Spirulina contains pseudocobalamin — chemically near-identical to real B12 but unusable by humans AND competes for absorption receptors. 'Vegan B12 from spirulina' is one of the most dangerous marketing claims on the atlas — serum B12 looks normal while nerve damage continues.
Two unrelated molecules the shelf conflates: real astaxanthin comes from the red microalga H. pluvialis and is an orange-to-blood-red ketocarotenoid; the blue Blue Majik is phycocyanin from spirulina. Blue astaxanthin is the two being sold as one.
Chlorophyll, chlorella and spirulina are marketed as binding microplastics with no binding evidence, and spirulina carries its own heavy-metal contamination problem. Cutting the source beats swallowing a binder.