Submerged macrophytes mitigate direct and indirect insecticide effects in freshwater communities. 2015

William R Brogan, and Rick A Relyea
Smithsonian Environmental Research Center, Edgewater, Maryland, 21037, United States of America.

Understanding how ecological interactions mitigate the impacts of perturbations such as pesticides in biological communities is an important basic and applied question for ecologists. In aquatic ecosystems, new evidence from microcosm experiments suggests that submerged macrophytes can buffer cladocerans from pulse exposures to the widely used insecticide malathion, and that mitigation increases with macrophyte density. However, whether these results scale up to more complex aquatic communities where ecological interactions such as competition can alter toxicity is unknown. Further, macrophyte abilities to mitigate different insecticide exposure scenarios (i.e. single versus repeated pulses) have never been tested. To address these gaps, we performed a factorial mesocosm experiment examining the influence of four macrophyte treatments (0, 10, 50, or 100 Elodea Canadensis shoots planted per mesocosm) crossed with three malathion exposure scenarios (no insecticide, single pulse, repeated pulses) on aquatic communities containing zooplankton, phytoplankton, periphyton, two snail species, and larval amphibians. In the absence of macrophytes, single malathion pulses caused short-term declines in cladoceran abundance followed by their rapid recovery, which precluded any indirect effects (i.e. trophic cascades). However, repeated malathion pulses caused cladoceran extinctions, resulting in persistent phytoplankton blooms and reduced abundance of one snail species. In contrast, with macrophytes present, even at low density, malathion had no effect on any taxa. We also discovered novel effects of macrophytes on the benthic food web. In the two highest macrophyte treatments, we observed trends of reduced periphyton biomass, decreased abundance of one snail species, and decreased amphibian time to and mass at metamorphosis. To our knowledge, this is the first evidence of negative submerged macrophyte effects on amphibians, a taxa of global conservation concern. Our findings suggest that facilitating macrophytes could be an important strategy for buffering freshwater communities from insecticides, though consideration of their impacts on animal species is necessary.

UI MeSH Term Description Entries
D007306 Insecticides Pesticides designed to control insects that are harmful to man. The insects may be directly harmful, as those acting as disease vectors, or indirectly harmful, as destroyers of crops, food products, or textile fabrics. Insecticide
D007814 Larva Wormlike or grublike stage, following the egg in the life cycle of insects, worms, and other metamorphosing animals. Maggots,Tadpoles,Larvae,Maggot,Tadpole
D008294 Malathion A wide spectrum aliphatic organophosphate insecticide widely used for both domestic and commercial agricultural purposes. Carbafos,Carbofos,Carbophos,Cythion,Karbofos,Prioderm,Sadophos
D010839 Phytoplankton Free-floating minute organisms that are photosynthetic. The term is non-taxonomic and refers to a lifestyle (energy utilization and motility), rather than a particular type of organism. Most, but not all, are unicellular algae. Important groups include DIATOMS; DINOFLAGELLATES; CYANOBACTERIA; CHLOROPHYTA; HAPTOPHYTA; CRYPTOMONADS; and silicoflagellates.
D004463 Ecology The branch of science concerned with the interrelationship of organisms and their ENVIRONMENT, especially as manifested by natural cycles and rhythms, community development and structure, interactions between different kinds of organisms, geographic distributions, and population alterations. (Webster's, 3d ed) Bionomics,Ecologies
D005618 Fresh Water Water containing no significant amounts of salts, such as water from RIVERS and LAKES. Freshwater,Fresh Waters,Freshwaters,Water, Fresh,Waters, Fresh
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia
D012908 Snails Marine, freshwater, or terrestrial mollusks of the class Gastropoda. Most have an enclosing spiral shell, and several genera harbor parasites pathogenic to man. Snail
D014874 Water Pollutants, Chemical Chemical compounds which pollute the water of rivers, streams, lakes, the sea, reservoirs, or other bodies of water. Chemical Water Pollutants,Landfill Leachate,Leachate, Landfill,Pollutants, Chemical Water
D015048 Zooplankton Minute free-floating animal organisms which live in practically all natural waters.

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