News from Underwater

Seafood has enough problems to keep biologists busy. A few new items:

Fast Enough. How fast is a snail's pace? At College Park, Md., U.S. Fish & Wildlife Service conchologists (mollusk fanciers) were measuring to find out. Dr. Paul Galtsoff puts a seagoing snail inside a drum of transparent plastic. When the snail moves (either forward or backward) the drum revolves, recording the snail's motion on a sheet of smoked paper. Conchs move fastest: an average 19 feet an hour. Little oyster drills, one inch long, move only a couple of feet.

Dr. Galtsoff has a practical objective: protecting U.S. oyster beds from snails, which eat about $6,000,000 worth of oysters each year. The drills gnaw a hole in the oyster shell with a filelike organ called a "radula"; then they insert the toothed front end of their stomach and nibble the oyster away. Conchs do their dirty work on the edge of oyster shells. When all the oysters have been eaten, they file holes in one another.

Pillar of Society. All along the U.S. Atlantic coast the eelgrass (Zostera marina) is flourishing again, which is cheering news to U.S. Fish & Wildlife people.

Until 1931, eelgrass was the pillar of saltwater mudflat society. Under its waving, tape-thin leaves, young and weak creatures sought shelter--and the hungry and strong sought food. But in 1931 and 1932, the eelgrass meadows vanished leaving flats of barren mud as far north as Nova Scotia. A microscopic fungus (Labyrinthula) streaked the eelgrass leaves with brown, killing them to the roots.

The scallop business was hardest hit; many Americans almost forgot what little bay scallops tasted like. Ducks, geese and brant were sufferers too (they eat eelgrass shoots). The disappearance of the eelgrass upset the entire balance of eastern shoreline life. The fungus became less virulent around 1940; patches of eelgrass appeared and grew bigger. This year the eelgrass is almost back to normal. Life among the seafood is almost normal, too.

The Amazons. From the Scripps Institution of Oceanography at La Jolla, Calif., Dr. Carl Hubbs reported on a small fish called Molliensia formosa. It is a native of Mexico with an odd family tree.

Dr. Hubbs collected his first "Mollies" in 1930, and was puzzled because he did not find a single male. He brought the females back to his aquarium in Michigan, watched them narrowly, discovered that they were Amazons.* Among the Molliensia formosa, there are no males at all. Their offspring (conceived internally) are all female. When Molly requires a male, she borrows him from a related species.

Dr. Hubbs raised 20 generations of Mollies in his aquarium, transferring the stock to La Jolla by airplane in thermos bottles. Never did he find a male, and none of the females produced by heterogeneous mating with alien fish showed any traits inherited from their fathers. Even when he mated a Molly with a male Gambusia (by artificial insemination), her offspring were female. Dr. Hubbs even tried to create artificial male Mollies--with no luck. By putting male hormones in their water, he made some Mollies brighter colored. But they remained Amazon, and did not attempt to be fathers.

Get the Needle. Three Boston biologists fared better as scientific matchmakers. Harvard's Dr. F. Parker Jr. and A. Loveridge, and Boston University's Dr. S. L. Robbins wanted to raise clawed frogs (Xenopus laevis), which are used in pregnancy tests. Thus far, these frogs have had to be imported from South Africa.

In their native haunts, clawed frogs have definite mating seasons. The females extrude eggs only when wooed by males. In their Boston surroundings, the males were not interested. So the scientists (developing a technique pioneered by H. A. Shapiro) injected both males & females with gonadophysin, a hormone extracted from sheep pituitaries.

Results were heartening. The males courted, and the females extruded eggs which the males fertilized. The tanks of tadpoles grew up into normal frogs. Now the U.S. need no longer depend on imported clawed frogs.

* The Amazons of Greek mythology were women who killed or drove from their territory all males, including their own male children. Once a year they got together with alien males for a brief visit and procreation.

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