Soil Microarthropods in A Secondary Rainforest, Rivers State, Nigeria - III- Partial Recovery after an Oil Spill

Investigations were undertaken at 4 habitat-types (unpolluted, oil-polluted 1year, 3 and 6 years pre-study) in a secondary rainforest, Nigeria, to determine trends in the natural recovery of soil micro-arthropods (mites and Collembolan) in the polluted habitats. Soil samples were taken monthly with an 8.5cm-diameter bucket-type auger over a 2yr-period (May, 2007 - April, 2009). Extraction was by the Berlese-Tullgren funnel. Identification was conducted with the aid of standard keys and comparisons of unidentified species with type specimens. Mean Total Hydrocarbon (THC) values were 10mg/kg (undisturbed) 630mg/kg (polluted 1 year pre-study) 260mg/kg (polluted 3 years pre-study) and 125mg/kg (polluted 6years pre-study) habitats. In all habitat-types, Cryptostigmata (Oribatida) were the most abundant mites. Three of the 11 Oribatid species were absent from the habitat polluted, 1-year pre-study but re-colonized the habitat polluted 3 years pre-study, while 4 of the 5 Mesostigmata species re-colonized this habitat. In the habitat polluted 6years pre-study, two more Oribatid species and the Mesostigmata Prodinichidae species re- colonized this habitat. In contrast, approximately 8 years after the oil spill, 5 Oribatid species and the Mesostigmata, Uropopidae spp never recovered. The Collembolan sp Hypogastina, absent from the habitat, polluted 1 year pre-study, re-colonized the habitat, polluted 3 years pre-study. There were significant positive correlations between total mite and collembolan densities and the length of the intervening periods between occurrence of spill and commencement of the study. (Fcal=4.63; Ftab=3.62; P< 0.05; Fcal=7.80; Ftab =3.62; P<0.05). The implications of these results in the bio-monitoring of oil- polluted habitats are discussed.