The open ocean - A Fascination for Fish: Adventures of an Underwater Pioneer - page 259

out producing the free-swimming form. This explains why some years
jellyfish are everywhere and other years there are none. In any event,
to provide us with a reliable supply of exhibit jellies, we needed our
own colony of jelly-producing polyps.
Yoshitaka Abe, then curator of the Ueno Aquarium in Tokyo, had
written two papers on the culture and exhibit of the moon jelly. We
contacted Abe, and he kindly gave us some of his jelly polyps attached
to a piece of plastic. The little polyps thrived, multiplied, and soon be-
gan producing tiny free-swimming jellies. With regular feeding, these
grew and were soon large enough to be put on display.
Rather than try to reinvent the wheel, we decided to base our exhibit
on Abe-san's plans. Using his design, aquarist Mark Ferguson built our
first tank for moon jellies, the back of which consisted of a curved vinyl
sheet perforated with hundreds of holes. The adult animals did well and
were soon producing microscopic larvae by the thousands, which in turn
settled out on surfaces in the jelly exhibit and developed into colonies
of polyps. Freya used a razor blade to carefully transfer the polyps to
sheets of plastic, where they were cultured in holding tanks and would
hopefully provide a reliable supply of moon jellies for exhibit.
Although Abe's moon jelly tank was quite successful at keeping the
jellies healthy, we thought its aesthetics could be improved. This par-
ticular challenge couldn't have been better timed. UCLA marine biol-
ogist William Hamner stopped in to see the success we had with the
moon jelly exhibit and life cycle. He had designed and built a small
tank for keeping planktonic animals on shipboard. It was modeled
after an early German design called a “Planktonkreisel” that had been
developed to study planktonic animals in a research laboratory. Kreisel
is the German word for a child's spinning top—an appropriate name
because of the circular water flow in the tank. Hamner said we could
borrow his tank for a while and try it out.
Jellies are part of the plankton, which is made up, by definition, of
organisms that are pretty much at the mercy of the currents. In con-
ventional tanks with conventional seawater systems, plankton end up
fatally stuck on the overflow screen or sucked into the pump. The se-
cret to Bill Hamner's tank design was that the supply water flows smoothly
across the outflow screen, gently blowing the animals safely away from