Mangrove Spiders (Araneae) of Peninsular Malaysia
This study examines the diversity and distribution of
spiders in the mangrove areas in Peninsular Malaysia which is hoped to
contribute towards understanding the dynamics of the mangrove ecosystem.
Little research has been done on local spiders and inventory from this
habitat is rare. From faunal samples taken along transects from upper
to lower zones of Morib mangrove forest and studies on available museum
specimens in the Raffles Museum of Biodiversity Research (RMBR), yielded
26 species belonging to 10 family groups. There exist 4 species as new
records for Malaysia which are Clubiona meraukensis, Dolomedes
mizhoanus, Pardosa zhanjiangensis and Telamonia dimidiata.
The jumpers or family Salticidae has an overall wide distribution across
all zones sampled. Generally, the spider distribution depended on the
zone location and floral diversity. Spider zonation pattern is probably
influenced by complex factor combinations rather than one factor which
include biotic relationships such as competition and predation.
Mangroves are unique inter-tidal habitats that have been rapidly destroyed
for development of coastal zones throughout the tropical world. Damage to the
system can result in irreversible coastal erosion. Malaysia has 4,800 km coastline
and 15% of this is lined with areas of mangrove in character (Lim,
2007) of which much of that are scarred by adjacent developments. Reclamation
of the mangrove swamps for various development projects means destruction of
the Rhizophora and Brugeria zones. However, the future of local
mangroves may not be so bleak. In Malaysia there have been several attempts
at replanting of mangroves with varying degree of success. Bamboo poles were
used in the seventies to hold the mud while waiting for the mangroves to establish
themselves. More recently, Lim (2007) reported the formulation
of a feasible concept using sausage shaped geotubes named Pillowtubes designed
to absorb the wave actions have been utilized to protect not only mangrove seedlings
from being washed to sea but enabling young mangrove saplings to sprout and
take root within the mudflats. There are suggestions from the public that the
existing 100,000 ha of mangrove remains should be gazetted as protected areas.
The diversity of mangrove plants of Peninsular Malaysia comprised of 33 true
and 36 transitional species (Wee and Corlett, 1986). Mangroves
colonize the coastal mudflats in a series of succession (Berry,
1963; Macnae, 1968; Liow, 2000).
The pioneer species are the Avicennia and once this zone has established
itself, the landward mangrove belt will have low salinity due to the landward
influence giving rise to the succession of Rhizophora and the Brugeria
species. Erosion of the muddy coasts are damaging, causing the roots of
the mangroves fringing the sea (Avicennia) to be exposed which eventually
collapse. Erosion is slowed down in the Rhizophora and Brugeria zones which
have prop roots that anchor deep into the mud to withstand the natural forces.
Retaining the mangroves has the added bonus of preserving the fauna that depends
on these habitats. Of late issues pertaining to man-induced extinction of species
have increasingly gained importance in a global context. Ong
(1994) highlighted the paucity of baseline data pertaining to mangroves
which still harbors wildlife. The Southeast Asian mangroves are said to be biologically
richer than anywhere else in the world. Realization to conserve wildlife, including
those found in the mangroves is inevitable (Liow, 2000).
A baseline data is urgently needed for the mangroves whether it is taxonomic,
community, ecological or biochemical. The lack of information impedes impact
assessment, proper management and contingency plans for the faunal component
of the mangroves (Liow, 2000).
Spiders are present in local mangrove forests around Malaysia but virtually
nothing is known about their specific diversity and ecology. Some pertaining
information can be found embedded within work done by Koh
(1991) dealing with araneids in the mangrove and Ng and
Sivasothi (1999). The present study, therefore, takes this into account
and was done to provide necessary quantitative observations of the diversity
and distribution of spiders in mangrove forests. The findings will assist in
providing the background against which any future environmental deterioration
in specifically Malaysian coastal mangrove forests might be assessed.
MATERIALS AND METHODS
Two types of studies were conducted for this work. For the spider diversity
aspect besides field sampling that was conducted in the mangrove areas
of Morib, Malaysian specimens that are available in the Raffles Museum
of Biodiversity Research (RMBR), National University of Singapore (NUS)
were examined in October 2006. Data on spiders zonation and distribution
were collected during a field survey in Morib, Selangor, Peninsular Malaysia.
