Limnetica 38

We dedicate this paper to the late Maria Rosa Miracle, who was a key researcher in the shallow lakes community, always enthusiastically dedicated to science, and always ready to discuss and guide younger scientists and fellow colleagues on the dynamics of zooplankton as well as on shallow lakes functioning at large. She will be sadly missed.

Plant habitat complexity can buffer against predator-prey interactions by offering physical refuges, and also novel microhabitats for alternative prey. In shallow lakes, submerged and free-floating plants affect predator-prey interactions with expected differences related to climate-driven differences in fish community structure. We tested the overall hypothesis that fish predation shapes the structure of plant-associated macroinvertebrate communities. By introducing artificial free-floating and submerged plants in a total of 14 shallow lakes under contrasting climate regimes (temperate and subtropical), we predicted that higher densities of macroinvertebrates would occur in the temperate zone where littoral fish predation is comparatively weaker than in the subtropics. We also tested the hypothesis that different structural complexities and % PVI would lead to different association patterns. Taxonomic richness, diversity, and densities of plant-attached macroinvertebrates were several fold higher in the temperate lakes. Macroinvertebrate densities per unit of plant weight were generally higher on the more complex free-floating than on the more abundant (as % PVI) submerged plants. The structure of littoral macroinvertebrates showed no clear relationship with the trophic state gradient. Fish communities, whose structure (biomass, density and habitat use) differed consistently between the temperate and subtropical locations, seemingly shaped the macroinvertebrate communities, most likely via predation and in the subtropics potentially also by competition. Free-floating plants appeared as a better anti-predation refuge or a preferred habitat for macroinvertebrates, particularly in the subtropics, but with increasing water turbidity this pattern became less distinct. In contrast, in the temperate lakes, the use of artificial plants by macroinvertebrates was rather related to the biomass of periphyton than to their refuge capacity, thus suggesting stronger bottom-up effects. A stronger fish predation pressure, which is to be expected with climate warming and eutrophication, may reduce the richness and abundance of plant-associated macroinvertebrates, with potentially strong impacts on shallow lake functioning. A warming-driven expansion of free-floating plants could, if moderate, weaken such effects, but a more diverse macrophyte community would facilitate co-existence of macroinvertebrate and fish.