Note 2 - Significant Accounting Policies - Revenue By Product (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Net sales	$ 5,179	$ 9,419	$ 11,895	$ 18,383
Packaged Astaxanthin [Member]
Net sales	2,854	4,015	6,379	8,054
Packaged Spirulina [Member]
Net sales	1,061	1,796	2,572	4,538
Packaged Products [Member]
Net sales	3,915	5,811	8,951	12,592
Bulk Astaxanthin [Member]
Net sales	333	509	827	914
Bulk Spirulina [Member]
Net sales	784	2,985	1,877	4,569
Bulk Products [Member]
Net sales	1,117	3,494	2,704	5,483
Contract Extraction [Member]
Net sales	$ 147	$ 114	$ 240	$ 308