Emergence of Aquatic Insects from 2 Habitats in a Small Wetland of the Southeastern USA: Temporal Patterns of Numbers and Biomass

• Published in: Journal of the North American Benthological Society 1998-03, Vol.17 (1), p.37-53
• Main Authors: Stagliano, David M., Benke, Arthur C., Anderson, David H.
• Format: Article
• Language: English
• Subjects: Adult insects; Aquatic insects; Biomass; Chironomidae; Emergence; Freshwater; Freshwater ecology; Insect larvae; Insecta; Ponds; Taxa; Wetland ecology; Wetlands
• ISSN: 0887-3593; 1937-237X
• DOI: 10.2307/1468050

Emergence of aquatic insects from freshwater systems can provide information that is useful from both taxon-specific and ecosystem perspectives. Although numerous studies of emergence have been conducted in high-latitude systems, relatively few studies have been done in warm-water systems, particularly in wetlands, where multiple generations and long emergence periods are likely. We used emergence traps in a small beaver-impounded wetland in the southeastern USA to measure density and biomass of emerging insects, and deposition basins to measure adult return and potential export from the system. We focused on 2 major habitats of the wetland: a shallow (0-1.0 m) vegetated zone dominated by the white water-lily Nymphaea odorata and a deeper (>1 m) open-water zone. Insects (primarily Chironomidae) emerged from the Nymphaea zone throughout the year, but peaked in April at 205 individuals·m-2· d-1 and then declined from mid June to November to 20-50· m-2· d-1. Emergence from November through January was $33% of the emergent biomass in the Nymphaea zone, whereas Chaoborus punctipennis and Cladopelma sp. accounted for 19% and 21% of the emergent biomass, respectively, from the open-water zone. The emerging densities and biomasses of at least 6 taxa were significantly higher in the Nymphaea zone than in the open-water zone, and only Chaoborus was higher in the open water. Depositional trapping showed that deposition of adult insects in the aquatic environment averaged 25% of emerging numbers and biomass. The mayfly Caenis diminuta was common in deposition traps (1253 individuals·m-2· y-1), but avoided emergence traps. Both emergent and depositional trapping appeared necessary to quantify terrestrial activities of aquatic insects. Future comparisons of emergence and deposition data with larval production in the wetland will enable us to determine the fraction of production that is represented by emergence and the fraction that returns to the aquatic environment.