Nee Soon Swamp Forest Under Threat? – Distribution of Introduced ...

Nee Soon Swamp Forest Under Threat? – Distribution of Introduced
Cichlid Acarichthys heckelii (Müller and Troschel, 1849) in
Singapore’s only Remaining Freshwater Swamp Habitat
Liew J. H. 1 and Tan H. H. 2
Department of Biological Sciences. The National University of Singapore. Blk S2, 14 Science
Drive 4. Singapore, 117546.
Abstract:
With the increasing loss of biodiversity, especially in the tropics, biological
invasion has become an important factor to consider in conservation efforts. This is
especially true in Singapore where the other drivers of extinction, namely, the
exploitation of natural resources and habitat degradation have been largely halted in
recent years. The introduced cichlid, Acarichthys heckelii has recently been reported
to be present in one of the streams at Nee Soon Swamp forest, arguably the most
important freshwater habitat in Singapore, to the alarm of biologist. Therefore, this
study was launched to investigate if the fish had established a naturally reproducing
population in the swamp forest, chart out its distribution in connected water bodies
and assess the threat that it poses on the swamp habitat. The results of the study
indicate that A. heckelii had not been successful in invading Nee Soon as a result of
unsuitable abiotic parameters, although a feral population was found in the connected
stream at Sungei Seletar, along with several other introduced species. This finding,
coupled with the high accessibility of the streams at Nee Soon from Sungei Seletar
points to the fact that Singapore’s last freshwater swamp habitat remains at risk of
invasion by exotic species.
Introduction:
The last few decades have seen biodiversity loss is occurring around the globe at a
rate faster than ever recorded leading some to believe that a mass extinction event
unprecedented since the Permian extinction is taking place (Sodhi et al., 2007;
Benton, 2005). One of the chief drivers of extinction is Biological Invasion although
its gravity is very often underestimated. Recent studies have reports have indicated
the presence of an introduced cichlid, Acarichthys heckelii in Nee Soon Swamp forest,
arguably the most important primary freshwater habitat in Singapore to the alarm of
Biologists (Tan & Lim, 2008). Therefore, this study determine if the Acarichthys
heckelii has indeed established a naturally breeding feral population in the Nee Soon
Swamp Forest as well as to chart the distribution of the cichlid in the connected water
bodies. By achieving such, the study hopes to assess the threat that the introduced fish
poses on Singapore’s only remaining freshwater swamp habitat.
Materials and Methods:
Surveys were conducted at several sites along the stream running through Nee
Soon Swamp Forest, the stream at Lorong Banir, and along Sungei Seletar. All three
1 Student
2 Supervisor

locales are connected water bodies with the former being furthest upstream, and the
latter the furthest downstream. Sampling was conducted with the use of large and
small bottle traps as well as cast nets where the width of the river is permitting. A.
heckelii specimens obtained were euthanised on ice and deposited at the Raffle’s
Museum of Biodiversity Research at the National University of Singapore where the
Standard Length (SL) was recorded. Abiotic parameters at the sampling locales were
measured with the use of the Multi-Parameter PCSTestr TM 35 probe.
Results:
Distribution Survey:
Upon the completion of the survey at all three locales, a total of forty-four
specimens were obtained, all from Sungei Seletar. The fishes acquired ranged from
juveniles measuring an SL of 49.9mm to adults measuring at 105mm SL. No
Acarichthys heckelii fishes were caught at any of the sampling sites at the Nee Soon
Swamp forest and the stream at Lorong Banir. The presence of the fish was also
confirmed via in situ observation at Sungei Seletar but not at the other two survey
locations.
Survey of Abiotic Factors:
The sampling sites at Nee Soon Swamp forests were most acidic of the three
survey locations while the sites at Sungei Seletar measured to be least acidic. In
addition to that, of the three survey locations, only Sungei Seletar recorded a mean
pH value that falls within the pH range of the Acarichthys heckelii’s native habitat
(Liebel, 1984). While other abiotic parameters, namely, water temperature ( ° C),
salinity (ppt) and conductivity (μS/cm) were similar at sites located at both Lorong
Banir and Nee Soon Swamp Forest, the measurements were significantly higher at
Sungei Seletar.
Species Richness of the Survey locations:
Of the three locations, Nee Soon Swamp Forest recorded the highest species
richness (12 species), consisting mainly of species listed as being endangered, while
Sungei Seletar has the lowest species richness (3 species) and Lorong Banir recorded
an intermediate value (4 species). Also, no introduced fish species were recorded at
Nee Soon Swamp Forest or Lorong Banir while in Sungei Seletar, almost all the fish
species caught were non-native with the exception of the indigenous Dermogenys
pusillus.
Discussions:
Examining the distribution of Acarichthys heckelii and the presence of established
feral populations:
Although A.heckelii have been found in Nee Soon Swamp Forest and Lorong
Banir in the past, this study shows that the fish were unable to establish themselves at
the two said locations. However, a naturally reproducing feral population was present
downstream at Sungei Seletar. One of the possible explanations of the inability of
A.heckelii to successfully invade Nee Soon is the presence of abiotic barriers in the
form of acidic waters and the lack of suitable substrate.

