Small but Mighty Phytoplankton

In the Journal “Ecotoxicology”, Amy L. Downing, Kristen M. DeVanna, C. Nichole Rubeck-Schurtz, Laura Tuhela and Heather Grunkemeyer have published an important article about the effects of a common pesticide on invertebrate communities and their ability to bounce back after disturbance.
This topic is a highly important one because, as mentioned in the article, “the rate of extinction of freshwater fauna is five times higher than the rate for terrestrial fauna”. One of the greatest reasons for this is the impacts of agriculture, which include habitat loss, eutrophication and the run-off of herbicides and pesticides. How does the run-off of these chemicals affect communities? Many previous studies have examined the consequences for single species or small groups of species, but Downing et. al. attempted to examine the results for entire communities or ecosystems.
Using a natural community of zooplankton, phytoplankton and microbes collected from a nearby pond, they set up a system of experimental mesocosms. To these artificial ponds, they added pulses of the commonly used pesticide “Sevin” with the active ingredient carbaryl at different concentrations. They then recorded the changes in 7 different response variables that served to reflect the health of the ecosystem.
What they found was that after 30 days the differences in carbaryl concentrations were completely unnoticeable as it was broken down into the system. At the highest concentration, only 2 of the 7 response variables (zooplankton diversity and oxygen concentration) showed a complete return to original levels. Zooplankton richness, diversity and abundance had all declined, while abundance of phytoplankton and microbes had actually increased. This is supposed to be due to the decrease in predatory pressure from the zooplankton.
Downing et al. found these results to be encouraging, as partial or complete recovery was made very quickly in the communities that had been treated with lower concentrations, and even in those treated with the higher concentration. But reminded the reader to take these results with a grain of salt as there several limitations to their experiment existed. Firstly, the communities were made up of only invertebrates, not macrophytes, macroinvertebrates and vertebrates who might have different reactions to the carbaryl. As well, these invertebrates had much shorter generation times than other, more complex, organisms, and this allowed for such a rapid recovery time. Finally, in reality, ecosystems would most likely be pulsed with pesticide run-off more than once a year, as was done in the experiment. There might be more serious effects for an ecosystem from long term exposure.
Downing et al.’s work helps open our eyes to how ecosystems cope with stress and reveals the adaptability and recovery a community of invertebrates is capable of.
Source
Downing, Amy L., Kristen M. DeVanna, C. Nichole Rubeck-Schurtz, Laura Tuhela and Heather Grunkemeyer. “Community and ecosystem responses to a pulsed pesticide disturbance in freshwater ecosystems”. Ecotoxicology. 17 (2008):539–548