National Geographic : 1974 Oct
Al Giddings surfaced looking perplexed. "It sure is beautiful down there," he remarked, "and I think I have some super pictures of divers, but what were you looking at?" If transparent plankton are hard to see, imagine how much more difficult it is to pho tograph them. Yet instantaneous photography was clearly needed. The Gulf Stream here moves at nearly two knots through the Straits of Florida, and the plants and animals we saw one day would be 50 miles north of Bimini the next. Dr. Robert F. Mathewson, then director of the Lerner laboratory, explained to us: "The transparent tissues of the animals don't reflect light for even the most sensitive film, but if you fire a strobe obliquely behind the animal, some of that light will be refracted through the tissue toward the lens. The tissue has a refractive index slightly different from that of seawater; therefore this refracted light should be bright enough to show up on film." It worked with some organisms, but others still eluded the camera until our divers added to their equipment plastic squirt bottles loaded with harmless dyes. We found that particles of dye will stick to delicate animals-revealing, for example, PHOTOGRAPHS BYL. P. MAIN; UIAGIBAM BY LIJA oIbAnItu-LI s .lrr llI water shows how the house gathers food front screens of a house clog, or the ani for its occupant. The drawing (left) dia- mal becomes alarmed, it simply slips out grams the process. By wriggling its tail, of an escape hatch (D) and builds a new the larvacean pulls food-laden water structure within an hour. through a set of front screens (A) that When abandoned, larvacean houses admit only the smallest unicellular become pastures for small crustaceans plants. The plants are trapped inside by that feed on plants trapped in the screens. a complex, microscopically fine filter (B) Most collecting methods destroy such that leads to the animal's mouth. The delicate houses, whose importance in the water, seen above as a stream of green ocean's ecological system has probably dye, spurts out at bottom (C). When the been underestimated.