Trichome Lengths of the Heterocystous N2-Fixing Cyanobacteria in the Tropical Marginal Seas of the Western North Pacific

Calothrix rhizosoleniae and Richelia intracellularis are heterocystous cyanobacteria found in the tropical oceans. C. commonly live epiphytically on diatom genera Chaetoceros ( C-C ) Bacteriastrum B-C while R. endosymbiotically within Rhizosolenia R-R ), Guinardia G-R Hemiaulus H-R ); although, they occasionally freely (FL- C FL- R ). Both species have much shorter trichomes than other marine filamentous such as Trichodesmium spp. Anabaena gerdii . We investigated trichome lengths of South China Sea (SCS) Philippine (PS) between 2006 2014. On average, had shortest (3.5 cells/trichome), followed by (4.9–5.2 cells/trichome) (5.9 , longest (7.4–8.3 cells/trichome). Field results showed did not vary seasonally or regionally. However, from SCS during cool season longer trichomes, where/when ambient nutrient concentrations were higher. also regional seasonal variations length. Ultrastructural analysis no gas vesicles cells to assist buoyancy regulation. Results suggest that might be regulated their hosts’ symbiotic styles nutrients. Short length help stay euphotic zone regardless whether free-living symbiotic.