Tube worms like it hot, but larvae not. (Earth Science).

The larvae of some tube worms that attach themselves to the seafloor around hydrothermal vents can't stand the heat there. If they drift into chilly waters, however, they go into suspended animation until they find water at a temperature in between. This phenomenon, researchers say, could explain how animals of nonmobile species that depend upon the hot water and nutrients gushing from isolated vent systems can nonetheless be found at widely dispersed locations.

The tube worm species Alvinella pompejana live around vent systems all along the East Pacific Rise, an undersea geological formation that stretches for thousands of miles. These worms thrive in water temperatures between 20 [degrees] and 80 [degrees] C, says Francoise Gaill, a marine biologist at Pierre and Marie Curie University in Paris.

However, Gaill says, experiments show that the tube worms' larvae die within 48 hours if they're kept at these temperatures. At temperatures typical of the zone near the base of hydrothermal chimneys, between 10 [degrees] and 14 [degrees] C, up to 90 percent of the embryos survive and continue their development. At 2 [degrees] C--the typical temperature of ocean water at a depth of 2,500 meters, if it isn't heated by hydrothermal vents--the embryos don't grow but remain intact. Gaill and her team present these results in the Oct. 18 NATURE.

Gaill suggests that the tube worm embryos that drift away from the vents or are carried upward by the vent's heated plume quickly reach cool water, enter a state of arrested development, and then ride the ocean currents until they reach a suitably warm spot to continue their growth.

--S.P.