First, the artificial cultivation of seaweed involves a structured process that includes two main stages: filament growth and frond development.
In the filament culturing stage, mature fronds are harvested in late spring. These fronds are subjected to dry stimulation before being placed in a container filled with seawater to release spores. Once the spore concentration reaches the desired level, the fronds are removed. The spore-infused water is then sprayed onto a cultivation pond containing shells, allowing the spores to attach to the shells. Over time, the spores germinate and grow into filaments. As the water temperature drops in the fall, the shells mature and release spores again. These spores are collected on a net curtain, which is then placed in the sea and suspended on an artificial frame, marking the beginning of the frond development phase. Throughout the filament growth period, regular maintenance such as shell cleaning, water changes, fertilization, and shading is essential to ensure healthy growth.
The frond development stage can be carried out using three primary methods. The first is pillar cultivation, where parallel stakes or bamboo poles are used as supports, and net curtains are hung horizontally for algae growth. This method yields 100 to 500 grams of seaweed per square meter but is not widely used in China. In Japan, it remains a common technique. The second method is semi-floating rake cultivation, where the truss floats during high tide and can be raised on the beach during low tide. This allows the net curtains to be exposed to air, promoting better seedling growth and increasing yield to 500 to 1000 grams per square meter. The third method is full floating pod cultivation, suitable for shallow seas. Here, the net curtains float on the surface, and if properly managed, the yield is comparable to semi-floating systems. However, without periodic drying, the fronds may suffer from poor health, so exposure to air is necessary within 20 to 30 days after submersion.
Once the fronds reach about 20 cm in length, they are ready for harvest. The harvesting season typically begins in mid-November for certain species, with multiple harvests possible every 10 to 14 days, usually up to 7 to 8 times per season.
Second, common diseases occur during both the filament and frond development phases. During the filament stage, diseases such as maculopathy, muddy red disease, green disease, white circle disease, tortrichia disease, shark skin disease, erythrocytic disease, and white spot disease can affect the growth. Maculopathy and muddy red disease are microbial in nature, while green disease is physiological. If left untreated, these diseases can cause mass die-offs. For example, maculopathy leads to yellow spots on the shells, which expand over time. Treatment options include soaking in low-density seawater, freshwater, or solutions of sulfanilic acid or potassium permanganate. Muddy red disease causes a sticky, smelly coating on the shells, which can be treated with bleach or low-density seawater. Green disease, caused by nutrient deficiency, requires proper nutrition and reduced light exposure.
During the frond development phase, diseases like scab, brucellosis, white rot, chlorosis, cancer, and rotten disease may occur. Red rot, for instance, appears as small red spots that spread rapidly, causing fronds to fall off. It can be controlled with surfactants or by increasing drying time. White rot results from excessive drying, poor water flow, and insufficient light. Proper spacing of the net curtains, ensuring adequate drying, and timely harvesting help prevent this issue. Chlorosis, where fronds turn green and decay, can be managed by adjusting water levels and applying fertilizer. Cancer disease causes fronds to shrink, turn yellow and black, and become leathery, often due to industrial pollution. Avoiding contaminated areas is crucial. Rotten seedling disease affects young algae, causing them to fade and rot. Preventive measures include avoiding overcrowding and proper layout of the trusses, with cold storage being an effective method used in Japan.
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Zhoushan City Shuangying Aquatic Products Co., Ltd.  , https://www.shuangying-aquatic.com