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A Comparison of Brachyuran Crab Community Structure at Four Mangrove Locations under Different Management Systems along the Melaka Straits-Andaman Sea Coast of Malaysia and Thailand

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Brachyuran crab community structure was compared between mangrove sites under different management systems from four locations along the Melaka Straits-Andaman Sea Coast. Klong Ngao, a mangrove estuary in Ranong Province of southern Thailand, lies within a Biosphere Reserve designated in 1997. Sites were positioned in plantations at a former charcoal concession forest, a disused tin mine, and an abandoned shrimp pond along this estuary. The Merbok estuary in Kedah, Malaysia, is partially managed: the mangroves are cut for charcoal and poles on a small scale and the forests are left to regenerate naturally. The Matang Mangrove Forest Reserve in Perak, Malaysia, is heavily exploited but well managed, forRhizophora wood to produce charcoal, and has been for 100 years. Sites were positioned in plantations of different ages. Kuala Selangor Nature Park, Selangor, Malaysia, was established as a nature reserve in 1987 and contains mature mangrove forest regenerating naturally from previous selective felling. At Klong Ngao and Matang, mature reserve forest sites were also studied for comparison with plantation sites. The sites included both upstream and downstream locations and were of similar area, minimizing effects from possible species-area relationships. Sites were chosen with similar environmental conditions and with a dominance ofRhizophora spp. At each site per location, the brachyuran crabs were sampled quantitatively in 100 m2 quadrats by three independent 15-min timed crab catches. The crab community recorded was analyzed by univariate and multivariate statistical techniques. Management history plays an important role in moderating the crab community structure. The crab community also changes with the age of the mangrove forest stand. Sesarmid crabs consistently dominated in mature forests, whereas young plantations were colonized mainly by ocypodid crabs. The findings show that heavily effected sites—e.g., disused tin mining areas, former concession forests, and abandoned shrimp ponds—can be rehabilitated by planting mangroves and that the crab community is a useful ecological indicator of habitat status.
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1461Q2003 Estuarine Research Federation
Estuaries Vol. 26, No. 6, p. 1461–1471 December 2003
A Comparison of Brachyuran Crab Community Structure at Four
Mangrove Locations under Different Management Systems along
the Melaka Straits-Andaman Sea Coast of Malaysia and Thailand
E
LIZABETH
C. A
SHTON
1,
,
*, P
ETER
J. H
OGARTH
2
, and D
ONALD
J. M
ACINTOSH
1
1
Centre for Tropical Ecosystems Research, Department of Ecology and Genetics, Building 540, Ny
Munkegade, University of Aarhus, 8000 C, Denmark
2
Department of Biology, P. O. Box 373, University of York, York YO1 5DD, United Kingdom
ABSTRACT: Brachyuran crab community structure was compared between mangrove sites under different management
systems from four locations along the Melaka Straits-Andaman Sea Coast. Klong Ngao, a mangrove estuary in Ranong
Province of southern Thailand, lies within a Biosphere Reserve designated in 1997. Sites were positioned in plantations
at a former charcoal concession forest, a disused tin mine, and an abandoned shrimp pond along this estuary. The
Merbok estuary in Kedah, Malaysia, is partially managed: the mangroves are cut for charcoal and poles on a small scale
and the forests are left to regenerate naturally. The Matang Mangrove Forest Reserve in Perak, Malaysia, is heavily
exploited but well managed, for Rhizophora wood to produce charcoal, and has been for 100 years. Sites were positioned
in plantations of different ages. Kuala Selangor Nature Park, Selangor, Malaysia, was established as a nature reserve in
1987 and contains mature mangrove forest regenerating naturally from previous selective felling. At Klong Ngao and
Matang, mature reserve forest sites were also studied for comparison with plantation sites. The sites included both
upstream and downstream locations and were of similar area, minimizing effects from possible species-arearelationships.
Sites were chosen with similar environmental conditions and with a dominance of Rhizophora spp. At each site per
location, the brachyuran crabs were sampled quantitatively in 100 m
2
quadrats by three independent 15-min timed crab
catches. The crab community recorded was analyzed by univariate and multivariate statistical techniques. Management
history plays an important role in moderating the crab community structure. The crab community also changes with the
age of the mangrove forest stand. Sesarmid crabs consistently dominated in mature forests, whereas young plantations
were colonized mainly by ocypodid crabs. The findings show that heavily effected sites—e.g., disused tin mining areas,
former concession forests, and abandoned shrimp ponds—can be rehabilitated by planting mangroves and that the crab
community is a useful ecological indicator of habitat status.
Introduction
Large areas of mangrove forest in Southeast Asia
have been destroyed or degraded over the past few
decades. Thailand’s Andaman Sea coast lost
142,200 ha between 1961–1989 (Aksornkoae et al.
1993) and Peninsular Malaysia lost 18,700 ha be-
tween 1980–1990 (Chan et al. 1993). The major
reasons for mangrove loss are population growth,
conversion to aquaculture, agriculture, and coastal
urban and industrial development (Clough 1993;
Ong 1995; Field 1996; Macintosh 1996). The scale
of mangrove loss in Thailand up to 1986 was 64%
(110,300 ha) due to the conversion to shrimp
ponds and 26% (45,200 ha) due to coastal devel-
opments; other activities included salt ponds (6%)
and tin mining (3%) (Aksornkoae et al. 1993).
* Corresponding author; tele:
1
45 8942 3341; fax:
1
45 8942
3350
† Current address: Institute of Aquaculture, University of Stir-
ling, Stirling FK9 4LA, Scotland, UK. tele:
1
44 1786 467885;
fax:
1
44 1786 472133; e-mail: e.c.ashton@stir.ac.uk
Large areas have also been selectively cut for char-
coal, firewood, poles, and construction materials.
Poor shrimp farming practices, disease epidem-
ics, and acid sulphate soils have led to many ponds
being unproductive and left disused or abandoned
(Macintosh 1996; Stevenson 1997). Salt ponds and
tin mining areas have also been abandoned, cre-
ating large areas of degraded land. Concern about
the loss of mangroves and increased awareness of
the ecological, environmental, and socio-economic
values of mangrove ecosystems—for example, in
protection against coastal erosion (Pearce 1996)
and as feeding and nursery grounds for commer-
cial fish and shellfish species (Chong et al. 1990)—
has led to rehabilitation and restoration projects
(Field 1996).
Field (1996; p. 17) defines restoration of an eco-
system as ‘‘The act of bringing an ecosystem back
into, as nearly as possible, its original condition,
renewing it or bringing it back into use.’’ Rehabil-
itation on the other hand is a more general term
to denote any activity, including restoration and
1462 E. C. Ashton et al.
habitat creation, which converts a degraded system
to a stable alternative (Stevenson et al. 1999). Man-
grove forests can be managed for a variety of rea-
sons; for example, commercial production of char-
coal, coastal protection, or as bird sanctuaries, na-
ture parks, or other reserves for the conser vation
of habitat and wildlife.
The success and failure of rehabilitation, resto-
ration, and management projects are often not re-
corded (Field 1996; Stevenson et al. 1999), but
such information would help guide the planning
and implementation of future conservation efforts.
Success depends on the objectives of management,
but it could be defined as reconstitution of the pre-
vious state (this however is often unrecorded), or
it could be defined as maintaining a sustainable
functioning ecosystem. Assessing success is subjec-
tive, but ecological indicators of habitat status that
can easily be measured would be a useful tool to
help managers record the effect of management
interventions in mangrove forest ecosystems.
