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Abstract
We experimentally examined effects of shrimps on in-situ leaf litter decomposition rates in two headwater streams by manipulating their presence and absence in pre- and post-hurricane conditions. We used Bayesian mixed-effects models to test the effect of biotic and abiotic factors on decomposition rates in 50-day experiments conducted in each of three consecutive years (2017, 2018, 2019). The main driver of decomposition in both study streams was shrimp abundance. The larger study stream had 1.8-fold greater shrimp and 22-39% faster decomposition rates than the smaller stream. Stream flow was only an important driver in the absence of shrimp and in the larger of the two study streams. Hurricanes Irma and Maria occurred after our first experiment in 2017 and did not appear to affect decomposition rates in subsequent experiments despite an x 1.9-fold increase in shrimp numbers post-hurricane, which suggests a threshold level of shrimp abundance at which decomposition rates plateau.