Macrofaunal spatial patterns in relationship to environmental variables in the Richibucto estuary, New Brunswick, Canada

Estuarine macrobenthos respond to a variety of environmental gradients such as sediment type and salinity, and organic enrichment. A relatively new influence, organic loading from suspended bivalve culture, has the potential to alter this response. A study on soft-bottom macrobenthic communities was carried out in the Richibucto estuary (46 degrees 40'N, 64 degrees 50'W), New Brunswick, Canada, with samples collected from 18 stations in late September and early October 2006. The site consisted of a large tidal channel originating upstream in a small river. The channel was punctuated by bag culture of oysters along its length. A total of 88 species were recorded. The mean values of abundance, species richness, and diversity (H') of macro-fauna were 11,199 ind. m(-2) (ranged from 4,371 to 19,930 ind. m(-2)), 23.4 species grab(-1) and 3.29 grab(-1), respectively. In general species richness and H' increased from the upper estuary to the estuarine mouth. Multivariate analyses clearly exhibited the spatial distribution in community structure, which coincided with the locations along the estuary (the upper, the lower and the mouth), as well as inside and outside the channel. Species richness and diversity H' showed strong positive correlations with salinity (21.2-25.2 ppt), and abundance was positively correlated with water depth (1.0-4.5 m). Abundance and species richness were negatively correlated with both of silt-clay fraction (3.3-24.8%) and sorting (sI). Species richness was also negatively correlated with organic content (1.9-12.7%). The BIO-ENV analyses identified silt-clay fraction, sI and salinity as the major environmental variable combination influencing the macrofaunal patterns, and silt clay fraction as the single best-correlated variable.