Finding some quiet time for reproduction

 Algae that spend their days soaking in cool waters off an uninhabited Swedish island offer animals and other plants an important lesson in reproduction.

 Don't bother trying during turbulent times--wait for your environment to settle down.

 Many marine organisms like the alga Fucus vesiculosus reproduce by releasing sperm and eggs into the water. These gametes must fuse to grow into a new individual. However, researchers have suspected that this approach to fertilization has a low success rate. In experiments where scientists have released various plant or animal gametes into the ocean, egg and sperm have often failed to meet.

 One common type of algae, and probably other forms of marine life, is savvy about reproduction. It determines when the surrounding water becomes calm and only then releases large amounts of eggs and sperm, report Ester A. Serrao of the University of Maine in Orono and her colleagues in the May 28 Proceedings of the National Academy of Sciences.

"This paper shows there is at least one elegant mechanism out there," asserts Mark Denny of Stanford University. Some marine organisms, such as sea urchins, just spew out lots of gametes to increase the odds of fertilization.

 Serrao and her colleagues collected eggs, sperm, and zygotes from two beds of F. vesiculosus off Asko, Sweden, during the 2-month reproductive season. They noticed that the algae released eggs and sperm only in calm water--slower than about 0.2 meter per second--and only in late afternoon. The proportion of gametes to zygotes indicated almost 100 percent fertilization.

 The scientists then put the algae's receptacles, which store either sperm or eggs, in tubes anchored in the ocean. Like intact plants, the receptacles released gametes only in calm water. The researchers found signs of a sperm's nucleus in almost every egg released.

 The investigators then measured the response of F. vesiculosus and two other algae in the same family to agitation in laboratory water. They put the algae's receptacles in flasks and shook them for various amounts of time up to a week, Serrao explains. The receptacles released their gametes only during the early evening of the day after the shaking stopped. The longer the period of shaking, the more eggs and sperm were released.

 These algae appear to be responding to at least one characteristic of calm water--a low concentration of dissolved inorganic carbon, the team learned recently. In quiet water, algal photosynthesis depletes the carbon from the thin layer of static water surrounding the receptacles, and little new carbon mixes in.

 When the researchers removed all dissolved carbon from water in the lab, the algae released their gametes, even when the water was turbulent. When the team added carbon, the plants released no gametes, even under calm conditions.