Picoplankton: Contribution to Phytoplankton Production in the Strait of Messina*

Abstract

Abstract. Biomass and primary production rates derived from photosynthesis‐light curves on picoplankton (< 1 um fraction) and total phytoplankton were compared for the Strait of Messina. Picoplankton biomass ranged between 0.063 and 0.094 mg Chi a m‐5 and accounted for 56–63 % of the total. Total primary production rates were between 0.22 and 1.56 mg C‐m‐2‐h‐1 of which the picoplankton contribution ranged from 24 to 43%. In this turbulent nearshore environment, the contribution of picoplankton to total phytoplankton production is considerably less than in calmer open‐ocean waters. Carbon assimilation numbers (Pmb), the initial slope (a), adaptation parameter (Ik), optimal irradiance (Im) and compensation intensity (Lm,) for the picoplankton were lower than for the > 1 μm fraction. Fitted respiration (RmB) for the picoplankton was, however, on the average higher (10.3 % of PmB) than for the > 1 μrn fraction (6.6 %). Assimilation numbers for the > 1 μm fraction in the southern stations were of higher magnitude (8.5–12.0 mg C mg Chi a‐1 h‐1) than in the northern station, possibly due to the impact of upwelled water flowing southward along the Sicilian coast.