Zooplankton feeds on bacteria, but will not touch fecal ones

Zooplankton are very small aquatic animals that feed on bacteria and algae. It includes protozoa, rotifers, crustaceans, tunicates and insect larvae. For example, the fry of most freshwater fish species feed on zooplankton.

A 2017 water quality inventory study in the United States found that water in more than 50 percent of rivers, bays and estuaries (funnel-shaped estuaries) could not be used for recreational purposes, for example, in many cases due to contamination with fecal bacteria. “When sewage is released into clean bodies of water and people are exposed to it, it can lead to illness,” said Dr. Lauren Kennedy, an assistant professor of civil engineering at the University of Texas at El Paso. – Our research aims to understand what factors can prevent pathogens from infecting humans. In other words, how long will it take for the water to become safe for recreational use again without any outside intervention, she added.

As Kennedy explained, water from sewage and septic tanks can accidentally enter freshwater bodies due to accidents, inadequate water treatment or corroded infrastructure.

Therefore, scientists from the University of Texas at El Paso (UTEP) and Stanford University hypothesized that zooplankton would consume or neutralize fecal microorganisms found in the water. To their surprise, they found that zooplankton – both those found in fresh and salt water – did not clean up water contaminated with fecal microorganisms. An article on this topic was published in early October in the “mSphere” magazine. What did the research look like? Scientists added viruses (MS2 bacteriophages) and E. coli bacteria to freshwater and saltwater samples collected from the San Francisco Bay Area in California. MS2 and E. coli are considered scientifically useful indicators of water pollution because they occur in high concentrations in wastewater and their presence often indicates fecal contamination of the environment. As it turned out, zooplankton had no significant effect on the inactivation of pathogens, while in the presence of salt they were inactivated faster than in fresh water. This included, for example, ocean water taken from San Pedro Beach. According to the authors, the study results are an important step forward in understanding the limitations of zooplankton as natural “purifiers” of contaminated water. The next phases of research will focus on the impact of salinity on the survival of pathogens in contaminated waters.