## 1 Introduction  
Marine secondary metabolites possess outstanding structural and functional diversity related to their different metabolic pathways [1]. While the volatile organic compounds (VOCs) of terrestrial plants have attracted attention since antiquity, the VOCs of marine algae have been much less investigated. Therefore, the target of the present research are VOCs of two brown seaweeds from family Dictyotaceae, order Dictyotales: _Taonia atomaria_ ([PERSON]) [PERSON], 1848 and _Padina paavonica_ ([PERSON]) [PERSON], 1960. _T. atomaria_ (family Dictyotaceae, order Dictyotales, class Phaeophyceae) is a brown seaweed widespread in the Mediterranean Sea. Taondiol and atomic acid, cyclised macroditerpenoids, were isolated from this alga collected in Canary Islands [2; 3; 4]. The chemical investigation of _T. atomaria_ from the northern Adriatic Sea describes the identification of sesquiterpenes 4-cadinene, cadina-4(14),5-diene, (\(-\))-germacrene D, axenol, (\(-\))-cubebol and epi-cubebol from its petrol extract [5]. Two novel cyclised meroditerpenoids, atomarianones A and B, were isolated from MeOH/CH\({}_{2}\)Cl\({}_{2}\) extract of _T. atomaria_ collected at Serifos island in the Central Aegegan Sea [6]. The freeze-dried alga _T. atomaria_, after exhaustive extraction with CH\({}_{2}\)Cl\({}_{2}\)/MeOH, followed by chromatographic separations, afforded the compounds of tetraprenyl toluoquinone class, e.g., (Z)- and (_E_)-sargaquinone and sargaol [7]. _T. atomaria_ sulfolipids were characterised by high contents of palmitic acid and the main constituents were sulfoquinovosyl-di-acylglycerol and sulfoquinovosyl acylglycerol [8]. The extracts of _T. atomaria_ exhibited: (a) anticancer activity due the presence of algal sulfolipids [8], the compounds stypodiol [9] and stypoldione were determined as in vitro inhibitors of microtubule polymerization [10]; (b) antifungal activity due to taondiol presence [11]; (c) antibacterial activity due to algal sulfolipids [8]; (d) insecticidal activity related to isoepitaondiol [12]; (e) antiviral activity related to the algal sulfolipids [8]. In addition, the extracts of _T. atomaria_ exhibited the best radical-scavenging activity (RSA) using DPPH and chemiluminescence (CL) tests in comparison to the extracts of the other 12 algal species from the island Crete, Greece and approached the activity of powerful antioxidant standards [13]. The isolated metabolites taondiol, isoepitaondiol, stypodiol, stypoldione, sargaquinone and sargaol were found to possess marked RSA. Recently, it was found that the surface metabolites of _T. atomaria_ exhibit the ability to regulate epibiosis [14]. _P. pavonica_ belongs to the family Dictyotaceae, order Dictyotales, class Phaeophyceaeae and is widespread in the Adriatic Sea. The characteristic brown algal polysaccharides alignates and laminarans were found in _P. pavonica_[15]. Chlorophyll C\({}_{1}\) and C\({}_{2}\), fucoxanthin, fucoxanthin and diatoxanthin were the most typical pigments in _P. pavonica_[16]. The chemical composition of this seaweed from the southern Adriatic Sea was investigated [17] and 12 sterols were identified in CH\({}_{2}\)Cl\({}_{2}\)/MeOH extract, the main ones being cholesterol and fucosterol. The most abundant fatty acid was palmitic acid, followed by oleic acid and myristic acid. The toluene extract was subjected to 4-h simultaneous distillation-extraction (SDE; [17]); and in the volatile fraction, aromatic esters, benzyl alcohol, benzaldehyde, and free fatty acids dominated with low concentrations of terpenids, phenols and sulfur containing compounds. _P. pavonica_ collected from Red sea coast, Egypt was subjected to direct SDE and bis-2-ethylhexyl phthalate was the major compound. _P.