Crayfish behave more boldly after exposure to antidepressants – study

Antidepressant drugs in water can alter the behaviour of crayfish, making them bolder and more outgoing, and therefore more vulnerable to predators, researchers have found.

Low levels of antidepressants – excreted by humans or disposed of incorrectly – are found in many water bodies. Researchers from the University of Florida assessed the impact of these medicines on crayfish, which are a fundamental component of many aquatic food webs – given they eat almost everything, from plants, insects, leaf litter to small fish (even cannibalising each other).

When exposed to low levels of antidepressants, the crayfish were more outgoing – emerging from hiding relatively quicker and spent more time foraging, behaviours that make them more susceptible to predators, according to the study published in the journal Ecosphere.

Researchers have long evaluated the impact of pharmaceuticals and personal care products that are found in the environment. Often these chemicals are not considered harmful because they are found in concentrations low enough to not kill, but changes in aggression, the ability to smell, and courtship have been observed in animals exposed.

In this study, researchers recreated the crayfish’s natural environment in the lab. Two groups of crayfish were placed in artificial streams – one group was exposed to an antidepressant belonging to a family of drugs called selective serotonin reuptake inhibitors (SSRI), while the control group was not, over a 14-day period.

The crayfish exposed to the antidepressants were bolder – more likely to go out and explore and forage. This suggests that in the real world this behaviour could make them more vulnerable to predators and also consume more resources, which could change food web dynamics, said lead author AJ Reisinger, an assistant professor in the soil and water sciences department at the University of Florida.

The researchers also measured changes in algal biomass and organic matter, and found that the exposed crayfish increased the amount of algae in the water column of the streams.

“We think that’s because they are both stirring up a little bit of sediment on the bottom but also they are excreting when they feed on stuff on the bottom of the stream,” said Reisinger, who conducted the study as a postdoctoral researcher.

“So crayfish are changing kind of where and how many different microbial components of the ecosystem are located.”

In addition, the researchers evaluated the rate of photosynthesis and energy consumption of entire ecosystem, but found that the presence of the antidepressant didn’t really manifest in any obvious way on the those metrics, he said. “One reason for that might be that we simply just didn’t let the experiment run for long enough, because it takes a little while for the crayfish behaviour to change, and that greatest behaviour change takes a while to affect the ecosystem itself.”

Alex Ford, professor of biology at the University of Portsmouth, who was not involved in the study, said the study echoed previous research and that such changes to “normal” crayfish behaviour might mean there is less energy for other activities such as finding mates, evading predators or simply growth.

“We also have to remember when wastewater treatment plants are functioning correctly they can’t filter out all these contaminants,” he added, noting that in recent years stormwater overflows are being activated meaning these contaminants are being released into waterways completely untreated.