Associations between gizzard shad Dorosoma cepedianum (Lesueur, 1818) relative abundances and limnological parameters in small impoundments

Abundant gizzard shad Dorosoma cepedianum (Lesueur, 1818) are thought to contribute to phytoplankton blooms by translocating nutrients from sediments to the water column where they can be readily taken up by phytoplankton and by consuming herbivorous zooplankton that might control phytoplankton. To assess the influence of gizzard shad relative abundance on lentic ecosystems, we sampled 12 small impoundments located in the Great Plains, USA over 4 years. We used linear mixed models to test for associations with limnological characteristics, including total nitrogen (TN) and total phosphorus (TP), zooplankton densities, and phytoplankton abundances. Gizzard shad relative abundance was associated with elevated TN and TP and a general reduction in zooplankton densities. There was substantial within-lake temporal variation in gizzard shad abundance across sampling months, with a negative association between TP and gizzard shad abundance in June but a positive association in August. We did not provide evidence that gizzard shad relative abundance was associated with cyanobacterial abundance or total phytoplankton abundance. The lack of a relationship between these factors might have been obscured by the discontinuous polymictic mixing regimes of the study impoundments, the rapid turnover of phytoplankton, and other drivers, such as variable nutrient runoff across our study impoundments.