Neptune’s Harvest Organic Crab Shell is an excellent dry organic source of NPK, Calcium and Magnesium. It will also help with nematode and fungus problems. Here’s why: Crab Shell is high in Chitin, which promotes the growth of Chitin eating bacteria in the soil. The exoskeletons of fungus and nematode eggs are high in chitin. When added to the soil crab shell helps to create a hostile environment for the fungus and nematodes by feeding the biological life that eats chitin and chitin based organisms.