Blue-green algae and Cyanobacterial

Blue-green algae noun - Predominantly photosynthetic prokaryotic organisms containing a blue pigment in addition to chlorophyll; occur singly or in colonies in diverse habitats; important as phytoplankton.

Cyanobacterial and blue-green algae are semantically related. In some cases you can replace term "Cyanobacterial" with "Blue-green algae", this terms are similar.

Cyanobacterial adjective - Relating to or caused by photosynthetic bacteria of the class Cyanobacteria.

Blue-green algae and cyanobacterial are semantically related. You can use "Blue-green algae" instead a noun "Cyanobacterial".