Status of the freshwater habitat at Nee Soon Swamp Forest:
The study has shown that the status of the freshwater habitat at Nee Soon Swamp
forest is currently satisfactory and rather encouraging due to the presence of many
fish species listed as being endangered coupled with the absence of introduced species
(Nparks, 2006). However, the lack of substantial barriers to a biological invasion from
a connected habitat which is occupied mainly by introduced species, under
circumstances of close proximity and high accessibility means that Nee Soon Swamp
Forest remains in a precarious situation and is still very much at risk of a biological
invasion from connected waterways consisting mainly of disturbed freshwater
habitats.
The future of freshwater biodiversity conservation at Nee Soon Swamp Forest:
With more support from the public, it is hopes that a stricter enforcement of laws
against the release of animals into the wild by Nparks and AVA could help safeguard
Nee Soon Swamp Forest from biological invasion. In addition to that, instalment of
physical barrier at Lorong Banir to prevent the migration of introduced species from
Sungei Seletar upstream without interfering with the flow of the river is also a matter
of importance should the upstream migration of introduced species at Sungei Seletar
be avoided. A possible invasive threat to Nee Soon in the near future was observed at
Sungei Seletar in the form of the Cyprinus carpio, a species that has already formed
feral population damaging to native fauna in other parts of the world.
Conclusion:
Due to the high accessibility of the streams of Nee Soon Swamp Forest from
Sungei Seletar where several potential invasive species are found, it is a matter of
considerable importance that quick preventive measures are taken in order to avert
damaging biological invasion events in the last stronghold of most of the endangered
freshwater fish species in Singapore (Tan & Lim, 2008).
References:
Baensch, S. H. & R. Riehl, 1993. Aquarium Atlas Volume 2. Verlag GmbH Hans A.
Baensch, Germany. 180pp.
Benton, M J (2005). When Life Nearly Died: The Greatest Mass Extinction of All
Time. Thames & Hudson
Brook, B. W., N. S. Sodhi & C. J. A. Bradshaw, 2008. Synergies among extinction
drivers under global change. Trends in Ecology and Evolution, 23(8): 453-
460.
Cichocki, F.P. 1976. Cladistic history of Cichlid Fishes and Reproductive Strategies
of the American Genera Acarichthys, Biotodoma, and Geophagus.
Unpublished Ph.D. Dissertation, University of Michigan.
Flajhans, M & G. Hulata, 2006. Common carp – Cyprinus carpio. Genetic effects of
domestication, culture and breeding of fish and shellfish, and their impacts on
wild populations, Genimpact Final Scientific Report.
IUCN (2005) IUCN Red List of Threatened Species. World Conservation Union,
Gland. (online) (Accessed 3 January 2009).
Koehn, J., A. Brumley & P. Gehrke, 2000. Managing the Impacts of Carp. Bureau of
Rural Sciences.

Liebel, W., 1984. Heckel's Thread-Finned Acara Acarichthys heckelii (Mueller and
Troschel 1848). Freshwater and Marine Aquarium Magazine. (online)
(Accessed 11 November
2008).
Liebel, W. S, 1997. The Maintenance of Cichlids. Perth Cichlid Society Magazine, 28
(online) < http://ovas.ca/index.php?page=77> (Accessed 2 March 2009).
Lim, K. K. P & P. K. L. Ng, 1990. A guide to the freshwater fishes of Singapore.
Singapore: Singapore Science Centre. (Online)
(Accessed 9 September 2009).
Linhart, O., S. Kudo, R. Billard, V. Slechta, & E. V. Mikodina, 1995. Morphology
composition and fertilization of carp eggs: a review. Aquaculture, 129:75-93.
Mcgrouther, M., 2008. Fish Terminology. Australian Museum Fish Site. (online) <
http://www.australianmuseum.net.au/fishes/fishfacts/fish/glossary.htm>
(Accessed 30 December 2008).
Newsome, A. E & I. R. Noble, 1986. Ecological and physiological characters of
invading species. Ecology of Biological Invasions. Edited by R. H. Groves and
J. J. Bourdon. Cambridge: Cambridge University Press. pp 1- 15.
Nparks (2006) List of Freshwater Fisher Present in Singapore. (online)
(Accessed 21
January 2009).
Ng, P. K. L & K. K. P. Lim, 1992. The conservation status of the Nee Soon
Freshwater Swamp Forest of Singapore. Aquatic Conservation, Marine and
Freshwater Environments, 2: 255- 266
Robins, C. R., R. M. Bailey, C. E. Bond, J. R. Brooker, E. A. Lachner, R. N. Lea &
W. B. Scott, 1991 World fishes important to North Americans. Exclusive of
species from the continental waters of the United States and Canada. American
Fisheries Society Special Publication, (21): 243pp.
Sodhi, N. S., B. W. Brook & C. J. A. Bradshaw., 2007. Tropical Conservation
Biology. Blackwell Publishing. Pg. 332pp.
Tan, H. H & K. K. K. P. Lim, 2008. Acarichthys heckelii (Müller and Troschel) An
introduced Cichlid fish in Singapore. Nature in Singapore 2008, 1: 129- 133
Tan, H. T. W., L. M. Chou, D. C. J. Yeo, & P. K. L. Ng, 2007. The Natural Heritage
of Singapore. 2 nd Edition. Pearson Education. 244pp.
Wilson, E. O, 1993. Is humanity suicidal? Biosystems, 31(1993): 235- 242.
Wiles, G. J., J. Bart, R. E. Beck Jr. & C. F. Aguon, 2003. Impacts of the Brown Tree
Snake: Patterns of Decline and Species Persistence in Guam’s Avifauna.
Conservation Biology, 17(5): 1350- 1360.
Wong, J. Q. H. How Safe is Nee Soon Swamp Forest? Preliminary study on the
Invasive potential of the Red-Claw Crayfish. Unpublished paper. Department
of Biological Sciences, National University of Singapore.