Influence of Cladophora sp. on the Composition and Spatial Distribution of Macroinvertebrate Communities in Streams

Nitrogen and phosphorus from agricultural runoff cause blooms of the green alga, Cladophora. This alga provides surface area for epiphytes and invertebrates to colonize. However, Cladophora is not nutritious and hard to digest for many invertebrates, which could impact invertebrate communities around this alga. The purpose of this research was to determine how invertebrate communities differ between patches in streams where Cladophora is present and absent in the Susquehanna River watershed. To do this, 13 streams were sampled. Invertebrates were collected using a Surber sampler by collecting five composites and combining them into one sample per patch type. In streams where Cladophora was present, patches consisted of areas that either contained or did not contain Cladophora. In streams where Cladophora was not present, a single sample was collected. The samples were preserved in ethanol and macroinvertebrates were identified to the family level. The communities were compared between patch types from Cladophora streams using four metrics: percent Ephemeroptera, Plecoptera, and Trichoptera (%EPT), Hilsenhoff Biotic Index (HBI), Shannon-diversity index and percent Chironomidae (%Chironomidae). Densities were compared between patch types from Cladophora streams and non-Cladophora streams. Data loggers were left at sites to collect dissolved oxygen and temperature data every 15 minutes for a week. Percent Chironomidae was greater in Cladophora patches than non- Cladophora patches (p<0.005) which decreased Shannon diversity in Cladophora patches (p<0.05). Densities of invertebrates per m2 were higher in Cladophora patches than non-Cladophora stream patches (p<0.05). Stream type and percent agriculture within the stream watershed both directly impacted invertebrate communities (p<0.05). iii Logistic regression supported the prediction of Cladophora presence or absence in streams using alkalinity as a predictor (p=0.0516). This research supports that agriculture and the alga, Cladophora affect invertebrate communities at both patch and stream-level spatial scales in the Susquehanna River watershed by increasing invertebrate densities and decreasing diversity.