Spirulina, a blue-green algae, might cause small black spots on you food. This is happens during freezing as water in the spirulina's cells crystallise and puncture the cell walls. When defrosted, the phycocyanin leaks out, which can make the spirulina appear black or dark blue. Rest assured the food is perfectly safe to eat.
Spirulina contains anti-oxidants and may have health benefits to support body functions such as immune support, cholesterol management: blood pressure: blood sugar, allergies, skin health