Brachyuran crabs are abundant and diverse con-
stituents of mangrove forests ( Jones 1984). They
play an important role in the ecological function-
ing of the mangrove ecosystem (Lee 1998),
through litter turnover (Robertson 1986), seed
predation (Smith 1987), and bioturbation of the
soil (Smith et al. 1991), and also provide an im-
portant food source for coastal fisheries (Macin-
tosh 1984). For these reasons Smith et al. (1991)
suggested grapsid crabs as possible keystone spe-
cies. Mangrove crabs are also affected by physical
and biotic factors (e.g., Macintosh 1988; Hogarth
1999; Lee 1999; Ashton et al. 2003). The objectives
of this study were to describe and compare the bio-
diversity and community structure of brachyuran
crabs at mangrove forest sites with different man-
agement histories and regimes; and to determine
whether brachyuran crabs can be used as indica-
tors of mangrove habitat status.
Materials and Methods
S
TUDY
A
REA
The four study locations in Southeast Asia were
Klong Ngao (9
8
5
9
N, 98
8
3
9
E) in southern Thailand,
and Merbok (5
8
30
9
N,100
8
25
9
E), Matang (4
8
50
9
N,
100
8
37
9
E), and Kuala Selangor (3
8
20
9
N, 101
8
15
9
E)
in Peninsular Malaysia. These locations lie along
the Andaman Sea and Melaka (
5
Malacca) Straits
coastline of the Thai-Malay Peninsular.
The four locations are under different manage-
ment systems. Klong Ngao forms part of a 30,000
ha Biosphere Reserve established in 1997 for con-
servation and sustainable use of its mangrove for-
ests. The reserve is managed using a zoning system
involving three zones differing in the level of pro-
tection they provide. The core zones contain a to-
tally protected forest (5,970 ha); buffer zones sur-
round the core zones and include areas converted
previously for tin mining and more recently for
shrimp farming (5,288 ha); while transition zones
include areas converted into roads, agriculture
plantations, and residential areas (Thulstrup
1998). Degraded areas are replanted using seed-
lings reared in nurseries. The Merbok mangrove
forests (5,400 ha) were designated as a forest re-
serve in 1951 and are under the jurisdiction of the
Kedah State Forest Department (Ong et al. 1980;
Wetlands International 1996). They are partially
managed; they are cut for charcoal and poles on a
low scale and the forests are left to regenerate nat-
urally. The Matang Mangrove Forest Reserve
(40,200 ha) borders the Selinsing River in Perak
and is heavily used but well managed for Rhizophora
timber to produce charcoal, and has been for 100
yr. The forest is managed on a 30-yr rotation cycle
with thinnings at 15 and 20 yr. About 1,000 ha are
clear felled annually in areas of a few ha. A 3-m
buffer zone is left along the riverbank to prevent
erosion (Gan 1995). Natural regeneration is assist-
ed where necessary by planting seedlings reared in
nurseries. The Kuala Selangor Nature Park bor-
dering the southeast shore of the Selangor River
estuary was established as a nature reserve in 1987
and the mangrove forest of about 300 ha has not
been logged since then, except to provide access
via walkways. It consists of primary forest near the
foreshore and secondary forest inland with natural
regeneration (Chan et al. 1993).
In all four locations the climate is hot and hu-
mid with high rainfall. The rainfall patterns are
similar with a Southwest monsoon from April to
October and a Northeast monsoon from October
to February. Ranong Province is the wettest place
in Thailand with an annual rainfall of 4,200 mm at
Ranong City (Ranong Provincial Meteorological
Station unpublished data), although this measure-
ment is taken 10 km from the coast and at Klong
Ngao the rainfall is lower. The locations in Penin-
sular Malaysia have lower annual rainfall (about
2,000 mm) but Taiping 10 km inland from Matang
is the wettest place in Peninsular Malaysia with an
annual rainfall of 4,092 mm (Saad unpublished
data). The highest astronomical tides are greatest
for Kuala Selangor and Klong Ngao at 5.4 and 4.4
m, respectively, with those at Merbok (3.3 m) and
Matang (2.7 m) lower but similar. Merbok was
studied July–December 1995, Matang was studied
August–December 1997, Kuala Selangor was stud-
ied June 20–July 12, 1999, and Klong Ngao July 15–
August 3, 1999. The four mangrove locations cover
considerably different total areas, with Kuala Selan-
gor having the lowest area at 300 ha and Matang
Crabs as Indicators of Mangrove Management 1463
the highest at 40,200 ha. Sites of similar area were
selected in order to minimize possible species-area
relationships.
As far as possible, the sites selected also featured
similar environmental conditions and dominance
of Rhizophora trees, but with different management
histories (Table 1). In Klong Ngao (KN) the sites
were a 10-yr-old Rhizophora mucronata Lamk. 1804
plantation on a disused tin mine site (KNTin), 5-
yr-old Rhizophora apiculata BL. 1827 (KNCRa) and
R. mucronata (KNCRm) plantations on an area pre-
viously designated as a concession area for timber
extraction for charcoal production and a seven
year old mixed Rhizophora spp. plantation in an
abandoned shrimp pond (KNSh). More details of
the Klong Ngao sites are provided in Macintosh et
al. (2002). In Merbok (MB) Rhizophora zonation
was observed and sites were used from a tributary
upstream called Sungai Pasir (MBSP) and then
downstream the Merbok estuary at Upper Merbok
(MBUM), Middle Merbok (MBMM) and Lower
Merbok (MBLM) (Ashton 2002). The sites had a
few large mature trees (
.
40-yr old). In Matang
(MT) a young (7–10 yr old) and mature plantation
(30-yr old) were sampled upstream (U) and down-
stream (L) of the Selinsing river. In Kuala Selangor
(KS) a Rhizophora zone was sampled upstream
(KSR) and downstream (KSS). The seaward site
was adjacent to an old collapsed walkway. In both
Klong Ngao and Matang a mixed mature reserve
forest site was also chosen as a reference site for
the plantations and to assess the extent of regional
differences in the fauna (KNRes and MTRes, re-
spectively).
D
ATA
C
OLLECTION
A 100 m
2
vegetation quadrat was sampled at
each site. Within each quadrat the number of man-
grove tree and sapling species and the number of
indiv within each species was determined (Tomlin-
son 1986). The circumference at breast height of
each individual was recorded and from this the
cross-sectional area, or basal area (BA), was calcu-
lated (English et al. 1994).
Replicate measurements (n
5
3 to 10) of envi-
ronmental variables were made in each vegetation
quadrat. The number of senescent and decaying
leaves was recorded from ten 1-m
2
quadrats. Soil
pore water salinity was recorded using a refractom-
eter, soil temperature recorded using a thermom-
eter, and tidal inundation regime recorded using
the method of English et al. (1994).
Crabs were sampled quantitatively by conducting
three independent time-based collections in every
100 m
2
vegetation quadrat. The crabs were sam-
pled at low (spring and neap) tide, with the as-
sumption that brachyuran crab faunas do not
change significantly over this time scale (Ashton et
al. 2003). The method devised by Ashton (1999)
was found to provide a good representative sample
of the crustacean population present at the site.
Crab catch per unit effort was one 15 min catch
per person. The area covered in each 15 min
timed period was approximately one-third of the
100 m
2
quadrat. As many crabs and types of species
were caught as possible; this was best done by hand
using a trowel and a plastic beaker. To reduce bias
towards common or slow-moving crabs, more time
and effort was allocated to catching the less com-
mon or elusive species. The crabs were put into
labelled resealable plastic bags and carefully trans-
ported back to the laboratory. The crabs were put
in the freezer to sedate them before they were de-
scribed and then preserved in 4% formalin for lat-
er species identification.
