# Seasonal Variability of Volatilome from _Dictyota dichotoma_
## 2 Results and Discussion
### Statistical Analysis of the VOCs Obtained by Hydrodistillation  
The PCA results for VOCs of fresh and air-dried \(D\). _dichotoma_ obtained by hydrodistillation are shown in Figures 6a-d and 7.  
In fresh samples, the first two PCs described 79.72% of the initial data variability. The correlation loadings of the first two PCs (Figure 6a) showed high correlations between two groups of compounds. Unsaturated hydrocarbons (oct-1-en-3-one, (\(E\))-oct-2-en-1-ol, (\(Z\))-octadec-9-en-1-ol) and higher saturated aldehydes (tridecanal, pentadecanal) were the variables with the highest variable contributions, based on the correlations. The PC2 was associated by methyl (all \(Z\)) eicosa-5,8,11,14-tetraanoate and pachydictyol A abundance in the samples. The score plot (Figure 6b) showed the position samples in the multivariate space of the first two PCs. Similarities were observed for May and June, and August and September, while June was segregated based on lower content of aliphatic compounds (oct-1-en-3-one, oct-1-en-3-ol, (\(E\))-oct-2-en-1-ol, octan-1-ol, tridecanal, heptadecane, and pentadecanal) and diterpene alcohol gleenol, but significantly higher content of (\(Z\))-octadec-9-en-1-ol, (\(Z\))-octadec-9-enoic acid and diterpene alcohol, cembra-4,7,11,15-tetraen-3-ol.  
Figure 6: Correlation loadings (**a**,**c**) and score plot (**b**,**d**) of the dominant VOCs of fresh (**a**,**b**) and air-dried (**c**,**d**) \(D\). _dichotoma_ samples obtained by hydrodistillation.  
In dry samples, aliphatic compounds (heptadecane, pentadecanl, (Z)-octadec-9-en-1-ol) and diterpene alcohol cembra-4,7,11,15-tetraen-3-ol were variables with the highest contribution to PC1, while octa-1-ol and tridecanal, contributed the most to PC2.  
Oct-1-en-3-one, oct-1-en-3-ol, (_E_)-oct-2-en-1-ol and octan-1-ol positively correlated with each other, but negatively with (_Z_)-octadec-9-en-1-ol and (_Z_)-octadec-9-enoic acid. The positive correlation could be seen between saturated higher aldehydes tridecanal, heptadecane and pantadecanl, but they negatively correlated with (_Z_)-octadec-9-enoic acid.  
PCA of all dominant VOCs obtained by hydrodistillation showed clear separation between fresh and dried samples (Figure 7). There were more similarities in seasonal variation between fresh samples. The dried samples appeared in the left part of the plot. The distribution was along the PC1 axis and was in the relation to aliphatic compounds (oct-1-en-3-one, oct-1-en-3-ol, (_E_)-oct-2-en-1-ol, octan-1-ol, tridecanal, and heptadecane) and (_Z_)-octadec-9-enoic acid abundance, while the distribution along the PC2 axis was related to sesquiterpene alcohols (cempha-4,7,11,15-tetraen-3-ol and gleenol) and methyl (all _Z_) eicosa-5,8,11,14-tetraenoate) abundance in the samples. Similar was observed for the fresh samples, and their vertical distribution was related to high cembra-4,7,11,15-tetraen-3-ol and low gleenol abundance. No correlation was found between the compounds' content change over months and temperature change.  
Figure 7: Score plot of the dominant VOCs of fresh (Fr) and air-dried (Dr) _D. dichotomous_ samples obtained by hydrodistillation.