Although invertebrate communities are used in the evaluation of created freshwater wetlands, spatial patterns of invertebrate community structure are frequently ignored. Invertebrate distributions are generally associated with plant community distribution in natural aquatic ecosystems. In this study, 180 core samples were collected to examine associations between chironomid (Diptera) genera and emergent vegetation communities in a single created freshwater herbaceous wetland in central Florida. Three of the five common genera were significantAy more abundant (p <0.05, Wilcoxon Rank Sum Test) in areas with greater than 50% cover by emergent vegetation than in open water, but no differences were found between areas dominated by Pontederia cordata and areas dominated by mixed emergent vegetation. Samples from an area of open water and an area with over 80% cover by P. cordata showed significant differences in abundances of all common chironomid genera (P<0.05, Wilcoxon Rank Sum Test). Results suggest that sampling designs for studies comparing benthic invertebrate communities from natural and created wetlands should consider the possible associations between vegetation and invertebrate communities.
This study compares densities of common larval dipterans collected from areas dominated by Pontederia cordata in t0 natural and 10 created freshwater herbaceous wetlands in central Florida. At each wetland, 7 core samples were collected from each of 5 stations during summer 1993. In addition, stem densities, vegetation areal coverage, pH, dissolved oxygen, water temperature, water depth, conductivity, sediment quality, and leaf litter were measured at 3 locations near each of the 5 stations in each wetland. Of the 57 dipteran taxa collected, 20 occurred with sufficient abundance to justify statistical comparison. Despite a large sampling effort, there were no significant differences in densilies of 20 commonly occurring taxa found in created and natural wetlands after considering the effect of multiple univariate tests. Comparison of environmental variables showed significant differences in stem densities for vegetation other than P, cordata, pH, conductivity, and sediment quality. Canonical correspondence analysis, used to relate environmental and biological variables, suggests that pH, conductivity, and sediment quality are only weakly related to dipteran community structure. Despite differences in environmental conditions, there is no convincing evidence of differences in natural and created wetland dipteran communities.
Changes following culvert removal in the production of the saltmarsh mosquito, Aedes vigilax (Skuse), and the cover and occurrence of halophytes were investigated on Kooragang Island, New South Wales, Australia. Mosquito eggshells were collected from saltmarsh soil and used as an index of mosquito production. Saltmarsh bordering each of four tidal creeks was sampled prior to the removal of culverts from two of these creeks in 1995. All creeks were resampled two years later. In most instances, eggshell densities decreased significantly at saltmarshes affected by culvert removal, with relatively small change at reference saltmarshes. However, oviposition by Ae. vigilax was initiated in upland areas following culvert removal at one site. Sarcocornia quinqueflora cover decreased significantly at sites affected by culvert removal relative to reference sites. The cover of Sporobolus virginicus and frequency of occurrence of Triglochin striata increased significantly at one modified site, while the frequency of occurrence of Avicennia marina seedlings increased significantly at the other modified site. We suggest that culvert removal and other alterations intended to increase tidal flushing will lead to vegetation patterns and mosquito eggshell densities that typically occur in the more frequently inundated saltmarsh–mangrove complex.
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