University of Wisconsin–Milwaukee

Laura L. Hunt

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Feb 17, 2009 
Strickler receives international  award
Photo by Alan Magayne-Roshak
J. Rudi Strickler J. Rudi Strickler, UWM Shaw Distinguished Professor of biological sciences, works with one of his high-speed cameras.
J. Rudi Strickler, UWM Shaw Distinguished Professor of biological sciences, has won an international award recognizing research that has redirected the course of inquiry in aquatic science.

Strickler was given the John Martin Award by the American Society of Limnology and Oceanography (ASLO) for research published in 1981 with Mimi Koehl, a professor at the University of California, Berkeley. The award is reserved for papers at least 10 years old that have led to fundamental shifts in subsequent research. 

The paper describes the novel method the scientists used to determine exactly how tiny aquatic organisms, called copepods, feed in a watery environment that, at their scale, is thick and sticky. Strickler and Koehl were honored in February at the Aquatic Sciences Meeting in Nice, France.

Groundbreaking movies
A clip from a high-speed 16 mm movie made in 1979 by Tim Cowles, Mimi Koehl, Gus Paffenhofer, and Rudi Strickler in Strickler’s laboratory.
In the 1970s, the prevailing view of copepod feeding was that the animal created water currents by moving its outer mouth parts very rapidly, bringing food particles, such as alga, close enough to be “raked in” by the outer mouth. Food was then thought to pass through a kind of sieve in the inner mouth that blocked large particles. Strickler and Koehl disproved this theory, showing how copepods manipulate the water around them so that targeted food particles are swept into a “feeding current.”

The inner mouth parts remain motionless until food is nearby and detected. Then a fast movement is executed to capture it. Using high-speed cameras, they demonstrated that copepods taste their food, eating certain particles and “spitting out” the rejects. Food particles are neither scooped up nor left behind, because water adheres to both the mouth and the food. Instead, the animal has sensors to tell it that the food is within reach.

More Strickler Films
Wednesday, March 4 – 7 p.m. Free Screening, Union Theatre "Underwater Noise of Rain" A special live audio/visual performance by four Milwaukee-based artists and researchers. Lane Hall and Lisa Moline will be presenting video permutations of Dr. J. Rudi Strickler’s aquatic 16mm research films. Composer Christopher Burns will provide a live score.
“This is not filter-feeding,” says Strickler. “It is choosing its food.”

Filming the live copepod presented a challenge. The animal, barely visible, also moves its mouth parts at 60 times per second. So Strickler devised a technique to tether one to a single dog hair and then place it back in its environment with food available. Koehl introduced a stream of india ink to track the flow of water. 

“The movies gave foolproof evidence that the old way of thinking was out the window,” Strickler says. “Without the movies, I wouldn’t have been able to convince others.”

High praise
Gaussia Another Strickler subject, Gaussia princeps
The ASLO awards committee wrote of Strickler and Koehl’s work: “This paper’s straightforward explanation of the role of viscosity in governing particle motion at very small spatial scales has been incorporated into many introductory-level textbooks…. It has been cited over 200 times.”

Strickler joined the UWM faculty in 1990 with financial support for his professorship and high-tech laboratory from the Shaw Family Foundation, through the Greater Milwaukee Foundation. Before coming here, he was on the faculty at Johns Hopkins, Yale, Southern California and Boston universities and the University of Ottawa, Canada. 

In 2000, the National Science Foundation recognized Strickler in its bound report, 50 Years of Ocean Discovery, citing his research on zooplankton as one of four landmark achievements in biological oceanography. ASLO is a leading professional organization for researchers and educators in the field of aquatic science and is the publisher of the journal Limnology and Oceanography.

To see videos of copepod feeding, go to and clock on "open all" in the left-hand column. Recommendations (under ("Food Handling"): “Alga Arrives” and “Many Algae.”