International Journal of Marine Science, 2017, Vol.7, No.34, 344-352
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1.2 Sampling procedure
Monthly surveys were conducted to study the burrowing pattern during low tide timings from April 2013 to
March 2014. Total 10 transects (100 meter away from each other) were laid parallel to the shore line from upper
to lower part of the sandy shore. Total 5 quadrats (1 x 1 m) were laid on each transect (5 meter away from each
other) every month at each site. The total numbers of burrows were counted in the quadrats and the burrow
opening diameters of few randomly selected burrows in each quadrate were measured using digital vernier
calipers (± 0.01 mm; INSIZE Model No. 1137-150). Few randomly selected burrows in each quadrate were
excavated after measuring their burrow opening diameter and crabs which emerged from these burrows were
captured using hand picking method. Carapace width of the captured individual (as this was considered the most
relevant metric, given that the crabs enter the burrow in sideways fashion) was measured to find out its
relationship with burrow opening diameter of the respective excavated burrow. The quantified monthly quadrate
data of burrows were integrated for different seasons like summer (March to June), monsoon (July to October)
and winter (November to February) because climatic conditions of the study area do not change much in the
successive months (Mishra and Kundu, 2005). The quantitative seasonal burrow data was then analyzed for three
different ecological attributes like density (Total number of burrows from all the quadrates/ total number of
quadrate laid), Abundance (Total number of burrows/ total number of quadrates where presence of burrow
recorded) and frequency of occurrence (Total number of quadrate where burrow recorded ˟
100/ total number of
quadrate laid).
1.3 Physico-chemical parameters
Abiotic variable such as sediment surface temperature, pH and salinity were also recorded at 1 hour interval
during low tide on the day of survey of respective month at each site. The monthly data of abiotic variables was
also analyzed for three different seasons. The probe of Digital thermometer (Eurolab ST9269B, ± 0.1°C) was
inserted in the sediment till 1 cm depth for measurement of sediment temperature. For measurement of sediment
pH and salinity, a scoop of sediment was collected from 1 cm depth and 5 gm of sediment was dissolved in 25 ml
of distilled water and stirred well. After the solid particles settled on the base of the flask, the pH and salinity of
the supernatant was measured using digital pH meter (HANNA pHep Model ±0.1 pH) and Hand refractometer
(ERMA ±1‰) respectively (Blakemore et al., 1987).
1.4 Statistical analysis of data
Two way ANOVA with replication was used to investigate the variation in the mean values of different ecological
attributes and abiotic variables. Regression analysis was employed to investigate the relationship between various
abiotic factors and mean abundance of the burrows of the
O.
ceratophthalmus
. Regression analysis was also
employed to investigate relationship between
O. ceratophthalmus
body size and burrow opening diameter. All the
statistical analyses were carried out using Microsoft EXCEL.
2 Results
2.1 Sediment abiotic variables
Mean sediment temperature varied significantly between different seasons (ANOVA F: 131.31, p < 0.001) but it
did not vary significantly between different sites (ANOVA F: 1.98, p = 0.21). All sites showed a similar pattern of
temporal variation in sediment temperatures, reaching a maximum in summer while minimum sediment
temperatures were recorded in the winter season and this variation was recorded maximum in Kodinar. Mean
sediment pH varied significantly between different seasons (ANOVA F: 61.71, p < 0.001) but it did not vary
significantly between different sites (ANOVA F: 2.03, p = 0.20). The highest sediment pH was recorded in
summer at all the study sites while minimum pH was recorded in the monsoon, and this pattern was similar for all
sites. Mean sediment salinity varied significantly between different seasons (ANOVA F: 107.78, p < 0.001) as
well as between different sites (ANOVA F: 9.05, p < 0.01). The sediment salinity was recorded very high in
summer at Dhamlej while minimum salinity was recorded Sutrapada and Kodinar in monsoon (Table 1).
