The effects of subsampling and sampling frequency on the use of surface-floating pupal exuviae to measure Chironomidae (Diptera) communities in wadeable temperate streams

Abstract

Community, diversity, and biological index metrics for chironomid surface-floating pupal exuviae (SFPE) were assessed at different subsample sizes and sampling frequencies from wadeable streams in Minnesota (USA). Timed collections of SFPE were made using a biweekly sampling interval in groundwater-dominated (GWD) and surface-water-dominated (SWD) streams. These two types of stream were sampled because they support different Chironomidae communities with different phenologies which could necessitate sampling methodologies specific to each stream type. A subsample size of 300 individuals was sufficient to collect on average 85% of total taxa richness and to estimate most metrics with an error of about 1% relative to 1,000 count samples. SWD streams required larger subsample sizes to achieve similar estimates of taxa richness and metric error compared to GWD streams, but these differences were not large enough to recommend different subsampling methods for these stream types. Analysis of sample timing determined that 97% of emergence occurred from April through September. We recommend in studies where estimation of winter emergence is not important that sampling be limited to this period. Sampling frequency also affected the proportion of the community collected. To maximize the portion of the community, collected samples should be taken across seasons although no specific sampling interval is recommended. Subsampling and sampling frequency was also assessed simultaneously. When using a 300-count subsample, a 4-week sampling interval from April through September was required to collect on average 71% of the community. Due to differences in elements of the chironomid community evaluated by different studies (e.g., biological condition, phenology, and taxonomic composition), richness estimates are documented for five sampling intervals (2, 4, 6, 8, 10, and 12 weeks) and five subsample sizes (100, 200, 300, 500, and 1,000 counts). This research will enhance future studies by providing guidelines for tailoring SFPE methods to study specific goals and resources.

Use of Chironomidae (Diptera) Surface-Floating Pupal Exuviae as a Rapid Bioassessment Protocol for Water Bodies

“…Even with multiple, seasonally targeted sampling events, a proportion of the community will remain undetected, although these are often rare taxa 31 . For sampling frequency recommendations, see Bouchard and Ferrington 9 for streams and Rufer and Ferrington 23 for lakes. The main concern regarding sampling methodology relates to SFPE floating distance.…”

“…7,[16][17][18][19] ), and biological assessments (e.g., [20][21][22] ). Additionally, some studies have addressed different aspects of sample design, sample size, and number of sample events required for achieving various detection levels of species or genera (e.g., 8,9,23 ). These studies indicate that relatively high percentages of species or genera can be detected with moderate effort or expense associated with sample processing.…”

Seasonal variation in Chironomid emergence from coastal pools

“…From April to October, 2010, six sampling rounds occurred approximately monthly, with each round was clustered in a 3-9 day period: April 22-28, May 9-17, June 3-8, July 3-9, August 3-6 and October 2-4. Monthly sampling was expected to be sufficient for detecting a majority of richness (Bouchard and Ferrington 2011). At each site in each round, six chironomid pupal exuviae samples were collected, with 143 total samples (one less than expected due to a dry pool on 3 June).…”

Characterization of Chironomidae (Diptera) surface-floating pupal exuviae sample sort time from coastal tropical aquatic systems

“…In comparison to collections of larvae from benthic samples, SFPE collections improved taxonomic resolution by enhancing ease of genus and species identification, increased the number of taxa detected, and allowed for collection from a range of microhabitats, including those difficult to sample with other sampling methods (e.g., wood, hyporheic, sand, and deep water) ). In addition, this method provides estimates of individuals that survived as immatures and emerged as functional adults; therefore, SFPE collections can be considered a better measure of the water quality characteristics of the aquatic system, since they correspond to an organism that successfully utilized the habitat (Bouchard and Ferrington 2011) (for a more in-depth review of the advantages and disadvantages of the SFPE method, see Kranzfelder et al (in press)). …”