They are harvesting a delicacy called mozuku that grows around Okinawa, according to a site about local resources:
This mozuku seaweed could only be harvested in the beautiful ocean of Okinawa. The characteristics are that it is thicker than any other mozuku seaweed in other parts of Japan. The slimy surface is rich in fucoidan. It is said that fucoidan has an antibacterial function, strengthens the immune, improves lifestyle-related diseases such as arterial sclerosis, has a cancer preventative effect balances intestinal health. Also it contains dietary fiber which improves the intestinal condition such as alginic acid, calcium which is effective in preventing osteoporosis minerals such as magnesium that enhances the absorption of calcium. To add to that, it is a low calorie healthy food. Mozuku seaweed is a remarkable food that has supported the health longevity of Okinawa.
Seaweed may become a much larger part of diets worldwide, as many kinds are very resilient and easy to grow. Youm!