bacterioplankton
noun
bac·te·rio·plank·ton bak-ˌtir-ē-ō-ˈplaŋ(k)-tən 
-ˌtän
: plankton composed of bacteria
… a 2-year study off the New Jersey coast detected seasonal patterns of bacterioplankton communities with distinct clusters of samples separated by season for each year and a distinction between summer and winter communities evident in the entire data set.
Stephen J. Giovannoni and Kevin L. Vergin, Science, 10 Feb. 2012
Stephen J. Giovannoni and Kevin L. Vergin, Science, 10 Feb. 2012
Word History
First Known Use
1923, in the meaning defined above