DO DIATOM DIETS ACT AS BIRTH CONTROL PILLS FOR MARINE COPEPODS?

Ianora, A. Stazione Zoologica A. Dohrn, Villa Comunale 80121 Naples, Italy Traditionally, diatoms have been regarded as providing the bulk of the food that sustains the marine food chain to top consumers and important fisheries. However, this view has recently been challenged on the basis of laboratory studies showing that these small, unicellular algae possess anti‐mitotic properties similar to the cytotoxic compounds isolated from numerous marine and terrestrial higher plants. In fact, when copepods, the principal predators of diatoms, are fed diatom diets, they produce abnormal eggs that either fail to develop to hatching or hatch into malformed nauplii that die soon afterwards. The aldehydes responsible for this anti‐cell growth activity have recently been isolated and these compounds have been shown to arrest not only the development of copepod and sea urchin embryos, but also the proliferation of human carcinoma cells. In terrestrial environments, there are many reports of secondary metabolites produced by plants that interfere with the reproductive capacity of grazing animals, and which act as a form of population control. But this type of biological model is new for the marine environment where most of the attention on plant‐animal interactions has focused on feeding deterrents and poisoning compounds. Such “birth‐control” compounds may discourage herbivory by sabotaging future generations of grazers, thereby allowing diatom blooms to persist when grazing pressure would normally have caused them to crash.