Data for: Interactive effects of light and snail herbivory rather than nutrient loading determine early establishment of submerged macrophytes

Submerged macrophytes play a key role in maintaining a clear-water phase
and promoting biodiversity in shallow aquatic ecosystems. Since their
abundance has declined globally due to anthropogenic activities, it is
important to include them in aquatic ecosystem restoration programs.
Macrophytes establishment in early spring is crucial for the subsequent
growth of other warm-adapted macrophytes. However, factors affecting this
early establishment of submerged macrophytes have not been fully explored
yet. Here, we conducted an outdoor experiment from winter to early spring
using the submerged macrophytes Potamogeton crispus and Vallisneria
spinulosa to study the effects of shading, nutrient loading, snail
herbivory (Radix swinhoei) and their interactions on the early growth and
stoichiometric characteristics of macrophytes. The results show that the
effects strongly depend on macrophyte species. Biomass and number of
shoots of P. crispus decreased, and internode length increased during low
light conditions, but were not affected by nutrient loading. P. crispus
shoot biomass and number showed hump-shaped responses to increased snail
biomass under full light. In contrast, the biomass of the plant linearly
decreased with snail biomass under low light. This indicates an
interaction of light with snail herbivory. Since snails prefer grazing on
periphyton over macrophytes, a low density of snails promoted growth of P.
crispus by removing periphyton competition, while herbivory on the
macrophyte increased during a high density of snails. The growth of V.
spinulosa was not affected by any of the factors, probably because of
growth limitation by low temperature. Our study demonstrates that the
interaction of light with snail herbivory may affect establishment and
growth of submerged macrophytes in early spring. Macrophyte restoration
projects may thus benefit from lowering water levels to increase light
availability and making smart use of cold-adapted herbivores to reduce
light competition with periphyton.