AUTHOR=Deng Lixia , Cheung Shunyan , Liu Hongbin 

TITLE=Protistal Grazers Increase Grazing on Unicellular Cyanobacteria Diazotroph at Night

JOURNAL=Frontiers in Marine Science

VOLUME=7

YEAR=2020

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2020.00135

DOI=10.3389/fmars.2020.00135

ISSN=2296-7745

ABSTRACT=<p>In this study, we have for the first time analyzed diel microzooplankton grazing selectivity on unicellular cyanobacterial diazotroph (i.e., <italic>Crocosphaera watsonii</italic> WH8501) and non-diazotrophic unicellular microalga (i.e., <italic>Chlorella autotrophica</italic>). A mixed diet consisting of these two phytoplankton was supplied to four species of protistal grazers during daytime and nighttime, respectively. <italic>C. watsonii</italic> fixes nitrogen during nighttime and showed a stronger diel pattern of cellular C:N ratio than <italic>C. autotrophica</italic>. All four grazers ingested more nighttime <italic>C. watsonii</italic> than daytime <italic>C. watsonii</italic>, suggesting the diazotroph became more nutritious (inferred by C:N ratio) and thus a preferred prey for grazers when it fixes nitrogen. In particular, <italic>Oxyrrhis marina</italic> changed from preferring <italic>C. autotrophica</italic> during daytime to preferring <italic>C. watsonii</italic> during nighttime. The rest grazers showed species-specific grazing preferences, which could be explained by extracellular polysaccharide production of <italic>C. watsonii</italic>, feeding mode, cingulum size and cell size of grazers.</p>