D
ATA
A
NALYSIS
The vegetation univariate data calculated for
each site using the species abundance data were
total number of species present, Shannon-Wiener
diversity index, and the Simpson’s dominance in-
dex. The environmental data were tested for sig-
nificant differences between the sites using a one-
way analysis of variance (ANOVA) followed by a
Tukey-Kramer multiple comparison test, where ap-
propriate. If the data could not be transformed to
normality a non-parametric Kruskal-Wallis test was
used. The environmental variables were correlated
using the Spearman rank correlation.
Crabs were described using the univariate mea-
sures of abundance, number of species, Margalef’s
species richness, Shannon-Wiener diversity index
calculated using log
e
, and Pielou’s evenness.
Where necessary, univariate measures were trans-
formed using log or log
1
1 to normality and dif-
ferences between sites was tested using a one-way
ANOVA, followed by a Tukey-Kramer post hoc test.
A lower triangular similarity matrix was construct-
ed using the Bray-Curtis similarity coefficient on
non-standardised, square-root transformed crusta-
cean data. Formal significance tests for differences
between sites were performed using the one-way
ANOSIM permutation test on the crab similarity
matrix (Clarke and Green 1988; Clarke 1993). The
crab species contributing to dissimilarities between
the sites were investigated using the similarities
procedure (SIMPER) (Clarke 1993). PRIMER
(Plymouth Routines In Multivariate Ecological Re-
search) software package was used for these statis-
tical analyses (Clarke and Warwick 1994).
Relationships between the crab community
structure, the forest structure and management
and the environmental variables were assessed with
Canonical Correspondence Analysis (CCA) (Ter
1464 E. C. Ashton et al.
TABLE 1. Summary of the history, forest management, vegetation, and environmental characteristics at each site. Res
5
reserve forest; Tin
5
tin mining area; C
5
charcoal
concession area; Sh
5
shrimp pond area; SP
5
Sungai Pasir; UM
5
Upper Merbok; MM
5
Middle Merbok; LM
5
Lower Merbok; U
5
upstream; L
5
downstream; 7, 10,
30
5
age of plantation; R
5
river transect; S
5
sea transect; Ra
5
Rhizophora apiculata;Rm
5
R. mucronata.
1
indicates
x
2
value.
Site History Planting Age in
years
Percentage
of
Rhizophora
Basal
Area
(cm
2
/
100 m
2
)
Density
in
100 m
2
Tree
Spe-
cies
Shan-
non
Diver-
sity
Simpson
Domin-
ance
Soil
Temperature
(
8
C)
Senescent
leaves
(no. m
2
2
)
Decaying
leaves
(no. m
2
2
)Salinity
(‰)
Tidal
inundation
(no. of
days
covered/yr)
Klong Ngao
Res Conserved back man-
grove
Natural
.
40 Ra 40 4,303 33 6 1.36 0.30 26
6
0.35 5.2
6
3.5 7.6
6
11 9
6
0 295
6
28
Tin Tin mining area until
1985
Man in 1989 10 Rm 68 812 22 4 0.93 0.51 28
6
0.35 1.0
6
0.94 1.0
6
0.94 20
6
0.58 365
6
0
CRa Charcoal concession
area until 1994
Man in 1994 5 Ra 100 259 44 1 0 1 27
6
0.50 4.5
6
2.9 7.4
6
4.7 20
6
13 334
6
10
CRm Charcoal concession
area until 1994
Man in 1994 5 Rm 96 Ra 4 195 23 2 0.18 0.92 27
6
0 2.4
6
3.0 1.5
6
1.9 23
6
2.8 323
6
7.0
Sh Shrimp pond until
1988
Man in 1992 7 Rm 52 Ra 44 1,394 133 6 0.87 0.47 27
6
0 6.8
6
3.0 37
6
14 25
6
0.71 305
6
6.8
Merbok
SP Charcoal concession
low scale
Natural
.
50 Ra 67 Rm 33 4,652 17 2 0.68 0.52 26
6
0.76 1.6
6
012
6
020
6
0.52 343
6
37
UM Charcoal concession
low scale
Natural
.
50 Ra 33 Rm 67 4,431 12 2 0.64 0.56 28
6
0.42 2.4
6
035
6
019
6
1.5 361
6
2.5
MM Charcoal concession
low scale
Natural
.
50 Ra 73 3,019 22 3 0.78 0.57 28
6
0.17 1.1
6
057
6
020
6
1.6 254
6
70
LM Charcoal concession
low scale
Natural
.
50 Ra 91 3,360 22 3 0.37 0.83 25
6
0.15 20
6
066
6
020
6
2.4 246
6
18
Matang
Res Conserved forest Natural
.
90 Ra 34 Rm 7 8,234 44 3 0.86 0.47 26
6
0.14 14
6
5.7 114
6
41 20
6
1.4 43
6
16
U7 Charcoal concession
large scale for 100 yr
Natural
1
Man
7 Rm 73 Ra 27 2,018 205 2 0.59 0.60 27
6
0.25 5.8
6
2.6 46
6
36 12
6
0.58 153
6
48
U30 Charcoal concession
large scale for 100 yr
Natural
1
Man
30 Ra 94 Rm 3 3,960 32 3 0.28 0.88 27
6
013
6
11 77
6
60 11
6
0.63 129
6
27
L10 Charcoal concession
large scale for 100 yr
Natural
1
Man
10 Ra 99 Rm 1 2,622 104 2 0.05 0.98 26
6
0.17 8.3
6
3.9 128
6
63 17
6
2.2 2
6
0
L30 Charcoal concession
large scale for 100 yr
Natural
1
Man
30 Ra 79 Rm 11 4,388 19 3 0.66 0.65 26
6
0.21 8.0
6
6.5 29
6
17 16
6
2.1 19
6
7.0
Kuala Selangor
R Protected since 1987 Natural
.
40 Rm 26 Ra 16 2,575 61 4 1.36 0.26 28
6
0.50 12
6
6.6 87
6
33 34
6
2.7 311
6
0
S Protected since 1987 Natural
.
40 Ra 28 2,131 114 4 1.09 0.4 26
6
014
6
6.6 93
6
22 27
6
3.5 311
6
0
F value
1
p value
145.94
1
,
0.001
112.24
,
0.001
13.17
,
0.001
44.73
,
0.001
142.29
1
,
0.001
Crabs as Indicators of Mangrove Management 1465
Braak 1986), using the software package Multi-Var-
iate Statistic Package (MVSP), ver. 3.1 (Kovach
1998). The CCA ordination technique uses trends
in crab species similarity to produce a matrix,
which is shown for each site as points on a biplot.
The sites are also related to ordinations of collect-
ed environmental, vegetation, and management
parameters that are plotted as additional axes in
the direction of the trend defined by the parame-
ter concerned.
Results
V
EGETATION
Table 1 gives a summary of the forest manage-
ment and vegetation characteristics at each of the
study sites. The exact ages of the plantations in
Klong Ngao and Matang are known and at both
localities the mangrove trees in each site are simi-
lar in age. The mangroves in the other sites studied
included trees of different age classes and their age
could only be estimated from past records. The
Matang reserve site is known to be the oldest pro-
tected site but some of the trees at Merbok and
Kuala Selangor may be of a similar age. The basal
area of the trees followed the same pattern as the
age of the stands with the Matang Reserve Forest
having the greatest values followed by the Merbok
sites, the Klong Ngao Reserve site and the 30-yr-
old plantations in Matang. The Kuala Selangor
sites had lower basal areas than expected for their
age, probably reflecting the effects of selective tree-
felling that seems to be on-going even though it is
now illegal.
