Faunal Assemblages and Biota-substrate Interactions in Tropical Nigerian Tidal Flats: Influence of Sediment Grain Size and Physicochemical Parameters

Abstract

This study investigates benthic faunal assemblages and their relationships with sediment grain size and physicochemical parameters in the tropical tidal flats of the Calabar and Great Kwa Rivers, southeastern Nigeria. Systematic seasonal sampling was carried out from July 2011 to March 2012, encompassing both the wet (April-November) and dry (December-March) seasons. This seasonal variation allowed for an examination of how temporal environmental shifts affect benthic faunal assemblages. The study employed quadrat and core sampling techniques to collect benthic fauna, with environmental parameters such as dissolved oxygen, salinity, and temperature measured in situ using portable multi-parameter probes. These methods provided a robust dataset for analyzing faunal distribution with sediment characteristics and physicochemical conditions. Results revealed that sediment texture is a key determinant of faunal community composition, with coarser sediments favouring burrowing crabs (Afruca tangeri, Cardisoma armatum) and finer sediments supporting polychaetes and bivalves. The two dominant species in the study, Uca tangeri and Cardisoma armatum, exhibited different distribution patterns related to sediment grain size and environmental conditions. In addition to the macrofauna, the study also identified meiofauna (organisms between 0.1 and 0.5 mm) and microfauna (organisms smaller than 0.1 mm) in sediment samples. These organisms were most abundant in fine sediments. Dissolved oxygen was identified as a critical environmental variable influencing species diversity and abundance. Spatial and temporal variations highlight the dynamic nature of these intertidal ecosystems, with anthropogenic activities such as dredging and urban runoff negatively impacting faunal diversity and sediment quality. This multidisciplinary approach fills significant knowledge gaps in West African tropical tidal flat ecology and provides essential baseline data to guide coastal habitat conservation and sustainable management under environmental change.