samples t-test
was used to study the differences between surface and bottom salinity. Spearman,
Rho Correlation was performed to indicate relationships between salinity and
copepod. All statistical analysis was run on SPSS version 13. Multivariate cluster
analysis was conducted on spatial and temporal data of salinity and copepod
occurrence data using Multivariate Statistical Package version 3.1 (MVSP).
||(a) Location of study area showing sampling stations (b) Mean
river water salinity (psu) according to sampling stations
The distribution of salinity in Perai river estuary is given in Fig. 1. Mean river water salinity from the river mouth (ST1) to the upper region (ST5) was found to range from 22.54 psu (maximum of 34 psu) to 1.61 psu (minimum of 0 psu). Results indicated that seawater moved into the estuary by tidal action to as far as the upper region (ST5) which is located approximately 20 km from the river mouth (ST1). One-way ANOVA showed that there were significant differences in salinity between stations. Paired-sample t-test showed that surface and bottom salinity readings were significantly different. No significant difference was found between months.
A total of 28 species of copepods were recorded from the samples (Table 1). They comprised of 14 families, Paracalanidae, Oithonidae, Corycaeidae, Acartiidae, Calanidae, Centropagidae, Eucalanidae, Pontellidae, Pseudodiaptomidae, Tortanidae, Ectinosomatidae, Euterpinidae, Clausidiidae and Cyclopidae. A total of 17 genera were recorded namely Acartia, Canthocalanus, Corycaeus, Bestiolina, Labidocera, Centropages, Eucalanus, Acrocalanus, Parcalanus, Pseudodiaptomus, Halicyclops, Hemicyclops, Oithona, Microcyclops, Euterpina, Microsetella and Tortanus.
Cluster analysis on copepod data revealed two groups of salinity regimes (Fig. 2). The Perai river could be separated into two groups (A) euryhaline-polyhaline (16-34 psu) and (B) oligohaline-mesohaline (0-14 psu). The separation of salinity regimes could be explained by the species composition of copepods in the salinity regime. Group A comprised of 25 euryhaline-polyhaline copepod species (marine affiliated) while Group B comprised of 3 oligohaline-mesohaline copepod species (fresh water affiliated).
The relationship between the distributions of copepod species and salinity
were tested using Spearmans Rho correlation analysis. All species of copepod
were found to be significantly correlated to the salinity gradient. However,
the correlation coefficient varies from 0.24-0.82. Among these, eleven species
were found having the correlation coefficient higher than 0.60 (Table
2). The copepod species which were correlated positively to salinity were
comprised of Acartia spinicauda, Euterpina acutifrons, Microsetella
norvegica, Oithona nana, Oithona simplex, Paracalanus crassirostris,
Paracalanus elegans, Paracalanus parvus, Pseudodiaptomus sp.
and Hemicyclops sp. The copepod species Pseudodiaptomus dauglishi
were negatively correlated with salinity.
|| Copepod species recorded from Perai river estuary
||Classification of copepod assemblages and salinity regimes
based on minimum variance clustering and squared Euclidean distance
|| Salinity range, frequency and correlation coefficient of
copepod species distribution in Perai river estuary
The Perai river can be classified as a slightly stratified estuary and is heavily
influenced by tidal movements. The Perai river exhibited salinity characteristics
similar to definitions by Dyer (1997) where salinity varies
along the estuary at any depth, but surface salinity is always lower than bottom
salinity. This intrusion of seawater would affect the species composition and
distribution of flora and fauna in the river system (Green,
1968). Chang and Fang (2004) found that copepod
species, abundance and diversity were high correlated with salinity, where salinity
varied according to tidal phases.
The copepod species of Perai river were primarily comprised of a mixture of
marine and freshwater affiliated species. Copepod species from the genus Pseudodiaptomus,
Acartia, Paracalanus, Temora and Oithona have been
widely reported to be dominant in coastal estuarine waters including mangrove
estuaries (Ara, 2004; Krumme and
Liang, 2004). Marine affiliated species however, were more numerous representing
25 species out of 28 species of copepods which were correlated with salinity.
Copepod species in group A were positively correlated with salinity while species
from B were negatively correlated with salinity. Copepod species group (A) dominated
at stations located at the river mouth up to the middle reach of the river (ST1
and ST2). These stations were highly influenced by the intrusion of seawater,
thus the species observed here are able to tolerate lower levels of salinity.
Salinity at this station never dropped down below 10 psu. Copepod species found
here such as Acartia spinicauda, Microsetella norvegica, Oithona
nana, Oithona simplex, Euterpina acutifrons and Paracalanus crassirostris
are well reported as the dominant estuarine copepods (Rezai
et al., 2004; Tam et al., 2000). Paracalanus
parvus has been known to be a dominant tropical copepod species in coastal
waters (Nguyen and Truong-Si, 2006; Chang
and Fang, 2004; Yahia et al., 2004). The
copepod species Acartia spinicauda have been reported to prefer warmer
water conditions and lower water salinity compared to Acartia pacifica
in Malaysian coastal waters (Yoshida et al., 2006).