In the study sites the number of mangrove tree
species was low and dominance of Rhizophora spp.
high. The Klong Ngao Reser ve forest and the Kua-
la Selangor River transect had the highest tree di-
versity and lowest dominance. The lowest tree di-
versity and highest dominance was found at
KNCRa because the site was 100% R. apiculata. The
Kuala Selangor Sea transect had the lowest Rhizo-
phora dominance (28%).
The stem density was greater in the young plan-
tations, as expected, since the trees were younger
and therefore more dense but smaller in average
size. Mangrove seedlings are planted in Matang at
1.2 m intervals, but there is also natural regener-
ation (Gan 1995). At the Klong Ngao shrimp pond
seedlings were planted by students sometimes as
close at 0.1 m
3
0.1 m (Macintosh et al. 2002).
The Klong Ngao charcoal concession and tin min-
ing sites were planted at 0.5 m
3
0.5 m intervals
but problems with weeds in the former site (Mac-
intosh et al. 2002) and in the latter deep tidal in-
undation (Macintosh personal observation) and
poor soil properties (Komiyama et al. 1996), re-
sulted in a lower survival rate and density. The Kua-
la Selangor Sea transect also has a high stem den-
sity because of the large number of saplings that
have established near the disused walkway. The
other, older sites have low densities, because of nat-
ural thinning, or thinning in the course of forest
management.
E
NVIRONMENT
Mean values for the environmental variables
measured are shown in Table 1. All the environ-
mental variables were significantly different be-
tween the sites (p
,
0.001) and many of them were
correlated. Soil temperature ranged from 25
8
Cat
the Lower Merbok site to 28
8
C at the Klong Ngao
tin mining site. Soil temperature was negatively
correlated with the number of senescent and de-
caying leaves (
r
s
52
0.37, p
,
0.001, and
r
s
5
2
0.24, p
,
0.01, respectively). The Klong Ngao tin
mining site had the least leaf litter both of senes-
cent and decaying leaves at 1 m
2
2
. The highest
number of senescent leaves were recorded from
the Lower Merbok and Matang Reserve sites and
the highest number of decaying leaves were re-
corded from the Matang downstream 10-yr-old site
and the Matang Reserve site. The numbers of se-
nescent and decaying leaves were highly correlated
(
r
s
5
0.57, p
,
0.001). The low salinities recorded
at the KNRes site and the Matang upstream plan-
tations were due to the presence of a stream which
received a large influx of freshwater during the
sampling period. Salinity was positively correlated
with tidal inundation (
r
s
5
0.41, p
,
0.001). The
number of days the sites were tidally covered each
year was significantly lower at the Matang sites. The
most exposed site was MTL10, which was sub-
merged only during extreme high tides. In con-
trast, the low-lying former tin mining plantation
was covered by every high tide. Tidal inundation
was also positively correlated with soil temperature
(
r
s
5
0.37, p
,
0.001) and negatively correlated
with the number of senescent (
r
s
52
040, p
,
0.001) and decaying leaves (
r
s
52
0.55, p
,
0.001).
C
RABS
Thirty-one brachyuran crab species were record-
ed from the study sites. This included 18 grapsid
species, 11 ocypodid species, and 2 pilumnid spe-
cies. Nine species were recorded from only one
site, 7 of which were only from Klong Ngao in
Thailand. No species were recorded from all the
sites, but Clistocoeloma merguiense De Man 1888 and
Sesarma (Perisesarma) onychophorum (De Man 1895)
were widely distributed, being recorded from all 4
locations and from 14 of the 16 sites.
The sites differed significantly in total crab abun-
1466 E. C. Ashton et al.
TABLE 2. Mean univariate measures
6
SD of crabs caught per person in 15 min for each of the study sites and results from one
way ANOVA between sites. Site abbreviations as in Table 1.
Abundance Species Richness Diversity Evenness
Klong Ngao
Res
Tin
CRa
CRm
Sh
15
6
4.0
41
6
12
46
6
20
52
6
27
22
6
13
5.3
6
1.5
3.7
6
1.2
6.3
6
2.9
7.0
6
1.0
4.3
6
0.58
1.6
6
0.41
0.71
6
0.25
1.5
6
0.90
1.6
6
0.39
1.2
6
0.30
1.4
6
0.33
0.38
6
0.0
1.1
6
0.82
1.5
6
0.22
0.99
6
0.16
0.83
6
0.00
0.30
6
0.00
0.55
6
0.34
0.76
6
0.11
0.69
6
0.16
Merbok
SP
UM
MM
LM
5.0
6
1.7
8.0
6
6.1
10
6
3.2
10
6
3.2
2.3
6
1.5
5.0
6
3.6
5.7
6
1.5
3.0
6
1.7
0.74
6
0.85
1.8
6
1.1
2.0
6
0.48
0.86
6
0.76
0.66
6
0.67
1.3
6
0.78
1.5
6
0.41
0.75
6
0.65
0.94
6
0.00
0.91
6
0.00
0.89
6
0.10
0.81
6
0.00
Matang
Res
U7
U30
L10
L30
5.3
6
3.2
5.7
6
2.5
7.7
6
0.58
8.0
6
1.7
21
6
3.2
2.3
6
1.2
3.0
6
0.0
2.0
6
1.0
2.7
6
0.58
4.7
6
1.2
0.91
6
0.91
1.3
6
0.46
0.48
6
0.48
0.80
6
0.26
1.2
6
0.43
0.65
6
0.58
1.0
6
0.0
0.49
6
0.45
0.67
6
0.22
1.1
6
0.47
0.89
6
0.16
0.94
6
0.00
0.82
6
0.00
0.68
6
0.00
0.68
6
0.19
Kuala Selangor
R
S
7.3
6
2.5
7.7
6
1.2
3.3
6
0.58
4.3
6
0.58
1.2
6
0.14
1.7
6
0.36
1.2
6
0.14
2.3
6
0.23
0.96
6
0.00
0.87
6
0.00
F value
p value
9.38
,
0.001
2.74
,
0.01
1.66
0.11
1.85
0.07
4.79
,
0.001
dance, species number, and evenness (Table 2).
The Klong Ngao plantations KNTin, KNCRa, and
KNCRm had the highest crab abundances. The
KNCRm plantation supported a significantly high-
er number of crab species than MTU30, and
KNTin had significantly lower evenness than all the
other sites. One-way ANOSIM results between the
study sites for the brachyuran community similarity
matrix also show that the Klong Ngao tin mining
site and shrimp pond site plantations contained
brachyuran crab communities significantly differ-
ent in structure to those in all the other sites. The
two charcoal plantation sites at Klong Ngao were
not significantly different from each other, but
were from all the other sites.
