Crayfish become bolder on antidepressants

Medications washed into waterways could affect crayfish behaviour and upset ecosystems
22 June 2021

Interview with 

Lindsey Reisinger, University of Florida


Lake Irene in Colorado.


Medications that we use can end up in the environment, where they can alter the behaviour of wild animals, potentially upsetting the ecosystem. That’s the finding of a new study from the University of Florida. Eva Higginbotham has been hearing from Lindsey Reisinger what happens when crayfish are exposed to the antidepressant citalopram, which can pass from wastewater treatment plants into the streams where they live. So why crayfish?

Lindsey - They tend to be really abundant so they can have large impacts. They're major processors of things like algae and leaf litter at the bottom of the stream, so dead leaves that fall in the stream, and also are predators on other small aquatic organisms like aquatic insects. And then they're a major connection to higher level predators. So they're eaten often by predatory fish or by wading birds or mammals like raccoon or mink. So we were really interested in their behavior because they're so ecologically important, and we thought that changes in their behaviour might change aspects of the ecosystem. We specifically wanted to know how an antidepressant, in this case citalopram, which is one of the most commonly prescribed antidepressants, affected the behaviour of crayfish. And we were also interested in how that might alter the impacts of crayfish on the ecosystem.

Eva - So how did you go about studying the effects of antidepressants on crayfish?

Lindsey - We set up a study in artificial streams. So these are tanks that have water circulation, and we put natural components of streams into the tanks. We collected rocks, we put packs of leaves that had been set out in streams and were colonised by invertebrates living in the stream, so small aquatic insects and crustaceans. Then in half of the streams, we put three crayfish that we also collected from the same stream where we got all the other organisms and we added about five milligrams per litre of this common antidepressant, citalopram. So we're probably on the high end of what's common, but definitely in the range of what you would find in the natural environment.

Eva - And did you see a difference in the crayfish that had been exposed to the antidepressant stream versus the non-antidepressant stream?

Lindsey - Yes we did. So after two weeks in the experimental streams, we removed the crayfish and we tested their behaviour. And we found that crayfish that had been exposed to the antidepressant were bolder. So we put them inside a shelter and they came out of the shelter into a novel environment almost twice as fast as the crayfish that had not been exposed. And then we also offered them a choice of water that had different scents in the experiment. So on one side of our tank, we had water coming in that smelled like another crayfish of the same species, and on the other side, we had water coming in that smelled like a really great food source. And when crayfish had been exposed to the drug, they spent almost three times more time in the section that smelled like a food source. And the other crayfish really just walked around the tank and spend an equal amount of time in both sections.

Eva - And do you think that this change in behaviour in the crayfish, do you think that could have consequences if that were happening in the wild?

Lindsey - Yes, we do think it could. So we did measure the ecological effects of crayfish in these tanks, but we didn't see that crayfish that were exposed to the drug had different ecological effects than those that were not exposed, but this might be because we didn't run it for long enough. So in retrospect, we've thought that it probably takes some time for the drug to accumulate in the crayfish and change the crayfish's behaviour. And then it probably takes more time for those changes in behavior to affect the ecosystem. We would try to run this over a longer time period and look for if these changes in behaviour could have larger effects.

Eva - Is there anything we need to do? Is there anything that we should be changing to prevent that from happening?

Lindsey - So I think the easiest thing that we could change would be to make sure we're properly disposing of medications. So some ways that you can do that is there are lots of programmes that will take back medications that are unused. So that would be most ideal thing to do. And if that's not possible, the best thing to do is to put the medication in a container with something absorbent that would be unpalatable to animals. So coffee grounds is a great example and then enclose it in that container before you throw it away.


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