Passage IV

Marine Entomology—The Study of Ocean Insects

Scientific curiosity is often motivated by observable phenomena. Sometimes though, as with the research of entomologist Dr. Lanna Cheng, that curiosity is fueled by what seem to be absent. Her interest in a curious paradox in nature has stimulated the growth of a new branch of oceanography.

Early in her career, Dr. Cheng became intrigued by the fact that because insects are the earth's most abundant and diverse organisms, they are virtually absent from and nonexistent in the world's largest habitat, the ocean. To try to solve this riddle, Dr. Cheng began studying the genus Halobates, the only known open-ocean insects. (50) She became the first scientist to capture these insects alive and the bringing them back to the laboratory for study.

Through her research on Halobates and other insects, Dr. Cheng has considered—and then dismissed一three hypotheses concerning the scarcity of marine insects. The first offering the oceans high, salt content as an explanation. But Dr. Cheng has found species of flies that can tolerate more than three times the salt content of the sea. The second hypothesis states that the ocean is too deep and underwater pressure too great for insect larvae to complete it's life cycle. Research has found, however, that some fly larvae can survive at greater depths than those of the deepest-diving marine mammals. A third hypothesis asserts that ocean water contains too little oxygen for insects. Similarly, some fly larvae can survive months without oxygen, while other insect species live in very polluted waters with similarly low oxygen levels.

Dr. Cheng believes that a fourth hypothesis is the likely explanation. She suspects insects are less successful at sea because they so readily adapted to land. While the insects were colonizing land, the crustaceans, their main marine competitors, were effectively adapting to the saltwater environment. As partial evidence, Dr. Cheng cites the fact that Halobates spend their lives walking on top of the water; thus eliminating the need to compete with the crustaceans below.