Introduction

1. An analysis of the aquatic insect communities of McMichael Creek, PA under open and closed canopies Christopher Hartzler, James Hartzler, Bradley Rehnberg Department of Biological Sciences, York College of Pennsylvania • Introduction • Aquatic insect communities are highly diverse in their trophic adaptations, having different feeding preferences and mechanisms for obtaining food. Among them are guilds spread across several taxa that use appendages adapted to filtering food, that build structures to capture food, collect organic matter from streambeds, or are predaceous to other insects(McCafferty 1998). Other guilds consume living or dead particulate matter at various states of decomposition. • By studying the diversity in the exploitation of food sources among aquatic insect guilds, and sampling different habitats, it has been shown that quality of those sources is held above quantity. Habitats that differ in riparian canopy have been found to have significant differences in aquatic insect diversity and total abundance (Hawkins et al. 1982). Riparian canopies play a crucial role in determining both food quality and availability through the production of leaf litter (Short et al. 1980). Streams with open canopies have been shown to have higher abundance both in total number and among certain taxa and feeder types (Hawkins et al. 1982). • By continuing to study abundance and diversity in aquatic insect communities under different canopy types, the ecology of benthic habitats may be further understood. McMichael Creek in the Poconos of PA was the site of this study. Three tributaries (Hypsy Creek, Bower’s Creek, and Fall Creek) converge to form McMichael, which then runs 32 Kilometers to empty into the Brodhead Creek in Stroudsburg, PA. Artificial substrate baskets were placed into the stream at areas with open and closed canopies, and colonized by insects for several weeks, then were removed for counting and identification. • Discussion of Results • Canopy type was found to have a significant impact on the aquatic insect population (Table 4), with the open canopy samples yielding a higher total abundance. Unpaired t-tests showed significant differences between open and closed canopies in each of the 3 collections (p-values given in Table 4). • Differences in diversity of the aquatic insect population between canopy types were negligible, with the closed canopy showing slightly higher diversity according to the Shannon-Weaver diversity index. Dominance-diversity curves for canopy type (Figure 3), however, suggest that the closed canopy had slightly higher diversity according to slope of its curve. • Analysis of feeding behavior among taxa (Tables 2 and 3) showed collector-gatherers to be the highest in density, with collector-filterers being the next highest in density under both open and closed canopies. Variation in the densities of some feeder types between canopy type were similar to Hawkins et al. (1982) in that scrapers, which are expected to be higher in density under open canopies, were actually found in higher densities in closed canopies. Another similar result showed shredders, which are thought to benefit from a primarily deciduous canopy (as it was in the closed canopy site), represented a lower percentage in the closed canopy than in the open canopy. • Between the 3, 6, and 9 week colonization times (Figures 2 & 4), total insect yield in closed canopy samples showed a 4.7% decrease in the second (6 weeks) collection, then a 99.8% increase in the 3rd (9 weeks) collection. In the open canopy samples, total insect yield increased 9.1% in the second collection, and an increase of 94.0% in the third collection. Table 2. Percentages of feeder types between open and closed canopy sites (per 645cm2). Table 3. Mean densities of invertebrates and their feeding morphology between open and closed canopy sites (per 645cm2). • Goals of this study • Observe any significant difference in the total abundance of aquatic insects under open and closed canopies. • Observe any variation among taxa and feeding morphology of the insect communities under open and closed canopies. • Show how different colonization times in artificial substrate replicates may impact abundance in samples. • Conclusions • Canopy type should be considered a variable when sampling streams for aquatic insects, as it can affect total abundance and alter representations of population and diversity of taxa. • Diversity in feeding morphology of aquatic insect communities can be influenced by canopy type. There has not yet been enough consistent evidence to support any guild preferring a canopy type. While this study focused primarily on analyzing abundance and diversity of aquatic insects as it relates to canopy type, the relationship of feeding morphology requires further research into McMichael Creek’s crop of benthic food sources. • Kick nets, Surber samplers, and other in-stream sampling techniques are some of the most commonly used practices in collecting benthic samples. The use of artificial substrate baskets and trays may also be used, however there has been little research done to establish an adequate basis for what length of time artificial substrates should stay in streams during sampling. Further study on the colonization of artificial substrates may offer new ways of sampling benthic communities and how they are represented. Figure 1. Mean density of the 4 dominant orders of aquatic insects per basket (645cm2) for each collection. Table 1. Families of macroinvertebrates and their total abundances found in open and closed canopy basket samples. Out of the 19 families found in both open and closed canopy samples, 13 were more abundant in the Open canopy, 5 were more abundant in the Closed canopy, and 1 was found equally in both. * = Identified to genus • Methods • Artificial substrate baskets (25.4 x 25.4 x 10.2 cm) containing 2.5-7.6 cm riverstone were placed in McMichael's Creek in May of 2010. • A total of 36 baskets were used and divided evenly between two locations with similar dimensions, water velocity, and geographical location. One location had an open tree canopy with no vegetation directly overhead the sample site, while the other had a riparian canopy of primarily deciduous trees. • At 3, 6, and 9 weeks after initial placement, six baskets from each site were randomly selected to be removed, cleaned of all debris and animals, and preserved in alcohol. • All suspension samples were searched for aquatic insects, identified to family, and counted. Table 4. Total aquatic insects found in samples from each collection under open and closed canopies. Unpaired t-tests showed significant differences in all 3 collections. P-values were as follows: collection 1 = 0.0112, collection 2 = 0.0014; collection 3 = 0.0022. For all collections, open canopy had higher total insects. Works Cited Hawkins, Charles P.,Murphy, Michael L., Anderson, N.H. 1982. Effects of canopy, substrate composition, and gradient on the structure of macroinvertebrate communities in Cascade range streams of Oregon. Ecology. Vol. 63:1840-1856. McCafferty, Patrick W. 1998. Aquatic Entomology: The Fisherman’s and Ecologist’s Guide to Insects and Their Relatives. Jones and Barlett Publishers, Sudbury, MS. Short, Robert A., Canton, Stephen P., Ward, James V. 1980. Detrital processing and associated macroinvertebrates in a Colorado mountain stream. Ecology. Vol. 61:727-732. Open Closed Figure 3. Dominance-Diversity curve showing diversity among the 22 families found in Open canopy samples and the 23 families found in Closed canopy samples. A steep curve (higher slope) indicates a community dominated by the most common taxa, and therefore, proposes an uneven distribution among taxa. Open canopy yielded a slightly higher slope in its curve. slope of Open curve = -0.16, slope of Closed curve = -0.14 Figure 4. Mean densities of the major orders found in closed canopy sites over 3 collections (3, 6, and 9 week intervals). Densities of Ephemeroptera and Trichoptera decreased in the second collection, while Diptera and Plecoptera increased. All orders increased in density in the third collection. Figure 2. Mean densities of the major orders found in open canopy sites over 3 collections (3, 6, and 9 week intervals). Decreases of Ephemeroptera and Plecoptera, and increases in Diptera and Trichoptera density occurred for the second collection. All orders increased in density in the third collection. • Acknowledgements • I’d like to thank the Pohoqualine Fish Association for the use of their private trout stream, and Bradley Hartzler for his assistance in placing and retrieving samples.