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Antidepressants don't just change people's moods. They might also make crayfish act more outgoing when these drugs wind up in ponds or streams, according to a new study.
Riskier crayfish behavior could get them snatched up as food by predators more often, the researchers noted. These common water critters play an important role in the food web by eating anything from insects and young fish to bacteria and algae. That means straying from their typical behavior could throw plant and animal populations out of balance.
The study, published in Ecosphere, suggested that even low levels of these drugs could lead to unpredictable changes in the wildlife community.
Synthetic chemicals such as drugs, pesticides and industrial materials pollute freshwater ecosystems around the world. In the case of medicines, after humans ingest and excrete them, they flow through wastewater treatment plants that are unable to filter them out. Waste flowing directly from drug-manufacturing facilities can also contaminate water sources. In one example of a worrying outcome, a study in 2015 found that estrogen hormone pollution was turning male fish into females in the northeastern United States.
Crayfish, hardy and aggressive, can handle polluted environments well. They live in waters near dense human populations more frequently than sensitive creatures, so they're also more likely to encounter chemicals and experience any potential consequences.
The authors set up water tanks with rocks, leaves, bugs and algae from a local stream. They added small amounts of a common antidepressant known as citalopram to mimic levels found in contaminated streams.
Different paths
In their experiments, the crayfish started inside a shelter at one end of the setup and could move down one of two separate paths. One path had water flowing from a source with fish gelatin, to signal the presence of food. The other flowed from a source containing another crayfish, which could provoke aggression.
Although the study authors expected the crayfish to show some level of behavioral response to the antidepressants, "I don't think any of us really expected such drastic changes in the crayfish behavior," said A. J. Reisinger, a biogeochemist and ecologist at the University of Florida and lead author of the study.
The crayfish exposed to the drug appeared to spend more time foraging for food and be less careful about avoiding predators.
They emerged from their shelters almost two times faster than crayfish that hadn't been exposed. They also spent almost double the amount of time searching for food. Overall, the time the citalopram-exposed crayfish spent in the area with fish-flavored water was more than three times the amount of time they spent anywhere else in the experimental stream.
"I think the novelty of this paper is that they weren't just trying to look at the [crayfish] in a vacuum," said Lauren Mathews, an ecologist of freshwater systems at Worcester Polytechnic Institute who was not involved in the study. Rather than watching isolated crayfish, the authors tried mimicking natural streams to make the experiment more relevant to real-world conditions.
Although crayfish populations could dip from more predation, they could also increase their impact on the food chain by consuming more food. This study doesn't confirm either yet.
"Ecosystems are really complex, and extrapolating out what's going to happen from the removal or increase of one species is really difficult," added Mathews. "But there probably would be an impact."
Scientists have repeatedly shown that human actions have downstream effects on wildlife communities. According to Reisinger, this study shows that antidepressants influencing aquatic animal behavior is just another example of environmental change caused by humans.