# Seasonal Variability of Volatilome from _Dictyota dichotoma_
## 2 Results and Discussion
### Variations of Headspace Volatilome of Fresh D. dichotomous
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline  & & & \multicolumn{2}{c}{**May**} & \multicolumn{2}{c}{**June**} & \multicolumn{2}{c}{**July**} & \multicolumn{2}{c}{**August**} & \multicolumn{2}{c}{**September**} \\ \cline{3-14}
**No. ** & **Compound** & **RI** & \multicolumn{1}{c}{**Fr**} & **Dr** & **Fr** & **Dr** & **Fr** & **Dr** & **Fr** & **Dr** & **Fr** & **Dr** & **Fr** & **Dr** \\ \cline{3-14}  & & & & & & & & & & & & & & \\ \hline \multicolumn{14}{c}{**Area (\%)**} \\ \hline
1 & Dimethyl sulfide & \textless{}900 & - & - & - & - & 0.29 & - & 2.09 & - & 1.03 & - & 3.14 \\
2 & Pentanal \({}^{\text{a}}\) & \textless{}900 & - & - & - & 0.29 & - & 0.31 & - & 0.13 & - & 0.08 \\
3 & Pent-1-en-3-ol & \textless{}900 & - & 0.07 & - & 0.27 & - & 0.10 & - & 0.05 & - & 0.12 \\
4 & (Z)-Pent-2-en-l-ol & \textless{}900 & - & - & 0.71 & - & 0.29 & - & 0.20 & - & 0.43 & - \\
5 & Hexanal \({}^{\text{a}}\) & \textless{}900 & - & 0.05 & 0.53 & 0.20 & 0.41 & 0.32 & 0.19 & 0.27 & 0.31 & 0.09 \\
6 & 3-Methylbutanoic acid & \textless{}900 & - & 0.10 & - & 1.73 & - & 0.30 & - & 0.31 & - & 0.37 \\
7 & 2-Methylbutanoic acid & \textless{}900 & - & - & - & 0.41 & - & - & - & - & - \\
8 & Hexan-1-ol \({}^{\text{a}}\) & \textless{}900 & - & - & - & - & 0.37 & - & 0.52 & - & 0.47 & - \\
9 & Heptanal \({}^{\text{a}}\) & 907 & - & - & - & 0.16 & - & 0.30 & - & 0.36 & - & - \\
10 & Benzaldehyde \({}^{\text{a}}\) & 970 & 0.20 & 0.06 & 2.04 & 1.11 & 1.31 & 0.67 & 0.99 & 0.23 & 4.00 & 0.13 \\
11 & 1,3,5-Trimethylbenzene \({}^{\text{a}}\) & 976 & - & - & 0.23 & - & 0.16 & - & 0.16 & - & 0.24 & - \\
12 & Oct-1-en-3-one & 980 & - & 0.21 & - & 0.53 & - & 0.37 & - & 0.13 & - & 0.06 \\
13 & 3,5,5-Trimethylhex-2-ene & 980 & 0.43 & - & 9.33 & - & 5.06 & - & 6.35 & - & 5.99 & - \\
14 & Oct-1-en-3-ol & 984 & 0.92 & 0.65 & 27.25 & 1.36 & 17.59 & 1.95 & 23.19 & 0.93 & 24.37 & 0.27 \\
15 & Octan-3-one & 991 & 0.59 & - & 2.00 & - &  
Another abundant compound from June to September was oct-1-en-3-ol (up to 19.85% (I); 27.25% (II)) with the lowest percentage in May (0.41% (I); 0.92% (II)). The same trend was noted for other major aliphatic acyclic C\({}_{8}\)-compounds: (_E_)-oct-2-enol (up to 5.54% (II) in June), (_E_)-oct-2-en-1-ol (up to 10.74% (I) or 15.97% (II) in September) and octan-1-ol (up to 7.42% (I) or 9.98% (II) in September). The aliphatic C\({}_{8}\)-compounds were found previously in HS of fresh _D. dichtoma_[14], but not in the research of [PERSON] et al. [15]. Minor percentages of hexanal, nonanal, (_E_,_E_)-deca-2_4-dienal and pentadecanal were also periodically found (Tables 1 and 2). Lower aliphatic compounds were not so represented in _D. dichtoma_ from the Yellow Sea of China [15]; however, (_E_)-hept-2-en-1-ol was the most abundant (4.62%). Other found aliphatic compounds were dictyoplerenes: dictyoptenere D\({}^{\prime}\) (up to 4.42% (I) or 8.22% (II)) and periodically dictyoptenere C\({}^{\prime}\) (up to 0.54% (I) or 1.69% (II)). Dictyopteneres as C\({}_{11}\)-hydrocarbons (cyclopropanes and cycloheptadienes) and their derivatives appear to be most abundant in the brown algae of the genus _Dictyopteris_[16]. Dictyoptenere C\({}^{\prime}\) (also known as dictyotene) was found as a minor compound in the essential oil of vegetative parts of _Dictyopteris_[16], and also in freshly released eggs of marine brown alga _D. dichtoma_, as the substance that attracts spermatozoids [17]. Our previous research [14] also detected dystoplerenes in this alga. The striking differences were found for HS-FrDd collected in May in comparison to other collection periods, which is particularly notable for the higher abundance of sesquiterpenes. They can be divided into the following types (Tables 1 and 2): derivatives of cadinane and selinate followed by a minor abundance of aromadendrane, carophyllane and other derivatives. Selinate and cadinane are the two main types of the sesquiterpenes reported in brown algae [18].