Boat-generated turbulence as a potential source of mortality among copepods

Abstract

Motorized boats present a wide array of stressors to aquatic organisms, but their impacts on zooplankton have not been studied in detail. This study investigated boat-generated turbulence as a potential source of mortality for copepods through a combination of field observations and laboratory experiments. Field sampling in the lower Chesapeake Bay showed that carcasses comprised 34% of the copepod population at a site with a high volume of boat traffic, whereas only 5.3–5.9% of the copepods were dead in the other two, less disturbed, nearby sites. Direct sampling behind passing vessels showed that the percentage of copepod carcasses increased from 7.7% outside the wakes to 14.3% inside the wakes. Laboratory experiments further showed that the fraction dead of the copepod population increased with increasing turbulence intensity, indicating that turbulence was causing mortality. In coastal waters with high volumes of boat traffic, boat-generated turbulence could be an important source of zooplankton mortality, altering trophic interactions among the plankton and shunting zooplankton biomass to the microbial loop.