Burrowing behaviour of the shore crab Ocypoda macrocera H. Milne Edwards from Sundarban, West Bengal

3 Pages·1998·1.8 MB·

by  N C Nandi

140 JOURNAL, BOMBAYNATURAL HIST. SOCIETY, Vol. 95 (1998)
BURROWING BEHAVIOUR OF THE SHORE CRAB OCYPODA MACROCERA
33.
MILNE EDWARDS FROM SUNDARBAN, WEST BENGAL
H.
With one text-figure)
(
Although brachyuran crabs comprise one ofburrow diameters ranging from 40 to 50 mm.
ofthe major components ofcoastal macrofauna This indicates that the crabs inhabiting burrows
mm
ofthe Sundarban delta, very little is known about of 30 - 50 diameter were dominant over
theburrowingbehaviourofthese crabs, especially others. However, the crabs occupying burrows
mm
ocypodid crabs, from this region (Bakshi et al. of40 - 50 diameter appear to be more active
1980; Chakraborty et al. 1986; Bhunia et al. burrowers.
1989; Mandal and Nandi, 1989; Nandi and Dev The burrows wereusually locatedonmoist
Roy, 1991; Nandi and Pramanik, 1994; Bairagi, mid-littoral sand-flats having moisture content
1995). This study deals with structure and ranging from 11.8 - 23.0%, and burrow
distribution of burrows of the ocypodid crab, temperature 25.5 - 27.5 °C when air temperature
Ocypoda macrocera H. Milne Edwards. was 20.0 - 22.5 °C. The number ofburrows was
Initially we studied the sea-shores of found to vary from 2-10 per squaremetre with
Bakkhali and Jambudwip in 1986, and an average of 3.6 per sq. m. The maximum
subsequently reinvestigated Bakkhali beach, densitywasrecorded atthe middle ofmid-littoral
Sundarban, in 1996. In all, 188 burrows, 75 in zone, wherein an average density of 6.5 per sq.
m
1986 and 1 13 in 1996 (Table 1) were studied, to wasencounteredinJanuary, 1996. The average
ascertainthe course of theburrows. The burrows density of burrows near the brick embankment
were round slightly inclined and descending at Bakkhali beach was also found to be on the
downwards (Fig. 1) and were found at the sand- higher side (5.9/sq. m.) in December 1986. But
flats between High Water Spring Tide (HWST) in 1996, the same site was foundtobe abandoned
and High Water Neap Tide (HWNT). They by the crabs, probably due to increased winter
usually had one external opening and fishing activities around this area. The depth of
occasionally up to three openings with inter- burrows nearthe embankmentsite was invariably
connections between them. The diameter ofthe low and the crabs below the brick zone could be
external opening varied from 1.9 to 7.2 cm, captured easily.
descending to a depth of7.9 to 46.2 cm (Table 1). The literature on the ecological distribu-
It is evideht from Table 1 that more than tion ofocypodid crabs (Ono, 1965; Jones, 1972;
mm mm
60%burrows were of30 to 50 diameter. Lighter, 1974; Crane, 1975; Warner, 1977;Murai
The depth ofthe burrow reaches its peak in case et al 1982, Macintosh, 1984) indicates that the
Table
1
DISTRIBUTIONANDDEPTHOFBURROWSOF OCYPODAMACROCERA FROM SUNDARBAN
Burrow Burrow Occurrence(%)ofburrowsat
diameter(mm) depth(cm) Bakkhalibeach Jambudwip
1996(N=l 13) 1986 (N=42) 1986 (N=33)
mm
Upto20 9.0-10.5 1.7 2.4 3.0
mm
20 to 30 7.9-23.0 34.5 21.4 18.1
mm
30 to40 11.1-32.6 39.8 33.3 30.3
mm
40to 50 17.2 -46.2 20.3 33.3 36.3
mm
50 to 60 26.0-30.0 2.6 4.7 9.1
mm
60to 70 26.0 0.9 2.4 3.0
mm
70 to 80 - 2.4 -
MISCELLANEOUS NOTES
141
crabs. Thus the absence of this fascinating red
shore crab species from some areas in the beach
indicates their sensitivity to increased human
interference andstressesthe need forcoastal zone
management.
Acknowledgements
We
thank the Director, Zoological Survey
of India (ZSI), Calcutta and the Officer-in-
Charge, Sundarban Field Research Station, ZSI,
Canning, for research facilities and Dr. R.K.
Varshney, Addnl Director, ZSI, for kindly
reviewing the manuscript.
Fig. 1. Ocypoda macrocera burrows with single August 24, 1996 N.C. NANDI
external opening (A, C, D) and three external SOBHANAPAUL
openings (B).
Zoological Survey ofIndia, M-Block,
distribution, depth and zonation of burrows are New Alipore, Calcutta-700 053.
associated with the nature of the substratum, M.K. DEV ROY
food availability, humidity, temperature, Wildlife Preservation (E.R.)
desiccation and water stresses of the intertidal Udalbakra, Lai Ganesh,
