Chironomidae: Linking Biodiversity and Bioassessment I
Presiding: S Gresens, Towson University; D R Francis, Department of Geosciences, University of Massachusetts
NB21C-01 INVITED 08:30h
Monitoring With Midges: Body Size, Bias and Biomonitoring.
Effective use of Chironomidae in biological monitoring programs requires accurate assessments of taxonomic composition and relative abundance. Simultaneous collections of surface-floating pupal exuviae (SFPE) and d-net samples for larvae (DNL) in studies based in Pennsylvania and Kansas reveals that samples of SFPE consistently result in higher species richness estimates and differing patterns of taxonomic composition and relative abundance, especially for smaller species (ie., maximum larval length of 5-6 mm). Calculations of Biotic Index values (BI) yield higher values for DNL than SFPE, primarily related to increased tolerances to lower dissolved Oxygen of larger species of Chironomini (maximum larval length greater than 10 mm) in DNL. Simulations employing selective deletions of smaller species from SFPE samples collected from several sample sites in Minnehaha Creek (MN) substantially increase calculated BI values, in some cases 2-3 points. We conclude that under-representation of smaller species in DNL samples can be a wide-spread and pervasive problem that results in inflated BI values, which can lead to inaccurate judgments regarding water quality. These results, combined with previous studies indicating that SFPE are more cost-efficient to process and quantify, clearly demonstrate that SFPE should be integrated into biological monitoring programs if Chironomidae are to be properly utilized.
http://www.entomology.umn.edu/midge/index.htm
NB21C-02 INVITED 08:45h
Midge Diversity and Bioassessment in the Everglades
Everglades midge community composition is strongly dependent upon hydroperiod (HP) and water quality. Longer HPs are generally associated with higher alpha diversity, species density, and total species richness. However, the development of extensive calcareous periphyton growth in marshes with 4-10 month HPs strongly influences community structure, and diversity and richness measures show no change along marl prairie HP gradients. Increases in species density with hydroperiod represent increases in habitat volume and productivity, not changes in community structure. Beta diversity is greatest when transitioning from marshes with 7-10 month HPs to those with >10 month HPs. At these HP lengths / water depths, plant communities that permit extensive periphyton growth are replaced by plant communities that inhibit periphyton growth, enable more organic soil development, and provide habitat for more specialized species. Point-source nutrient enrichment produces strong shifts in Everglades midge community composition, thereby increasing gamma diversity along nutrient gradients. Biologists studying invertebrate communities have reported either little structural change, or increases in species density, diversity and richness near sources of enrichment. I will report on midge community structural responses along a variety of nutrient gradients in the Everglades, and discuss important differences between pupal exuviae sampling and conventional larvae sampling.
NB21C-03 INVITED 09:00h
Using Midges to Assess Past Climate Change in New England and the Canadian Arctic.
Paleolimnology has become an important tool in environmental monitoring programs because it can provide baseline data often unavailable by other means. Remains of midges (Chironomidae and other Diptera) have proven useful in paleolimnological biomonitoring of anoxic conditions, nutrient loading, toxic pollutants, and climate change. Analyses of lake sediment cores from Baffin Island highlight faunal changes during the Holocene and indicate warm conditions in the early Holocene. Diversity tends to be low in late-glacial sediments and then increases as climate warms and the landscape develops. In New England lake cores, the much more subtle climate change known as the Little Ice Age can be seen in changes in the chironomid fauna. Using midges as paleoindicators requires modern "training sets" that quantify larval midge distributions across environmental gradients. Surficial sediment samples collected for training sets contain head capsule remains from the whole lake and represent an integrated sample of the modern fauna. These techniques may be useful for investigating chironomid diversity. Typically, head capsule remains can be identified only to genus but since many rapid biological assessment methods take the Chironomidae only to the family level, collection of head capsule remains could be a useful alternative.
NB21C-04 INVITED 09:15h
Revealing the Biodiversity in Chironomidae (Diptera): Results From an Emergence Trap Study of a Ravine Spring-run in Northern Florida
Research for this project was conducted as part of a larger scale investigation of the aquatic insect fauna of a Florida spring-run ravine system that focused especially on stonefly and caddisfly taxa. The present research focused largely on documenting chironomid midge species diversity, emergence phenology, and overall composition by utilizing repeated emergence trap sampling at a single site within a first order, forested ravine stream in the Florida panhandle area. The approximate two year survey revealed a rich and distinctive chironomid fauna, with a variety of feeding types and microhabitat specific taxa. Many of the study species were considered to be common and widespread; however, several species and two genera were new records for the state. Several undescribed species were also noted. Emergence occurred in all months but with greatest densities generally recorded from December through March of the second year. The single location examined to date on this ravine stream ranks near the upper range of chironomid species richness reported on a world-wide basis for first order lotic systems. Other aspects of composition and apparent community patterns, was well as the importance and significance of first order stream biodiversity, are examined and discussed.
NB21C-05 INVITED 09:30h
Chironomid Size Distributions in Constructed and Natural Ponds: Responses to Land use and Water Quality
Farm ponds in southeastern Minnesota are primarily constructed to prevent off-site soil erosion and to provide wildlife habitat in this predominantly agricultural landscape. Consequently, these ponds are subject to a variety of disturbances from agriculture, especially sedimentation and eutrophication. Natural ponds are rare and are located primarily at low elevations along tributaries to the Mississippi River. We examined chironomid richness, community structure and size-frequency distribution in response to a gradient of land use and water quality in 40 randomly selected ponds. Ponds were classified as natural or constructed; constructed ponds were further classified based on land use adjacent to the pond. Chironomid larvae and water quality were sampled 3 times in summer 2001. Chironomid generic richness significantly differed among pond type and community composition was strongly associated with adjacent land use. Size-frequency distributions were analyzed for the 10 most ubiquitous taxa: Polypedilum, Glyptotendipes, Chironomus, Tanytarsus, Procladius, Endochironomus, Ablabesmyia, Cricotopus, Dicrotendipes and Cladopelma. In general, slopes of normalized size-spectra for these taxa co-varied along the land use/water quality gradient. These results suggest that chironomid-body size may be a useful metric in biological assessments to evaluate the ecological integrity of constructed-pond ecosystems.