International Journal of Marine Science, 2016, Vol.6, No.11, 1-10
6
The multi branch burrows (MB) (Figure 2f) (n = 4) had mean volume of 365.06 ± 248.30 cm
3
with mean opening
diameter of 19.50 ± 5.16 mm. The MB burrows looked similar to JBB shape burrows, but they all had an extra
branch attached to the base of the secondary branch. In MB burrow except primary arm no other branch reach the
surface and they all ended with spherical blind lobe. The extra branch attached with secondary branch base had
multiple chambers. The burrows were constructed by the crab having mean carapace length of 12.82 ± 4.32 mm
(n=3). The burrows inclined vertically with mean inclination angle of 96.63 ± 22.19°. The burrow had mean depth
of 26.25 ± 7.99 cm in which the mean depth of extra branch (15± 4.10 cm) was significantly higher than the mean
depth of primary arm (11.25 ± 4.03 cm; paired t test, t = 2.35, df = 3, p<0.01). The total mean length of the burrow
was 31.08 ± 8.91 cm and the horizontal distance of the burrow was 8.09± 8.91 cm.
The J shaped burrows (J) (Figure 2a) (n = 7) had mean burrow volume of 215.32 ± 110.08 cm
3
with an average
burrow opening diameter of 14.43 ± 4.61 mm. The burrows were vertically inclined with mean inclination angle
of 98.65 ± 15.88°. The J shaped burrows were constructed by crab with mean carapace length of 8.87 ± 3.41mm
(n = 5). The mean depth and length of the burrow were 14.11 ± 5.88 cm and 24.30 ± 8.03 cm respectively. The
horizontal length of the burrow was 12.11 ± 2.22 cm. The mean length and width of the chamber situated on the
base was 2.32 ± 1.04 cm and 6.24 ± 2.28 cm.
The Y shaped burrows (Y) (Figure 2h) (n = 4) had mean volume of 265.81 ± 101.20 cm
3
with an average opening
diameter of 15.25 ± 3.93 mm. The burrows were constructed by crabs with mean carapace length of 9.69 ± 3.45
mm (n = 3). The primary and secondary arm of the burrows joined the main shaft and ended with small chamber
at the base. The burrows were inclined down with an average inclination angle of 88.64 ± 11.04°. In all the burrow
casts obtained, the secondary branch did not reach the surface and ended up with blind spherical end. The mean
depth of the burrow was 26.25 ± 7.21 cm. The depth of the primary arm (9.0 ± 2.68 cm) was significantly longer
than the secondary arm (6.9 ± 2.14 cm; paired t test, t = 2.38, df = 3, p<0.01). The mean horizontal distance of the
burrow was 4.82 ± 3.14 cm. Total mean length of the burrow was 24.67 ± 9.12 cm. The chamber attached at the
base had length of 2.44 ± 1.16 cm and width of 3.82 ± 1.02 cm.
3.2 Vertical temperature profile of burrows
The depth wise variation in burrow temperature was studied for various burrow shapes recorded in the present
study. Results revealed similar pattern in temperature variation for all the burrow shapes. The sand surface
temperature recorded was 42-45°C which remained similar for all the burrow types. The temperature declined to
33 °C at a depth of 5 cm. After the depth of 5 cm the rate of temperature drop decreased to 1 to 1.5°C at every 5
cm. The temperature recorded at the deepest part of the burrow that could be measured up to 25 cm was
28-29.5°C, which was 14-15.5°C cooler than the surface temperature (Figure 4).
4 Discussion
In the present study, the burrow morphology of brachyuran crab
Ocypode ceratophthalmus
burrows showed
variation in size, shape and complexity of structure ranging from single tube structure with single opening and no
branches to multi branched burrows with multiple opening. The size of the crab species is measured in terms of
carapace length. The carapace length affects the burrow opening size because crabs walk sideways direction. In
the present study, the crab carapace length showed strong correlation with burrow opening diameter, burrow
volume and burrow length which showed that the larger crabs had greater burrow diameter, larger burrow volume
and larger depth as compared to medium sized and juvenile crabs. Lim (2006) found similar kind of relationship
of crab- carapace size with burrow opening in brachyuran crab
Uca annulipes
and
Uca vocans
. She suggested that
the burrow of
U. vocans
were larger in size as compared to
U. annulipes
because
U. vocans
is larger species as
compared to the other species and it requires larger burrow opening which enables the species to move
comfortably inside the burrow.
8 different shapes like single tube burrow, J shape with branch at the base, J shape, Bulb shape, Y shape burrow,
multi branched burrow, Y shape with double opening and U shape burrow were recorded for burrow architecture
