This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: While most people are aware of how plastic, arsenic and various industrial chemicals can pollute bodies of water, the effects of caffeine on freshwater environments remain largely unknown. Nonetheless, traces of caffeine, the stimulant contained in coffee and tea, often pass through wastewater treatment systems, entering rivers and streams.
Researchers at the University of Bonn and Manchester Metropolitan University recently carried out a study aimed at better understanding how caffeine concentrations comparable to those detected in freshwater environments affect the amphipod (i.e., shrimp-like crustacean) Gammarus pulex. Their findings, published in Biology Letters, suggest that a high caffeine concentration makes this amphipod more active and less inclined to avoid light than a low concentration, which could increase its exposure to predators. "Caffeine is an emerging environmental contaminant in freshwater ecosystems that is primarily introduced through wastewater," wrote Elias Fritzsche, Hannah Otto and their colleagues in their paper.
"Even at low concentrations, caffeine can affect the physiology and behavior of aquatic organisms. Still, its ecological significance remains little understood." Gammarus pulex, sometimes referred to as freshwater shrimp or scud, is a small, grayish-brown freshwater amphipod crustacean that can grow up to 21 mm in length. To assess the effects of caffeine exposure on this shrimp-like crustacean, the researchers studied 120 individuals under different conditions.
"We examined the impact of environmentally relevant caffeine concentrations on the antipredator behavior of the freshwater amphipod Gammarus pulex," wrote the authors. "Gammarids play a central role in aquatic decomposition processes and are a primary food source for various aquatic predators. We examined the effects of caffeine in relation to a well-documented effect caused by the manipulative parasite Polymorphus minutus." The researchers placed the crustaceans in 12 tanks containing either a low or high caffeine concentration.
Each tank contained five individuals infected with a parasite called P. minutus and five uninfected individuals. All the animals were exposed to their respective caffeine concentration for 20 hours. "This acanthocephalan parasite manipulates the antipredator behavior of its intermediate host, the gammarid, by altering its photophobia, thereby increasing its transmission to the final host, water birds," explained the authors.
"Using a two-choice experimental design, we assessed the phototactic behavior of P. minutus-infected and uninfected G. pulex after 20 h of high- and low-concentration caffeine exposure." In their experiments, the researchers observed that individuals exposed to a high caffeine concentration were more active and displayed less photophobia than those exposed to a low concentration. In other words, Gammarus pulex swimming in water containing the high caffeine concentration were more active and less prone to avoiding light. Notably, the observed reduction in photophobia linked with exposure to a high caffeine concentration was comparable to that observed in Gammarus pulex individuals infected with the P. minutus parasite.
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