The experiments were done with 3 different species of bacteria. At the end of their lab experiments, the team found labeled bacteria were transported in both upward and downward directions in the cylinders containing Daphnia, confirming their "conveyor-belt" hypothesis. Field studies of Daphnia and bacteria from a local lake further strengthened their laboratory findings.
The team's study, says Tang, clearly shows that "bacteria, including pathogens, are able to travel and cross aquatic boundaries by hitchhiking on migrating organisms, thus facilitating exchanges between separate microbial communities and allowing access to otherwise inaccessible resources."
The authors note that "unlike slowly sinking aggregates and other detritus that mostly transport bacteria downward, mobile and migrating hosts can cover long distances rapidly and disperse bacteria in all directions repeatedly and effectively."
Tang cautions that in natural environments with diverse species of zooplankton, "dispersal of hitchhiking bacteria will not be uniform and can occur both vertically and horizontally, and on different time and space scales, from daily to seasonal migrations over millimeters to kilometers."
Although the team conducted their study in freshwater lakes and with freshwater organisms, Tang says their findings likely pertain to ocean ecosystems as well. "Many species of marine zooplankton migrate long distances vertically on daily or seasonal time scales, or during different stages of their life cycle," he says. "They may therefore transport and disperse bacteria over long distances, affecting the ecology and physiology of even deep-sea microbes."
|Contact: Kam Tang|
Virginia Institute of Marine Science