Purple Sea Urchins usually spawn within the early months. Purple Sea Urchins live at a certain level in the ocean where the temperature and sodium amount is quiet frequent. If the environment temperature changes significantly, they will die. They are as sensitive to sodium as temperature but the affects are different. Sodium arouses their sexual organs which causes them to spawn. That is why I think that if Purple Sea Urchins are exposed to too much sodium, they will spawn at any moment.