IMCC Journal of Science

Abstract: 

Fiddler crabs are abundant bioturbators in tropical intertidal flats and are often used as sentinels of sediment quality. This study evaluated whether burrow architecture and basic population metrics vary along an oil-contamination gradient near an industrial shoreline in Iligan Bay, Philippines. Transect–quadrat sampling was conducted at an impacted site in Kiwalan, Iligan City, and at a reference site in Bacolod, Lanao del Norte. Oil and grease (O&G) were quantified in sediments and surface water; crabs were identified to species and measured for carapace length (CL) and width (CW). Burrows were cast and measured for horizontal burrow diameter (HBD), total burrow length (HTBL), total burrow depth (HTBD), and volume (HBV). Sediment O&G was higher at Kiwalan versus Bacolod (307.74 vs 56.03 mg/kg); water O&G was 0.30 vs 0.20 mg/L. Forty-two crabs were collected: Uca dussumieri (n=15), U. jocelynae (n=8), U. vocans (n=19). Mean CL/CW were 1.61/1.97 cm (Kiwalan, n=15) and 1.76/2.12 cm (Bacolod, n=27). Burrow metrics were larger at Bacolod: HTBL 15.83 vs 8.63 cm (t=3.687, df=19, p=0.002), HTBD 10.83 vs 6.98 cm (t=3.125, df=19, p=0.006), HBV 741.67 vs 291.67 cm³ (t=3.582, df=19, p=0.002). Correlations between O&G and CL/CW were negative (r=−0.200, −0.217) but non-significant. Elevated sediment O&G near industry coincided with shorter, shallower, smaller-volume burrows, indicating functional habitat alteration. Burrow architecture appears to be a practical biomonitoring endpoint for shoreline O&G contamination, suggesting the value of expanded sampling and tissue contaminant analyses.

Keywords: bioturbation; carapace morphometrics; transect–quadrat sampling