Morib is situated about 50 km south of Port Klang on the west coast of
Peninsular Malaysia (2° 44′N, 101° 28′E). Three rivers,
Sungai Langat, Sungai Morib and Sungai Kancong drain into the sea near
the study site. Manual sampling was done in 12 successive sessions beginning
in June 1997 during low tides.
The sampling zonation within the mangrove areas in Morib can be described
and divided into 1 to 5 major zones and within zone 2 can further be subdivided
into 3 subzones that is 2a-c (Table 1). Manual samplings
and the beating method were conducted within line transects of 100 m in
all major and subzones. The number and species of spiders in each major
and subzones were recorded. Due to accessibility reasons arachnids were
sampled at heights of 1.65 m and below.
The statistical software program statgraphic Version 2.6 was used for
data analysis. To test for significant numerical differences the t-test
was used. Cluster analysis was also employed to test the similarity in
distribution of spider species between zones.
|| Descriptive and sampling zones through the Mangrove
forest in Morib, Peninsular Malaysia
The mangrove trees have different animals living upon them in differing
abundances at various horizontal and vertical zonations. Other than the
arachnids, the insects present in field samplings, belonged to the Order
Coleoptera, Diptera, Hemiptera, Homoptera, Hymenoptera, Lepidoptera, Mantoidea,
Neuroptera, Odonata and Orthoptera. Identification of spiders from field
collections and museum work, yielded 27 species belonging to 10 family
groups (Table 2). The country distributions where these
species are also found are shown in Table 2. Presence
of these species in the mangrove habitat had been reported in other references
(Table 2) except for 4 species considered as new records
for Malaysia. These new records are Clubiona meraukensis, Dolomedes
mizhoanus, Pardosa zhanjiangensis and Telamonia dimidiata.
The proportional abundance of the spiders in the field in descending
order as indicated in the pie chart (Fig. 1) are as
follows: the most dominant in numbers are the jumping spiders, Salticidae,
comprised of 42% followed by the lynx spiders, Oxyopidae with 25%, in
moderate numbers are the nursery web spiders, Pisauridae (16%) and long
jawed spiders, Tetranagthidae (11%) and smaller densities are the daddy
long legs, Pholcidae (4%) and Psecridae (2%).
||Diversity list of mangrove spiders found in specific
areas in Peninsular Malaysia and distribution within South East Asia
reported as in references indicated
|Named localities within Malaysia are given in full while other
countries abbreviated as: C: China, IN: Indonesia, JV: Java, MY: Myanmar,
NG: New Guinea, PH: Phillipines, SL: Sri Lanka, SP: Singapore, SU: Sumatra,
SUL: Sulawesi, TH: Thailand, TW: Taiwan and VT: Vietnam). The presence of
reported local species besides from our current study are also in reference
to Murphy and Murphy (2000), Ng and
Sivasothi (1999), Platnick (2006) and Song
et al. (2002)
||The overall percentage (%) availability of spider family
groups found from the study site in Morib, Peninsular Malaysia
||The frequency distribution of spider family groups (individual
numbers) across species found in all sampling zones (zone 1 to 5)
in the mangrove forest of Morib, Peninsular Malaysia
There was a great variation in the diversity and densities of spiders
among zones (Fig. 2). The greatest density and diversity
of species occurred in the middle zones (zones 2b and c) with the greatest
faunal heterogeneity rather than other zones of the forest especially
which contained homogeneous mangrove trees of Avicennia species.
This is shown by the marked difference (t-test: t(1,5) = 6.32456,
p = 0.0015) between mixed forest zone (zone 2b) and monogeneous Avicennia
trees, adjacent to the sandy beach (zone 3). Generally, the density
depended on the zone location and floral diversity. Interestingly, the
salticids occurred in all zones of the mangrove forest.
The spider fauna in all zones were also compared by means of cluster
analysis. In reference to the associated fauna and most dissimilar point,
3 main clusters are suggested (Fig. 3). This revealed
similarities in components of zones 2a and 5, these are neighboring areas
of Avicennia forests. Zones 3 and 4 are more linked in their spider
components although comprised of different floral species but they are
areas fringing open habitats and closely associated to human presence.
