Soil micro-arthropods in a secondary rainforest, Rivers State, Nigeria: Ecosystem health indicators of oil pollution

Abstract

Comparisons were made of the species richness and densities of soil micro-arthropods- (mites,
collembolans) from a relatively undisturbed secondary forest and a nearby area, where there had been
an oil spill, approximately 1 year before the commencement of the 2 yr study, May, 2007 to April, 2009.
Soil samples were taken monthly with an 8.5 cm diameter bucket -type auger. Extraction was by the
Berlese-Tullgren funnel. Identification was undertaken with the aid of standard keys and comparisons
were made with type specimens. Mean Total Hydrocarbon (THC) values were 630 mg/kg (43.0 to 1000.0)
and 10 mg/kg at the polluted and undisturbed habitats respectively. Among the mites, Cryptostigmata
(Oribatids) were dominant in both undisturbed (69.85%) and polluted (74.25%) habitats; the least
abundant were the prostigmates. Within the oribatids, Scheloribates spp., Galumnidae spp.,
Parallonothrus nigeriensis and Bichythermamia nigeriana were collected from both habitat types. In
contrast, Mixacarus sp., Aunecticarus sp., Atropacarus sp., Bellidae sp., Cephalidae sp., Oppia sp.,
Basilobellidae sp., Epilohmaunia sp., Mesoplophora sp., Aecheogozettes magnus and Northrus
lasebikani were restricted to the undisturbed habitat. In the Mesostigmata, only Parasiticidae sp . and
Rhodacaridae sp. were found in both habitat types; Polyaspidae sp., Uropodidae sp. and Asca sp. were
restricted to the undisturbed habitat. The Prostigmata, Bellidae sp. were collected from undisturbed and
polluted habitats. Among Collembolans, Cryptophagous and Paranolla were found in both habitat types
while Hypogastina, was restricted to the undisturbed habitat. Abundance and densities of mites and
collembolans were respectively significantly reduced in the polluted habitat (p < 0.05; df = 9; F = 20.5; p
< 0.05; df = 9; F = 30.08). These findings are discussed within the context of the use of monitor (tolerant)
and indicator (sensitive) species in bio-monitoring and assessment of oil pollution.