Ecologia e Fisiologia - Comunicações orais

Calcified rhodophytes have a structural defense mechanism against herbivory, reducing nutritional value due to high calcium carbonate content. They may also produce distasteful compounds, providing an additional defensive effect. Dichotomaria marginata exhibits anti-herbivory activity knowledge to few marine herbivores, while Arthrocardia variabilis lacks biological activity and chemical profile records. This study evaluated deterrence activity and chemical profiles of D. marginata and A. variabilis non-polar extracts against Pachygrapsus transversus (Gibbs, 1850). The specimens were collected from Tarituba (Paraty) and Vermelha Beach (Rio de Janeiro), sorted, dried, ground, and extracted using dichloromethane. Pachygrapsus transversus was collected in Niterói/RJ and acclimated with Ulva sp. as food for 24 hours. Artificial diets containing extracts of 2 g of each dried alga were offered for three days (N=19), ending at 30% consumption. LC-MS/MS analysis used ESI and APCI sources in both ionization modes. The chemical data were processed with MZmine v. 2.53, statistically evaluated on MetaboAnalyst 5.0, and annotated in GNPS platform. Anti-herbivory assays showed crab preference for control over treatment of D. marginata (p=0,0009), while A. variabilis had no statistical difference at the same quantity (p=0,246). However, A. variabilis extracts displayed anti-herbivory activity at 4 g (p=0,00006). ESI(+) analyses provided higher ion abundance and intensity for subsequent assays. PCA analysis indicated natural sample separation, revealing significant chemical differences between the species. The PLS-DA assay validated the discriminant model with an accuracy of 0.94 (R²=0.95, Q²=0.91). VIP-score identified m/z 458, 502, 546, 590, and 634 ions for species separation. Molecular networks showed clusters of phenolic compounds, phytosterols/phytostanols, and terpenoids. These results enhance our understanding of calcified red algae’s defense mechanisms, with highly calcified species relying mainly on calcium carbonate armor and less on chemical compounds for protection, while less calcified species depend primarily on metabolite diversity and abundance.