When we take drugs, legal or otherwise, nature essentially takes some too. The knock-on effect isn’t direct, and if you need to take medicine it’s certainly not something to feel guilty about, but it is something that needs to be taken into account when trying to conserve our wild spaces. Medications can escape into our waterways as the result of wastewater contamination (remember London’s eel-cocaine problem?) and have all sorts of effects on wildlife, such as the dopamine-induced Daphnia magna baby boom. It's been established that pharmaceutical pollution is a thing, so the question that remains is how it changes the affected ecosystems?

A new study, published in the journal Ecosphere, decided to answer just that in the instance of crayfish, looking specifically at how they might be affected by the presence of antidepressants. The drug they focused on was citalopram, a selective serotonin reuptake inhibitor (SSRI) used to treat depression and panic disorders. It’s used globally, making it a key candidate for pharmaceutical pollution.

The team worked on the study at the Cary Institute of Ecosystem Studies using 20 artificial streams filled with water, rocks and leaf matter already colonized with a juicy cocktail of microbes, invertebrates, and algae, to best recreate natural conditions. These faux streams were then allocated one of four treatments; citalopram on its own, citalopram with crayfish, crayfish on their own and a control to which no crayfish or citalopram were added. Each of the crayfish-containing streams had three males, and the citalopram-treated streams were given small doses on alternate days to mimic the volume of pharmaceutical pollution expected in urban rivers and streams.

The researchers measured the oxygen, temperature and light penetration of the water, as well as the amount of algae. These are typical indicators of ecosystem function in the wild so would reveal to the observers how the various artificial streams were changing under their specific conditions.

They measured how long it took each crayfish to emerge completely from the shelter, as well as how long they spent in the sardine or crayfish sides of the scented tank.

The crayfish exposed to citalopram was found to be bolder than those in citalopram-free conditions, taking less time to emerge from their shelter in search of intriguing smells. They were also considerably more interested in food than other crayfish, spending triple the amount of time on this side of the tank. Those not exposed to citalopram were more hesitant in their investigations and showed no preference for the food or for scents, spending an equal amount of time investigating both smells.

“Less time spent hiding and more time foraging could make crayfish more vulnerable to predators, meaning more get eaten,” said lead author Alexander Reisinger, an Assistant Professor at the University of Florida, in a statement. “We would expect increased crayfish foraging to lead to higher rates of leaf litter decomposition and biofilm turnover, altering in-steam nutrient flows. Either of these changes could have cascading effects.”

The streams themselves showed no signs of change in the presence of citalopram alone, but it’s possible that the altered behavior of the crayfish under the influence of citalopram could hold wider ramifications.

"With just two weeks of citalopram exposure, we saw marked changes in crayfish behavior,” explained Reisinger. “Over months to years, we would expect these changes to magnify. Fewer crayfish could reduce populations of the fish that eat them like trout, bass, and catfish. Changes in algal growth or turnover would alter oxygen levels and nutrient dynamics - key aspects of stream functioning that could cause harmful imbalances in the system."