Abstract
![Figure][1] Churning up sediments and redistributing nutrients and organic matter, burrowing marine worms are sometimes described as ecosystem engineers. But how do these creatures move through their sticky environment? Kelly Dorgan from the University of California Berkeley explains that
Highlights
When sperm cells are released, they have a simple objective: find the egg and do it fast
Filming bull sperm swimming in circles at 250 frames s–1 through a phase contrast microscope, Riedel-Kruse accurately measured the position of the beating flagellum and sperm head within less than 1 mm
‘ this cannot be done accurately by hand,’ explains Friedrich, so Riedel-Kruse developed accurate computer algorithms to determine the position of the flagellum
Summary
When sperm cells are released, they have a simple objective: find the egg and do it fast. Comparing his calculations with the movies of swimming sperm, Friedrich found that the perpendicular friction coefficient is 80% higher than the parallel friction coefficient, giving him a drag anisotropy factor of 1.8 Using this value, he was able to calculate the radius of curvature of the sperm’s circular path and found that it agreed perfectly with the movies. As the turbulence increased, Clay’s calculations suggested that the four- and eight-armed larvae tilted and swam horizontally until they became trapped in downward plumes of water, while the intermediate six-armed larvae were tilted and drawn toward up-welling flows Clay admits that she was surprised that the differences in the larvae’s shapes had such a significant effect on their calculated movements.
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