Chla-specific productivity of picophytoplankton not higher than that of larger phytoplankton off the South Shetland Islands in summer

Abstract

Size-fractionated chlorophyll a (Chla)-specific productivity (μgC μgChla ⁻¹ h⁻¹) was measured at 11 stations off the northern coast of the South Shetland Islands during summer. The Chla-specific productivity of the 2- to 10 or 10- to 330-μm fraction was highest at 100% and 23% light depths. The Chla-specific productivity of the 2- to 10-μm fraction was generally highest, and that of the <2 or 10- to 330-μm fraction was sometimes highest at 12% and 1% light depths. Temperature was less than 3°C within the euphotic zone at all stations. The hypothesis of Shiomoto et al., according to which Chla-specific productivity of picophytoplankton (<2 μm) is not significantly higher than that of larger phytoplankton (>2 μm) in water colder than 10°C, was supported on condition that light is not limited for larger phytoplankton.