BURROWING CRAB ACTIVITY AS AN EARLY INDICATOR OF HYDROCARBON CONTAMINATION IN MANGROVE SEDIMENTS: INTRODUCING THE BURROW ACTIVITY RATIO (BAR)

Monitoring acute environmental disturbances in mangrove ecosystems poses significant challenges due to substrate complexity and logistical constraints. This study introduces the Burrow Activity Ratio (BAR) as a novel, non-invasive bio-indicator for rapid assessment of hydrocarbon contamination. Field investigations were conducted in a tropical mangrove system following an acute oil spill, utilizing a comparative framework between disturbed and reference sites. Three distinct biological metrics were evaluated: (1) the BAR of brachyuran crabs, (2) a Gastropod Sentinel Indicator System (GSIS), and (3) a Biofilm Damage Index (BDI). Our results demonstrate that hydrocarbon exposure induced a significant suppression in faunal vigor, with BAR declining from 77.9% to 55.3% (p = 0.0057). Concurrently, mollusk density plummeted from 144 to 55 individuals per plot (p = 0.016), accompanied by severe degradation of pneumatophore-associated biofilms. The high sensitivity and statistical significance of BAR suggest its efficacy as a robust early-warning tool. This research provides a cost-effective, real-time monitoring proxy that bridges the gap between chemical analysis and ecological impact assessment in sensitive intertidal zones.