Growth rates of summer nanoplankton (<10 ?m) populations in lower Narragansett Bay, Rhode Island, USA

Abstract

Growth rates of summer (June–September) phytoplankton assemblages and constituent species were measured in 30 diffusion culture experiments. Size-fractionated (<10 μm) phytoplankton assemblages were incubated in situ or under simulated in-situ conditions in outdoor tanks connected to a running seawater system. Doubling rates of important species and groups (such as microflagellates) were compared to community biomass doubling rates estimated from 14C uptake and changes in chlorophyll a concentrations. Division rates of dominant diatom species generally equalled or exceeded community biomass doubling rates, while those of flagellates and non-motile ultraplankters were slower. Maximum division rates of sixteen common diatom species exceeded 2.1 divisions d-1, while nine had maximum division rates in excess of 3 d-1. Mean division rates of 12 diatom species exceeded 1 d-1. Maximum division rates of flagellated species, uncharacterized microflagellates and non-motile ultraplankton assemblages were 2.1, 1.5 and 1.4 d-1, respectively. Microflagellate and non-motile ultraplankton assemblage doubling rates were less than 0.5 d-1 in over half of all growth experiments.