The researchers caution that there are untold millions of zooplankton in the world's aquatic systems, so that when viewed at a global scale, the portion of copepods killed by boat-generated turbulence is probably minimal.
"The importance of turbulence as a source of mortality among copepods would be of much greater importance at a local scale," says Bickel, "including highly trafficked areas near harbors and marinas, and within closed freshwater systems such as lakes."
The research team studied propeller-induced mortality both in the field and laboratory. During the spring of 2010, they sampled copepods at three sites near the mouth of the Hampton River, a tributary of Chesapeake Bay. One site was a marina with numerous boats but minimal turbulence due to an imposed speed limit. The second was in a high-traffic area of a nearby navigational channel, where fast-moving boats generated considerable turbulence in their wakes. The third site was a tranquil shoreline opposite from the marina, with few boats and little or no boat-generated turbulence.
They compared the percentage of live and dead copepods collected from these sites using a dye that is only taken up by living copepods. The results of their comparison showed a much higher fraction of dead copepods in the channel (34%) than in the marina (5.9% dead) or along the shoreline (5.3%).
A field experiment in the York River near the VIMS campus confirmed the results of the Hampton River study. Here, they sampled copepods from within the wakes of passing boats, and again found a link between turbulence and mortality: the percentage of copepod carcasses i
|Contact: David Malmquist|
Virginia Institute of Marine Science