Valeriia Makarenko

This study uses data of nearshore invertebrate benthic communities on the Canadian side of Lake Ontario surveyed by Ministry of Environment in 1981, 1991 and 2003 at a depth of 5 and 20 m. In total 52 sites were sampled along the shoreline from just west of the Niagara River in western Lake Ontario to just off Kingston, in eastern Lake Ontario. The study was designed to determine if the nearshore community structure reflected land-use practice within associated drainage area and changes in land-cover within a ten year period. The comparison also was made to determine the extent at which benthic community reacts to the invasion Dreissena bugensis (quagga mussel). The changes in land-cover were calculated with Remote Sensing (RS) technologies. Demographic changes were calculated based on Census Canada data. Five descriptors of community structure were chosen: Abundance, Richness, Shannon-Weiner index, Simpson‘s Diversity index and Modified Environmental index.
In general, both 5 and 20m communities reflected the expected changes within two periods from 1981 to 1991 and from 1991 to 2003. A significant decline in richness and abundance, a domination of the P. Arthropoda group, a general growth in diversity indices, and a reduction of values of the environmental index demonstrate the trend of recovering and changing of lake conditions to oligotrophic. However, the invasion of D. bugensis distorted the picture significantly. Between 1991 and 2003 a significant growth of benthos abundance at both 5m and 20m depth was registered. Both Shannon-Weiner and Simpson‘s Diversity indices were strongly correlated and showed a significant shift in structure of community with a trend to homogeneity. Homogeneous structure of community was formed by prevalence of D. bugensis and worms (P. Annelida). The environmental index significantly increased indicating the eutrophic changes within the lake.