**5. Conclusion**

Essential oils from terrestrial plants have been known for a very long time. They have been applied in different domain, particularly in aromatherapy. Essential oils from seaweed are much more recent. The fragrant note of marine origin is becoming more and more interesting among perfumers, the species of the genus *Dictyopteris* and *Dictyota* could be considered as the best example. This importance is related to the great biodiversity and chemodiversity of the marine environment compared to the terrestrial environment. The chemical composition of essential oils and volatile fractions of macroalgae contains compounds usually found in terrestrial essential oils. These include hydrocarbons, oxygenated hydrocarbons, terpenes, and fatty acids. However, they contain specific products such as halogenated products, C11 hydrocarbons, sulfur compounds, and halogenated terpenes. The specific compounds play a very important role on the chemical ecology; they are involved in defense mechanisms and chemical communication. The volatile fractions of algae show a broad spectrum of biological activity, such as antibacterial, antifungal, anticancer, and antibiotic activities.

## **Acknowledgement**

This work is supported by the General Directorate of Scientific Research and Technological Development (DGRSDT)—Algeria.
