Temporal Patterns and Station-Wise Variation in Heavy Metal Concentrations in Gladiator Crab (Callinectes Pallidus) From Awoye River, Ondo State, Nigeria

Heavy metals in aquatic organisms provide important information on biological exposure and accumulation in coastal environments. This study evaluated station-wise, monthly and seasonal variations in Fe, Zn, Mn, Cu, Ni, Cd, V, Cr and Pb concentrations in gladiator crab (Callinectes pallidus) from Awoye River, Ondo State, Nigeria. Crab samples were collected from NNPC Platform, Stone Jetty and Awoye Gulf between January and June 2015, acid-digested and analysed using atomic absorption spectrophotometry. Fe showed the strongest spatial variation, with the highest mean concentration at NNPC Platform (75.74 ± 35.97 mg/kg), while Mn and Cr also showed significant differences between selected stations. Monthly variation was evident for several metals, with Zn, Mn, Cu, Ni, Cd, V, Cr and Pb attaining their highest mean concentrations in June, whereas Fe peaked in March. Seasonal comparisons showed higher numerical concentrations of most metals during the rainy period across the three stations, although Fe at NNPC Platform showed the opposite pattern. The study concludes that heavy-metal accumulation in C. pallidus was metal-specific and varied spatially and temporally rather than following a uniform accumulation pattern. Continued monitoring of metals in aquatic organisms alongside environmental matrices is recommended to improve assessment of biological exposure and changes in the aquatic environment.