Abstract
<title>Abstract</title> <p> Contemporary coastal ecosystems worldwide are experiencing accelerating environmental change driven by natural processes and human activities. Marine sedimentary environments are highly dynamic, with benthic macrofauna serving as important biological indicators for assessing environmental quality. Placentia Bay is a subarctic embayment on the southeast coast of Newfoundland (47.1030 °N, 54.1859 °W) that has been identified as an Ecologically and Biologically Significant Area (EBSA) exposed to anthropogenic stressors. This study examines spatial patterns in macrofaunal communities among six inshore sites in the bay in relation to environmental and anthropogenic factors, including sediment characteristics and contaminants (e.g., total organic matter, sediment grain size, chl- <italic>a</italic> , phaeopigment, heavy metals, and polycyclic aromatic hydrocarbons [PAHs]). Spatial patterns were consistent among abundance, presence/absence, and biomass datasets with the head of the bay representing the most distinct community. Low macrofaunal density, species richness and diversity, at the head of the bay, were associated with elevated levels of total organic matter, while community patterns were most closely associated with heavy metal concentrations. Three heavy metals (i.e., arsenic, chromium, copper) exceeded interim sediment quality guidelines, indicating potential for occasional adverse biological effects, with the highest concentrations observed in the upper western channel, where lead also exceeded quality guidelines. In contrast, PAHs were not associated with macrofaunal community patterns and remained below available sediment quality guidelines. Understanding spatial variation in macrofaunal composition and abundance is essential for identifying long-term ecological change and its drivers. This study provides the first contemporary evaluation of sediment contaminants in this dynamic subarctic embayment, supporting ongoing monitoring and management. </p>