A Great Lakes Coastal Wetland Invertebrate Community Gradient: Relative Influence of Flooding Regime and Vegetation Zonation

Wetland invertebrate community composition is affected by habitat conditions associated with flooding regimes and vegetation characteristics, yet distinguishing among these influential factors is difficult because they tend to co-vary spatially. We studied a Great Lakes coastal wetland invertebrate community along an elevation gradient as Lake Huron water level rose and fell over a three-year period. This hydrologic variation caused changes in the gradient of flooding conditions, while plant zonation remained relatively unchanged. Multivariate analysis indicated that the invertebrate community varied continuously along the elevation gradient, and that it changed substantially within vegetation zones as water level changed. Variation across the gradient decreased because the high-elevation wet meadow community became more similar to lower-elevation communities as a result of upslope expansion in distributions of many taxa, and substantial increases in dominance of a subset of taxa. Invertebrate density increased dramatically with high-water conditions, and diversity decreased in general. Results suggested that invertebrate community composition was influenced by flooding conditions more than vegetation. These results may have important implications for conservation of high-elevation wetland zones as high-water refuges for wet-meadow invertebrates, and for coastal wetland monitoring schemes based on vegetation zones as habitat for particular invertebrate assemblages.