Understanding crayfish community ecology in the context of local and regional environmental change

Previous work on Shield lakes located in central Ontario has indicated that crayfish populations have experienced significant declines in their relative abundances over the past 18 years. The purpose of this study was to identify the important environmental factors relating to crayfish species distribution, abundance and community composition. Additionally, we were interested in identifying environmental changes that may be associated with the observed changes in crayfish relative abundance. For instance, it has been recently hypothesized that decreasing lake calcium could be contributing to population declines in zooplankton. In order to address these questions, one-hundred lakes were surveyed for crayfish abundance and a number of chemical and environmental parameters. Historical survey records from the early 1990s were then used to determine whether significant changes in crayfish ecology and/or environmental characteristics have occurred. Our results indicate that a number of abiotic and biotic factors are important in shaping crayfish abundance, distribution and community composition, and that the importance of these factors has changed over time. Furthermore, we have found that changes in a number of environmental characteristics may be negatively impacting the abundance and richness of these important biological indicators.