## 1 Introduction
Beyond supporting food, pharmaceutical, and material supply chains, seaweed aquaculture contributes to carbon sequestration, habitat restoration, and nutrient cycling, making it a promising approach to achieving environmental and economic sustainability [23]. Cultivating seaweed has become essential to ensure a sustainable and abundant biomass supply to meet the rising demand from various industries. Traditionally harvested from natural habitats, red seaweed harvesting has reached a point where continued wild collection could threaten local ecosystems and reduce biodiversity. Transitioning to aquaculture produces high-quality biomass on a large scale, safeguarding wild populations while supporting blue economy industries [21; 23]. Also, cultivating indigenous seaweed species, rather than introducing non-native varieties, is essential to protect ecosystem integrity and prevent potential invasions that can disrupt native biodiversity and marine habitats [24; 25]. However, the main commercial sources of carrageenanan are the Asian species _Eucheuma_ and _Kappaphycus_ species, which account for over 90% of global production [9]. As there are only a few cultivated species, it is important to find indigenous species that can be domesticated to increase the number of cultivated species and provide the market with a wide range of biological raw materials [25]. The genus _Chondracanthus_ has previously been cultivated in North America [26], Latin America [27; 28], and in the Iberian Peninsula [29]. The interest in the cultivation of _Chondracanthus_ arises from its richness in carrageenanans, with yields of up to 61.1% with the gametophyte-producing hybrid kappa-iota carrageenanans [30; 31]. The high protein and fibre contents of the genus, together with the mineral content, also highlight the possibility of using _Chondracanthus_ as a nutraceuticali [32]. In addition, the genus has antifungal [33] and anti-hypertensive [34] activities. As a cosmopolitan perennial red alga with a wide Atlantic and Mediterranean distribution [23], _Chondracanthus acicularis_ (formerly _Gigartina acicularis_) is usually found in abundance in the intertidal zone, where it forms a dense turf (Figure 1a). It has also been indicated that the species is resistant to urbanization [35]. The species exhibits a dense, cartilaginous morphology, with irregular branching (Figure 1b) that enables it to attach firmly to substrates in high-energy coastal environments, contributing to its resilience and adaptability [36; 37]. The species reproduces mostly by vegetative reproduction, while sporogenesis is uncommon [38]_C. acicularis_ shows a combination of photoperiod and temperature control of gametogenesis, and cystacorps and tetrasporangia are only recorded between late autumn and winter, being influenced by temperature and photoperiod [24]. The species is known to grow between 13 and 20 \({}^{\circ}\)C and produces tetrasporangial sori between 16 and 20 \({}^{\circ}\)C. At 16 \({}^{\circ}\)C, the tetrasporangia formation shows a true photoperiodic response, with spore release being higher during shorter daylengths [38]. Gametogenesis is also confined to a relatively narrow temperature and photoperiod (14-18 \({}^{\circ}\)C and 12:12 h) [39]. Hence, a high seasonality can be observed, with populations increasing in the number of tetrasores in autumn while growing later in spring [36; 40]. _C. acicularis_ is an important species owing to its high yield of co-polymers of kappa-iota carrageenanan [31; 41; 42], while lambda-type carrageenanan has been identified by FTIR [43]. Figure 1: _Chondracanthus acicularis_ specimens were captured: (**a**) in its natural habitat at Tamargueira beach in January 2024; (**b**) in the laboratory, highlighting the tip of the thallus (scale bar represents 0.5 cm). Due to their acknowledged applications, _C.