Improving human mental health is having some serious unintended consequences for our friends in the ocean. Exposure to antidepressants makes shrimp five times more likely to place themselves in life-threatening situations, and the broader effects could damage the entire ecosystem.
Exposure to the antidepressant fluoxetine causes shrimp to radically alter their behavior. While normal shrimp are more likely to avoid swimming towards light because it's often associated with prey like birds or fishermen, those exposed to fluoxetine become five times more likely to swim towards light than away from it. That change in behavior places them in harm's way, and if enough shrimp are exposed to the antidepressant the entire population could be at risk.
Alex Ford, a marine biologist at the UK's University of Portsmouth, explains how that can reverberate throughout the oceanic ecosystem and why this is a serious concern:
Crustaceans are crucial to the food chain and if shrimps' natural behaviour is being changed because of antidepressant levels in the sea this could seriously upset the natural balance of the ecosystem. Much of what humans consume you can detect in the water in some concentration. We're a nation of coffee drinkers and there is a huge amount of caffeine found in waste water, for example. It's no surprise that what we get from the pharmacy will also be contaminating the country's waterways.
Ford exposed some shrimp to the same amount of fluoxetine that humans excrete into the waste water that gets carried out to sea. He found that even this seemingly small amount was enough to trigger this major behavioral change in the shrimp. He had been motivated to investigate this question by a parasite that is known to cause such changes by altering serotonin levels in shrimp. He wanted to find out whether the same deleterious result could be obtained using human antidepressants; the answer, sadly, is yes.
He explains how small individual amounts of antidepressants adds up to a big problem:
Effluent [outflowing waste water] is concentrated in river estuaries and coastal areas, which is where shrimps and other marine life live — this means that the shrimps are taking on the excreted drugs of whole towns.
Prescriptions for antidepressants have skyrocketed in recent years, but this is one of the very first attempts to figure out what ecological impact all that pharmaceutical sewage could have. The most worrying part of it all is that this might just be the tip of an ecosystem-altering iceberg - there are lots of other drugs other than fluoxetine that affect serotonin levels, and Ford hasn't even tested any of those yet to see what they do to shrimp and other marine organisms.