Note 14 - Product Line and Geographic Information - Net Sales by Product Line (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Total net sales	$ 31,899	$ 30,202	$ 34,115
Packaged Astaxanthin [Member]
Total net sales	17,811	18,792	20,560
Packaged Spirulina [Member]
Total net sales	7,986	7,867	8,815
Packaged Products [Member]
Total net sales	25,797	26,659	29,375
Bulk Astaxanthin [Member]
Total net sales	1,151	966	1,090
Bulk Spirulina [Member]
Total net sales	4,404	2,340	3,650
Bulk Products [Member]
Total net sales	5,555	3,306	4,740
Contract Extraction [Member]
Total net sales	$ 547	$ 237