| Summary: | Studies examining biological communities in relation to environmental factors over time are essential for understanding natural sources of community variation (i.e., structure and function), as well as their response to stressors. Benthic macrofauna are important biological indicators used to assess environmental quality in marine ecosystems. Placentia Bay is a large subarctic embayment on the southeast coast of Newfoundland (NL) that has been identified as an Ecologically and Biologically Significant Area (EBSA) that is exposed to anthropogenic stressors (e.g., fisheries and hazardous substances). The overarching aim of my thesis research was to assess the influence of various environmental factors on the community structure and functional traits of macrofauna in Placentia Bay using contemporary and historical biological and environmental data. Comparison of macrofauna at 8 stations sampled in 1998 and 2019–2020 (n=77) showed significant temporal changes in community structure and function, without loss of function (i.e., 36 morphological/behavioral modalities). The historical community had significantly higher densities, but lower evenness and diversity compared to contemporary years. Macrofauna were dominated by highly tolerant (82.3%) subsurface deposit feeders (62.1%) having small body sizes, whereas contemporary communities had a higher proportion of medium tolerant species/taxa (7.2 vs. 36.7%) and nearly equal proportions of subsurface and surface deposit feeders (26.7 and 29.1%) with small-medium body sizes. These changes are likely a reflection of the large reduction in the relative proportion of polychaetes (91 vs. 58%). Community patterns were related to the sedimentary habit. Sediments have become coarser with higher levels of sedimentary total organic matter in the contemporary compared to the historical years. Interestingly, while grain size has also become coarser between 2019 and 2020 communities were similar. Moreover, even though contaminants (examined in 2020 only) were not above probable ...
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