# Seasonal Variability of Volatilome from _Dictyota dichotoma_
## 2 Results and Discussion
### Statistical Analysis of the Headspace VOCs  
The dominant compounds (>2%) from HS-FrDd and HS-DrDd were subjected to principal component analyses (PCA) to describe the variations among the volatiles in  
Figure 1: Total ion chromatogram (TIC) comparison of HS-FrDd (black) and HS-DrDd (blue) samples from May (chromotograms were zoomed to 45 min).  
relation to material preparation (fresh or dry) and seasonal effect. The PCA results for headspace volatiles (two different fibres) are shown in Figures 2a-d and 3.  
The correlation plot and score plot of the dominant components from fresh samples are shown in Figure 2a,b. The first two PCs described 78.25% of the initial data variability while the remaining PCs each accounted for less than 1% of the total variance. The correlation between certain groups of the compounds was observed (Figure 2a). The highest variable contribution, based on correlation, was observed for oct-1-en-3-ol, octan-1-ol, \(\upbeta\)-gurjunene, \(\upalpha\)-humulene, epi-bicyclosesquiphellandrene, \(\upalpha\)-amorphene, pentadec-1-ene, germacrene C and \(\updelta\)-cadinene. Dictyopetrene D' and pentadecane had the highest values of factor coordinates for the PC2, with the highest variable contributions, based on the correlations. The position of the samples in the multivariate space of the first two PCs is shown in Figure 2b. Scores were arranged in two areas with a clear separation between May samples and other sampling months. The compounds that significantly affect the separation of the May sample from other months belong to the group of sesquiterpene hydrocarbons (\(\upbeta\)-gurjunene, \(\upalpha\)-humulene, epi-bicyclosesquiphellandrene, \(\upalpha\)-amorphene, germacrene D, germacrene C and \(\updelta\)-cadinene) and two sesquiterpene alcohols (dactylol nad epicubenol). They all strongly correlate with each other  
Figure 2: Correlation loadings (**a,c**) and score plots (**b,d**) of the dominant compounds from the headspace volatiles obtained by two different fibres for HS-SPME/GC-MS: divinylbenzene/carboxon/polydimethylsiloxane (I) and polydimethylsiloxane/divinylbenzene (II) of fresh (**a,b**) and dried (**c,d**) \(D\). _dichotoma_ samples.  
The correlation plot and score plot of the dominant components from dried samples are shown in Figure 2c,d. The first two PCs described 70.36% of the initial data variability. Oct-1-en-3-ol, benzyl alcohol, octan-1-ol, dictyopterenc C', and pentadecane showed the highest variable contribution to PC1 and factor-variable correlation. The July (fibre II) samples were separated in the right part of the plot based on the lowest pentadecane content, while for PC2 August sample showed the highest case contribution with the highest pentadecane content. A negative correlation was observed between pentadecane and oct-1-en-3-ol as well as pentadecane and germacrene D.  
When the data were analysed together, clear separation was observed between fresh and dried samples. The dried samples appeared in the upper right corner of the plot, while the fresh ones were placed in the lower right corner (Figure 3). Based on the higher content of sesquiterpenes, sesquiterpene alcohols and pentadec-1-ene, as well as the lowest content of pentadecane, the fresh samples from May (both fibres) were segregated in the left part of the plot. There was no clear separation between the other sampling months nor correlation with temperature change over months.