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Indian Journal of Geo-Marine Sciences
Vol. 41 (2), April 2012, pp. 146-151
Spatiotemporal variations of hermit crab (crustacea: decapoda) inhabiting rocky
shore along Saurashtra coast, western coast of India
Ashok Vaghela & Rahul Kundu*
Department of Biosciences, Saurashtra University, Rajkot-360005, Gujarat, India
*
[E-Mail: [email protected], [email protected]]
Received 17 February 2011; revised 24 June 2011
Spatiotemporal variations in the population ecology of two dominant hermit crabs on four major shores along the
Saurashtra coastline (India) off the Arabian Sea during September 2008 to August 2009 had been examined. There were
no spatial and temporal variations of the population of hermit crabs in all four sampling stations. Population dynamics
were slightly higher at Dwarka and Mangrol than Veraval and Kodinar coasts. Population dynamics of these species
were apparently affected by anthropogenic pressure at Veraval and somewhat lesser degree at Kodinar.
[Keywords: Arabian Sea, Hermit crab, Population ecology, Spatial and Temporal variations]
Introduction
Hermit crabs represent a significant part of benthic
community, where they play an important role in the
marine food chain. Gastropod shells are very much
necessary for hermit crabs as being the most essential
factor/resource required for their existence1,2. The
distribution of the hermit crabs has been described on
the basis of their habitat selectivity in the intertidal
zone and has shown the occupancy of the gastropod
shells which are available in the intertidal habitats2,3.
Hermit crabs have evolved to the point where they are
dependent on a microhabitat as a resource4,5, and
therefore, non-availability of adequate shells causes
heavy mortality of hermit crabs6. Desai and Mansuri 7
studied on the population ecology and biology of
hermit crabs of South Saurashtra coastline and
reported that the hermit crabs occupy gastropod shells
which are available in those particular intertidal
habitats. Further, the empty gastropods shells are
movable objects in relation to tidal currents8 and
therefore, hermit crabs have been reported to exploit
different rocky substratum available throughout the
intertidal zone. However, as empty shells are essential
for hermit crabs, they occupy whatever the type
of shells they get in their specific in habitat zone.
Moreover, the distribution of these two species of
Clibanarius was reported to be restricted to mostly
supra and mid-littoral zones of the intertidal zone at
——————
*Corresponding Author
research site, which conforms the observation made
by Vance9,10. Bach11 and Abram12 reported that
Clibanarius sp. tend to occur mostly in higher
intertidal level. Abiotic factors are mostly control the
activities of these organisms. Buchanan and Stoner13
suggested that abiotic factors must be considered
because some ecological interactions are the main
cause of seasonal and spatial distribution of
individuals. Each organism occupies one definitive
space where the environmental and biotic conditions,
are at least, the minimum necessary to propitiate its
survival14.
Present investigation was undertaken to study the
spatial and temporal variations in the population
ecology of two hermit crabs, Clibanarius nathi and
Clibanarius zebra inhabiting the rocky intertidal area
of South Saurashtra coastline, which is fast becoming
a fevourite place for mega industries.
Materials and Method
In the present study four different stations along the
South Saurashtra coastline (Gujarat State, India)
which differs by the types of intertidal habitat
and degree of anthropogenic pressure were selected
(Fig. 1). Dwarka (22° 13’ N, 68° 58’ E), Mangrol
(21° 07’ N, 70° 07’ E), Veraval (21° 35’ N, 69° 36’ E)
and Kodinar (20° 41’ N, 70° 46’ E) were selected
for the study. Human interference to the coast is
comparatively high in two areas. The intertidal belt
of Dwarka consisted of large rocks and boulders
which cause immense resistance to upcoming wave
VAGHELA & KUNDU : SPATIOTEMPORAL VARIATIONS OF HERMIT CRAB
147
Fig. 1—Map showing sampling locations.
and hence, generates harsh water splash. Thus, the
tearing force of the tidal wave at Dwarka is quite
higher than that of other stations. The rocky intertidal
belt of Mangrol is interspersed with many tide pools,
puddles, crevices and small channels with occasional
sandy patches. The upper portion of the intertidal
belt is generally covered with an admixture of silt
and sand studded with pieces of broken shells.