Similarities percentages analyses of square-root
transformed brachyuran crab abundance data re-
vealed that the sites at Matang had the highest sim-
ilarity (50%) and the sites at Klong Ngao the lowest
(27%). The plantations had the highest crab com-
munity structure similarity—for example MTL30
(68%), KNTin (67%), and KNSh (64%)—and the
naturally regenerated sites the lowest—for exam-
ple, MBSP (16%) and KNRes (26%). The discrim-
inating species that contributed to 60% dissimilar-
ity between all pairwise plot combinations are
shown in Table 3; there are 20 species in total. The
discriminating species for each site have been not-
ed. The crab community in the former tin mining
site in Klong Ngao was more than 90% dissimilar
to all the other sites. It is discriminated by the high
abundance of Metaplax elegans DeMan 1988 and
the presence of Tylodiplax tetralyphora De Man
1895, found only at this site. The Klong Ngao char-
coal sites are discriminated by the high abundance
of Uca triangularis (A. Milne Edwards 1873) and
Uca rosea (Tweedie 1937), whereas the other sites
were predominantly grapsid crabs. Klong Ngao re-
serve site was discriminated by high abundances of
C. merguiense and Sesarma lenzii (De Man 1894) and
low abundances of a number of sesarmid species.
The brachyuran crabs were divided into grapsids
and ocypodids. Figure 1 shows the grapsid and ocy-
podid crab abundances between the study sites.
There was a significantly greater (F
5
10.6, p
,
0.001) number of grapsid crabs at the Klong Ngao
tin mining plantation than at the other sites. This
was because of the dominance of M. elegans. Ocy-
podid crab abundance was also significantly differ-
ent between the study sites, with sites KNCRa and
KNCRm having higher densities than the other
sites (F
5
7.7, p
,
0.001). There were no signifi-
cant differences in the number of grapsid species
between the study sites, but the number of ocy-
podid species was significantly different (F
5
6.1,
p
,
0.001), with the highest recorded from KNCRa
and KNCRm (Fig. 1).
The abundance of grapsid and ocypodid crabs
are plotted against tidal level (computed as the
number of days per year each site is tidally inun-
dated). Figure 2 shows that both the abundance of
grapsid and ocypodid crabs was not related to tidal
Crabs as Indicators of Mangrove Management 1467
Fig. 1. Mean number of grapsid and ocypodid crabs caught
per person in 15 min collecting periods in each study site
6
SE.
KN
5
Klong Ngao; MB
5
Merbok; MT
5
Matang; KS
5
Kuala
Selangor; Res
5
reserve forest; Tin
5
tin mining area; C
5
charcoal concession area; Sh
5
shrimp pond area; SP
5
Sungai
Pasir; UM
5
Upper Merbok; MM
5
Middle Merbok; LM
5
Lower Merbok; U
5
upstream; L
5
downstream; 7, 10, 30
5
age of plantation; R
5
river transect; S
5
sea transect; Ra
5
Rhizophora apiculata;Rm
5
R. mucronata. a) abundance and b)
species.
Fig. 2. Mean number of grapsid and ocypodid crabs caught
per person in 15 min for each site against the tidal inundation
(number of days covered by tide each year). a) abundance and
b) species.
Fig. 3. Biplot illustrating the relative position of each site
and the brachyuran crab community structure with the environ-
mental and forest management characteristics. Site abbrevia-
tions are: A
5
KNRes, B
5
KNTin, C
5
KNCRa, D
5
KNCRm,
E
5
KNSh, F
5
MBSP, G
5
MBUM, H
5
MBMM, I
5
MBLM,
J
5
MTRes, K
5
MTU7, L
5
MTU30, M
5
MTL10, N
5
MTL30,
O
5
KSR, P
5
KSS.
level. The same pattern was obtained for the num-
ber of species present.
Figure 3 shows the canonical correspondence
analysis biplot of the brachyuran crab species
abundance for each site as the points in relation
to the environmental and forest management char-
acteristics plotted as arrows. Tidal cover varies in-
versely with the number of senescent leaves along
axis 1, while on axis 2 soil temperature, tree diver-
sity, tree age, and tree basal area vary in the op-
posite direction to tree dominance. The Klong
Ngao tin mining site clearly separates out from the
other sites in the direction of high soil tempera-
tures. The Klong Ngao reserve site and charcoal
concession sites show a relationship with tree dom-
inance and tidal cover. The other sites are clus-
1468 E. C. Ashton et al.
TABLE 3. Summary of crustacean average abundances (mean number of individuals caught in 15 min per 100 m
2
) between the sites.
15
1–3 crabs caught in 15 min,
11
5
4–10 crabs caught in 15 min,
111 $
11 crabs caught in 15 min. Species in bold are good discriminating species for that site.
Crab species
Klong Ngao
Res Tin CRa CRm Sh
Merbok
SP UM MM LM Res
Matang
U7 U30 L10 L30
Kuala
Selangor
RS
Clistocoeloma merguiense
Episesarma versicolor
Metaplax elegans
Metaplax sheni
Sesarma (Perisesarma)darwinensis
Sesarma (Perisesarma)eumolpe
111
1
1
11
1
111
11
1
1
11
1
1
11
11
1
11
1
11
11
11
11
1
111 11
1
11
11
1
111
1
1
111
11
11
111
1
11
1
1
1
Sesarma (Perisesarma)
onychophorum
Sesarma (Perisesarma) sp. 1
Sesarma (Perisesarma)lenzii
1
11
1
11
11
11
111 11
1
1
1
1
11 111 1111
Sesarma (Parasesarma) sp. 1
Sesarma (Parasesarma) sp. 2
Sesarmoides krausii
Ilyoplax punctata
11
11
1
1
1
1
1
1
1
1
1
1
Paracleistostoma depressum
Paracleistostoma longimana
Uca lactea
Uca rosea
Uca sp.
Uca triangularis
Tylodiplax tetralyphora
1
1
11
11
11
111
111
111
111
1
111
1
1
1
11
11
1
111
11
1
1
11
1
11
tered together and correlated with tree age, tree
basal area, and tree diversity.
Discussion
This study demonstrates that the brachyuran
crab fauna reflects habitat status when natural
mangrove forests and plantation forests are com-
pared, although it is difficult to clearly separate
natural (environmental) differences between sites
with management-induced ones. Within the con-
straints and limitations of the sampling, two aspects
of management appear to affect the brachyuran
crab community structure most strongly: the pre-
vious history of the site and the age of the forest
stand.
Biogeographical and regional influences on the
faunal assemblages studied are minimised because
the locations are on similar latitudes (3
8
to 9
8
) and
longitudes (98
8
to 101
8
). The mature reserve sites
in Klong Ngao, Thailand, and Matang, Malaysia,
did not have similar crab species compositions (Ta-
ble 3). The sampling method employed may not
have been able to record all crab species present
because the Matang reserve site had a high stand-
ing crop of leaf litter. Assessment of the density
and diversity of burrowing crabs in mangrove hab-
itats presents formidable methodological prob-
lems. Total excavation and extraction by sieving is
generally impractical, for logistical reasons as well
as the destructive nature of the method. Visual ob-
servation and burrow counts provide at best crude
estimates of population density, even where a sin-
gle species is concerned (Macia et al. 2001; Skov
and Hartnoll 2001). Neither visual observations
nor burrow counts can readily be applied to multi-
species assessment. The time-based crab sampling
method used in this study is subject to both qual-
itative and quantitative bias, and does not aim to
provide exhaustive census information on the spe-
cies present. It does provide a rapid and practical
assessment, which if applied at different sites, en-
ables between-site comparison of multi-species
crab fauna to be made.
The low frequency of tidal inundation at Matang
may be a reason for the absence of some crab spe-
cies from this location. Mangrove crabs are well
known to show a zonation of species with shore
level ( Jones 1984; Macintosh 1988): in the present
study we found the abundance or number of crab
species was not influenced by tidal level per se (Fig.