E. acutifrons is a copepod species with the ability to survive in a wider
range of salinity (Moreira, 1975; Moreira
et al., 1982; Turner, 1994).
The middle point of the river (ST3) exhibited fluctuating salinity condition.
Salinity varies greatly from 2 psu to 18 psu thus indicating a transition area
between freshwater to moderately saline water. The species composition of copepods
here reflected this phenomenon. The copepod species that could tolerate such
a change in salinity thrives at this station. Species such as Halicyclops
sp., Oithona nana and Oithona simplex are characteristically
found in inshore and shallow waters. These species were reported to suite low
salinity water and dominant in mangrove estuaries (McKinnon
and Klumpp, 1997; Nishida, 1985).
Species composition of copepod changes distinctly from the river mouth to the
upper reaches as salinity decreased to zero at ST4 and ST5 (group B). At these
stations, the composition of copepods were represented by three freshwater affiliated
species namely, Pseudodiaptomus dauglishi, Halicyclops and Microcyclops.
The copepods species, Microcyclops have been reported to be restricted
to saline habitats while Halicyclops occurred in tidal saline waters
of many Malaysian rivers (Fernando and Ponyi, 1981).
The occurrence and distribution of P. dauglishi in the current study
is similar to the findings by Sewell (1933), in which
the species was found in an almost pure culture as in the Kurau river, Malaysia.
The Perai river estuary is a slightly stratified estuary with strong tidal influences where salinity is a major factor in influencing the spatial distribution of copepod species in the estuary. Two major groups of copepod assemblages can be clearly distinguished representing euryhaline-polyhaline (marine affiliated) and oligohaline-mesohaline (freshwater affiliated) species. A total of 11 species of copepod were found to be significantly correlated with salinity representing 10 marine affiliated species and 1 freshwater affiliated species.
The authors are grateful to the technical staff of Universiti Sains Malaysia, Dr. Amir, Mr. Zarul, Mr. Yaakob and Mr. Hamzah for their assistances in the field works. This research was supported by RESTORPEAT No: 304/Pbio/650248/E104 (European Commission Research Grant).
1: Ara, K., 2004. Temporal variability and production of the planktonic copepod community in the Cananeia Lagoon estuarine system, Sao Paulo, Brazil. Zool. Stud., 43: 179-186.
Direct Link |
2: Boxshall, G.A., 1979. The Planktonic Copepods of the Northeastern Atlantic Ocean: Harpacticoida, Siphonostomatoida and Mormonilloida. British Museum (Natural History), London, pp: 201-264
3: Boxshall, G.A. and S.H. Hasley, 2004. An Introduction to Copepod Diversity. The Ray Society, London, UK., Pages: 966
4: Bradford-Grieve, J.M., 1994. The Marine Fauna of New Zealand: Pelagic Calanoid Copepoda: Megacalanidae, Calanidae, Paracalanidae, Mecynoceridae, Eucalanidae, Spinocalanidae, Clausocalanidae. National Institute of Water and Atmospheric Research (NIWA), New Zealand, ISBN-13: 9780478083330, Pages: 160
5: Chang, W.B. and L.S. Fang, 2004. Temporal and spatial variations in the species composition, distribution and abundance of copepods in Kaohsiung Harbor, Taiwan. Zool. Stud., 43: 454-463.
Direct Link |
6: Chua, T.E., 1970. A preliminary study on the plankton of the Ponggol estuary. Hydrobiologia, 35: 252-272.
7: Chua, T.E., 1973. An ecological study of the Ponggol estuary in Singapore. Hydrobiologia, 43: 505-533.
8: Dyer, K.R., 1997. Estuaries: A Physical Introduction. 2nd Edn., John Wiley and Sons, New York, USA., ISBN-13: 9780471974703, Pages: 195
9: Fernando, C.H. and J.E. Ponyi, 1981. The freeliving freshwater cyclopoid copepoda (crustacea) of Malaysia and Singapore. Hydrobiologia, 78: 113-123.
10: Green, J., 1968. The Biology of Estuarine Animals. 3rd Edn., Sidgwick and Jackson, London, UK., Pages: 401
11: Heron, G.A. and J.M. Bradford-Grieve, 1995. The Marine Fauna of New Zealand: Pelagic Copepoda: Poecilostomatoida: Oncaeidae. New Zealand Oceanographic Institute, New Zealand, ISBN-13: 9780478083507, Pages: 57
12: Huys, R., J.M. Gee, C.G. Moore and R. Hamond, 1996. Marine and Brackish Water Harpacticoid Copepods. Linnean Society of London, UK., ISBN-13: 9781851532568, Pages: 352
13: Jayasinghe, R.P.P.K., F.M. Yusoff and A. Arshad, 2003. Zooplankton Populations in Tropical Estuaries: A Review. In: Aquatic Resource and Environmental Studies of the Straits of Malacca: Managing the Straits through Science and Technology, Japar Sidik, B., Z. Mutaharah, A. Arshad and A. Kawamura (Eds.). Malacca Straits Research and Development Centre (MASDEC), Universiti Putra Malaysia, Serdang, Malaysia
14: Johan, I., B.A.G. Idris, A. Ismail and H. Omar, 2002. Distribution of Planktonic Calanoid Copepods in the Straits of Malacca. In: Tropical Marine Environment: Charting New Strategies for the Millennium, Yusoff, F.M., M. Shariff, H.M. Ibrahim, S.G. Tan and S.Y. Tai (Eds.). (MASDEC). Putra Malaysia, Serdang, Malaysia, pp: 393-407
15: Krumme, U. and T.H. Liang, 2004. Tidal-induced changes in a copepod-dominated zooplankton community in a macrotidal mangrove channel in Northern Brazil. Zool. Stud., 43: 404-414.
