Comparison of benthic recruitment with pelagic growth of bloom-forming cyanobacteria

In eutrophic lakes, overwintering bloom-forming cyanobacteria such as Microcystis re-inoculate the water column in the spring, contributing to pelagic development as a cell source for initial pelagic growth and a direct inoculum for continued pelagic development as well. In the present study, recruitment and pelagic growth of cyanobacteria were monitored by using migration traps and phytoplankton chambers at a study site near Meiliang Bay (1.5 m deep) in Taihu Lake from March to June, 2008. Cell abundance from both sources was compared synchronously; in the meantime water temperature was recorded using an automatic sonde. Results showed that recruitment and pelagic growth of cyanobacteria already started at 11°C, and showed changing patterns over the time of the study. Benthic recruitment only accounted for a small portion of pelagic growth, which is similar to that found in deep lakes. Taken together, these findings suggest that studies on cyanobacteria blooms development should be mainly focused on the pelagic population development.   Key words: Colony, cyanobacteria, Microcystis, pelagic growth, recruitment