environment. Human activities also play an Guwahati-781 034,
important role in the distribution of ocypodid Assam
.
References
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&
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(
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Decapod Brachyura from Sundarbans mangrove behavioural characteristics relatedto foodsupplyand
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5(1): 55-68. vocans vocans and Uca lacteaperplexa. Mar. Biol.,
Crane,J. (1975): FiddlercrabsoftheWorld. Ocypodidae: 66: 191-197.
Genus Uca. Princeton University Press, Princeton, Nandi, N.C. & M.K. Dev Roy (1991): Burrowing acti-
pp 736. vity and distribution of Scylla serrata (Forskal)
Jones,D.A. (1972): Aspectsoftheecologyandbehaviour from Hooghly and Matla estuaries, Sundarban,
of Ocypode ceratophthalmus (Pallas) and O. kuhlii West Bengal. J. Bombay nat. Hist. Soc. 88(2): 167-
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142 JOURNAL, BOMBAYNATURAL HIST SOCIETY, Vol. 95 (1998)
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DISTRIBUTION AND HOMING OF TREE SNAIL RACHISBENGALENSIS
34.
LAMARCK (GASTROPODA) ON A NEW HOST PLANT
The tree snail Rachis bengalensis Lamarck mauritiana.
(Gastropoda), was found only in six districts of Fromourobservations, wecan concludethat
WestBengal viz. Calcutta, Hooghly, Malda, North the snails are not very specific to their host plant.
24-Parganas, South 24-Parganas, and Purulia Moreover, theirfirstpreference was for Codiaeum
(FAUNA OF WESTBENGAL- STATEFAUNA SERIES-3; Part variegatum, followed by Aganosoma dichotoma,
&
9, mollusca; Z.S.I. Calcutta 1992; Raut Biswas Zizyphus mauritiana and other plant species.
1991. But the same species (Z.S.I., lot no. Moll- Accordingto ourstudythese snailsgenerally
906 IR No. 20196) was also found by us from the prefer semi-decomposed leaves rather than bark,
school compound of Baishnabchak (15 km from as their food. Regarding homing, in most cases
Kolaghat Station, beside the river Rupnarayan) (85%) afterforaging, they were able to comeback
Midnapur, West Bengal, India. Despite thorough to the same host plant day after day. The snails
observations, the authors did not find this snail at travelled about 240 (30 - 735 ± 86) cm, in anight,
any other places in this district except at though the distance coveredby this snail depends
Baishnabchak. on its size and amount ofrainfall during thenight.
Though Gude (1914) described its Regarding egg laying, our findings are similar to
& &
taxonomic characters and Raut Biswas (1991) those ofRaut Biswas (loc. cit.). We, however,
describeditsnatural history,ourobservations differ observed that a few snails laid their eggs on the
&
in a fewpoints. According to Raut Biswas (loc. dorsal surface of the leaf of Aganosoma
cit.)thesnailswereveryspecific forhardwoodtrees dichotoma, but these failed to hatch.
We
viz. Mangifera indica, Aegle marmelos, Zizyphus thank Mr. K. V. Surya Rao, Deputy
mauritiana, Erythrina indica, Citrus aurantifolia Director, Zoological SurveyofIndia, Calcutta, for
and Lannaea coromandelica. But we observed identification ofthe snail. We are also thankful to
that, although all the above mentioned trees were the Headmaster, Baishnabchak M.C. High School
present in the garden in large numbers, the snail, for his permission, co-operation and for the
Rachis benghalensis was found only on Codiaeum facilities provided, and lastly to the villagers of
variegatum and Aganosoma dichotoma. Both Baishnabchak.
these species are bushy shrubs. The snails were
observed on these plants in colonies. They May 5, 1997 SUBHAMOY DAS
occasionally came down from their host plants at BaishnabchaLM.C. High School,
night, butneverclimbed Mangifera indica, Aegle Baishnabchak, Midnapur-721 158.
marmelos, Erythrina indica and Citrus SONALI BHAUMIK
A
aurantifoliasituatednearby. fewsnailshowever, B/7, Saswati Estate, 87/1, A.K.M. Road,
were observed occasionally on Zizyphus Calcutta-700 090.
References
Gude, G.K. (1914): The faunaofBritish India. Mollusca the tree snail Rachis bengalensis Lamarck
II. TaylorandFrancis, London. (Gastropoda: Enidae).BullofMalacology, R.O.C. 16:
&
Raut, S.K. A. Biswas (1991): Natural History of 75-80.