Wakame seaweed is very commonly used for cooking in some Asian country including Japan, Korea and China. It adds sea-flavour to cooking and it's beneficial to health. In the UK where I live, you can find packet of dry wakame sold in Chinese supermarket and it is pretty cheap. I have seen it in major supermarkets and Japanese super markets with higher prices. You can add any vegetables, for example Leek,sweet potato,cabbage and parsnip would go really well in this soup.