Data from: Warming alters juvenile carp effects on macrophytes resulting in a shift to turbid conditions in freshwater mesocosms

1. Multiple stressors such as climate change and eutrophication are
responsible for the global decline of macrophytes in lakes. The loss of
this key component can result in turbid conditions and a loss of important
ecosystem functions and services, particularly in shallow lakes.
Benthivorous fish, which can increase in abundance during eutrophication,
can adversely affect macrophytes through physical disturbance, cascading
effects on turbidity, suspended and attached algae (phytoplankton and
periphyton) and direct consumption. However, whether warming amplifies
their effects on macrophytes and can trigger regime shifts remains
unexplored. 2. Here, we tested the single and combined effects of warmer
water (+4.5°C) and the widespread benthivorous juvenile common carp
(Cyprinus carpio) on two different types of aquatic macrophytes in 24
mesocosms (2500 L each). We monitored phytoplankton, periphyton, turbidity
and the abundance of the submerged curly-leafed pondweed (Potamogeton
crispus) and the floating-leaved water chestnut (Trapa bispinosa) during
their growing season. These species dominated successively in spring and
summer. 3. Warming alone advanced the growing season of P. crispus by 17
days. Juvenile carp decreased the abundance of the more palatable P.
crispus, but promoted the abundance of T. bispinosa, supporting an
ecosystem shift to a dominance of floating-leaved macrophytes. Fish also
substantially increased water turbidity and the biomass of phytoplankton
and periphyton. Warming amplified juvenile carp effects on turbidity and
submerged macrophytes, but also decreased the abundance of floating-leaved
macrophytes leading to an overall macrophyte decline and increase in water
turbidity. 4. Synthesis and applications. Our study provides the first
experimental evidence for a warming-induced regime shift from clear water
conditions dominated by submerged or floating/floating-leaved macrophytes
to a turbid state in shallow aquatic ecosystems. The regime shift was
triggered by impacts of warming on benthivorous fish (juvenile common
carp) rather than on macrophytes. Lowering nutrient loading and other
measures to reduce the abundance of benthivorous fish (e.g., fish removal
and piscivorous fish restocking) thus may become increasingly important
for the management of shallow lakes under global climate change.