Focus on Cyanobacteria

Can produce dense blooms or benthic mats reproduction typically by fission unique characteristic:
can utilize atmospheric nitrogen for growth and metabolism process known as "nitrogen fixation" common in nearshore environment, rare in offshore, common in legumes (beans) can form symbiotic relationships with other orgs such as diatoms (Rhizosolenia spp.) often found attached to other organisms)

Marine Primary Producers by Dr. Joe Fox