National Geographic : 1952 Jul
The National Geographic Magazine things of entrancing beauty. It is no easy task to catch their air of delicate fragility on paper. Nor is it easy to paint a glassy clear animal, as transparent as the water in which it lives, revealed only by glancing re flections of light and such patches of color as it may contain. Eyes Seemingly Without an Owner Sometimes I have spent five minutes exam ining a dish of live plankton before noticing an inch-long lobster baby that was swimming right under my nose. Even then it was re vealed only as a pair of dark eyes, apparently swimming around all by themselves. I had been looking right through the body without noticing it. This transparency may make things diffi cult for us, but it gives us an X-ray-like ability to watch such processes as the beating of a heart. On the other hand, it must be a great advantage to a baby lobster which is being hunted by a fish to wear a cloak of in visibility that prevents the fish from seeing its prospective meal. We tried painting these transparent babies on white paper, and they looked beautiful but unnatural. We tried again with a black background, which came closer to the natural conditions in which they live. This was bet ter, but they looked much too solid and harsh. At this stage, Nature stepped in to justify an old adage by sending a very ill wind-in fact, a hurricane-to Miami. This was too much for the roof of my laboratory, and the next thing we knew there was a torrent of water pouring out under the door and down the stairs. Sadly trying to dry out wet papers next day, we came on one of Craig Phillips's sketches. Somehow the rain water had washed out the black background to just the right shade of blue and softened the outlines of the painting until we had exactly the effect we had been seeking. The reader can judge how well the artist has profited from this heaven sent tip. It would take a whole book to describe the life found in these waters, but Jacqueline Hutton has captured the general atmosphere in her two paintings (pages 48, 49). The em phasis in these is on the crabs, fishes, and other reef animals rather than on the corals themselves. It is these other animals which provide so many of the plankton babies which we find in the Gulf Stream as it runs north ward outside the reefs off Miami. To the many visitors to Miami and Miami Beach who enjoy good sea food, the spiny lobster may appeal as one of the most impor tant inhabitants of the reefs. They may de- bate the relative merits of Florida and Maine lobsters, but perhaps our best escape from the argument is to say that they are quite different animals. Northern baby lobsters look rather lobster like when a few weeks old; the southerners spend the first six months of their life swim ming around in the plankton and looking much more like squashed spiders (page 51). Only the hint of a lobster tail at the end of their leaflike bodies points to their future shape. Most of the animals grow more or less con tinuously, but the lobster, like its relatives the crabs and shrimps, saves up its growth to expand in sudden jumps each time it molts. The armor plating which it wears will not stretch; so at intervals it has to throw this off and replace it by a size larger, incidentally changing its shape at the same time if this is necessary. One important result of our work in the Gulf Stream has been the tracing of the 11 stages through which the Florida lobster passes before it is ready to settle to the bottom as a lobsterling. It must have traveled far on the current during its six months afloat; wandering plankton is providing important clues to the movement of ocean currents. Transformation of a Baby Crab We have mentioned already that the baby stages of crabs were a puzzle to early zoolo gists. Page 50 shows the Zoea stage of a porcelain crab similar to the one shown on the bottom on page 49. We say similar, because this is one of the many cases where we know only the approximate parentage. We are not sure yet to which of several kinds of porcelain crabs these babies belong. With long-drawn-out spines in front and behind, they look, when swimming, absurdly like medieval knights charging, lance in hand. Later, in the Megalopa stage, the creature begins to look quite like a crab (pages 50, 51). True, its tail still sticks out behind like a lob ster's, instead of being neatly tucked away underneath the body as the parent has it. On the other hand, the claws are obviously those of a crab, and, in the case of the one on page 51, the keel along the top of the claw points strongly to the box crab as parent (page 48). These claw ridges, when the little crab set tles to the bottom, will fit tightly against the front of its shell and help keep sand grains from its mouth and gills as it burrows into the bottom. In much the same way, the backward hinged claw tips of the ghostly little mantis shrimp shown on page 50 foreshadow the pen knife action of the claws which have earned the adult the local name of "split thumb" (page 48).