The sex life of a seaweed seems at first glance haphazard--sperm and eggs spill into the water, to either fuse or die. But University of Maine ecologists Ester Serrão, Gareth Pearson, and their colleagues have found that for the common bladder wrack, or Fucus vesiculosus, fertilization is anything but hit or miss. This northern coastal seaweed shuns sex when the sea is rough and can carry its gametes--the sperm and eggs--away. When shaken in the lab, or when thrashed by turbulent currents in its natural habitat, the seaweed’s two sexes hold on to their gametes, releasing them only when the water is tranquil. In calm water, says Pearson, fertilization is nearly 100 percent successful. He thinks that calm waters may impede the flow of carbon dioxide--a gas needed for photosynthesis--from the sea into the plant. This slows photosynthesis and may cue the release of sperm and eggs. People have always imagined that things just cast their gametes into the sea, and it’s just kind of luck-- who knows how they meet or if they meet, says Pearson. This is some of the first really good evidence that organisms can sense environmental water motion and use that to time gamete release.