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International Journal of Marine Science 2014, Vol.4, No.61, 1-13
http://ijms.biopublisher.ca
10
pleuronectes
were mostly found in mud and silt
substrates (Figure 3a, 4a).
Although there was no direct influence towards the
scallop growth, type of sediment might be expected to
affect the distribution associated with its ability to
adapt. Study on the sediment types of Brebes District
in 1986 (Tahrir et al., 1986) shown that the type of
sediment in location which had been the catching area
of
A. pleuronectes
was silt and mud. It indicated that
the scallop in this area had long adapted on those both
types of substrates, at least for more than 2 decades.
Scallop in the study area could be captured at 5-20 km
from the estuary. Scallop were not found at a distance
of < 5 km because it was too close to the mainland
where many rivers flowing down to the estuary
leading to a very high sedimentation avoided by
scallop. Franklin et al. (1980) stated that
Amusium sp.
could be found distance from the estuary in order to
avoid sedimentation. While the scallop was not found
at a distance of > 20 km, it was allegedly because of
the lack of data catching on that distance. Fishermen
might notice the economical value if they had to reach
a distance over 20 km considering the high cost
expended just to reach such distance.
Scallop at the study area were mostly captured on the
current velocity ranged from 0.07-0.09 m/sec and
were not found in other current velocity range, either
weaker or stronger (Figure 3e, 4e). However, when the
current velocity was relatively strong to medium, only
2.8 %, then it was ignored, thus scallop tended to
choose a location with a stronger current velocity from
the existing current in all the study areas.
Water current played an important role for the
suspension-feeder organism to get their food as well
as food reserves distribution from one location to
another. With relatively limited movement,
suspension-feeder benthic organism relied a lot on
water current near the seabed to obtain food reserves
(Mortensen, 2001).
Scallop had a preference of the seabed with higher
salinity than the average salinity of the study area
(Table 4, Figure 3g, 4g). Low salinity at the study
areas was located in the waters close to the mainland,
especially around the estuary in the eastern part of
study area and relatively high salinity was found in
open ocean. In contrast to the salinity in the deep sea
that was relatively homogeneous (Gage and Tyler,
1996), salinity in shallow waters was fluctuated
(Gross, 1990). Lower salinity around the mainland
was due to the input of freshwater from the mainland
through the rivers.
All organisms had optimal salinity for its life
including scallop. Salinity affected the diffusion of
oxygen vertically (Hutabarat and Evans, 2000),
therefore it effected the organisms and the
environment living in it. In addition, salinity was also
a determining factor on the organism growth and
survival. By having the ability to migrate,
Amusium
sp.
(though limited), allowing these species to search
suitable seabed salinity as its habitat.
The temperature distribution pattern in the study area
was inversely to the depth gradient (Figure 3f, 3b).
The entry of warmer water from the river, followed by
shallow water, had caused temperature around the
estuary in the west tended to be higher. In the shallow
areas, the penetration of sunlight could penetrate
deeper into the waters so that the temperature at that
location was higher if compared to the deeper waters.
While in front of the Pemali River in the east, with
deeper water depth, temperature was relatively low
even at a distance that was not too far from the estuary
(Figure 3b).
Although the temperature range of the seabed waters
at the study area was relatively homogeneous, scallop
had a special preference for temperature conditions.
These species tended to choose the lower temperature
than the temperature in the entire study area (Figure 3f,
4f). Tropical fish species, including scallop, could not
grow well at temperatures below 24 °C whereas the
tolerable daily temperature change in laboratory was
4 °C at most (BBL Ditjen Perikanan, 1994).
Marine organism including scallop was generally
cold-blooded animals in which body temperature
was strongly influenced by the temperature of the
surrounding environment and did not have the
ability to adjust its body temperature. With low
temperature, the rate of metabolism did not work
too fast, so that the energy savings used for both
growth and reproduction were more.