Has the importance of photoautotrophic picoplankton been overestimated?

Abstract

Postincubation differential filtration (PIDF), preincubation differential filtration (PreIDF), and track autoradiography (TA) were compared for estimating cell‐specific and total photoautotrophic picoplankton production. Experiments were performed in Lakes Michigan and Huron and in the Gulf of Mexico. When Synechococcus dominated the photoautotrophic picoplankton community (>70% of total picoplankton abundance), PIDF estimates of cell‐specific and total picoplankton production were ∼3.0 × (range, 2.0–3.8×) higher than TA estimates. PreIDF estimates of cell‐specific and total picoplankton production, however, were only slightly higher than TA estimates (mean, 1.4×; range, 1.4–1.5×). The higher PIDF estimates were attributable to breakage and damage of larger photoautotrophs during postincubation filtration and to retention of this labeled material on the smaller (0.2 µm) pore‐size filter. Results from PIDF experiments must be viewed with caution and previous estimates of picoplankton production, cell‐specific or total, based solely on PIDF may need to be re‐evaluated.