The intertidal pools in the upper littoral zone have
a thin layer of sand settled over the rocky base.
The intertidal zone is wide with moderate wave
action. The substratum of Veraval coast is mainly
rocky with few sandy patches. The lower littoral zone
of Veraval ends up at steep vertical decline towards
subtidal zone. The intertidal belt of this area is not
uniform and exposure of this predominantly rocky
shore is not significantly long. The intertidal zone
covers a distance of about 60-90 m during spring
tides. The available intertidal zone of Kodinar is hard
flat rocky littoral area having small sized depressions
in interspersed with many rocky pools and puddles.
The spray zone is covered by sand. The intertidal belt
is interrupted by many small tide pools. The upper
littoral zone sharply ends up at spray zone.
The distribution pattern and population ecology of
hermit crab species were studied by transects method
monthly for a complete year (from October 2008 to
September 2009), in the rocky littoral area of South
Saurashtra coastline. The Quadrates of 0.25 m2 were
laid at every 10-15 meters distance in the transect
while following an oblique direction from upper
to lower littoral zones covering maximum area at
almost regular occurrence. Quadrate frequency was
determined on the basis of the total length of the
available intertidal area during low tide. In each
littoral zone at least ten quadrates were laid. Among
the ecological attributes, density (total number
of individuals from all the sample plots/number
of sample plots studied) and abundance (total number
of individuals/number of sample plots where the
individuals occurred) of C. nathi and C. zebra
in each sampling stations were calculated15. The
obtained monthly data were integrated as seasonal
data viz., post-monsoon (September to November),
winter (December to February), summer (March to
May) and monsoon (June to August). All collected
data were subjected to different statistical analyses
for their cumulative acceptability. One way ANOVA
was employed to test the differences between the
stations during seasons. All statistical analyses were
done as per Sokal and Rohlf16.
Results and Discussion
Underwood and Chapman17 suggested that
understanding of ecological processes in the rocky
intertidal assemblages depends on better perception of
spatial and temporal variations. Among this study,
Clibanarius nathi and Clibanarius zebra were most
148
INDIAN J. MAR. SCI., VOL. 41, NO. 2, APRIL 2012
abundant species of Hermit crabs, studied at the
selected sampling station, which inhabits different
gastropod shell species18. Hermit crabs are quite
commonly seen in the tide pools of intertidal area.
Both the hermit crab species were found inhabiting
the soft bottom and stony rocks of intertidal zone with
or without algal mats. C. nathi was prominent species
in terms of numerical abundance, found at almost all
sampling sites. Its abundance was much higher than
its density at all the stations (Fig. 2). Seasonal density
values showed fluctuations in case of the selected
species (Fig. 3). It was observed that minimum
density and abundance values of both hermit crab
species found during summer season, than it was
increased in monsoon and maximum values observed
during post-monsoon and winter seasons (Figs 3, 4).
However, maximum density and abundance were
observed at Mangrol during post-monsoon season.
Among the two hermit crabs C. zebra showed least
value for all the parameters studied at all the sampling
station. There did not observe much variation in any
ecological attributes at spatial scale. The density value
of C. zebra was very low compared to C. nathi at all
the sampling stations throughout the study (Fig. 2).
Both the density and abundance of this species were
high at almost sampling sites during post-monsoon
and winter (Fig. 2).
