Propellers' effect on marine life studied

WILLIAMSBURG, Va., April 19 (UPI) -- U.S. researchers say they've confirmed turbulence from boat propellers can kill large amounts of copepods, small crustaceans important in marine food chains.

The study was carried out in Chesapeake Bay by students at the Virginia Institute of Marine Science and Hampton University, a VIMS release said Tuesday.

The study was designed to give a better understanding of how propeller-induced mortality among copepods could affect local food chains in the bay and other high-use waterways, the release said.

Copepods -- shrimp-like crustaceans about the size of a rice grain -- serve an important role by feeding on algae and other microscopic floating plants and them moving energy up the marine food chain.

"If turbulence from boat propellers is killing off large numbers of copepods," VIMS graduate student Samantha Bickel said, "it could be reducing the supply of food energy available to fish, and reducing zooplankton grazing of algal blooms.

"It's like cutting down the number of zebras in a herd," she said. "That would affect not only the zebras, but also the grass they eat and the lions that eat them."

The research team studied three sites -- a marina with numerous boats but minimal turbulence due to an imposed speed limit, a high-traffic area of a nearby navigational channel where fast-moving boats generated considerable turbulence in their wakes, and a tranquil shoreline opposite from the marina.

Their study showed a much higher fraction of dead copepods in the channel, 34 percent, than in the marina or along the shoreline, both with only slightly more than 5 percent.