Direct Link |
16: Kuipers, B.R., H.J. Witte and S.R. Gonzalez, 1993. Zooplankton distribution in the coastal upwelling system along Banic d'Arguin, Mauritia. Hydrobiologia, 258: 133-149.
17: McKinnon, A.D. and D.W. Klumpp, 1997. Mangrove zooplankton of North Queensland, Australia. Hydrobiologia, 362: 145-160.
18: Matsuo, C. and M. Masaaki, 1997. An Illustrated Guide to Marine Plankton of Japan. Tokai University Press, Tokyo, Japan, pp: 700-1000
19: Moreira, G.S., 1975. Studies on the Salinity Resistance of the Copepod Euterpina acutifrons (Dana). In: Physiological Ecology of Estuarine Animals, Vernberg, F.J. (Ed.). University of South Carolina Press, Columbia, pp: 73-79
20: Moreira, G.S., J.B. Jillett, W.B. Vernberg and M. Weinrich, 1982. The combine effects of temperature and salinity on the survival of Euterpina acutifrons (Dana) (Copepoda, Harpacticoida) from New Zealand and Brazilian coasts. J. Plank. Res., 4: 85-91.
21: Nasser, A.K.V., P. Siraimeetan and T. Matsumura-Tundisi, 1998. Dynamics of a perturbed estuarine zooplankton community: Port of Suape, PE Brazil. Proc. Int. Assoc. Theor. Applied Limnol., 26: 119-120.
22: Nguyen, C. and H.T. Truong-Si, 2006. Zooplankton abundance and species diversity in Qui Nhon coastal waters, South Central Vietnam in June 2004. Coast. Mar. Sci., 30: 328-335.
Direct Link |
23: Nishida, S., 1985. Taxonomy and Distribution of the Family Oithonidae (Copepoda, Cyclopoida) in the Pacific and Indian Oceans. Ocean Research Institute, University of Tokyo, Japan, Pages: 167
24: Omori, M. and T. Ikeda, 1984. Methods in Zooplankton Ecology. John Wiley and Sons, New York, USA., Pages: 332
25: Rezai, H., F.M. Yusoff, A. Arshad, A. Kawamura, S. Nishida and O.B.H. Ross, 2004. Spatial and temporal distribution of copepods in the Straits of Malacca. Zool. Stud., 43: 486-497.
Direct Link |
26: Sewell, R.B.S., 1933. Notes on a small collection of marine Copepoda from Malay States. Bull. Raffles Museum, 8: 25-31.
Direct Link |
27: Abdul-Rahman, S.N., J. Ismail and M. Mansor, 2010. The distribution of riparian corridor plants and the relations to river water salinity along Perai river, Penang, Malaysia. Wetland Sci., 8: 48-56.
Direct Link |
28: Tam, P.F., C.K. Wong, Q. Chen, Y. Fu, L. Huang and J. Yin, 2000. Planktonic copepods of the zhujiang estuary, 1991-1996. Proceedings of the International Symposium on Marine Biology in Taiwan, May 26-27, 1998, Taiwan -
29: Turner, J.T., 1994. Planktonic Copepods of Boston Harbour, Massachusetts Bay and Cape Cod Bay, 1992. In: Ecology and Morphology of Copepods, Ferrari, F.D. and B.P. Bradley (Eds.). Kluwer Academic Publishers, Belgium, pp: 405-413
30: Yahia, M.N.D., S. Souissi and O.D. Yahia-Kefi, 2004. Spatial and temporal structure of planktonic copepods in the bay of Tunis (Southwestern Mediterranean Sea). Zool. Stud., 43: 366-375.
Direct Link |
31: Yoshida, T., T. Toda, F.M. Yusoff and B.H.R. Othman, 2006. Seasonal variation of zooplankton community in the coastal waters of the Straits of Malacca. Coastal Mar. Sci., 30: 320-327.
Direct Link |
32: Yamaji, I., 1986. The illustrations of the Marine Plankton of Japan. Hoikusha Publishing Co. Ltd., Osaka, Pages: 538
33: Zhong, Z., 1989. Marine Planktology. China Ocean Press, Beijing, China, Pages: 454