Differences in leaf litter consumption and breakdown between Ohio streams with native and non-native crayfish

Krystal Pocock
Graduate (MS)
Lauren Pintor
Environment and Natural Resources

As the dominant consumers of leaf litter in streams, crayfish play a critical role in the transformation of energy by breaking down leaf material. Yet the replacement of native crayfish by non-natives can result in the alteration of ecosystem processes. In particular, the non-native Rusty crayfish, Faxonius rusticus, has been shown to reduce standing leaf litter stocks in streams outside of their native range. Additionally, leaf breakdown rates by crayfish may be species-specific, driven by differences in behavioral traits. Non-native Rusty crayfish have begun to competitively displace native Sanborn crayfish, Faxonius sanbornii, in Ohio. The impact of this species replacement on leaf breakdown is poorly understood. Here, my two main objectives were to 1) determine species-level differences in leaf consumption, and 2) determine species-level differences in leaf decomposition rates in a stream dominated by Rusty crayfish and a stream dominated by Sanborn crayfish. I predicted that Rusty crayfish would consume more leaf material and accelerate leaf decomposition at sites where they were present. To test these predictions, I completed a laboratory experiment to quantify leaf consumption between species. Additionally, I completed a field leaf pack experiment to quantify leaf decomposition in one stream dominated by Rusty crayfish and one stream dominated by Sanborn. The field and lab experiments together suggest that Rusty and Sanborn crayfish do not have a direct consumptive effect on leaf litter biomass, but rather the reduction in ash-free dry mass (AFDM) of leaf litter in these two stream systems is due to consumption by macroinvertebrates. However, leaf litter loss due to macroinvertebrates, as well as the total loss of AFDM from the leaf pack experiment were greater in the Sanborn stream. This suggests that leaf decomposition by macroinvertebrates is different in streams where Rusty crayfish are present. Overall, this may suggest that replacement of Sanborn by Rusty crayfish alter rates of leaf decomposition either through direct (e.g., consumptive) or indirect (e.g., behavioral) effects on macroinvertebrates.