In the case of C. nathi and C. zebra, no clear
seasonal variations were observed in any of the three
vertical zones (Figs. 3, 4). Present study showed
irregular pattern of ecological attributes at each
sampling sites. This may be to the fact that much
spatial variations were also not found between the
four sampling sites. Desai and Mansuri7 studied the,
ecological status of C. nathi and C. zebra in this coast,
studied that the density and abundance of these are
totally dependent of the availability of suitable empty
gastropod shells, for these hermit crab species. In few
sampling sites, however, significant variation was
observed in some ecological attributes of the species
studied in the lower littoral zones (Table 1). This
variation is essentially a spatial variation due to the
variation in coast characteristic, substratum types
and other such factors within stretch of coastline.
It is possible that local migration towards the
upper portion of middle littoral zones in order to find
bigger empty gastropod shell as the animal grows7.
Therefore, it can be concluded that the coastal
stretches from Dwarka to Kodinar can biologically be
treated as continuous coastline where ecological
attributes of these two key hermit crab species did not
differ significantly. Several species of hermit crabs
inhabit rocky and sandy mid-to-low tide areas of
intertidal zones and are found skittering about in
deserted snail shell19. Since the gastropod shells
influence the hermit crab populations in many ways,
shell selection for them seems to be important
criteria2. The hermit crabs C. nathi and C. zebra
inhabiting the coast mostly occupy the empty
gastropod shells of Cerithium caeruleum, Rhinoclavis
sinensis, Clypeomorus sp., Murex sp., Turbo
intercoastalis and Nucella sp. At majority of the areas
in intertidal zones, both hermit crabs species showed
their habitat preferences and indicated segregation
of habitat selection to avoid competition for shell
selection. Therefore, in such areas where individual
species of the two hermit crabs were found to inhabit,
C. nathi was observed to occupy larger size of
gastropod shells available in those areas. Thus,
differences between the habitat preferences by the two
species of the Clibanarius hermit crabs inhabiting the
coasts could be interpreted as an attempt made by
hermit crabs towards minimization of competition.
However, an overlapping or co-existence between
C. nathi and C. zebra was observed at certain places
in the intertidal zone. Studies on distribution and
Fig. 2—Spatial variation in density and abundance values of C. nathi and C. zebra during the study period.
VAGHELA & KUNDU : SPATIOTEMPORAL VARIATIONS OF HERMIT CRAB
149
Fig. 3—Seasonal and Spatial Variations in mean density (±SD) values of (a) C. nathi and (b) C. zebra in different littoral zones of
selected sampling stations.
variation in the abundance and density of various
hermit crabs species during different seasons are
very negligible1.
The spatial distribution of marine organisms is
reported to be determined by environmental
factors interactions20. The results suggested no
significant variations in the ecological attributes
like abundance and density for both the species.
Thus, it is apparent that both species do not have any
temporal variations in the sampling sites studied.
INDIAN J. MAR. SCI., VOL. 41, NO. 2, APRIL 2012
150
Fig. 4—Seasonal and Spatial Variations in mean abundance (±SD) values of (a) C. nathi and (b) C. zebra in different littoral zones of
selected sampling stations.
Table 1—Results of the ANOVA of the mean seasonal density
and abundance values of the two hermit crab species at the four
stations. Tabulated ‘F’ value at p = 0.05 level is 3.49029
Clabinarius nathi
Clabinarius Zebra
Density
Upper
Middle
Lower
0.15985
0.08549
0.14248
0.66667
0.45763
0.25641
Abundance
Upper
Middle
Lower
0.77257
0.29458
0.58316
0.55166
0.83808
0.82513
Conclusion
During the study period there is no significant
temporal variations in the population density
and abundance of C. nathi and C. zebra. The
abundance was relatively high than the
density values. Generally hermit crabs are mobile
animal and therefore, vertical zonation did not
show any much variation. However, due to
nature of substratum of the intertidal area,
wave action was dissimilar at all the selected
stations, these spatial variations found during
the entire study.
VAGHELA & KUNDU : SPATIOTEMPORAL VARIATIONS OF HERMIT CRAB
Acknowledgements
Authors are thankful to UGC for financial support
and one of the author (AV) also acknowledges UGC
for the award of Junior Research Fellowship.
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