Photosynthetic Characteristics of Coral Sea Picoplankton (<2 μm size fraction)

AbstractLight-dependent photosynthetic (P-I) responses of size-fractionated (>2 μm, 2 μm fraction. PBm values calculated for near-surface picoplankton (¯ = 6.30) and larger phytoplankton (¯ = 2.87) were five times maximum values in deep-living populations (¯ = 1.24 and 0.57, respectively). Near-surface picoplankton photosynthesized at near-maximal rates over a broad range of irradiances between 400 and 1300 μE m−2s−1, but were photoinhibited at >2200 μE m−2s−1 m−2s−1. Deep-living assemblages of picoplankton and larger phytoplankters became photoinhibited at irradiance levels between 200 and 400 μE m−2s−1. Diurnal time series of photosynthesis measurements made with all size classes of phytoplankton from shallow Great Barrier Reef lagoons had broad midday photosynthesis...