Results

Transient fauna found feeding in the drain were the Common Sandpiper (Actitis hypoleucos).  Two species of swimming crabs (Scylla olivacea and Varuna yui) were found in large crevices and cracks in the concrete.  Since they are swimming crabs, it is not possible to determine if they were transient or resident species.  Resident crab species include the Episesarma spp, Uca annulipes, Perisesarma eumolpe and the endangered Uca rosea.  The mean crab density of Uca annulipes is estimated to be 25 individuals m^-2.  Mud mounds with occasional mud lobster (Thalassina anomala) occupants were also observed.  Other resident fauna present include slender mudskippers (Periophthalmus gracilis) and one Malayan Water Monitor Lizard (Varanus salvator) frequently spotted in its nest or feeding along the drain. 

Drain water salinity is the highest at the junction of the drain where water from concretised Sungei Ketapang overflows into the drain during high tide.  The salinity of the water decreased along the drain as the distance away from this junction increases (Table 1).  Most of the brachyurans were found at the junction.

Table 1. Summary of descriptive statistics for salinity of drain water at different sections of the drain.

Variable (Location of Drain)	n	Mean ± S.D.
Junction	24	6.57 ± 1.34
Mid	24	4.16 ± 1.17
Beginning	24	0.78 ± 0.28

One-way analysis of variance (ANOVA) of sediment salinity of the site, East Coast Park, Pulau Hantu and Pasir Ris indicated that sediment salinity differed significantly in the four locations (F_3,8 = 15.71, p = 0.001), with the salinity of the study site significantly lower than that of all other locations
(ie., Study Site < East Coast Park ≈ Pulau Hantu ≈ Pasir Ris).  Sediment analysis of sediments from study site, East Coast Park and Pasir Ris revealed that the sediments were very similar and belonged to the textural group of gravelly sand.

Probit analysis (Fig. 2, Fig. 3 and Fig.4) of the LC₅₀ of Uca annulipes from study site, East Coast Park and Pasir Ris showed that the individuals were able to tolerate high salinity levels for the 72 hour period.  However, the specimens were unable to tolerate long periods of low salinity or freshwater conditions with the LC₅₀ found to be between 0.067 ± 0.313 to 0.075 ± 0.331 (Table 2). No crabs perished at mid-range salinities of 10 ‰, 20 ‰, 30‰.

Fig. 2. Probit analysis for samples collected from the study site

Fig. 3. Probit analysis for samples collected from East Coast Park

Fig. 4. Probit analysis for samples collected from Pasir Ris

Table 2. Summary of LC₅₀ of Uca annulipes from Site, East Coast Park and Pasir Ris

Location	LC50 ± S.D.
Study site	0.067 ± 0.313
East Coast Park	0.067 ± 0.313
Pasir Ris	0.075 ± 0.331

One-way analysis of variance (ANOVA) of the LC₅₀ of Uca annulipes from Site, East Coast Park and Pasir Ris also showed that the LC₅₀ of the various locations did not differ significantly from one another (F_2,12 = 0.002, p > 0.05) (i.e., Study Site ≈  East Coast Park ≈ Pasir Ris ).