Impacts of Inorganic Pollution on Marine Benthic Communities

Abstract

Anthropogenic pollution in marine ecosystems have greatly increased globally resulting to serious negative impacts on the lives of benthic communities (meiofauna and macrofauna). The impact of heavy metal pollution on these organisms was studied in two sites (Mikindani in Tudor creek and Dabaso in Mida creek) that had different levels of pollution. Samples were collected and analyzed during the dry season (January/February 2017) and wet season (November/December 2017) for dissolved oxygen (DO), biological oxygen demand (BOD), heavy metals, total organic matter (TOM), sediments grain size and macrofauna and meiofauna. Results showed that TOM was significantly (p=0.019) higher in Dabaso (23.9±0.7%; 23.9±0.03%) than in Mikindani (6.6±0.2%; 5.9±0.1%) (p=0.03) during dry and wet season respectively. BOD was significantly (p=0.039) higher in Mikindani (4.8±0.2 mg/L) than Dabaso (3.4±0.1 mg/L) in the dry season while in the wet season it was significantly (p=0.041) higher in Dabaso (3.5±0.03 mg/L) than Mikindani (2.8±0.03 mg/L). The concentration levels of all heavy metals identified (Ti, Mn, Rb, Zr, Fe, Zn, Pb) were higher in Mikindani as compared to Dabaso. Macrofaunal densities were significantly (0.024) higher in Dabaso (14470±2049; 42489±2896) ind/m2 compared to Mikindani (8879±376; 21507±1841) ind/m2 (p=0.013). Similarly, meiofaunal densities were significantly (p=0.027) higher in Dabaso (2729±387; 2805±387) ind/cm2 compared to Mikindani (604±114; 183±30) ind/cm2 (p=0.017) in dry and wet seasons respectively. A strong spatial variation between the two sites was exhibited in the structure of benthic communities. The study proves that heavy metals played a very significant role in structuring of benthic communities therefore contributing to better understanding of their response to marine inorganic pollution. Comprehensively, this study confirmed the assessment of impacts of marine inorganic pollution on benthic communities between two sites of different pollution levels. There is need to conduct further research to identify the exact source of sediments drained in Mikindani creek in order to determine whether heavy metals origin is from sediments in neighboring community or sewage.