Factors for Porphyra Mariculture
The substrate is crucial, as it provides a suitable place for the attachment of the seaweed. In mariculture, it is also important to find a substrate that is readily available and economical. It also must be able to stand the corrosiveness of seawater.
The temperature is extremely crucial, as it determines the timing of the release of the spores.
The thallus stage of Porphyra is better adapted to high light intensity, therefore in mariculture, there is a need to keep the flotaing raft (which contains nori) near the water surface to maximize light exposure. Also, light period is important in the release of spores and is closely regulated to maximize spore production.
The use of fertilizers in seaweed cultivation is a new field. Porphyra is often sprayed with fertilizer, along with Laminaria.
There are two major weed algae in Porphyra cultivation. The two are types of green algae (Chlorophyta) and diatoms. These two are controlled by three methods. 1) The attached spores are densely packed to allow little space for the weeds. 2) When handling the nets, workers are careful not to scrape off the nori, which would also minimize the area available for weed algae to grow. 3) In harvesting, not all the nori is collected at once. The larger thalli are picked, leaving the smaller ones to prevent infestation of weed algae.
There are three types of diseases: physiological and pathogenic diseases, and pests.
Physiological diseases are often as a result of temperature flunctuations and air pollution. In Japan, nori was often subject to "fog damage" which was later determined to be a result of air pollution. The large amount of sulphite in the smoke dissolved with seawater to form sulphurous acid, which has detrimental effects on algae. Crown-gall disease is caused by carcinogenic substances in the sewage, which causes cancer in the algae.
Red wasting disease and Green spot disease are examples of pathogenic diseases. Red wasting disease is caused by the fungus Pythium. Green spot disease is caused by the bacteria Vibrio and Pseudomonas, which produce enzymes which degrade the cell wall of the seaweed.
Lastly, pests can be found in nori fields. They are mostly herbivorous fishes, which are kept out with nets.
© 1999 Lisa Chen. All rights reserved. Use for educational purposes permitted with acknowledgment and notice.