2). The high frequency of tidal inundation and
higher soil temperatures are contributing to the
different crab community structure present at the
tin mining site in Klong Ngao, but these are also
the result of past management practices (Macin-
tosh et al. 2002).
The number of environmental factors recorded
Crabs as Indicators of Mangrove Management 1469
was limited and did not include others of possible
importance to crabs, such as soil particle size, hy-
drogen sulphide concentrations, and redox poten-
tial. Environmental measurements should be treat-
ed with caution; they only give a general indication
of conditions because they vary with the time of
day, and in relation to tidal inundation, seasons,
and weather (Ashton et al. 2003).
Tree age, tree basal area, and tree diversity were
correlated with the brachyuran crab community
structure. Brachyuran crab community structure
changes with the age of the stand. High ocypodid
crab abundance and species number dominate dis-
turbed and younger plantations, whereas large
abundances and species numbers of grapsid
crabs—in particular sesarmid crabs—dominate
mature forests once the canopy closes. Similar pat-
terns have been found elsewhere in Malaysia and
Thailand (Berry 1972; Macintosh 1984; Aksorn-
koae et al. 1993; Sasekumar and Chong 1998). Ak-
sornkoae et al. (1993) concluded that tree felling
and regeneration were responsible for much of the
observed disturbance and variation in the faunal
composition. It is probable that the textural qual-
ities of the soil change rapidly once mangrove veg-
etation becomes established, and that burrowing
crustaceans are an important element in the pro-
cess that leads to the soil becoming suitable for
other species to colonize (Berry 1972).
Relatively few mangrove species have been used
in restoration projects; species of the genus Rhizo-
phora are the most commonly used (Field 1996).
Ong (1995) commented on an apparent decline
in production at Matang and speculated that there
may be an ecological price to pay for the present
form of management because of the dominance of
Rhizophora spp. Increased habitat heterogeneity
and mangrove species diversity may support a
more diverse crab fauna. The heavily managed Ma-
tang mangroves and the previously heavily man-
aged Klong Ngao mangroves have brachyuran crab
community structures significantly different from
those of the less heavily exploited Merbok and
Kuala Selangor mangroves. Matang had the lowest
crab species number. The management has main-
tained a functioning ecosystem, perhaps at a re-
duced level of diversity. The long-term manage-
ment and consequent homogeneity of the habitat
may contribute to this low crab diversity.
Tan and Ng (1994) suggest the maintenance of
high crab species diversity is integral to the health
of the mangroves. Natural and human-induced dis-
turbances pose serious threats to the functioning
of mangrove ecosystems (Osborn and Polsenberg
1996). The reaction of natural ecosystems to dis-
turbances is often non-linear, discontinuous, deter-
mined by chance events, and therefore unpredict-
able (Holling et al. 1995). It is unknown at what
point human alteration has direct and irreversible
effects and which components are critical to sus-
tainability (Wells 1998).
Disused tin mining sites, former concession for-
ests, and abandoned shrimp ponds can become re-
colonized by a diverse and abundant crab fauna
(Macintosh et al. 2002). Macintosh (1984) record-
ed an annual total production for high densities of
U. rosea in a cleared Malaysian forest to be similar
to low densities of S. onychophorum in a mixed for-
est. The degraded areas can increase in productiv-
ity and ecological functioning with reforestation
but care must be taken because density does not
necessary reflect biomass and secondary produc-
tion (Macintosh 1984). Recolonization is possible
because crustaceans have lar val stages with good
recruitment potential into the intertidal zone
(Macintosh et al. 1991). In addition, adults can
move into new habitat from nearby mangrove sites.
Areas of mangrove near rehabilitation sites may act
as sources of recruitment; this may be important
for successful mangrove restoration. It is not clear
what factors control the crab community structure
that develops.
In 1985 before the tin mining site was replanted
there were virtually no crabs (Macintosh personal
observation). After 10 yr a crab fauna is present,
dominated by one species M. elegans. M. elegans
prefers soft silty sediment and lower shores (e.g.,
Tesch 1918; Jones 1986). The ecosystem has not
been restored to a mature condition, but replant-
ing has brought the ecosystem back into use. Fur-
ther time may change the crab community struc-
ture, or the anthropogenic effects may have made
irreversible changes preventing reversion of the
ecosystem to its original state. Aksornkoae et al.
(1993) gives examples of the environmental im-
pacts of mining on the plant and benthic com-
munity structures in Thailand. Mangrove refores-
tation was slow and seedling mortality high com-
pared to mangrove plantations in natural dis-
turbed mangrove forests. The faunal succession
was complex because species show different re-
sponses to environmental stresses, and because op-
portunistic species recolonize more quickly than
others. The benthic community appeared to have
reached equilibrium after 17 yr but with persistent
differences from the original community structure
(Aksornkoae et al. 1993).
The brachyuran crab community composition at
a site may give an indication of the habitat status.
High dominance of a species may indicate a stress-
ful environment, whereas a high diversity of grap-
sid crabs, especially sesarmids, may indicate a ma-
ture forest (Macintosh et al. 2002). Ghost crabs
have been used as a tool for rapid assessment of
1470 E. C. Ashton et al.
human impacts on exposed sandy beaches (Barros
2001). Given the environmental complexity of con-
ditions it is doubtful if one or two species could be
sufficiently sensitive to all major impacts affecting
complex ecosystems, such as mangroves, to serve
as indicator species. Monitoring changes in com-
munity structure provides an alternative and more
effective approach to assessing ecosystem health
(Cairns et al. 1993). Brachyuran crab communities
are ubiquitous throughout the region and are an
important component in mangrove food webs;
they are also good indicators of local conditions
because of their sedentary nature and reasonably
long life cycles. Changes in brachyuran crab com-
munity structure could be a useful tool for man-
agers to detect mangrove habitat status.
Past and present management practices play an
important role in moderating crab abundance, di-
versity, and composition. Further monitoring will
increase the knowledge and understanding on the
structure, dynamics, and resilience of mangrove
ecosystems. More rigorous approaches to the as-
sessment of past and current restoration efforts
must be developed (Stevenson et al. 1999) and fur-
ther research is required to understand the eco-
logical effects of disturbance to mangrove forests
and whether changes in crab community structure
with management are consistent in other locations.
A
CKNOWLEDGMENTS
This work was funded by a U.K. Darwin Initiative grant and
a British Natural Environment Research Council grant for the
Merbok and Matang studies and by DANCED (Danish Co-op-
eration in Environment and Development) under the Danish-
SE Asian Collaboration in Tropical Coastal Ecosystems Research
and Training (Denmark, Thailand, and Malaysia) project (ref-
erence number 1230324) for the Klong Ngao and Kuala Selan-
gor studies. We are very grateful to the collaborators—Dr. Ru-
pert Ormond, York University; Mr. Sopon Havanon, Head of
the Mangrove Forest Research Centre at Ranong; and Professor
Ong Jin Eong and Dr. Gong Wooi Khong at Universiti Sains
Malaysia—for their assistance with research at Merbok; Dr.
Chong Ving Ching and his team at Universiti Malaya for their
assistance at Matang; and Rasainthiran Menayah, Kuala Selan-
gor Nature Park Manager, for his assistance at Kuala Selangor.
We would also like to thank everyone else involved with this
research, including students from York University, and Thai and
Malaysian project staff and fishermen. Comments from the re-
viewers were invaluable and help from Garnet Hooper (Stirling
University, U.K.) and Thomas Nielsen (CenTER, DK) with the
CCA plot.
