## 1 Introduction  
The increasing salinization of soils and waters due to climate change is driving interest in salt-tolerant crops like sea fennel. This emerging halophyte, with an exceptional resilience to harsh environmental conditions, has developed unique adaptations to saline environments, including the production of biologically active compounds that boost both its survival and nutritional profile [1; 2]. Due to its potential as a \"cash crop\", sea fennel is gaining increasing attention as a sustainable agricultural option in coastal regions affected by soil deterioration and water pollution [3; 4; 5]. The use of sea fennel (_Crithum maritium_ L.) dates back to ancient times, when coastal communities consumed it mainly out of necessity. Sea fennel leaves were particularly valued for their role in human nutrition, as they are rich in vitamin C and were used to prevent scurvy, which was a significant concern among sailors and maritime populations [6; 7]. Today, however, it has been rediscovered and has rightfully earned its status as a star of coastal cuisine, but its application is also expanding into other sectors, such as cosmetics, food supplements, and the pharmaceutical industry [8]. The aerial parts of sea fennel contain a wealth of bioactive compounds, including essential oils (EOs), vitamins C and E, phenolics, carotenoids and essential fatty acids, essential amino acids, dietary fibers, and minerals, especially iodine. The distribution of metabolites varies among the different plant parts (leaves, flowers, stems, and fruits) [7; 9; 10; 11; 12]. The most significant difference among the sea fennel populations in the Mediterranean basin lies in the composition of their essential oils. The key distinguishing factor is the presence of the volatile compound dillapiole [13]. The Croatian sea fennel chemotype is completely free of dillapiole, which has been confirmed by various studies that have analyzed different parts of the plant, collected from various locations along the Adriatic coast and over different time periods [10; 14; 15]. Nowadays, we are witnessing a growing consumer demand for natural products and their derivatives. Due to their richness in bioactive compounds, essential oils (EOs) are increasingly being investigated for their potential as preservatives, flavorings, and therapeutic agents [16; 17]. Hydrolates (aromatic waters, hydrosols) are another highly valued natural product obtained as a by-product of the EO distillation process, and they are increasingly attracting interest in fields such as aromatherapy, perfumery, and food flavoring [18; 19]. Hydrolates are highly diluted mixtures of volatile compounds generated during the distillation and condensation of the oil and water vapors. Due to the immiscibility and differences in the densities of these two components, essential oils separate into the upper layer, while hydrolates, being denser, form the lower layer [20]. However, polar volatiles from EOs, mainly oxygenated compounds that are capable of forming hydrogen bonds, often migrate from the EOs into hydrolates, contributing to their aroma and properties. This is often the reason why the chemistry of EOs differs from that of their respective hydrolates [21; 22]. In addition to the chemistry of EOs and hydrolates, the bioactivity assessments of these fractions, including their antioxidant, antimicrobial, and anti-inflammatory properties, have attracted the interest of scientists over the last few decades, especially due to their more frequent application in food/pharmaceutical/cosmetic products [23; 24; 25; 26]. Although the EOs from sea fennel have been well characterized, there is little or no information on the corresponding hydrolates [21; 22]. Due to the increasing demand for natural products and their wide range of applications, this study conducted a comprehensive chemical and biological analysis of sea fennel essential oils and hydrolates.