Basic HTML Version
International Journal of Marine Science 2014, Vol.4, No.61, 1-13
http://ijms.biopublisher.ca
11
Based on the spatial distribution of the pH of the
seabed, scallop was found in a location with high pH
(> 7.3) (Figure 3h, 4h). Changes in water pH were
influenced by photosynthetic activity, temperature,
and waste disposal (Beveridge, 1987). Widowati et al.,
(1999) added that in Pekalongan waters, scallop
A.
pleuronectes
were found in waters with pH tended to
be alkaline. The seawater was generally alkaline with
pH range between 7.5 and 8.5, because the relatively
stable chemical composition contained. Seawater also
had a good buffer system so that the pH value was
relatively stable, due to the addition of alkali or acid
compounds proportionally (Beveridge, 1987). Effendi
(2003) also added that a low pH value (6-6.5) might
lead to a decrease diversity of plankton, thus reducing
food reserves for marine organism.
In contrast to the surface, pH generally tended to be
more alkaline (~8), pH of the seabed at the study area
tended to be lower. Depth and type of substrates
factors determined the pH value in which the level of
acidity in the deeper regions was relatively low
compared to more shallow areas (Usman, 2006).
Habitat suitability of scallop at the study area could
also be proved by biological data in the form of
scallop length distribution during the catch period of
2008-2010 (Widowati et al., 2008; Prasetya, 2009;
Kristianti, 2010). Suitable habitat allowed an organism
to grow and evolve during their life cycle in the same
location. This was supported by the discovery of
scallop with various sizes from small to a ready-catch
size (Figure 6) at the same location (Figure 5).
Figure 6 Scallop shell length based on catching period in
Brebes District waters (Source: Widowati et al., 2008; Prasetya,
2009; Kristianti, 2010)
ENFA model validation using AUC method produced
values of 0.94 (~1) showed that the model could be
said to be accurate and was very good (Hirzel et al.,
2006) for modeling scallop habitat in Brebes District.
The suitability maps resulted from the spatial
modeling and ENFA could be used as a guide for
fishermen, thus it could increase the efficiency of
fishing effort. Local government through the
Department of Marine and Fisheries Affairs in Brebes
District could utilize the habitat suitability map of
scallop as fisheries management guidelines,
particularly in providing spatial information of scallop
habitat.
4 Conclusion
The conclusions from this study were as follows:
Suitable habitat for scallop
Amusium pleuronectes
in
Brebes District waters was seabed with very different
conditions from the average habitat conditions
existing in the entire study area (p <0.05). The suitable
habitat was seabed with high plankton density
(11,001-14,500 ind/L), between 18-31 m water depth,
low suspended solids (<3.61 mg/L), fine sediments
(mud, φ ≥ 6) and a relative distant from estuary (> 5
km). In addition, the scallop also required habitat with
high current velocity and salinity (> 0.06 m/sec;
31.85-32.65 ‰) and relatively low temperature
(29.92-30.06 °C), while for the pH level, scallop were
relatively more tolerant (7.3-7.4).
Based on spatial modeling of scallop habitat
suitability in the study area, there were three
categories classified as follow: 1) suitable habitat
categories covering 4,629.01 ha (5.8%); 2) marginal
habitat 9,291.09 ha (11.5%); and 3) unsuitable habitat
covering an area of 66,682.68 ha (82.7%).
The suitable habitat for the scallop was at the eastern
seabed of the study area located relatively far away
from Pemali River estuary. Marginal habitat was
around the suitable habitat, while the unsuitable
habitat was outside area of both categories as
mentioned before, mainly located near the mainland,
in the central and western parts of the study area.
ENFA model could be said to be accurate and was
very good for modeling the habitat of scallop in
Brebes District with validation value of 0.94 (~1)
using the AUC method.