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Received for consideration, December 3, 2001
Revised, June 20, 2002
Accepted for publication, April 9, 2003
... While previous studies have assessed the macrofauna species composition and biomass in restored mangroves (Macintosh et al. 2002, Chen et al. 2007, Gorman and Turra 2016, only a few (e.g. Ashton et al. 2003, Ferreira et al. 2015 have compared faunal associations between restored and natural mangroves, while no study has attempted to use natural mangroves of the same age in the comparison in different intertidal zones. Such evidence is needed to examine the success of restoration efforts and convergence of macrobenthos communities in restored and natural mangroves of the same age. ...
... Here, the younger restored mangrove areas with a partially open canopy also supported the highest species diversity compared to the older restored areas. Intermediate forest stands (5-11 years), usually have higher macrobenthos abundance and diversity than mature mangroves (Ashton et al. 2003, Salmo et al. 2017, since this forest stage provides a heterogeneous environment that attracts species from open and forested areas, leading to increases in types of food resources such as feces for the macrobenthic fauna (Chen et al. 2007 ). Diverse food types, mangrove species composition, and local environmental settings, such as the presence of a freshwater channel, may account for the higher macrobenthos abundance in the oldest natural mangrove site examined here. ...
... To this end, older mangroves may provide more diverse and complex microhabitats for macrobenthos species, thereby increasing the overall diversity of the community (Gorman andTurra 2016 , Checon et al. 2023 ). They may also accumulate more organic matter and nutrients, enhancing their primary productivity, species richness, and abundance of macrobenthos (Ashton et al. 2003, Kristensen et al. 2008. As mangroves mature, they may also increase the connectivity among different mangrove patches, leading to the immigration of new species and the establishment of more diverse communities (Sheaves 2005, Friess et al. 2012. ...
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Mangrove restoration projects have become increasingly widespread to compensate for mangrove loss. Despite considerable investment in this restoration activity, post-restoration monitoring is often limited to vegetation recovery with no inclusion of faunal groups, such as macrobenthos communities, even though these groups are excellent bioindicators. Here, we used a space-for-time approach to examine whether restored mangrove macrobenthos communities are equivalent to natural mangroves of the same age (5-11 years after colonization). We focused our analyses on sediment samples collected from the lower, middle, and upper intertidal zones of restored and natural mangroves in the dry and wet seasons, along Guyana's coastline, South America. We observed an overall higher macrobenthos abundance in the natural mangroves compared to restored mangrove areas, which contrasted with higher species richness in the restored mangroves compared to natural mangroves. Nonmetric multidimensional scaling, analysis of similarities, and similarity percentage analysis revealed that macrobenthos species composition was not significantly different among the restored and natural mangrove habitats, ages, and seasons (P > .05). This suggests that the macrobenthos composition in restored mangrove areas quickly converges, after restoration activities, with communities observed in natural mangroves. Our findings indicate that, at least for biodiversity outcomes, macroinvertebrate communities occupying sediments in restored mangroves resemble natural areas rapidly post-restoration efforts.
... Given that Nahoon was an older and more established planted mangrove site compared to Tyolomnqa (Hoppe-Speer et al., 2015), we expected community structure to differ between sites with more mangrove-associated species at Nahoon. However, brachyuran community structure was similar between these two sites supporting hypothesis 2. Ashton et al. (2003) observed that grapsoid crabs (mainly sesarmids) dominated in both high abundances and diversity at mature mangrove forests, whereas ocypodid crabs (such as fiddler crabs) were found at high abundances in younger mangrove forests. We found similar patterns to Ashton et al. (2003) as the fiddler crabs T. urvillei and Paraleptuca chlorophtalmus inhabited the younger mangrove site (Tyolomnqa), while only grapsoidcrabs (mainly sesarmids) inhabited the older site (Nahoon) ( Table 1). ...
... However, brachyuran community structure was similar between these two sites supporting hypothesis 2. Ashton et al. (2003) observed that grapsoid crabs (mainly sesarmids) dominated in both high abundances and diversity at mature mangrove forests, whereas ocypodid crabs (such as fiddler crabs) were found at high abundances in younger mangrove forests. We found similar patterns to Ashton et al. (2003) as the fiddler crabs T. urvillei and Paraleptuca chlorophtalmus inhabited the younger mangrove site (Tyolomnqa), while only grapsoidcrabs (mainly sesarmids) inhabited the older site (Nahoon) ( Table 1). Other studies also found this trend in both Malaysia and Thailand (Berry, 1972;Sasekumar, 1974;Macintosh, 1984). ...
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Mangroves are expanding polewards due to global change, often encroaching into adjacent temperate saltmarshes. In both vegetated ecosystems, brachyurans are responsible for ecological processes and functions such as nutrient cycling and sediment bioturbation. South African mangroves occur at a latitudinal limit and are establishing further south due to past planting events and global change, making these ideal study systems for the effects of mangrove expansion and encroachment. Here, we investigated the effect of mangrove encroachment on brachyuran community composition at two saltmarsh sites with planted mangrove stands of different ages. Transects were laid perpendicular to each estuary where three habitat types were demarcated (mangrove, ecotone, saltmarsh). Sediment samples were collected for analyses and quadrats were used to measure pneumatophore density, saltmarsh cover, and brachyuran abundance and diversity. We found that brachyuran community structure at each site has significantly changed over seven years, with two mangrove-associated fiddler crab species, Tubuca urvillei and Paraleptuca chlorophthalmus, now recorded at the younger planted site, indicating a new southern distributional limit. Community structure was also significantly different amongst habitat types (p < 0.05) with Parasesarma catenatum dominating saltmarshes while Danielella edwardsii was more prominent in mangroves. However, community composition did not differ significantly between the two (differently aged) sites (p > 0.05). Pneumatophore density had a proportional relationship with crab abundance, diversity and richness, while saltmarsh cover had an inversely proportional relationship with crab abundance, diversity and richness. It is likely that as mangroves continue to expand into saltmarshes, more mangrove-associated species will move into saltmarshes, potentially altering ecosystem processes in this unique habitat.
... This species feeds mainly on mangrove leaves and detritus and is typically recognized as a decomposer that recycles organic matter within the ecosystem [9,10]. In Thailand, E. versicolor inhabits mangrove ecosystems, living in burrows excavated at tree bases in mangrove habitats along the Andaman Sea Coast and the Gulf of Thailand [9,11]. This crab is also widely exploited as a major source of protein-rich food [9,12]. ...
... ). Ils jouent également des rôles écologiques importants, puisque leurs activités de bioturbation et d'alimentation améliorent de manière substantielle les propriétés abiotiques et biotiques du sédiment, la colonisation des arbres, la productivité primaire et secondaire, le recyclage des nutriments et le flux d'énergie(Kathiresan & Thangam, 1990;Smith III et al., 1991). Ils sont donc considérés comme de bons bioindicateurs de la qualité de l'environnement, reflétant les conditions intégrées dans le benthos au fil du temps et formant un lien important entre les producteurs primaires et les consommateurs secondaires(Amaral et al., 2009;Ashton et al., 2003;Pagliosa & Barbosa, 2006;Smith III et al., 1991). Une étude en Malaisie démontre que parmi 43 indicateurs de l'état des mangroves testés, l'abondance des crabes toutes espèces confondues est l'un des indicateurs les plus fiables pour quantifier l'état des mangroves(Faridah-Hanum et al., 2019). ...
