In the last decade, there has been an increased awareness that secondary metabolites produced by marine diatoms negatively impact the reproductive success of their principal predators, the copepods. Several oxylipins, products of the enzymatic oxidation of fatty acids, are produced when these unicellular algae are damaged, as occurs during grazing. In the past, the dinoflagellate Prorocentrum minimum, which does not produce the oxylipin 2-trans,4-trans-decadienal (DD), has been used as a live carrier to calculate daily ingestion rates of this molecule by copepod crustaceans. However, since the interaction between oxylipins and live carriers is unknown, the question as to how much and for how long ingestion of these molecules affects copepod reproduction remains a critical point to understanding the functional role of such compounds at sea. In the investigation presented here we used giant liposomes ( approximately 7 mum) as a delivery system for the oxylipin DD, prepared in the same size range as copepod food and containing known amounts of DD. The aim of this work was to relate the ingestion of DD to the reproductive failure of the copepods Temora stylifera and Calanus helgolandicus. Liposomes were very stable over time and after 10 days of feeding, liposomes encapsulating DD reduced egg hatching success and female survival with a concomitant appearance of apoptosis in both copepod embryos and female tissues. Concentrations of DD inducing blockage were one order of magnitude lower that those used in classical feeding experiments demonstrating that liposomes are a useful tool to quantitatively analyze the impact of toxins on copepods.