Lipoxygenase-catalyzed peroxidative decomposition of unsaturated fatty acids occurs within seconds when diatoms are crushed or eaten, producing alkyls. DDA is a prominent member of this class of reactive compounds. Common ω-6 fatty acids such as linoleic acid, dihomo-ω-linolenic acid, and arachidonic acid can give rise to DDA. DDA reduces the hatching rate and has a strong teratogenic effect on the eggs of pelagic copepods, at concentrations around 1 µM. In human carcinoma Caco2 cells, DDA induces cell growth arrest at around 15 µM. DDA appears to be a natural defensive chemical designed to limit the reproductive success of copepods, the main predators of diatoms. It may also be a more general inducer of apoptosis.