Thesis
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Mangroves are unique coastal social-ecosystems situated in tropical and subtropical regions worldwide. They undergo degradation, compromising both their ecological functionalities and their numerous contributions to human societies. Faced with this observation, numerous mangrove restoration projects have been initiated. However, in the long term, a significant number of these initiatives have failed, highlighting a lack of understanding of the ecosystem and its relationship with human societies. In this context, the primary objective of this thesis is to address the following issue: How to improve the effectiveness of ecological restoration projects for mangroves? Three research objectives have emerged to address this question: (i) assess the effectiveness of restoration projects for nature and society, (ii) identify gaps leading to poor practices, and finally, (iii) propose solutions to enhance future projects. To achieve these objectives, a comprehensive geographic analysis of restoration projects on a global scale has been undertaken, examining each major phase of a mangrove restoration project: project conception, implementation of restoration measures, and project monitoring. In the conception phase, one major identified gap is the lack of standardized evaluation methods for the initial state of the restoration site, accessible to managers. To address this need, the basis of the Rapid Assessment Method for Mangroves (RAM MANGROVES) tool was developed. A bibliographic analysis, coupled with semi-structured interviews with experts in these ecosystems, supported by field testing, resulted in a method consisting of 16 ecological and socio-economic descriptors, along with a standardized field protocol. In the implementation phase, an overview of restoration measures and a synthesis of scientific recommendations to improve them have been conducted. To achieve this, a comparative analysis of restoration projects on a global scale and an in-depth study of a specific case in the Philippines were carried out. These analyses highlighted the crucial importance of a systemic approach, integrating ecological, social, and economic aspects to maximize the chances of success. They also confirmed a fundamental point: the rehabilitation of conditions conducive to mangrove development should be considered initially, and replantation restoration should only be envisaged if conditions have already Manuscrit de thèse. Lisa MACERA 2020-2024 7 been rehabilitated or not degraded. This work has also highlighted the fact that most scientific recommendations are not respected in many mangrove restoration projects. Finally, in the monitoring phase, a significant lack of project evaluation was identified. To encourage project managers to undertake this crucial step, a high-resolution remote sensing approach is proposed. This approach was used to assess the evolution of mangrove cover at six restoration sites in Costa Rica, Senegal, Benin, and the Philippines. This analysis utilizes Landsat and Sentinel images, all free and royalty-free, ensuring the replicability of the method. A multi-scale spatial and multi-temporal analysis was conducted to ensure the robustness of interpretations. The results revealed high precision in mapping, with an average Kappa index of 0.95, confirming the reliability of this approach. In summary, the effectiveness of mangrove restoration projects is closely linked to the quality of project conception, the relevance of selected restoration measures, active engagement of local communities, and the use of appropriate evaluation tools. Throughout the various phases of restoration projects, gaps have been identified, and concrete solutions have been proposed to enhance their overall effectiveness.
... crabs, echinoderm, or molluscs), which are particularly important for gleaners (Papers I-III) and are simultaneously considered to be 'bioindicators' (Prather et al., 2013), i.e. species that can represent the health or resilience of an ecosystem (Papers I, IV). Different crabs species have been used as bioindicators of degraded mangrove forests in Thailand (Macintosh et al., 2002), Indonesia (Geist et al., 2012), and Malaysia (Ashton et al., 2003a). In mangrove forests, for example, mangrove crabs are labelled as 'ecosystem engineers' to emphasize their ability to maintain or modify their physical environment (Agusto et al., 2021;Lee, 2008Lee, , 1998. ...
Thesis
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This thesis analyzes the impacts of global environmental change upon the interactions and connections between coastal ecosystems and small-scale fishers. The analysis builds on social and ecological data, obtained in four locations including: Unguja Ukuu, Zanzibar (Paper I); Malalison island, the Philippines (Paper II); Batan, the Philippines (Paper III); and Penang, Malaysia (Paper IV). Each of these locations is currently impacted by processes of global environmental change that challenge the sustainability of local livelihoods based on natural capital. These processes of global environmental change include environmental degradation (Papers I-III), and mangrove degradation due to land use change (Papers III-IV). Papers I-II focus on gleaning as a specific example of a coastal livelihood and found that gleaners over time struggle with local declines of the species they target. In Paper II gleaning was found to be important as a supplemental livelihood activity when local people were unable to perform regular SSF livelihood activities due to disturbances caused by e.g. typhoons. Environmental degradation was also present within the multi gear SSF at Batan (Paper III) within the mangrove estuary. Within the context of both Papers III-IV land use change fragmented the coastal ecosystems which likely impacted the biodiversity and structure of a mangrove forests. In conclusion, this thesis highlights an array of stressors that threaten these social-ecological system of small-scale fishing villages, in particular their coastal ecosystems found at their fringe. This work confirms the importance for local coastal management to understand different components of a SES to strengthen local livelihood security. Future work and management of these coastlines and livelihoods that are based on their environments need both ecological and social data to enable sound management. Alternative livelihoods could be one strategy to reduce dependency of livelihoods on SSF.
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Article
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Mangroves rehabilitated after deforestation by commercial exploitation must be monitored to confirm that key ecosystem functions are being restored. Brachyuran crabs are conspicuous mangrove macrofauna and were selected as potential indicators of ecosystem recovery. A deforested former mangrove charcoal concession area in Ranong was rehabilitated by planting Rhizophora (1994), Bruguiera and Ceriops (1995) seedlings in single-species blocks. A second area, deforested and heavily degraded by tin mining, was rehabilitated with R. mucronata in 1985. Crabs at these sites were compared with those in a mixed-species conservation forest. Timed collections were made in 1999, 2008 and 2019 to compare crab diversity and relative abundance between sites and years. Thirty-three brachyuran crab species were recorded. Fiddler crabs (Austruca triangularis, Tubuca rosea) and the signal crab, Metaplax elegans, were most abundant, followed by sesarmid crabs (15 species). Species composition differed significantly between sites but not between the four planted tree species blocks. We propose Metaplax elegans as an indicator of ecological development in low-lying/newly formed sediments; fiddler crabs as equivalent indicators in young mangrove plantations/open forest habitats; and a diverse sesarmid community to indicate ecological functioning in older plantations/dense forests.
Chapter
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The production of shrimp (Penaeus spp.) by means of coastal pond systems has been a traditional practice in Asia for hundreds of years. However, advances in technology coupled with an increased international market demand for shrimp led to the development of intensive aquaculture systems that departed from traditional sustainable systems. In many instances these intensive systems were poorly planned and/or managed and have since proven to be unsustainable, with the result that large areas of “land, ”much of it former coastal wetlands, now lie idle and unproductive, and new sites are being developed in an effort to maintain production output (Stevenson 1997).
Chapter
This volume reports key findings of the Biodiversity Program of the Royal Swedish Academy of Sciences' Beijer Institute. The program brought together a number of eminent ecologists and economists to consider the nature and significance of the biodiversity problem. In encouraging collaborative work between these closely related disciplines it sought to shed new light on the concept of diversity; the implications of biological diversity for the functioning of ecosystems; the driving forces behind biodiversity loss; and the options for promoting biodiversity conservation. The results of the program are surprising. It is shown that the core of the biodiversity problem is a loss of ecosystem resilience and the insurance it provides against the uncertain environmental effects of economic and population growth. This is as much a local as a global problem, implying that biodiversity conservation offers benefits that are as much local as global. The solutions as well as the causes of biodiversity loss lie in incentives to local users.