Ultraplankton Biomass, Productivity and Efficiency in Lac Matamec, a Precambrian Shield Lake1,2

In extremely oligotrophic Lac Matamec (Quebec, Canada) the ultraplankton (<15 μm) represented 47% of total phytoplankton biomass but accounted for 71% of the primary production and was 2.5 times more photosynthetically efficient than larger phytoplankton. Cell surface area was a good predictor of efficiency, while cell numbers and bio‐mass were not. High surface:volume ratios may explain the high efficiency of the ultraplankton.