Zone 2c is an outgroup which distinctly differed in spider species contents.
||A dendrogram formed using cluster analysis on the spiders
found in zones 1 to 5. The scale shows numerical similarities
Berry (1972) stated that mangroves bear a fascinating
fauna whose study can be highly rewarding to the hardy naturalist, ecologist
or other scientists. According to him the fauna can be broadly divided into
aquatic and terrestrial components in which spiders are included in the terrestrial
fauna living in the mangrove trees and thus revealed a vertical zonation of
the fauna from those in the soil up to those in the higher parts of the trees.
Berry (1972) stated the presence of Oecophylla smaragdina above 9.5
feet but with no mention of spiders in the vertical zonation range that was
sampled. Sasekumar (1974) briefly mentioned (no named
species) the availability of the mangrove spiders which he categorized them
as the tree fauna confined to the vegetation.
Liow (2000) highlighted the invertebrates being the
least known in the mangroves, thus giving rise to potentially new findings.
Here, four new records of spiders are reported for Peninsular Malaysia although
it is difficult to conclude whether these species are confined exclusively to
the mangroves due to sparse of data from previous local work or reports. The
extensive leafy canopy of the mangrove forests provide a cool, stable and shaded
environment subjected to great humidity for faunal colonization (Sasekumar,
1974; Ross and Underwood, 1997). This is supported
by Macnae (1968), who reported that mangroves are infested
with mosquitoes and midges (often mistaken for sandflies), bees visited mangrove
flowers, termites invaded dead wood together with cockroaches and beetles while
canopy dwellers such as ants, spiders with fireflies twilight aggregations.
The canopy provided shelter for spider retreat which otherwise would expose
them to greater risk of desiccation. Berry (1972) reported,
other than insects, organisms on trunks of trees were abundant from the surface
of the mud to 40 cm upwards with oysters, barnacles, limpets and grazing littorinid
snails on mangrove trunks.
The composition and properties of mangrove flora may affect the distribution
and abundance of spiders analogous to faunal zonation with possible dependent
variables such as, increasing distance from the seaward edge of the forest,
height above low tidal level, orientation of the substratum and biotic interactions
such as competition or predatory relationships. Macnae (1968)
stated that mangroves are limited to a few dominant groups, here the jumping
spiders, Salticidae are predominant and widespread throughout all zones, this
is incontrast to work reported by Macintosh and Ashton (2002),
who found abundance of web building spiders and Koh (1991)
discovered one new species, Argiope mangal (Family: Araneae) in Singapore
mangroves. The success of jumping spiders can be attributed to their known predatory
habits, aggressively stalking for wide ranging prey and the unrestricted foraging
strategies from canopy to the exposed ground when tide levels are low. This
kind of active hunting for prey is in concordance to the wolf spiders, Pardosa
known to adapt as semi aquatic life form and exploiting the juveniles of fiddler
crab as food resources (Macintosh and Ashton, 2002). In
other animals, Maza and Soberon (1998) revealed that
the multi taxonomic groups of butterflies species having distinct morphological
and ethological features are consistently associated with certain habitats.
Sasekumar (1974) described the distribution of macrofauna
and recognized their zonation in distribution. According to Macnae
(1968), the widest zones in the mangroves are the forested areas of Bruguiera
which are separated from the sea by Avicennia or Sonneratia fringes.
Here, the physical environment is potentially less severe due to the canopy
of the trees with extensive root growths and restricted movement of water (Ross
and Underwood, 1997). Such conditions provided suitable living quarters
for animals to thrive as shown in this study, where, maximum spider densities
are found in the middle zones of mixed forests (zones 2b and c). In contrast,
the open zone closest to the seaward edge (zone 5) appeared as rather a harsh
environment, too poor in fauna or flora to be of interest (Berry,
1972), here shown, able to support a minimum spider community especially
the more hardy species of salticids, lynx, long jawed and nursery web spiders.
Thus, there exist clear spatial patterns of spiders in the mangrove forests.
Understanding the dynamics and components of mangrove ecosystem is crucial from
many points of view especially now when national development is depleting and
encroaching into this fragile environment. Lim (2007)
quoted it takes more than good intentions to put the groove back into mangroves.
One likely response to this would be more data needed, more actions wanted and
only then more mangroves saved.
We wish to thank all involved that has made this study possible. The
first author wishes to acknowledge University of Malaya for financial
aid and National University of Singapore for sabbatical attachment and
especially staffs of RMBR and members of the Spider Laboratory for help,
support and many memories to treasure.
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