Biology Human impacts Pollution Toxicology

Prozac and Cons: How Marine Snails React to Antidepressants



Paper: Fong, P. P., Bury, T. B., Dworkin-Brodsky, A. D., Jasion, C. M., & Kell, R. C. (2014). The antidepressants venlafaxine (“Effexor”) and fluoxetine (“Prozac”) produce different effects on locomotion in two species of marine snail, the oyster drill (Urosalpinx cinerea) and the starsnail (Lithopoma americanum). Marine Environmental Research. doi:10.1016/j.marenvres.2014.11.010 


Pharmaceuticals have been discharged into our wastewater as long as we’ve been using it. Previous studies have looked into the effect of birth control hormones on fish – they change the gender ratio of the population – and the effect of antidepressants on Baltic clams – they cause them to spawn spontaneously (Honkoop et al. 1999, Palace et al. 2009). Antidepressants are a particular concern for marine molluscs (a group of animals that includes clams, mussels, snails, and squids), these creatures show an increased sensitivity to lower concentrations. Antidepressants cause molluscs to spawn more randomly, grow up faster, and change the speed at which they move.

This study uses two species of snails to test the concentrations at which two common antidepressants (Prozac and Effexor) impact crawling speed and the time it takes to reach the air-water interface. The two snails used in this study are fundamentally different in lifestyle and habitat. Researchers used the oyster drill, a carnivorous snail that lives in cooler water, and the American starsnail, an herbivorous snail that lives in warmer water.

Left: Oyster drill, Urosalpinx cinerea Right: American starsnail, Lithopoma americanum
Left: Oyster drill, Urosalpinx cinerea
Right: American starsnail, Lithopoma americanum

Crawling speed is important to these animals because it determines how quickly they can get away from predators. Obviously a snail is not going to be highly mobile, but a reduction in speed could mean the difference between life and being a predator’s lunch. The time to reach the air water interface is also crucial for these animals, but in a different way. Snails need oxygen in order to live, like all animals, but the tide pools they live in can become deoxygenated quickly. Moving to the air water interface allows the snails access to oxygen. It’s also another way to avoid predation, and to move to warmer surface layers of the water.

Researchers collected oyster drills and American starsnails from San Francisco Bay and Key West, respectively. To measure the amount of time it took the snails to reach the air-water interface, they were placed in small Pyrex dishes and the time it took for the snails to crawl from the center of the bowl to the top of the water line was measured. Before the timer started, the researcher added 25 mL of antidepressant-spiked water at the appropriate concentration. Control snails only received seawater.

Next, researchers measured the snail’s speed before the antidepressant was added in a flat, square dish outfitted with grid lines. There is a lot of variation in each snail’s crawling speed (some animals are fast, others slower), so measuring the speed before antidepressants were added gave the researchers a reliable control measurement for each snail individually. After that first measurement, snails were allowed to rest for 24 hours, then placed in the dish once again and the antidepressant was added. The researchers monitored the snails for 20 minutes and estimated the speed by how many grid lines the snail passed in that time.


In general, Effexor increased both snails’ mobility, while Prozac slowed them both down.


Graph 1











This first graph shows the time it took for each species of snail to reach the air-water interface under different concentrations of the two tested antidepressants. For the oyster drill, the trends are very clear. As the concentration of Effexor increases, the time to the water line decreases. In contrast, as the concentration of Prozac increases, the time to the water line increases. The trend was less clear for the American starsnail, especially in the Effexor trials, but the same general trend was still seen.


Graph 2













This second graph shows the ratio of the distance traveled before the antidepressant was added to the distance traveled after the antidepressant was added for both snails and both drugs. A ratio of one meant that there was no change in the snail’s crawling speed, whereas high ratios mean that there was a large change in crawling speed. Both the oyster drill and the American starsnail crawled faster when there was more Effexor present, and slower when there was more Prozac present.


The two tested drugs gave opposite results presumably because they’re different in the way they work in people. Antidepressants, as a general class of drugs, work by stopping the brain from metabolizing neurotransmitters – the theory is that more neurotransmitters in the brain keeps a person more balanced emotionally. Effexor acts on both serotonin and norepinephrine, whereas Prozac only acts on serotonin. That suggests that the leftover serotonin may be making these snails slower, whereas the increased norepinephrine may be making them faster.

The concentration of antidepressant tested in this experiment were higher than those found downstream of waste water systems, but the results found here are still relevant because these drugs can bioaccumulate in systems. Bioaccumulation (a term usually heard in regards to mercury poisoning) means that as these animals are exposed to the drugs, the drugs build up in their system. When other animals eat a lot of the exposed animals, they in turn get a higher concentration of the drug in their system. Bioaccumulation could become a real problem as these drugs get in the systems of animals that humans consume.

Changes in behavior like the ones seen here are seen as an early warning that there may be more severe effects ahead. Disrupting one behavior, like crawling speed or the time it takes to get to the air water interface, could have sequential effects – more snails could die, altering the community structure of tide pools. More work is needed in this area at ecologically relevant levels of antidepressant, as well as with other marker organisms, to fully understand the effect that human drugs are having on marine animals.

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