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The vertical and horizontal distribution of two burrowing mud crabs, Uca tangeri Eydoux (1935) (Ocypodidae) and Ocypode cursor Linne 1758 (Ocypodidae) are described for the Bonny Estuary (7" 00' E: 4" 20' N), S. Nigeria. Substratum preference is the most prominent factor influencing distribution, but lack of tolerance to low salinities (<6%,) is also important, and prevents Ocypode cursor from occurring close to freshwater. The two species have slightly different sediment organic content and grade size requirements. Ocypode cursor was concentrated in well drained sandy sediment above mid-tide-level, whilst Uca tangeri was found in water-logged areas slightly above and below Mid-tide-level. This vertical demarcation is attributed to differential feeding and burrowing adaptations related to different substrata, rather than to differential tolerances to desiccation.

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Quantitative surveys of the intertidal macro-fauna were conducted during September-October 1998 along transects established at various locations along the Nigeria coastline, following the rupture of a 24-inch pipeline at Idoho, off the Gulf of Guinea, southeastern Nigeria on 12 January 1998. Samples were taken within impacted areas and at control unpolluted sites approximately 5 km to the east of the Idoho off-shore platform. Spilled oil moved rapidly ashore and into river mouths, and estuaries and their mangals shortly after the spills. Biomass of macrofauna in the impacted areas tended to decrease with level of oiling, as the mean abundance decreased rapidly to about 50% of that found on the control unpolluted sites. Edible gastropod, mainly species of Tympanotomus fuscatus, and the brachyuran decapod, Uca tangeri, typically consumed by coastal inhabitants, had reduction in mean densities (up to 62%) in the oiled Bonny, Brass, Lagos and Forcados than in the non-oiled areas of Imo, Andoni and Cross River, showing partial recovery of the environment from the debacle after 9 months. The ecological implications of these findings are discussed. IntroductionA 24-inch oil pipeline ruptured at Mobil-Idoho platform on the inner shelf of the Atlantic coast of southeastern Nigeria on 12 January 1998 releasing over 40,000 bbls (approxi-mately 6,000 tones) of Qua Iboe light crude oil into the marine environment over the next three days. More than 700 km of the Nigerian coastline including estuaries were impacted. Within the impacted zone were a number of macro-benthic communities, the dominant species of which included the edible gastropod, Tympanotomus fuscatus, the Ocypodid brachyuran, Uca tangeri and Ocypode cursor, and several species of bivalves and polychaetes. Some of the estuaries that were oiled are known to be subject to pollution from a number of sources including hydrocarbon, sewage, metal, etc., showing that the spill was not in a pristine environment. It was, therefore, essential to include as many factors as possible in the sampling programme to look at the spill effects.In September 1998, 9 months after the oil came ashore, a rapid assessment survey was conducted at nearly all the estuarine/river mouths along the Nigerian coastline both within the oil impacted estuaries and at the clean control site, 5 km east of the ruptured point. This included measurement of physical and chemical parameters of sea water, and presence and absence of typical macrobiota, together with estimates of overall abundance at each site. Analysis of biota and physical characteristics demon-strated that a full range of Nigeria coastline habitat was present within the impacted area (Ewa-Oboho, 1998). As separation and classification of intertidal habitats were possible on the basis of macrobiota alone, this survey demonstrated that earlier predictions of massive species elimination were unfounded, and the result provided the basis for selection of permanent sites for longer-term studies published elsewhere (Ewa-Oboho, in press...