'algae-supportive' originates from Modern English as a compound of 'algae' + 'supportive', where 'algae' is the plural form used in biology (from Latin 'alga') and 'supportive' is formed from 'support' + the adjectival suffix '-ive'.

'algae' entered English via New/Scientific Latin 'alga' (used in biological nomenclature), itself adopted from classical languages for 'seaweed'; 'support' comes from Old French 'supporter' < Latin 'supportare', and the adjective 'supportive' developed in Modern English by adding '-ive' to 'support'. The compound 'algae-supportive' is a modern coinage combining these elements.

Initially, the components meant 'seaweed' ('algae') and 'providing support' ('supportive'); combined in modern usage they specifically denote conditions that promote algal growth.