Spatial patterns in sedimentary macrofaunal communities on the south coast of Newfoundland in relation to surface oceanography and sediment characteristics

This is the first comprehensive study of the community structure and spatial distribution of macrofauna in deep, muddy sediments of Placentia Bay, Newfoundland, and the adjacent shelf. The study examines the influence of water column (e.g. chlorophyll a [chl a], temperature and salinity) and sediment characteristics (e.g. grain size, carbon and nitrogen content) on infaunal patterns. Box-core samples were collected at 10 sites in June and July of 1998 from the head of the bay to the edge of the continental shelf. Multivariate analyses of community composition and environmental variation indicated inshore and offshore groupings. Inshore communities had lower species richness, diversity and densities. Fauna living deeper in the sediment were also more abundant in offshore areas. The inshore region was characterised by greater mixed-layer temperatures, higher surface chl a and large amounts of relatively fresh organic carbon (low C/N ratios) in sediments. Within the inshore sites, high levels of organic carbon influenced macrofaunal assemblages that were similar to those characteristic of organic-rich areas. Surface chl a concentration was positively correlated with sedimentary organic carbon, which was the most important predictor of infaunal abundance. At broad scales, surface chl a and sedimentary organic carbon were negatively related to infaunal abundance. Moreover, this pattern was confounded by particularly low densities at 3 inshore sites where organic levels were very high, and elevated densities at 1 productive offshore site. Low densities at these 3 inshore sites may be a result of sulphide production in sediments, or of poor food quality. Broad-scale patterns (inshore vs offshore) of community composition and abundance in Placentia Bay are largely influenced by surface oceanography through production export.