First, the artificial cultivation of seaweed involves a carefully managed growth process that consists of two main stages: the development of filaments and the growth of fronds.
In the filament cultivation phase, mature seaweed fronds are typically harvested in late spring. They are subjected to dry stimulation before being placed in a container filled with seawater, which helps release spores. Once the spore concentration reaches an optimal level, the fronds are removed. The spore-rich water is then sprayed onto a cultivation pond where shells have been placed, allowing the spores to attach to the shells. Over time, these spores germinate and grow into filamentous structures. As the water temperature drops in the fall, the shells mature and release spores again. These spores are collected on net curtains, which are then placed in the sea on artificial trusses, marking the transition to the frond development stage. Throughout this process, regular maintenance such as water changes, fertilization, and cleaning is essential to ensure healthy growth.
The frond development phase includes three primary cultivation methods. The first is pillar cultivation, where stakes or bamboo poles are used as supports, and net curtains are hung horizontally for growing seaweed. This method yields about 100 to 500 grams per square meter but is rarely used in China, though it remains popular in Japan. The second method is semi-floating rake cultivation, where the truss floats during high tide and can be raised during low tide. This allows the net curtain to be exposed to air, which helps prevent algae from attaching and promotes better growth. Yield here ranges from 500 to 1000 grams per square meter. The third method is full floating pod cultivation, suitable for shallow seas, where the net curtain floats on the surface. While this method can produce similar yields, it requires careful exposure to air within 20–30 days to maintain healthy growth.
When the fronds reach approximately 20 cm in length, they are ready for harvest. In China, the harvesting of Porphyra species usually begins in mid-November, with multiple harvests occurring every 10 to 14 days, typically up to seven or eight times throughout the season.
Second, common diseases during the seaweed cultivation process can significantly impact yield and quality. During the filament growth stage, several diseases may occur, including maculopathy, muddy red disease, green disease, white circle disease, tortrichia disease, shark skin disease, erythrocytic disease, and white spot disease. Maculopathy and muddy red disease are caused by microbial infections, while green disease is a physiological issue. If left unchecked, these diseases can lead to large-scale filament death. For example, maculopathy causes yellow spots on the shell surface, which gradually expand. Treatment options include soaking in low-density seawater, freshwater, sulfanilic acid, or potassium permanganate. Muddy red disease results in a sticky, smelly surface, and can be treated with diluted bleach or low-density seawater. Green disease, often due to nutrient deficiency, can be addressed by adjusting light and adding nutrients. Maintaining clean, filtered seawater is crucial to prevent disease outbreaks.
During the frond development phase, other diseases such as scab, brucellosis, white rot, chlorosis, cancer, and rotten disease may appear. These are often linked to poor water quality or excessive truss density. Red rot, for instance, causes red spots that spread quickly, leading to frond loss. Treatments include surfactants and ensuring adequate drying time. White rot occurs when fronds are not properly dried, so proper spacing and water flow are essential. Chlorosis leads to discoloration, and can be prevented by adjusting water levels and applying fertilizer. Cancer disease, often caused by industrial pollution, requires avoiding contaminated areas. Rotten seedling disease affects young plants, and preventing overcrowding and using cold storage techniques can help reduce its impact.
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Zhoushan City Shuangying Aquatic Products Co., Ltd.  , https://www.shuangying-aquatic.com