Note 2 - Significant Accounting Policies - Revenue By Product (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Net sales	$ 8,571	$ 7,690	$ 15,923	$ 15,761
Packaged Astaxanthin [Member]
Net sales	4,138	4,747	7,380	9,357
Packaged Spirulina [Member]
Net sales	2,126	1,731	3,968	3,645
Packaged Products [Member]
Net sales	6,264	6,478	11,348	13,002
Bulk Astaxanthin [Member]
Net sales	463	328	882	502
Bulk Spirulina [Member]
Net sales	1,684	744	3,214	1,977
Bulk Products [Member]
Net sales	2,147	1,072	4,096	2,479
Contract Extraction [Member]
Net sales	$ 160	$ 140	$ 479	$ 280