golden algae vs alga

golden algae and alga both are nouns.

Word	Noun	Adjective	Verb	Adverb
golden algae	Yes	No	No	No
alga	Yes	No	No	No

As nouns, alga is a hypernym of golden algae; that is, alga is a word with a broader meaning than golden algae:

golden algae: algae having the pigments chlorophyll and carotene and xanthophyll
alga: primitive chlorophyll-containing mainly aquatic eukaryotic organisms lacking true stems and roots and leaves

Other hypernyms of golden algae include algae.

golden algae (noun)	alga (noun)
algae having the pigments chlorophyll and carotene and xanthophyll	primitive chlorophyll-containing mainly aquatic eukaryotic organisms lacking true stems and roots and leaves