Recovery of infauna macrobenthic invertebrates in oil-polluted tropical soft-bottom tidal flats: 7 years post spill

Coastal oil spills constitute significant threat to biotic energy distribution, and biodiversity integrity amongst others. This study monitored the recovery of low-intertidal, soft-bottom infauna macrobenthic invertebrates in Bodo Creek intermittently over a 7-year period post oil spill. Samples were taken twice a month (spring and neap low tides) for 6 months (September 2015–February 2016) at sites previously studied (pre-spill baseline studies, 3-year and 5-year post-spill studies) for the effects of oil pollution using the same sampling methods used during initial studies of the same area. Comparatively, the initial studies reported Polychaeta as the dominant class against the dominant Crustacea reported in this 7-year post-spill study, indicating a change in the community structure of the study area. Infauna macro-invertebrate communities recorded showed an improvement (that is, increased species richness and number of individuals) over the initial 3-year and 5-year post-spill studies. However, relating the results to the initial baseline pre-spill studies, an annual average of 9.7% recovery rate was observed. Analysis of results showed that the total hydrocarbon content (THC) of the sediment remained high (90.08–12,184 mg/kg) but was markedly lower than levels observed during the initial post-spill study (6422–7186 mg/kg). Tidal flushing and biodegradation processes were deemed responsible for the reduction in THC. This study provides a rare dataset that describes the effects of oil pollution on a previously near-pristine estuarine environment in the tropics.