Documentation of Mangrove Species Composition and Human Impacts in the Bonny Estuary, Rivers State

The mangrove forests of the Bonny Estuary in Rivers State, South South Nigeria, are among the most ecologically significant in West Africa, yet they face escalating threats from petroleum activities and urban encroachment that require baseline botanical documentation. This study documented mangrove species composition, structural attributes, and human impact indicators along six transects established perpendicular to the waterway in the Bonny Estuary. Field surveys were conducted during the dry season, with all mangrove species within belt transects (50m x 10m) recorded. Stem density, basal area, tree height, and condition class for each species were measured. Human impact indicators including oil spill evidence, direct tree felling, and waste dumping were recorded at each station. Four mangrove species were documented: Rhizophora racemosa, Rhizophora harrisonii, Avicennia germinans, and Laguncularia racemosa, with R. racemosa dominating by stem density (68%) and basal area. Total stem density averaged 1,340 stems per hectare, and mean canopy height was 11.4m. Evidence of oil spill impact was recorded at 67% of transect stations, with affected areas showing significantly reduced stem density and elevated tree mortality. Selective logging scars were observed on 23% of sampled trees. The study concludes that the Bonny Estuary mangroves are under severe and multi-directional human pressure, and recommends emergency community-based mangrove restoration and mandatory environmental impact monitoring by oil operators in the estuary.

Keywords: mangrove, Bonny Estuary, species composition, oil spill, Rivers State