## 1 Introduction  
Seaweeds encompass a diverse array of marine species [1, 2], showing remarkable adoptability to challenging environmental conditions. In response to these adversities, seaweeds produce allelochemicals which contribute to their ability to compete for space, resist pathogenic microorganisms and predators, and hinder the establishment of epiphytes [3; 4]. Notably, seaweeds have been associated with various biological activities that offer health-promoting benefits related to human skin, immunity, and growth [5; 6; 7; 8]. These attributes position seaweed as a valuable source for pharmaceuticals, nutraceuticals, and cosmecuticals [5; 9; 10]. The seaweed market is expected to undergo significant growth, with projections indicating a 39.8% increase, reaching USD 24.98 billion from 2021 to 2028 [11]. Recognizing the potential of seaweed as a source of biomass in the pharmaceutical, food, and chemical industries, there is pressing need to adopt sustainable seaweed cultivation practices, with tissue culture emerging as a key strategy. Seaweeds can undergo in vitro cultivation through various methods, including (1) micropropagation, (2) protoplast isolation and regeneration, or (3) callus induction [12]. Among these techniques, micropropagation, which involves meristem or somatic embryogenesis, stands out as one of the most commonly employed methods for in vitro propagation of macroalgae [12; 13]. Tissue culture presents a sustainable approach for fostering tissue development and enhancing quality in seaweeds. The controlled cultivation of seaweed tissues has the potential to maximize biomass production and stimulate the synthesis of desired compounds [14]. Particularly vital for species like _Ecklonia cava_, characterized by limited wild stocks, tissue culture serves as a strategic response to challenges posed by climate change, pollution, and escalating demand, ensuring the availability of stocks. Tissue culture of seaweeds can be achieved through direct regeneration from explant tissues or indirectly through callus induction. While callus culture is a well-established technique in tissue culture engineering for terrestrial plants, its application in seaweed culture remains underdeveloped, despite the recognition of seaweeds for various applications such as functional foods, nutraceuticals, and pharmaceuticals. The brown seaweed, _E. cava_, found only in Japan, Korea's Jeju Island, and Busan [15; 16; 17], has been associated with various physiological benefits, including antioxidant, antibacterial, anti-thrombotic, anti-diabetic, anti-hypertensive, anti-obesity, and anti-inflammatory properties, making it a potential raw material for functional foods [18; 19; 20; 21; 22; 23]. However, industrialization has been limited to a few seaweed species from various genera that are suitable for cultivation and harvesting. The cultivation of _E. cava_ is particularly challenging due to farming difficulties and environmental issues such as microplastic and radioactive pollution, ocean desertification, and resource depletion. Countermeasures are essential, especially considering that Korea's Incheon-Gyeonggi coast and the Nakdong river estuary rank second to third globally in microplastic concentration [24; 25]. While indoor culture technology has advanced for land crops and mushrooms, tissue culture research for seaweeds, especially _E. cava_, is limited, with only the report on callus culture by [PERSON] and [PERSON] [26], examining the impact of collection time on callus development. The limited research on this species may be attributed to the restricted distribution of _E. cava_ resources, mainly in Korea and Japan. Considering the escalating marine pollution and global interest in the safety of marine resources, we aim to develop callus culture for _E. cava_ as a natural, year-round, and cost-effective food and pharmaceutical material, safe from marine pollution. Callus induction, a critical initial stage of proliferation and growth, is influenced by various abiotic factors.