The purpose of this study was to analyze the long-term density variation of the dominant species Theora lata in Gwangyang Bay, where industrial complex expansion has led to a continuous inflow of pollutants, and to examine its correlation with benthic environmental factors. To investigate the benthic habitat conditions and population density variations of T. lata, 23 seasonal field surveys were conducted between February 2008 and July 2012. Sampling was concentrated around Myodo, and 17 stations were selected, including areas influenced by the inflow of the Seomjingang River. The mean organic matter content across all stations was 8.74±1.41%, with the highest value of 13.62% recorded at Station 1 in July 2013. The total acid volatile sulfide (AVS) concentration averaged 0.44±0.49 mgS/g-dry, peaking at Station 1 in October 2008. The mean density of T. lata across Gwangyang Bay was 106±140 ind./m², with the highest recorded abundance of 2,445 ind./m² at Station 12 in April 2008. Although variations in organic matter content and AVS concentration were observed, statistical analysis showed no significant correlation between these factors and T. lata density. Seasonal fluctuations in T. lata density were evident, with population peaks in spring, followed by a sharp decline from summer onward. Overall, the variation in habitat density of the opportunistic species Theora lata appeared to be more significantly influenced by water environmental factors than by sedimentary environmental factors.